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Although more sustainable, feeding fish solely plant protein (PP) deteriorates their fillet quality more than animal counterparts, which additives can alleviate. This study investigated the effects of supplementing high PP diets with two additive mixtures on the fillet quality of rainbow trout (Oncorhynchus mykiss). Fish (∼2.2g) were fed with four isonitrogenous (42 % CP) and isolipidic (20 % lipid) diets: fishmeal-based (FM), plant-based (PP), PP + A1 (PP with a mixture of krill meal, taurine, and organic selenium) and PP + A2 (PP with a mixture of proline, hydroxyproline, and vitamin C) diets, for seven months. Different diets significantly (p < 0.05) affected fatty acid composition, textural profile, hydroxyproline and collagen content, and genes related to collagen synthesis. The short-term (ice vs. -20 °C) and long-term (-20 °C, 90 days) storage conditions showed significant (p < 0.05) effects on different fillet quality attributes, including protein secondary structures. Overall, supplementing additive mixtures improved the fresh and stored fillet quality., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Published by Elsevier Ltd.)

Exogenous enzymes are used to enhance ingredient digestibility, overall fish growth, and feed utilization; however, different administration methods have not been extensively studied. In this study, a mixture of carbohydrases (α-amylase, cellulase, xylanase, and β-glucanase) was applied before (at B3, B6, B12, and B24 hours), during (D), or after (A) the production of high-carbohydrate diets (33% carbohydrates) to assess their effects on the growth and feed utilization of rainbow trout. The enzymes were added to the diets at the minimum required levels, determined by a reducing sugar test with dinitrosalicylic acid (DNS) based on the available wheat flour and soybean meal in the diet. Seven isoenergetic (21 kJ/g) and isonitrogenous (40%) diets were formulated and fed to fish (n = 210, 17.41 ± 1.76 g) for 8 weeks. Overall growth parameters improved in the B6 and B3 groups, which also showed the lowest FCR values (0.84 and 0.85, respectively) and significantly higher weight gain, PER, and SGR compared to the other treatments. The apparent digestibility of protein, lipid, ash, and dry matter was significantly enhanced in the B3 group. Additionally, DHA and omega-3 fatty acid content increased in B3 (p < 0.05), although no significant differences were observed in fillet contents of EPA and ARA (arachidonic acid) between treatments (p > 0.05). The pretreatment of ingredients (B3 and B6) likely induced a protein-sparing effect, as indicated by higher PER and increased amino acid retention in the fillets (p < 0.05). Moreover, higher metabolizable energy and glucose levels led to significant upregulation of the ghrelin hormone (GHRL), growth hormone (GH), and insulin-like growth factor (IGF-I) genes in the B3 and B6 treatments (p < 0.05). In conclusion, pretreatment of ingredients (soybean meal and wheat flour) with optimized multienzyme doses improved digestibility and activated regulatory genes, resulting in enhanced growth, feed utilization, and fillet quality in high-carbohydrate diets for rainbow trout., Competing Interests: Declarations. Ethics procedure: All procedures involving animals were done according to the Tarbiat Modares University protocols, which seek to optimize handling and minimize animal suffering following the guidelines adopted from the Declaration of Helsinki (1975) and The Society for Neuroscience Animal Care and Use guidelines (1998) approved for implementation by the Medical Ethics Committee, School of Medical Sciences of the Tarbiat Modares University on 17th April 2006. Competing interest: The authors declare no competing interests., (© 2025. The Author(s), under exclusive licence to Springer Nature B.V.)

Rainbow trout (Oncorhynchus mykiss) with a starting weight of 397.28 ± 3.21 g were fed different ratios (G1-0.00%, G2-0.010%, G3-0.025%, and G4-0.050%) of boric acid-supplemented feed for 140 days. The effects of dietary boric acid on oxidative stress parameters, growth performance, haematology and some biochemical parameters were investigated after the feeding period. The addition of boric acid to trout feed positively affected growth performance; the final weights of the groups were 928.15 ± 5.73 g, 955.87 ± 8.67 g, 994.24994,75 ± 7.46 g, and 976.80976,80 ± 6.26 g for the control group and the three experimental groups, respectively. The lowest feed conversation ratio (FCR) was 1.19 (G3) whereas the highest was 1.42 (G1). The lowest protein efficiency ratio was 1.63 (G1), while the highest was 1.95 (G3). In this study, it was observed that boric acid added to the feed changed muscle and blood oxidative stress parameters in rainbow trout, increased the growth performance of rainbow trout, and affected blood and biochemistry values., Competing Interests: Declarations. Competing Interests: The authors declare no competing interests., (© 2024. The Author(s).)

Most steelhead trout hatcheries increase growth rate during rearing to produce and release yearling smolts for harvest augmentation, but natural steelhead exhibit variable age of smoltification, so this common rearing practice may not be ideal for programs focused on recovering imperiled wild stocks; therefore, it is important to investigate and compare alternative hatchery rearing methods that promote life history diversity. Over six consecutive years, the Winthrop National Fish Hatchery on the Methow River, WA reared and released paired groups of age-1 (S1) and age-2 (S2) steelhead smolts. To understand how the two rearing methods affected developmental ontogeny and life-history, fish were sampled prior to hatchery release for factors associated with smoltification (size, gill Na+/K+ ATPase activity, and a qualitative smolt phenotype) and sexual maturation (sex, pituitary and testis mRNA transcripts, gonadosomatic index, and plasma 11-ketotestosterone). Our objectives were to quantify levels of smoltification and male maturation during hatchery rearing, combine metrics to estimate residualism (failure to migrate upon release), and compare the treatments by sex. Overall, S2 rearing produced 7.8% more smolts and 44-fold (4.4 vs. 0.1%) more precociously mature males than S1 rearing. Conversely, S1 rearing produced 31.6% more residuals than S2 rearing. While the proportion of total male residuals was comparable between treatments, the S1 treatment produced approximately five-fold more female residuals (20.6 vs. 4.2%). Because residuals contribute minimally to adult returns and the number of returning adult females is critical to the success of salmonid supplementation efforts, developing rearing techniques that maximize migration in females is a management priority. Physiological assessments are useful for characterizing and quantifying the effects and risks of different hatchery rearing regimes on steelhead life-history, in addition to providing sex-specific guidance to inform and optimize conservation management goals in supplementation programs., Competing Interests: MAM is currently affiliated with the company Saltwater Inc., which provides professional consulting services to government organizations, non-governmental organizations, and the private sector. This does not alter the authors’ adherence to all the PLOS ONE policies on sharing data and materials, as detailed online in the guide for authors., (Copyright: This is an open access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication.)

This study assessed the impact of dietary Chlorella sp. and Schizochytrium sp. extracts on growth performance, feed utilization, body composition, and gene expression related to growth, digestion, antioxidant defense, and immune response in rainbow trout (Oncorhynchus mykiss). A total of 180 fish (average weight 8.92 ± 0.04 g) were randomly distributed into 12 fiberglass tanks (400 L, 15 fish per tank, three replicates per treatment). Fish were divided into four dietary groups for 60 days: 0 % (Control), 0.5 % Chlorella sp. extract (CH), 0.5 % Schizochytrium sp. extract (SC), and a combined 0.25 % Chlorella sp. and 0.25 % Schizochytrium sp. (CH + SC). At trial end, fish in the CH + SC group had a final weight (FW) of 27.06 ± 0.28 g, significantly higher than other groups (P < 0.05), with improved growth parameters (P < 0.05). While body composition showed no differences in moisture, lipid, or ash content, crude protein was significantly higher in CH + SC (P < 0.05). Gene expression analysis showed upregulation of the growth hormone GH-I gene in the CH + SC group (P < 0.05). Genes related to digestive enzymes (trypsin, lipase, amylase) were also upregulated in all microalgae groups, with the highest levels in CH + SC (P < 0.05). Additionally, antioxidant genes (SOD, CAT, GPx) and immune-related genes (LYZII, TNF-α, IL-1β) showed elevated expression in CH + SC (P < 0.05). This study demonstrated that a diet containing Chlorella sp. and Schizochytrium sp. extracts supports growth, enhances nutrient utilization, and upregulates genes related to antioxidant and immune function in rainbow trout. Further research is recommended to assess functional immune responses and enzyme activities to confirm these physiological effects., Competing Interests: Declaration of competing interest The author declares that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this article., (Copyright © 2024. Published by Elsevier Inc.)

In this study, sea buckthorn oil (SBO) was added to rainbow trout fish diets at 0.25%, 0.5%, and 1% rates in order to determine the effects on growth, feed conversion rate, survival rate, fillet quality, and physiological, biochemical and histopathological parameters. The experiment was designed in four groups with three replicates each including 20 fish with 18 ± 3 g and lasted for 45 days. Fish were fed three times a day and weighed biweekly. At the end of the experiment, significant differences were determined with respect to specific growth rates (SGR), weight gains (WG), and feed conversion ratios (FCR) (P < 0.05), except for survival ratios (SR) (P > 0.05). Sea buckthorn oil improved fish fillet quality and weight gain rates by up to 27% compared to control. The pepsin, amylase, lipase, and trypsin enzyme activities differed significantly (P < 0.05) from those of the control group. Serum lysozyme myeloperoxidase (MPO) and plasma nitro blue tetrazolium (NBT) levels differed significantly (P < 0.05) in the 0.5% and 1% groups compared to the control group, except for the 0.25% group. Liver catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx), and malondialdehyde (MDA) levels significantly differed in all groups, especially in the 0.5% and 1% groups compared to the control group (P < 0.05). SBO supplementation to feed caused significant changes in the FA profiles, especially 18:00 in ∑SFA; 16:1 in ∑MUFA; 20:5n-3 and 20:2n-6 in ΣPUFA; 20:5n-3 in ∑n-3; and 20:2n-6 in ∑n-6 in rainbow trout (P < 0.05). There were no histopathological changes between the control and the experimental groups. The determined data suggested that 1% SBO may be successfully used as a feed additive in rainbow trout., Competing Interests: Declarations. Ethics approval: Not applicable. Competing interests: The authors declare no competing interests., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)

Insulin-like growth factor-binding proteins (IGFBPs) regulate insulin-like growth factor (IGF) signaling, but IGFBP-specific functions are not well characterized in fishes. A line of rainbow trout ( Oncorhynchus mykiss ) lacking a functional IGFBP-2b was produced using gene editing and subsequent breeding to an F2 generation. This loss-of-function model [IGFBP-2b knockout (2bKO)] was subjected to either continuous feeding or feed deprivation (3 wk) followed by refeeding (1 wk). During continuous feeding, the 2bKO line displayed faster specific growth rate for both body weight and fork length, higher feed intake, and reduced feed conversion ratio compared with a wild-type (WT) line. However, loss of IGFBP-2b did not affect the feed deprivation or refeeding response in terms of weight loss or weight gain, respectively. Several components of the IGF/IGFBP system were affected by loss of IGFBP-2b. Total serum IGF-1 in the 2bKO line was reduced to 0.5- to 0.8-fold of the WT line, although the concentration of free serum IGF-1 was not affected. Gene expression differences include reduced abundance of igfbp1a1 , igfbp1b2 , igfbp5b2 , and igfbp6b1 transcripts and elevated igf2 and igfbp6b2 transcripts in liver of the 2bKO line. Collectively, these findings suggest that although IGFBP-2b is a carrier of circulating IGF-1 in salmonids, the presence of IGFBP-2a and compensatory responses of other IGF/IGFBP system components support an anabolic response that improved growth performance in the loss-of-function model. NEW & NOTEWORTHY Knocking out IGFBP-2b in rainbow trout improved food intake, growth performance, and feed conversion ratio and reduced serum IGF-1 by 0.5- to 0.8-fold, without changes in the concentration of free serum IGF-1. Based on these findings, we propose that, in addition to IGFBP-2b, the 32-kDa IGFBP (putative IGFBP-2a) also serves as a major carrier of circulating IGF-1 in salmonids.

Due to the growth of aquaculture and the finite supply of fishmeal and oil, alternative marine protein and lipid sources are highly sought after. Particularly promising is the use of side streams from the fish processing industry, allowing for the recovery and retention of otherwise lost nutrients in the food production chain. The aim of the present study was to evaluate the potential of three fish processing side streams as fish feed ingredients. The side streams originated from different stages of the production chain, were used without further processing, and included sprat trimmings (heads, frames, viscera), marinated herring (fillets), and mackerel in tomato sauce (fillets and sauce). The three side streams contained moderate levels of protein (28-32% dry matter) and high levels of lipid (34-43%). The sprat trimmings included ca. 29% ash and 1.5% phosphorous, which may add value due to the high level of essential minerals but needs to be considered in feed formulations. Three diets were formulated to include 50% of each side stream replacing all fishmeal and ca. 80% of the fish oil of the control diet, which contained 35% fishmeal and 10% fish oil. The diets were evaluated in a 12-week feeding trial using rainbow trout (Oncorhynchus mykiss). Fish fed the sprat diet displayed the highest feed intake and growth and showed no negative effects on the intestinal health. The mackerel side stream displayed a good digestibility but resulted in lower growth rates compared to the sprat trimmings. Fish fed the herring diet displayed the lowest performance regarding growth, feed intake, and digestibility. They further exhibited a reduction in nutrient uptake in both proximal and distal intestines, likely contributing to the observed lower digestibility and growth, and a reduction in plasma ghrelin levels. As part of a circular approach to increase marine lipid and protein production for fish feed, the tested sprat and mackerel side streams are promising raw materials; however, additional studies using more commercial-like feed formulations are encouraged., (© 2023 The Authors. Journal of Fish Biology published by John Wiley & Sons Ltd on behalf of Fisheries Society of the British Isles.)

The phenotype, genetic sex ratio and gonadal development characteristics were evaluated in randomly selected juvenile (15 months old), sub-adult (22 months old) and adult (30 months old) triploid hybrids of rainbow trout (Oncorhynchus mykiss) and brook trout (Salvelinus fontinalis). The examined fish originated from the family produced by application High Hydrostatic Pressure (HHP) shock (9500 psi for 5 minutes, applied 35 minutes post-fertilization at 10°C) to eggs stripped from five rainbow trout females and fertilized with sperm of two brook trout males. After hatching, all fish were reared under the same conditions for three years. The ploidy level and hybrid status of the fish were confirmed through cytogenetic analysis and DNA genotyping. Three distinct phenotypes; trout-like (Tr-l) phenotype, salmon-like (Sa-l) phenotype and intermediate (Tr/Sa-l) phenotype, with the following frequencies: f= 50.8 %, f= 31.7 % and f= 17.5 %, respectively, were observed among the sampled specimens. Genetic males exclusively detected among individuals with Tr-l phenotype developed macroscopically visible and histologically functional testes in their second year of life, representing the lowest value for the aquaculture production. A comparable proportion of males and females was recorded among individuals with Sa-l and Tr/Sa-l phenotypes. Males with these phenotypes developed macroscopically distinguishable and histologically functional testes in their third year of life. In the genetic males, underdeveloped intersex or completely reduced gonads were recorded. This study revealed that individuals with Sa-l phenotype represent the greatest value for commercial production because of their unique appearance and complete sterility (females) or delayed maturation observed only after reaching the market size (males)., Competing Interests: Declaration of Competing Interest None of the enclosed material has been published and is under consideration elsewhere, including on the Internet. All the authors have approved the manuscript for submission. None of the authors have any conflict of interest to declare., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

Salmonids, classified as physostomous fish, maintain buoyancy by ingesting air to inflate their swim bladders. Long-term submergence has been shown to cause body imbalance and reduced growth performance in these fish. Previous studies have demonstrated that extended photoperiod can promote growth in salmonids. This study aimed to investigate the regulatory effects of prolonged lighting on the growth of submerged rainbow trout ( Oncorhynchus mykiss ) by examining the transcriptional expression of genes in the growth hormone (GH)-insulin-like growth factor (IGF) axis. Rainbow trout were individually reared in one of the six environments, defined by the combination of three photoperiods (0L:24D, 12L:12D, and 24L:0D) and two spatial rearing modes (routine and submerged), for 16 weeks. We compared the growth performance of rainbow trout in different environments and further analyzed the transcription profiles and correlations of GH-IGF axis genes in the brain, liver, and muscle. The findings of this study were as follows: growth performance of rainbow trout gradually increased with photoperiod duration. Specifically, final body weight (FBW) and specific growth rate (SGR) increased, while feed conversion ratio (FCR) decreased. Extended photoperiod partially mitigated the adverse effects of long-term submergence on rainbow trout growth. Under 24L:0D photoperiod conditions, growth performance (FBW, SGR, and FCR) in submerged and routine rainbow trout was more closely aligned compared to 0L:24D and 12L:12D photoperiod conditions. In response to variations in the photoperiod, GH-IGF axis genes of rainbow trout exhibited significant transcriptional differences, particularly between treatments with 0L:24D and 24L:0D light exposure. An extended photoperiod facilitated the restoration of the expression of GH-IGF axis genes in submerged rainbow trout towards routine levels, including the up-regulation of sst and sstr2 genes in the brain. Correlation analysis implied differentiation of physiological functions of ghr and igfbp paralogs. This study provided insights into the feasibility of enhancing the growth performance of submerged salmonids through photoperiod manipulation.

Triploid Oncorhynchus mykiss is an important economic fish worldwide. Fishing stress can affect its growth and meat quality. This study first explored the effects of fishing stress on fatty acid and amino acid in triploid O. mykiss. Results showed fishing stress significantly reduced the content of docosadienoic acid, Gly, Arg, and DAA (P < 0.05). Targeted lipidomics analysis furthered suggested that some lipid molecules belonging to TG, DG, PC, Cer, ChE, and So were significantly up-regulated; while some lipid molecules belonging to Cer, LPE, LPC, PS, PC, and SM were significantly down-regulated, suggesting an accelerated glycolipid metabolism. Eventually, the glycolipid metabolism-related enzyme activity and gene expressions were examined, and the results indicated that O. mykiss was anti-oxidative stress by affecting relevant glycolipid metabolism signaling pathways and participating in cellular redox homeostasis. Findings of this study provide a theoretical foundation for further investigation into the mechanisms through which fishing stress affects O. mykiss., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Expression of the telomerase reverse-transcriptase (TERT) gene and activity of telomerase have been reported in the somatic tissues and gonads in fish irrespective of their age and size. Nevertheless, little is known about TERT expression in the fish eggs. In the current study, the presence of the TERT transcripts was confirmed in the rainbow trout ovulated eggs before and after activation with nonirradiated and UV-irradiated (gynogenesis) sperm. Eggs originating from eight females had high and comparable quality expressed by similar hatching rates. However, survival of the gynogenetic larvae that hatched from eggs activated with UV-irradiated sperm and further exposed to the high hydrostatic pressure (HHP) shock for duplication of the maternal chromosomes varied between females from 2.1 ± 0.4 to 40.5 ± 2.2%. Increased level of TERT transcripts was observed in eggs originating from two females, and gametes from only one of them showed improved competence for gynogenesis (27.3 ± 1.9%). In turn, eggs from the female that exhibited the highest survival after gynogenetic activation were characterized by the lowest expression of the TERT gene. Telomerase in rainbow trout eggs may compensate erosion of the telomeres during early embryonic development; however, its upregulation does not assure better development after gynogenetic activation., Competing Interests: Declarations Ethics approval The study was carried out in strict accordance with the recommendations in the Polish Act of 15 January 2015 on the Protection of Animals Used for Scientific or Educational Purposes, Journal of Laws 2015, item 266. The protocol was approved by the Local Ethical Committee for the Experiments on Animals in Bydgoszcz (resolution no. 27/2022). Conflict of interest The authors declare no competing interests., (© 2024. The Author(s).)

This project focused on evaluating the effects of maternal dietary choline intake on global DNA methylation profiles and related transcriptional changes in rainbow trout offspring. Three experimental diets were formulated to test different levels of choline intake: (a) 2065 ppm choline (Low Choline, 0 % supplementation), (b) 5657 ppm choline (Medium Choline, 0.6 % supplementation), and (c) 9248 ppm choline (High Choline, 1.2 % choline supplementation). Six rainbow trout families were fed experimental diets beginning 18 months post-hatch until spawning; their offspring were fed a commercial diet. Reduced representation bisulfite sequencing (RRBS) was utilized to measure genome-wide methylation in offspring immediately after hatching. When comparing to the Medium Choline offspring, differential DNA methylation occurred more in the Low Choline offspring than High Choline, especially in genic features like promoters. The differentially methylated CpGs (q ≤ 0.01) were identified evenly between CpG islands and shores in the genome, mostly found in the introns of genes. Genes such as fabp2 and leap2B associated with protein binding, fatty acid binding, DNA binding, and response to bacteria were differentially methylated and detected as differentially regulated genes by previous RNA-seq analysis. Although these findings indicate that levels of dietary choline available in broodstock diets alter offspring DNA methylation;, most differentially expressed genes were not associated with differential DNA methylation, suggesting additional mechanisms playing a role in regulating gene expression in response to maternal choline intake., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Background: Aquaculture, traditionally a form of biotechnology, has evolved to integrate innovative biotechnological applications, such as advanced feed formulations, aimed at improving the growth performance and health of farmed fish species. In the present study, the effects of feeding rainbow trout with novel feed formulations were investigated. Fish growth, gut and liver morphology, the concentration of fatty acids in the fillet, and volatile fatty acids in the gut were assessed. The study also validated scenarios from in vivo experiments using a nutrient-based model called FEEDNETICS™. This globally used model serves as a tool for data interpretation and decision support in the context of precision fish farming., Methods: Alternative protein and oil sources, including poultry by-product meal (PBM) and natural algae oil, were explored as sustainable replacements for fishmeal (FM) and fish oil (FO). A 90-day feeding trial was conducted using rainbow trout, comparing two isoproteic, isolipidic and isoenergetic diets. The control diet contained 15% FM, 5% PBM, and 8% FO, while the test diet replaced FM with 15% PBM and 5% feather meal hydrolysate (FMH), and fully substituted FO with VeraMaris ® natural algae oil and rapeseed oil., Results: PBM successfully replaced FM protein without negatively affecting feed intake, growth performance or feed utilization in trout. The combination of PBM and natural algae oil was well tolerated by the trout and showed no negative effects on gut health. A detailed analysis of fatty acids in the fillet revealed that PUFAs of the n3 and n6 series were significantly higher in the PBM group than in the FM group. Values of fatty acid-related health indexes, including atherogenicity index, and thrombogenicity index, confirmed the high nutritional value of trout filet, thus representing a healthy product for human. In addition, the predictions using the FEEDNETICS™ indicated that the tested novel alternative formulations are economically viable. The validation of the model for fish growth resulted in a Mean Absolute Percentage Error (MAPE) of 8%., Conclusions: The FEEDNETICS™ application enhances our ability to optimize feeding strategies and improve production efficiency in the aquaculture industry. VeraMaris ® algae oil and PBM could serve as viable and sustainable raw materials for fish feed, promoting environmentally friendly aquaculture practices., (© 2024. The Author(s).)

The effect of diets with various dietary MUFA content and n-6/n-3 ratios, diets 1 (55.33, 1.00), 2 (25.30, 1.00), 3 (55.13, 2.05), 4 (24.92, 2.03), 5 (54.94, 8.06) and 6 (24.91, 8.06) and a control diet with fish oil (FO), diet 7 (33.60, 5.97), was studied on growth and digestive physiology of rainbow trout, Oncorhynchus mykiss. Juveniles, 14.65 g ± 0.17, were fed the experimental diets for eight weeks. Those fish fed diet 1 (55.33, 1.00) had the lowest growth and nutritional indices, while fish fed diet 6 (24.91, 8.06) possessed the highest indices. However, fish fed D7 (33.60, 5.97) was intermediate in this regard. Proximate body composition results revealed no significant differences among various experimental groups (P > 0.05). Fish fed on diet 1 possessed the highest alkaline protease activity, while fish raised on diet 2 showed the lowest enzyme activity (P < 0.05). Fish fed on diets 1, 3 and 4 had the highest lipase activity (P > 0.05). Amylase activity and intestinal parameters did not differ among groups (P > 0.05). MUFA contents of liver and muscle reflected the MUFA contents of the diets; however, liver PUFA contents was not affected by dietary PUFA contents (P < 0.05). However, 18:3n-3 contents of liver decreased as dietary n-6/n-3 ratio increased (P < 0.05). Furthermore, the liver 20:4n-6 contents considerably increased as dietary n-6/n-3 increased to 8.06 (P < 0.05). Muscle 22:6n-3 content of groups 1 to 6 was lower than group 7 (P < 0.05). In conclusion, rainbow trout was considerably capable of de novo synthesis of 22:6n-3. Meanwhile, increasing dietary n-6/n-3 ratio to 8.06 decreased the muscle 22:6n-3 content which requires further considerations regarding fish immune competence and nutritional quality for human consumption., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)

Kynurenic acid (KYNA) is a metabolite of tryptophan formed on the kynurenine pathway. Its pharmacological effects are relatively well characterized in mammals, whereas its role in fish is poorly understood. Therefore, the aim of the study was to expand the knowledge of KYNA's presence inside a fish's body and its impact on fish development and function. The study was performed on zebrafish larvae and adult rainbow trout. We provide evidence that KYNA is present in the embryo, larva and mature fish and that its distribution in organs varies considerably. A study of KYNA's effect on early larval development suggests that it can accelerate larval maturation, especially under conditions that are suboptimal for fish growth. Moreover, KYNA in concentrations over 1 mM caused morphological impairment and death of larvae. However, long-lasting exposure of larvae to subtoxic concentrations of KYNA does not affect the behavior of 5-day-old larvae kept under standard optimal conditions. We also show that ingestion of KYNA-supplemented feed can lead to KYNA accumulation, particularly in the pyloric caeca of mature trout. These results shed new light on the relevance of KYNA and provide new impulse for further research on the importance of the kynurenine pathway in fish.

The need for fish meal constrains fish farming and significantly impacts sustainability of the aquaculture industry. Hence, it is important to investigate the use of plant-based protein sources in fish diets. The present study was conducted to determine the effects of different levels of fish meal (FM) replacement by pea protein (PP) in a 60-day feeding experiment in rainbow trout, Oncorhynchus mykiss. Effects on growth performance, body composition, hematology, serum biochemistry and immunology, and immune (TNF-α, IL1-ß and Il-8) and growth-related (GH and IGFI) gene expression were investigated. Five experimental diets (45% protein and 20% lipid) differed in replacement level of FM by PP at rates of 0% (control (PP0)), 25% (PP25), 50%(PP50), 75%(PP75) and 100%(PP100). Fish were fed with experimental diets in triplicate twice daily. The best growth performance was obtained in PP0 and PP25 groups. While fat ratios of fish fillets significantly differed (p < 0.05), there was no significant effects on protein ratios (p < 0.05). There was no significant change in the hematological values of fish, except those fed the PP100 diets, which displayed a reduction in eyrthocyte counts, hemoglobin content and hematocrit. As PP supplementation increased fish showed elevated serum glucose, total protein, cholesterol and myeloperoxidase activity and decreased glutamic pyruvic transaminase and alkaline phosphatase activity. Fish fed diets with between 25 and 75% replacement showed a decline in lactic acid bacteria in the gut. Significant increases in expression were observed in the liver of the PP25 fish relative to the 0% control for all immune and growth-related genes except for IL1-ß. These data suggest that up to 25% of FM can be replaced by PP without any adverse effects on rainbow trout., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Activin signaling is essential for proper embryonic, skeletal muscle, and reproductive development. Duplication of the pathway in teleost fish has enabled diversification of gene function across the pathway but how gene duplication influences the function of activin signaling in non-mammalian species is poorly understood. Full characterization of activin receptor signaling pathway expression was performed across embryonic development and during early skeletal muscle growth in rainbow trout (RBT, Oncorhynchus mykiss). Rainbow trout are a model salmonid species that have undergone two additional rounds of whole genome duplication. A small number of genes were expressed early in development and most genes increased expression throughout development. There was limited expression of activin Ab in RBT embryos despite these genes exhibiting significantly elevated expression in post-hatch skeletal muscle. CRISPR editing of the activin Aa1 ohnolog and subsequent production of meiotic gynogenetic offspring revealed that biallelic disruption of activin Aa1 did not result in developmental defects, as occurs with knockout of activin A in mammals. The majority of gynogenetic offspring exhibited homozygous activin Aa1 genotypes (wild type, in-frame, or frameshift) derived from the mosaic founder female. The research identifies mechanisms of specialization among the duplicated activin ohnologs across embryonic development and during periods of high muscle growth in larval and juvenile fish. The knowledge gained provides insights into potential viable gene-targeting approaches for engineering the activin receptor signaling pathway and establishes the feasibility of employing meiotic gynogenesis as a tool for producing homozygous F1 genome-edited fish for species with long-generation times, such as salmonids., (© 2024. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Traditional monoculture systems often face challenges related to solid waste production and nutrient use. This study addresses these concerns by investigating the impact of bicultural farming of burbot (Lota lota) and rainbow trout (Oncorhynchus mykiss) in a recirculating aquaculture system (RAS) and the subsequent alteration of production of solid waste, growth and physiological status. The rationale behind incorporating burbot lies in its potential as a supplementary species to improve overall system efficiency and sustainability. The experimental groups in triplicate represented the different ratios of rainbow trout (T) and burbot (B) in the stock: T70/B30, T85/B15 and T100/B0. Burbot, although not assessed in monoculture due to its limited commercial significance, was incorporated into the study as a supplementary species, expected to enhance the nutrient utilisation through its bottom-feeding behaviour and anticipated consumption of solid waste produced by trout. After 77 days of culture, the survival rates of trout remained consistent across experimental groups, averaging over 99%, while burbot exhibited comparable survival rates despite lower cumulative survival, averaging 88%. Feed conversion ratios showed no significant differences between the groups, indicating consistent feed utilisation. A significantly higher specific growth rate (SGR) in trout was observed in group T70/B30. The SGR values of burbot were marginally low and without significant differences between groups. Among biochemical markers of blood plasma, phosphorus concentrations were significantly higher in group T70/B30 for both trout and burbot, suggesting better access to the feed for both species. Elevated antioxidant activity and evidence of oxidative stress were found for both species in intestinal tissue. The presence of burbot in stock significantly affected the production of suspended solids per gram of applied feed. Therefore, group T100/B0 demonstrated the highest solid production at multiple time points, suggesting a relationship between burbot presence and the production of suspended solids. Starting at the 9-week, the trout monoculture group exhibited significantly higher phosphorus levels in sediments compared to group T70/B30, emphasising the role of burbot in shaping sediment nutrient dynamics in RAS, such as supplementary cleaning fish. After 11 weeks, group T100/B0 displayed significantly higher values of produced suspended solids and their composition: DM, organic DM, and phosphorus content per gram of feed applied. These results provide evidence of the influence of burbot on suspended solids production and characteristics. In conclusion, this study indicates the positive effects of burbot presence on solid production and sediment nutrient composition., (Copyright © 2024 The Author(s). Published by Elsevier B.V. All rights reserved.)

This study focuses on the comparative metabolic profiling and effects of two steroid types: natural and synthetic, specifically 17α-methyl testosterone (17α-MT) at varying concentrations (1.5, 2, and 3 mg/kg) in rainbow trout ( Oncorhynchus mykiss ). Over a 75-day feeding trial, growth metrics, such as feed efficiency, daily specific growth, live weight gain, total weight gain, and survival rate were systematically monitored every 15 days. At the end of the feeding trial, histopathology, immunohistochemistry, and metabolome analyses were performed in the high-concentration groups (3 mg/kg natural and 3 mg/kg synthetic), in which the lowest survival rate was determined. Key findings reveal that the type of hormone significantly influences growth parameters. While some natural steroids enhanced certain growth aspects, synthetic variants often yielded better results. The metabolomic analysis highlighted significant shifts in the metabolism of tryptophan, purine, folate, primary bile acids, phosphonates, phosphinates, and xenobiotics via cytochrome P450 pathways. Histopathologically, the natural hormone groups showed similar testicular, hepatic, muscular, gill, cerebral, renal, and intestinal tissue structures to the control, with minor DNA damage and apoptosis observed through immunohistochemistry. Conversely, the synthetic hormone groups exhibited moderate DNA damage and mild degenerative and necrotic changes in histopathology.

The central nervous system of Pacific salmon retains signs of embryonic structure throughout life and a large number of neuroepithelial neural stem cells (NSCs) in the proliferative areas of the brain, in particular. However, the adult nervous system and neurogenesis studies on rainbow trout, Oncorhynchus mykiss , are limited. Here, we studied the localization of glutamine synthetase (GS), vimentin (Vim), and nestin (Nes), as well as the neurons formed in the postembryonic period, labeled with doublecortin (DC), under conditions of homeostatic growth in adult cerebellum and brainstem of Oncorhynchus mykiss using immunohistochemical methods and Western Immunoblotting. We observed that the distribution of vimentin (Vim), nestin (Nes), and glutamine synthetase (GS), which are found in the aNSPCs of both embryonic types (neuroepithelial cells) and in the adult type (radial glia) in the cerebellum and the brainstem of trout, has certain features. Populations of the adult neural stem/progenitor cells (aNSPCs) expressing GS, Vim, and Nes have different morphologies, localizations, and patterns of cluster formation in the trout cerebellum and brainstem, which indicates the morphological and, obviously, functional heterogeneity of these cells. Immunolabeling of PCNA revealed areas in the cerebellum and brainstem of rainbow trout containing proliferating cells which coincide with areas expressing Vim, Nes, and GS. Double immunolabeling revealed the PCNA/GS PCNA/Vim coexpression patterns in the neuroepithelial-type cells in the PVZ of the brainstem. PCNA/GS coexpression in the RG was detected in the submarginal zone of the brainstem. The results of immunohistochemical study of the DC distribution in the cerebellum and brainstem of trout have showed a high level of expression of this marker in various cell populations. This may indicate: (i) high production of the adult-born neurons in the cerebellum and brainstem of adult trout, (ii) high plasticity of neurons in the cerebellum and brainstem of trout. We assume that the source of new cells in the trout brain, along with PVZ and SMZ, containing proliferating cells, may be local neurogenic niches containing the PCNA-positive and silent (PCNA-negative), but expressing NSC markers, cells. The identification of cells expressing DC, Vim, and Nes in the IX-X cranial nerve nuclei of trout was carried out.

In this study, we investigated the effects of swimming activity and feed restriction on juvenile rainbow trout (Oncorhynchus mykiss) in decoupled aquaponic systems. Our focus was on assessing their impact on water quality parameters within the aquaponic setup and evaluating the growth performance of the fish, including final weight (FW), condition factor (K), coefficient of variation (c.v.) in weight, specific growth rate (SGR), total feed intake (g/fish), feed conversion rate (FCR), hepatosomatic index (HSI), and viscerosomatic index (VSI), as well as the growth of lettuce (Lactuca sativa L. var. elmaria). The study involved 108 juvenile rainbow trout with an average initial weight of 26.54 ± 0.36 g and 60 ten-day-old lettuce seedlings, over a period of 42 days. We designed four treatment groups, each with three fish tanks: static ad libitum (SA), where fish were in static water conditions and fed to satiation; static restriction (SR), with fish in static water and a 25% feed restriction; current ad libitum (CA), where fish experienced forced swimming at 1 BL s -1 ; and current restriction (CR), with swimming exercise at 1 BL s -1 and a 25% feed restriction. Using a flow rate of 1 BL s -1 in the tanks for rainbow trout yielded several benefits. Notably, the fish in the CA group exhibited increased feed intake (60 ± 1.78 g fish -1 ) and enhanced fish growth with an FW of 91.72 ± 0.91 g, compared to the SA group (55.88 ± 0.88 g fish -1 for feed intake and 89.26 ± 0.81 g for FW). In contrast, the CR group showed a reduced feed intake (39.02 ± 2.78 g fish -1 ) and a lower FW (67.85 ± 1.49 g) compared to the CA group. In addition, the CA group demonstrated positive contributions to fish development with a reduced HSI (1.26 ± 0.02) in comparison to the SA group (1.56 ± 0.14). Inadequate nutrient provisioning in the SR and CR groups negatively impacted fish growth and system efficiency. Our findings suggest that optimizing water flow and feed benefits fish and plants and enhances system sustainability., (© 2024 The Authors. Journal of Fish Biology published by John Wiley & Sons Ltd on behalf of Fisheries Society of the British Isles.)

This study aimed to evaluate the efficacy of dielectric barrier discharge treatment (DBD) combined with phycocyanin pigment (PC) in extending the shelf life of Oncorhynchus mykiss rainbow fillets stored at 4 ± 0.1 °C. Microbiological, physicochemical, sensory and antioxidant properties were assessed over an 18-day storage period. The combined DBD and PC treatment significantly inhibited total viable counts and Psychrotrophic bacteria counts compared to the rest of the samples throughout storage. While Total Volatile Nitrogen concentrations remained below international standard until day 18, they exceeded this threshold in control sample by day 9. DBD treatment notably reduced Trimethylamine levels compared to controls (p < 0.05). PC and DBD combined inhibited DPPH and ABTS radical scavenging capacities by 80% and 85%, respectively, while demonstrating heightened iron-reducing antioxidant activity compared to controls. Analysis of 24 fatty acids indicated that PC mitigated DBD's adverse effects, yielding superior outcomes compared to controls. The ratio of n-3 to n-6 fatty acids in all samples met or fell below international standard. Thus, the combined use of DBD and PC shows promise in extending fillet shelf life by over 15 days at 4 °C., (© 2024. The Author(s).)

Copper and vitamin C are micronutrients needed for the living organism's functions. Vitamin C has a great effect on the immune system of fish. The present study aimed to evaluate the effects of dietary copper nanoparticles (Cu-NPs) and vitamin C (VC) supplementations on rainbow trout (Oncorhynchus mykiss) juveniles. So, 216 rainbow trout juveniles were randomly assigned to six groups with trial diets supplemented with Cu-NPs and VC including 0/0 (T1, control diet), 0/250 (T2), 0/500 (T3), 2/250 (T4), 2/500 (T5), and 2/0 (T6) mg Cu-NPs/VC per kg diet. After the feeding trial for 60 days, the fish were challenged with Yersinia ruckeri, and the survival rate was calculated for 15 days. Based on the data analysis, weight gain (WG), specific growth rate (SGR), protein efficiency ratio (PER), lysozyme, alternative complement activity (ACH50), hematocrit (Hct), hemoglobin (Hb), and mean corpuscular volume (MCV) were significantly (p < 0.05) increased in the fish fed on T4 and T5 diets compared with the control group. Catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPX) were significantly (p < 0.05) decreased in the fish fed with diets contain Cu-NPs and VC (T4 and T5). The expressions of TNF-α, IL-1ß, IL-10, SOD, CAT, and GPX genes were significantly (p < 0.05) decreased in the fish fed on T3, T4, and T5 diets versus the control. In addition, the dietary Cu-NPs and VC supplementations significantly enhanced resistance against pathogens and led to the control of infection in rainbow trout. In conclusion, Cu-NPs and VC administered as feed additives at 2/250-500 mg/kg elevated the growth performance, antioxidant capacity, and health of rainbow trout., (© 2021. The Author(s), under exclusive licence to Springer Nature B.V.)

In the brain of teleost fish, radial glial cells are the major type of astroglial cells. To answer the question as to how radial glia structures adapt to the continuous growth of the brain, which is characteristic of salmonids, it is necessary to study various types of cells (neuronal precursors, astroglial cells, and cells in a state of neuronal differentiation) in the major integrative centers of the salmon brain (telencephalon and tectum opticum ), using rainbow trout, Oncorhynchus mykiss , as a model. A study of the distribution of several molecular markers in the telencephalon and tectum with the identification of neural stem/progenitor cells, neuroblasts, and radial glia was carried out on juvenile (three-year-old) O. mykiss . The presence of all of these cell types provides specific conditions for the adult neurogenesis processes in the trout telencephalon and tectum. The distribution of glutamine synthetase, a molecular marker of neural stem cells, in the trout telencephalon revealed a large population of radial glia (RG) corresponding to adult-type neural stem cells (NSCs). RG dominated the pallial region of the telencephalon, while, in the subpallial region, RG was found in the lateral and ventral zones. In the optic tectum, RG fibers were widespread and localized both in the marginal layer and in the periventricular gray layer. Doublecortin (DC) immunolabeling revealed a large population of neuroblasts formed in the postembryonic period, which is indicative of intense adult neurogenesis in the trout brain. The pallial and subpallial regions of the telencephalon contained numerous DC+ cells and their clusters. In the tectum, DC+ cells were found not only in the stratum griseum periventriculare (SGP) and longitudinal torus (TL) containing proliferating cells, but also in the layers containing differentiated neurons: the central gray layer, the periventricular gray and white layers, and the superficial white layer. A study of the localization patterns of vimentin and nestin in the trout telencephalon and tectum showed the presence of neuroepithelial neural stem cells (eNSCs) and ependymoglial cells in the periventricular matrix zones of the brain. The presence of vimentin and nestin in the functionally heterogeneous cell types of adult trout indicates new functional properties of these proteins and their heterogeneous involvement in intracellular motility and adult neurogenesis. Investigation into the later stages of neuronal development in various regions of the fish brain can substantially elucidate the major mechanisms of adult neurogenesis, but it can also contribute to understanding the patterns of formation of certain brain regions and the involvement of RG in the construction of the definite brain structure.

Yellow mutant rainbow trout (YR), an economically important aquaculture species, is popular among consumers due to its excellent meat quality and attractive appearance. Skin color is a key economic trait for YR, but little is known about the molecular mechanism of skin color development. In this study, YR skin transcriptomes were analyzed to explore temporal expression patterns of pigmentation-related genes in three different stages of skin color development. In total, 16,590, 16,682, and 5619 genes were differentially expressed between fish at 1 day post-hatching (YR1d) and YR45d, YR1d and YR90d, and YR45d and YR90d. Numerous differentially expressed genes (DEGs) associated with pigmentation were identified, and almost all of them involved in pteridine and carotenoid synthesis were significantly upregulated in YR45d and YR90d compared to YR1d, including GCH1, PTS, QDPR, CSFIR1, SLC2A11, SCARB1, DGAT2, PNPLA2, APOD, and BCO2. Interestingly, many DEGs enriched in melanin synthesis pathways were also significantly upregulated, including melanogenesis (MITF, MC1R, SLC45A2, OCA2, and GPR143), tyrosine metabolism (TYR, TYRP1, and DCT), and MAPK signaling (KITA) pathways. Using short time-series expression miner, we identified eight differential gene expression pattern profiles, and DEGs in profile 7 were associated with skin pigmentation. Protein-protein interaction network analysis showed that two modules were related to xanthophores and melanophores. In addition, 1,812,329 simple sequence repeats and 2,011,334 single-nucleotide polymorphisms were discovered. The results enhance our understanding of the molecular mechanism underlying skin pigmentation in YR, and could accelerate the molecular breeding of fish species with valuable skin color traits and will likely be highly informative for developing new therapeutic approaches to treat pigmentation disorders and melanoma., (© 2022. The Author(s).)

The aim of this study was to examine the combined effects of thyme essential oil (TEO) and prebiotic (Immunogen ®) on growth performance, hematological parameters, innate immunity, and oxidative status of rainbow trout, Oncorhynchus mykiss. For this purpose, the fish (11.92 ± 0.06 g) were fed (3% of biomass) experimental diets that contained 0 (Control; without Immunogen and/or TEO); 1% TEO + 0.1% Immunogen (T1); 1% TEO + 0.2% Immunogen (T2); 2% TEO + 0.1% Immunogen (T3) and 2% TEO + 0.2% Immunogen (T4) for 60 days. According to results, all experimental treatments exhibited similar final weight, weight gain, specific growth rate (SGR), and survival rate (SR), which were significantly higher than those of the control treatment. Although all treatments reduced the feed conversion ratio (FCR) compared to the control group, the lowest value was observed in T4. All experimental treatments showed a significant increase in amylase and protease activity compared to the control group. Moreover, the fish fed on T4 and T1 diets showed the highest and lowest lipase activity. Dietary TEO and Immunogen supplementations significantly increased WBC count and Hb level compared to the control group. Fish fed on control and T2 diets displayed lower hematocrit than fish fed on other experimental diets. The highest and lowest MCH index were recorded in T3 and control groups, respectively. The fish fed diets supplemented with T3 diet presented significantly higher MCV index compared to the control and T2 treatment. All experimental treatments exhibited similar AST, and ALP activities, which were significantly lower than those of the control group. Also, the lowest ALT activity was observed in T2 and T4 treatments compared to other groups. Dietary TEO and Immunogen supplementations significantly enhanced skin mucus total Ig, total protein level, and ACH50, protease, and lysozyme. All experimental treatments exhibited enhanced intestine total Ig, ACH50, and lysozyme level. Dietary thyme essential oil and Immunogen supplementations significantly enhanced liver antioxidant parameters including catalase (CAT), glutathione reductase (GR), glutathione peroxidase (GPx) and superoxide dismutase (SOD) and decreased MDA production compared to fish fed on control diet. As a result, it can be suggested that the combination of thyme essential oil and Immunogen (specially 2% TEO + 0.2% Immunogen) is useful for enhancing the yield and well-being of farmed rainbow trout., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Salmonid fish raised in hatcheries often have lower fitness (number of returning adult offspring) than wild fish when both spawn in the wild. Body size at release from hatcheries is positively correlated with survival at sea. So one explanation for reduced fitness is that hatcheries inadvertently select for trait values that enhance growth rate under the unnatural environment of a hatchery, but that are maladaptive in the wild environment. A simple prediction of this hypothesis is that juveniles of hatchery origin should grow more quickly than fish of wild origin under hatchery conditions, but should have lower survival under wild conditions. We tested that hypothesis using multiple full sibling families of steelhead (Oncorhynchus mykiss) that were spawned using either two wild parents (WxW) or two first-generation hatchery (HxH) parents. Offspring from all the families were grown together under hatchery conditions and under semi-natural conditions in artificial streams. HxH families grew significantly faster in the hatchery, but had significantly lower survival in the streams. That we see this tradeoff after only a single generation of selection suggests that the traits involved are under very strong selection. We also considered one possible alteration to the hatchery environment that might reduce the intensity of selection among families in size at release. Here we tested whether reducing the fat content of hatchery feed would reduce the variance among families in body size. Although fish raised under a low-fat diet were slightly smaller, the variation among families in final size was unchanged. Thus, there is no evidence that reducing the fat content of hatchery feed would reduce the opportunity for selection among families on size at release., Competing Interests: The authors have declared that no competing interests exist.

The effect of Lactococcus lactis subsp. lactis strain PTCC 1403 as a potential probiotic was investigated on the growth, hematobiochemical, immune responses, and resistance to Yersinia ruckeri infection in rainbow trout. A total of 240 fish were distributed into 12 fiberglass tanks representing four groups (× 3 replicates). Each tank was stocked with 20 fish (average initial weight: 11.81 ± 0.32 g) and fed L. lactis subsp. lactis PTCC 1403 at 0 (control, T0), 1 × 10 9 (T1), 2 × 10 9 (T2), and 3 × 10 9 (T3) CFU/g feed for 8 weeks. The results showed enhanced protein efficiency ratio and reduced feed conversion ratio in the fish-fed T2 diet. Further, fish-fed T2 and T3 diets showed a significantly higher survival rate than the control (p < 0.05). Trypsin, lipase, and protease activities were increased in fish-fed L. lactis subsp. lactis PTCC 1403 compared to the control (p < 0.05). Fish fed with a T2 diet showed significantly (p < 0.05) lower glucose content than other groups. The blood lysozyme activity and IgM showed significantly (p < 0.05) higher values in fish-fed T2 and T3 diets than in other groups. The antioxidative responses were increased in fish-fed T2 and T3 diets (p < 0.05). After 7 days post-Y. ruckeri challenge, the cumulative mortality rate showed the lowest value in fish fed with T1 and T2 diets, while the highest value was recorded in the control group. In conclusion, the results revealed beneficial effects of L. lactis subsp. lactis PTCC 1403 on the feed efficiency, immune response, and resistance to Y. ruckeri infection in rainbow trout., (© 2021. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Hypoxia and hyperoxia are disparate stressors which can have destructive influences on fish growth and physiology. It is yet to be determined if hypoxia and hyperoxia have a cumulative effect in aquatic ecosystems that affect biological parameters in fish, and to understand if this is associated with gene expression. Here we address whether growth performance and expressions of growth, immune system and stress related genes were affected by hypoxia and hyperoxia in fish. Rainbow trout was chosen as the study organism due to its excellent service as biomonitor. After an acclimatization period, fish were exposed to hypoxia (4.0 ± 0.5 ppm O 2 ), normoxia (7.5 ± 0.5 ppm O 2 ) and hyperoxia (12 ± 1.2 ppm O 2 ) for 28 days. At 6 h, 12 h, 24 h, 48 h, 72 h and 28 days, samples were collected. Hypoxia and hyperoxia negatively affected weight gain (WG), specific growth rate (SGR), survival rate (SR) and feed conversion ratio (FCR). The best WG, SGR, SR and FCR values occurred in fish exposed to normoxia, whereas hypoxia was most suppressive on growth and hyperoxia showed intermediate suppression of these parameters. Gene expression analyses were performed in liver and results revealed that long term exposure caused reduced growth hormone-I (GH-I) and insulin like growth factor I-II (IGF I-II) levels in both hypoxia and hyperoxia-treated fish. Heat shock protein (HSP70) levels increased in both hypoxia and hyperoxia treatment, and both exposures caused elevation of leptin (LEP) expression in long-term exposure. Overall data indicate that both hypoxia and hyperoxia cause stress in rainbow trout and negatively affects growth parameters., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Four 'protein inhibitors of activated STAT' (PIAS) control STAT-dependent and NF-κB-dependent immune signalling in humans. The genome of rainbow trout ( Oncorhynchus mykiss ) contains eight pias genes, which encode at least 14 different pias transcripts that are differentially expressed in a tissue- and cell-specific manner. Pias1a2 was the most strongly expressed variant among the analysed pias genes in most tissues, while pias4a2 was commonly low or absent. Since the knock-out of Pias factors in salmonid CHSE cells using CRISPR/Cas9 technology failed, three structurally different Pias protein variants were selected for overexpression studies in CHSE-214 cells. All three factors quenched the basal activity of an NF-κB promoter in a dose-dependent fashion, while the activity of an Mx promoter remained unaffected. Nevertheless, all three overexpressed Pias variants from trout strongly reduced the transcript level of the antiviral Stat-dependent mx gene in ifnγ-expressing CHSE-214 cells. Unlike mx , the overexpressed Pias factors modulated the transcript levels of NF-κB-dependent immune genes (mainly il6 , il10 , ifna3 , and stat4 ) in ifnγ-expressing CHSE-214 cells in different ways. This dissimilar modulation of expression may result from the physical cooperation of the Pias proteins from trout with differential sets of interacting factors bound to distinct nuclear structures, as reflected by the differential nuclear localisation of trout Pias factors. In conclusion, this study provides evidence for the multiplication of pias genes and their sub-functionalisation during salmonid evolution.

This study was conducted to determine the effects of dietary valine (Val) on growth, hemato-biochemical parameters, immunity, enzymatic activities, antioxidant status and expression of target of rapamycin (TOR) and 4E-BP genes in rainbow trout, Oncorhynchus mykiss (1.57 ± 0.03 g; 5.10 ± 0.34 cm). Six isonitrogenous (450 g kg -1 ) and isoenergetic (20.90 kJ 100 g -1 , gross energy) diets were designed to represent varied Val levels (10.5, 13.0, 15.5, 18.0, 20.5 and 23.0 g kg -1 dry diet basis). Growth parameters improved significantly (P < 0.05) with the amelioration of dietary Val level up to 18.0 g kg -1 . Highest (P < 0.05) body protein content was noted at 18.0 g kg -1 dietary Val. Significant differences in hematological, intestinal enzymatic activities and antioxidant parameters were noted. However, plasma variables did not show any significant differences except aspartate transaminase and uric acid. Total protein content increased significantly, while the albumin and globulin content did not show any significant (P > 0.05) difference. Moreover expression of TOR mRNA and elF4E-binding protein (4E-BP) was observed higher (P < 0.05) at 18.0 g kg -1 Val. On the basis of results, optimum dietary Val requirement for maximal growth of rainbow trout was determined to be 18.19 g kg -1 of dry diet, corresponding to 40.42 g kg -1 of dietary protein., (© 2021. The Author(s).)

Aquaculture by-products have been of great interest for producing protein hydrolysates with multiple biological activities. The present experiment was carried out to evaluate dietary effects of a low-molecular fraction (<10 kDa) from shrimp waste hydrolysate in forms of unprotected and nanocapsulated on growth and immunity of rainbow trout. Therefore, six diets were designed including a control diet (no supplementation), D1 (1 g kg -1 of unprotected fraction), D2 (1 g kg -1 chitosan nanocapsules), D3 (1 g kg -1 liposome nanocapsules), D4 (1 g kg -1 of fraction-loaded chitosan nanocapsules), D5 (1 g kg -1 of fraction-loaded liposome nanocapsules). Fish (0.91 ± 0.15 g) were fed with experimental diets until apparent satiation for six weeks followed by a 5-day experimental challenge with Streptococcus iniae. Results revealed that growth is strongly affected in fish receiving the fraction with D4 treatment showing the highest weight gain, SGR, final weight and the lowest FCR (p < 0.05). Nanocapsules without fraction did not show remarkable effects when compared to control group. In terms of serum and mucus immune parameters of lysozyme, complement activity, myeloperoxidase activity, and total protease, fish from D4 group showed the highest measured values followed by D5 (p < 0.05). Key immune related genes of IL-6 and TNF-α were noticeably up-regulated in fish from D1, D4, and D5 groups, which were consistent with survival rate after 5 days challenge with Streptococcus iniae. All together, the present findings highlighted the application of chitosan and liposome nanocarriers in aquaculture and potential of low-molecular weight fraction (<10 kDa) from shrimp wastes hydrolysate to improve growth performance and immune status of rainbow trout., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

(2S)-3-(2-sulfanylidene-1,3-dihydroimidazol-4-yl)-2-(trimethylazaniumyl)propanoate (ergothioneine, ET) is hydrophilic antioxidant produced only by certain low-level organisms, but has been reported in the organs of some animals upon dietary intake, facilitated by the ergothioneine transporter (ETT). In this study, it was hypothesised that ETT is involved in the uptake of ET from diet in salmonids. The mechanism of ET uptake was evaluated through knockdown of candidate gene encoding ETT in a cell line (RTG-2) from rainbow trout (Oncorhynchus mykiss). ETT gene expression in blood cells and certain tissues from rainbow trout was also investigated as ET from the diet is expected to be carried over to the muscle. Knockdown of an ETT candidate (E1) in RTG-2 cells resulted in a remarkable decrease in E1 mRNA expression; uptake of ET was lower in the knocked group than in the control group suggesting that E1 functions as an ETT for rainbow trout. Furthermore, the expression of ETT gene in different tissues including the muscle points to ET uptake from the diet to the muscle of salmonids. In conclusion, this study partly reveals the possible pathway underlying ET uptake from the diet and its deposition in the muscle of edible fish species., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Environmental enrichment is used to increase structural complexity of captive rearing systems and has been shown to provoke a wide range of effects in the kept animals. Here we studied the effects of enrichment on DNA methylation patterns at the whole-genome level in the brain of rainbow trout reared in an aquaculture setting. We investigated the epigenetic effects between different types of enrichment (natural substrate vs. artificial substrate vs. barren) in three developmental stages (egg vs. alevin vs. fry) and as enrichment was discontinued at the fingerling stage by means of the Methylation-Sensitive Amplified Polymorphism (MSAP) technique. While enrichment did not affect growth in body size, we found enrichment to affected global DNA methylation in the brain at the egg and alevin stage, i.e., the period during development where the animals are in close physical contact with the substrate. At these stages, trout reared on the two substrates differed more from the control than the substrates differed from each other. Only minor differences between rearing environments were detected following emergence at the fry stage. When enrichment was discontinued during the rearing of fingerlings, no differences in DNA methylation patterns were observed between the rearing environments. Our results provide further evidence on the effects of enrichment in the captive rearing of fish and show that enrichment can even modulate epigenetic patterns. The effect on the epigenome may be causal for the previously reported effects of enrichment on gene expression, behaviour and brain development., (Copyright © 2021 Elsevier Inc. All rights reserved.)

This study was conducted to assess the impacts of prolonged fasting (70 and 120 days) on the morphological, biochemical, oxidative stress responses, immune-related gene expression, histopathology, and DNA damage in rainbow trout. Final weight (FW), hepatosomatic index (HSI), and condition factor (CF) significantly decreased in both 70 and 120 days of fasting compared to the pre-fasting group (p < 0.05). Fasting led to a significant reduction in serum blood metabolites (glucose, total protein, triglyceride, T. cholesterol, high-density lipoprotein (HDL), and low-density lipoprotein (LDL)) and endogenous reserves (protein and lipid). However, plasma acetylcholinesterase (AChE) activity, aspartate aminotransferase (AST), alanine aminotransferase (ALT), interleukin (IL1), tumor necrosis factor (TNF1α), and transferrin (TF) increased significantly (p < 0.05). While malondialdehyde (MDA) levels compared to the pre-fasting group increased in the liver and muscle tissues (70 and 120 days), glutathione (GSH) enzyme activities decreased significantly in both tissues (p < 0.05). Histopathologically, both fasting groups (70 and 120 days) when compared to the pre-fasting group led to steatosis, necrosis and degeneration in hepatocytes, inflammation and hyperemia in the liver tissue and hyaline degeneration, atrophy, and inflammation in muscle tissue. Additionally, 8-OHdG levels of the liver and muscle tissues at 120 days' fasting were more severe according to 70 days' fasting. Finally, blood, the liver, and muscle tissues may be helpful to assess the impacts of fasting and fasting stress in rainbow trout., (© 2021. The Author(s), under exclusive licence to Springer Nature B.V.)

In the present study, antioxidant activity, immune responses, and growth performance of rainbow trout (Onchorhynchus mykiss) juveniles fed with diets supplemented with dandelion (Taraxacum officinalis) and lichen (Usnea barbata) extracts were assessed. Four different concentrations of aqueous methanolic extract of the plants (0% (control), 0.1%, 0.5%, and 1% (D, dandelion; L, lichen) were added to the diets, and fish were fed for 75 days. On the 15 th , 45 th , and 75 th day of the study, liver antioxidant enzyme activities were determined, and immune responses were determined every 15 th day. The results showed that SOD activity increased in the fish group of 0.1% D on the 15 th and 45 th day compared to control; however, it was lower in all the lichen extract-treated groups than in control at almost all sampling times, except on the 15 th day in the 0.1% L group. CAT activity showed an increased value (P < 0.05) in 0.5% L and 1% L treated fish groups on the 15 th day, in fish of 1% D and 1% L groups on 45 th and on 75 th day in 0.1% D group. GPX activity increased on the 15 th day of the study in fish of 0.1% D group, on the 45 th day in 1% D and 1% L groups and on the 75 th day in fish of 0.5% D, 0.1% D, and 0.5% L groups (P < 0.05). G6PDH enhanced in all treatment groups compared to control on the 15 th day, except in 0.1% L and 0.5% L groups. An elevated G6PDH activity was also observed on the 75 th day of the study in 0.5% D, 1% D, and 0.5% L fish groups. An increase on lipid peroxidation (LP) was observed in all L groups on the 45 th day of the study. Lysozyme activity was determined to be the highest in 0.5% and 1% L on the 45 th day, in 0.1% L on the 60 th day and in the 0.5% L fish group on the 75 th day compared to control (P < 0.05). Myeloperoxidase was found to be the highest at the end of the study in 1% L fish group compared to the control (P < 0.05). In conclusion, we suggest the use of dandelion to combat oxidative stress and to lower FCR and the use of lichen to modulate the immune response in rainbow trout. The use of such products will be economical for aquaculture and harmless for the environment., (© 2021. The Author(s), under exclusive licence to Springer Nature B.V.)

Rainbow trout are considered as a poor user of dietary carbohydrates, displaying persistent postprandial hyperglycaemia when fed a diet containing high amounts of carbohydrates. While this phenotype is well-described in juveniles, less attention was given to broodstock. Our objective was to assess for the first time the short-term consequences of feeding mature female and male, and neomale trout with a low-protein high-carbohydrate diet on glucose and lipid metabolism. Fish were fed for two days with a diet containing either no or 32% of carbohydrates. We analysed plasma metabolites, mRNA levels and enzymatic activities of glycolysis, gluconeogenesis, de novo lipogenesis and β-oxidation in the liver. Results demonstrated that the glucose and lipid metabolism were regulated by the nutritional status in all sexes, irrespective of the carbohydrate intake. These data point out that carbohydrate intake during a short period (5 meals) at 8 °C did not induce specific metabolic changes in broodstock. Finally, we demonstrated, for the first time, sex differences regarding the consequences of two days of feeding on glucose and lipid metabolism.

Tradeoff theory, which postulates that virulence provides both transmission costs and benefits for pathogens, has become widely adopted by the scientific community. Although theoretical literature exploring virulence-tradeoffs is vast, empirical studies validating various assumptions still remain sparse. In particular, truncation of transmission duration as a cost of virulence has been difficult to quantify with robust controlled in vivo studies. We sought to fill this knowledge gap by investigating how transmission rate and duration were associated with virulence for infectious hematopoietic necrosis virus (IHNV) in rainbow trout (Oncorhynchus mykiss). Using host mortality to quantify virulence and viral shedding to quantify transmission, we found that IHNV did not conform to classical tradeoff theory. More virulent genotypes of the virus were found to have longer transmission durations due to lower recovery rates of infected hosts, but the relationship was not saturating as assumed by tradeoff theory. Furthermore, the impact of host mortality on limiting transmission duration was minimal and greatly outweighed by recovery. Transmission rate differences between high and low virulence genotypes were also small and inconsistent. Ultimately, more virulent genotypes were found to have the overall fitness advantage, and there was no apparent constraint on the evolution of increased virulence for IHNV. However, using a mathematical model parameterized with experimental data, it was found that host culling resurrected the virulence tradeoff and provided low virulence genotypes with the advantage. Human-induced or natural culling, as well as host population fragmentation, may be some of the mechanisms by which virulence diversity is maintained in nature. This work highlights the importance of considering non-classical virulence tradeoffs., Competing Interests: The authors have declared that no competing interests exist.

Flavobacterium columnare (Fc) is the causative agent for columnaris disease (CD) in several fish species and an emerging problem for rainbow trout aquaculture. We characterize the virulence phenotype of two Fc isolates, CSF-298-10 and MS-FC-4, against trout from two sources, NCCCWA and a production stock (PS), at the eyed egg and alevin life stages. Immersion challenges demonstrated that NCCCWA eyed eggs were susceptible to the Fc isolate MS-FC-4 (>97% mortality) but no mortality was observed against PS eyed eggs. The CSF-298-10 had little effect on any eyed eggs tested and was not highly virulent to any alevin till day six post-hatch, up to 38% for NCCCWA and ~80% PS alevin. The MS-FC-4 strain produced ≥80% mortality any day an immersion challenge occurred post-hatch. Significant difference in CFU counts was recorded between the Fc strains on 2 days post-hatch immersion challenges. Counts for the NCCCWA alevin were 4.4 × 10 3  CFU/ml -1 and 1.8 × 10 6  CFU/ml -1 for the CSF-298-10 strain and MS-FC-4 strain, respectively, and for the PS alevin CSF-298-10 measured 9.9 × 10 1  CFU/ml -1 and 3.8 × 10 5  CFU/ml -1 for MS-FC-4. These two Fc isolates present stark differences in virulence phenotypes to both eyed eggs and alevin and present an interesting model system for virulence kinetics and potentially alternative pathogenic pathways., (Published 2021. This article is a U.S. Government work and is in the public domain in the USA.)

The individual effects of temperature and dissolved oxygen (DO) on rainbow trout (Oncorhynchus mykiss), an important aquaculture species, are clearly established; however, little is known about the interactive effects of these parameters. In this study, the effects of temperature, DO, and their interaction on the growth, antioxidant status, digestive enzyme activity, serum biochemical parameters, and liver IGF-1 expression in rainbow trout were evaluated. Fish (initial weight, 109.98 ± 3.28 g) were reared in a recirculating system for 4 weeks and subjected to 6 treatments at three temperatures (13 °C, 17 °C, and 21 °C) and two DO contents (4.2 mg L -1 and 9.6 mg L -1 ). Physiological parameters were determined at the end of the trial. Specific growth rate and feed consumption were the highest at 17 °C and the lowest at 21 °C. Additionally, lysozyme, trypsin, lipase, and amylase activities, serum glucose and serum triglyceride contents, and IGF-1 expression decreased significantly at 21 °C and total serum protein and albumin contents were significantly higher at 21 °C than at 13 °C and 17 °C, indicating that high temperature impaired the immunity, digestion, and growth of rainbow trout. However, the adverse effects of high temperature can be alleviated by a high DO content, as evidenced by the smaller increments and decrements of these parameters under hyperoxic conditions than under hypoxic conditions. In response to high temperature stress, an increase in antioxidant enzyme activity led to the removal of oxygen free radicals under hyperoxic conditions; however, this increase was inhibited under hypoxia. Our results indicated that high temperatures have adverse effects on rainbow trout, and these harmful effects can be reduced by a high DO content., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

The objectives of this study were to evaluate the effects of different salinity levels on tissue histology, blood biochemistry, and genes transcription of the GH/IGF system in juvenile golden trout (Oncorhynchus mykiss). Five experimental salinity levels (0, 8, 16, 24, and 32‰) were selected to domesticate juvenile O. mykiss for 7 days. Histological characteristics changed with salinity, including higher ionocites area and epithelium thickness in gills, narrow lumen of collecting tubules in kidneys, and high numbers of goblet cells in the intestines. Similarly, increments in slits, degenerate hepatocytes, and individualization of hepatocytes have been shown in fish reared in the 32‰ salinity group. The lowest triglyceride (TG) and the highest level of total protein (TP) were detected in fish reared at the 32‰ group. The genes transcription of the GH/IGF system altered in response to the increase of salinity. The present results add to the understanding of the physiological responses of O. mykiss on salinity stress and would be helpful in formulating strategies to optimize the aquaculture of this species in environments with fluctuating patterns of salinity.

The effect of dietary grape (Vitis vinifera) seed extract (GSE) on growth performance and mucosal immune parameters in rainbow trout (Oncorhynchus mykiss) fry was studied. Fish (1.3 g mean weight) were randomly distributed in nine tanks (15 fish per tank) and fed diets containing GSE at 0 (control), 100, and 200 mg kg -1 for 60 days. The results showed that growth parameters were enhanced in both treatment groups compared to the control group. Histological examination of fish skin showed higher epidermis thickness, goblet cell density, and volume density in the GSE groups compared to the values of the control group. Furthermore, the villus height, goblet cell density, and intraepithelial lymphocytes were increased in the fish intestine in those fish fed GSE, with respect to control fish. Feeding fish with low dose of GSE (100 mg kg -1 ) up-regulated the expression of some immune-relevant genes, including complement component 3 (C3), lysozyme (Lys), omDB-3, interferon gamma (IFN-γ), and tumor necrosis factor-α (TNF-α) in different mucosal tissues. However, feeding fish the high dose of GSE (200 mg kg -1 ) mostly enhanced expression of these genes in the skin. Besides, skin mucus of fish fed GSE showed bactericidal activity against Yersinia ruckeri. It was concluded that GSE, especially at 100 mg kg -1 , modulates the growth performance and mucosal immunity of rainbow trout.

In this 21-day study, we examined the effects of the aqueous methanolic extract of thin-skinned plum (Prunus domestica) on growth, immune response and resistance to a pathogenic bacterium, Yersinia ruckeri in rainbow trout (Oncorhynchus mykiss). Fish were fed with diets containing thin-skinned plum extract doses as 0 (Control) 0.1 (PD01), 0.5 (PD05) and 1% (PD1) ad libitum twice in a day. At the end of the study, growth was affected positively but not significantly. Feed conversion ratio (FCR) was decreased in the PD01 group (P < 0.05). There were elevated respiratory burst and potential bacterial killing activities on the 7th day in the PD1 fish group. No differences were observed in lysozyme activity (P > 0.05). An increased myeloperoxidase activity was recorded on the 14th day of study. Expression of interleukin and COX-2 genes was elevated on the 7th day of study in the kidney and intestine of treated fish. Histological results indicated no marked changes in organs (gill, kidney, liver and spleen) of PD treated fish groups. Challenge results of fish in all plum extract-treated groups showed an increased survival rate against Y. ruckeri (P < 0.05). This study indicated that the thin-skinned plum aqueous methanolic extract could improve innate immunity, survival against Y. ruckeri and decrease the FCR level., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

The present study aimed at investigating interactive effects between dietary lipids and both short- and long-term exposures to a low, environmentally realistic, cadmium (Cd) concentration. Juvenile rainbow trout were fed four isolipidic diets (31.7 g/kg) enriched in either linoleic acid (LA, 18:2n-6), alpha-linolenic acid (ALA, 18:3n-3), eicosapentaenoic acid (EPA, 20:5n-3) or docosahexaenoic acid (DHA, 22:6n-3). From the 4th week of this 10-week experiment, the lipid level of the diet was increased (120.0 g/kg) and half of the fish fed each diet were aqueously exposed to Cd (0.3 μg/L) while the other half were not exposed to Cd (control). Fish were sampled and their liver was harvested for fatty acid profile, hepatic Cd and calcium concentrations, total glutathione level and gene expression assessment, either (i) after 4 weeks of feeding and 24 h of Cd contamination (day 29) (short-term Cd exposure) or (ii) after 10 weeks of feeding and 6 weeks of Cd contamination (day 70) (long-term Cd exposure). We found that both dietary lipids and Cd exposure influenced fatty acid homeostasis and metabolism. The hepatic fatty acid profile mostly reflected that of the diet (e.g. n-3/n-6 ratio) with some differences, including selective retention of specific long chain polyunsaturated fatty acids (LC-PUFAs) like DHA and active biotransformation of dietary LA and ALA into LC-PUFAs. Cd effects on hepatic fatty acid profiles were influenced by the duration of the exposure and the nutritional status of the fish. The effects of diet and Cd exposure on the fatty acid profiles were only sparsely explained by variation of the expression pattern of genes involved in fatty acid metabolism. The biological responses to Cd were also influenced by dietary lipids. Fish fed the ALA-enriched diet seemed to be the least affected by the Cd exposure, as they showed a higher detoxifying ability against Cd with an early upregulation of protective metallothionein a (MTa) and apoptosis regulator BCL2-Like1 (BCLx) genes, an increased long-term phospholipid synthesis and turnover and fatty acid bioconversion efficiency, as well as a lower long-term accumulation of Cd in their liver. In contrast, fish fed the EPA-enriched diet seemed to be the most sensitive to a long-term Cd exposure, with an impaired growth performance and a decreased antioxidant capacity (lower glutathione level). Our results highlight that low, environmentally realistic aqueous concentrations of Cd can affect biological response in fish and that these effects are influenced by the dietary fatty acid composition., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Aquaculture has become imperative to cover the demands for dietary animal protein. Simultaneously, it has to overcome prejudices from excessive use of antibiotics and environmental impacts. Natural supplements are traditionally applied orally. In this study, we demonstrated another pathway: the gills. Humic substances are immunostimulants and a natural part of every aquatic ecosystem, making them ideal to be used as bath stimulants. Five and 50 mg C/L of a fulvic acid-rich humic substance was added for 28 days to the water of juvenile rainbow trout (Oncorhynchus mykiss). This fulvic acid is characterized by a high content of phenolic moieties with persistent free radicals and a high electron exchange capacity. The high concentration of the fulvic acid significantly increased growth and reduced the food conversion ratio and the response to a handling-stressor. Phagocytosis and potential killing activity of head kidney leukocytes were increased, as well as the total oxyradical scavenging capacity (TOSC) and lysozyme activity in the gills. In conclusion, immunostimulation via gills is possible with our fulvic acid, and the high phenolic content improved overall health and stress resistance of fish.

Glyphosate is an herbicidal active substance (AS) entering in the composition of a large diversity of pesticide products (glyphosate-based herbicides; GBH) used in modern intensive agriculture. This compound has a favorable environmental safety profile but was suspected to induce deleterious effects in aquatic organisms, with a potential effect of some associated co-formulants. This study aimed to assess the impact of direct and chronic exposure to glyphosate on the health status of rainbow trout, Oncorhynchus mykiss. A total of 36 genitors were exposed daily for 10 months to a dose of glyphosate representative of environmental concentrations (around 1 μg L -1 ) using the AS alone or two GBHs formulations (i.e. Roundup Innovert® and Viaglif Jardin®) and findings were compared to an unexposed control group (n=12). The effects of chemical exposure on the reproductive capacities, hemato-immunologic functions, energetic metabolism, oxidative stress and specific biomarkers of exposure were analyzed over a period of 4 months covering spawning. A limited mortality between 15% and 30% specific to the spawning occurred under all conditions. No differences were observed in reproduction parameters i.e. mean weights, relative fertility and fecundity. Red blood cell count, hematocrit index, mean corpuscular volume and white blood cell counts were similar for all the sampling dates. Significant changes were observed two months before spawning with a 70% decrease of the proportion of macrophages in trout exposed to Viaglif only and a reduction of 35% of the phagocytic activity in fish exposed to the two GBHs. Trends towards lower levels of expression of tumor necrosis factor-α (between 38% and 66%) were detected one month after the spawning for all contaminated conditions but without being statistically significant. Biomarkers of exposure, i.e. acetylcholine esterase and carbonic anhydrase activities, were not impacted and none of the chemical contaminants disturbed the oxidative stress or metabolism parameters measured. These results suggest that a 10 months exposure of rainbow trout to a concentration of 1 μg L -1 of glyphosate administered using the pure active substance or two GBHs did not significantly modify their global health including during the spawning period. The immunological disturbances observed will need to be further explored because they could have a major impact in response to infectious stress., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Tissue engineering is an elegant tool to create organs in vitro, that can help obviate the lack of organ donors in transplantation medicine and provide the opportunity of studying complex biological systems in vitro, thereby reducing the need for animal experiments. Artificial intestine models are at the core of Fish-AI, an EU FET-Open research project dedicated to the development of a 3D in vitro platform that is intended to enable the aquaculture feed industry to predict the nutritional and health value of alternative feed sources accurately and efficiently.At present, it is impossible to infer the health and nutrition value through the chemical characterization of any given feed. Therefore, each new feed must be tested through in vivo growth trials. The procedure is lengthy, expensive and requires the use of many animals. Furthermore, although this process allows for a precise evaluation of the final effect of each feed, it does not improve our basic knowledge of the cellular and molecular mechanisms determining such end-results. In turn, this lack of mechanistic knowledge severely limits the capacity to understand and predict the biological value of a single raw material and of their different combinations.The protocol described herein allows to develop the two main components essential to produce a functional platform for the efficient and reliable screening of feeds that the feed industry is currently developing for improving their health and nutritional value. It is here applied to the Rainbow Trout, but it can be fruitfully used to many other fish species.

In the current study, we investigated the effect of a probiotic bacterium (Lactobacillus rhamnosus ATCC 7469) microencapsulated with alginate and hi-maize starch and coated with chitosan on improving growth factors, body composition, blood chemistry, and the immune response of rainbow trout (initial weight: 18.41 ± 0.32 g). Four experimental diets were formulated to feed fish for 60 days. They were control diet without any additive (C), diet added with beads without probiotic (E), a probiotic sprayed to the diet (L.r), and encapsulated probiotic supplemented diet (E-L.r). The results indicated that feeding with E-Lr significantly improved weight gain (84.98 g) and feed conversion ratio (0.95) compared to the other groups (P < 0.05). Also, fish fed E-Lr diet had a significantly higher value of whole-body protein (17.51%), total protein in the blood (4.98 g/dL), lysozyme (30.66 U/mL), alternative complement pathway hemolytic activity (134 U/mL), superoxide dismutase (203 U/mg protein), and catalase (528.33 U/mg protein) (P < 0.05) as compared to those fed the control diet. Similarly, a higher relative expression of immune-related genes such as interleukin-1 (Il-1) and tumor necrosis factor-alpha (TNF-1α) were reported in those fed E-L.r and L.r diets respectively. Interestingly, the fish fed dietary E-L.r had a significantly lower value of lipid in the whole body (4.82%) and cholesterol in the blood (160.67%) in comparison with those fed the control diet (P < 0.05). At the end of the experiment, all groups were challenged by Yersinia ruckeri where the survival rate of rainbow trout fed dietary E-L.r (70.36%) was statistically higher than that of the others (P < 0.05). Overall, the results suggested that encapsulated probiotic Lact. rhamnosus ATCC 7469 acted better than unencapsulated probiotic and has a potential to improve growth performance, flesh quality, and the immune response of rainbow trout.

Cerium oxide nanoparticles (CeO 2 -NP) have already been detected in the aquatic compartment, however, the evaluation of potential ecotoxicological effects on biota are scarce. The present study aimed to assess the toxic effects of CeO 2 -NP in Oncorhynchus mykiss in different organs/tissues (gills, liver and kidney) after acute exposure (96 h) to three concentrations: 0.25, 2.5 and 25 mg/L. Oxidative stress response (catalase - CAT; glutathione S-transferases - GSTs), lipid peroxidation (thiobarbituric acid reactive substances - TBARS), Na + /K + -ATPase activity, genotoxicity (genetic damage index - GDI) and histopathology (organ's pathological indices) were evaluated. CAT activity was increased in gills and decreased in liver of fish exposed to the highest CeO 2 -NPs concentration tested. However, GSTs and Na + /K + -ATPase activities and TBARS levels were not significantly altered in analysed organs. CeO 2 -NP caused marked changes in the gills (aneurysms, blood capillary congestion, lamellar hypertrophy and hyperplasia, secondary lamella fusion and epithelial lifting), in liver (pyknotic nucleus, hyperemia, enlargement of sinusoids and leucocyte infiltration) and kidney (shrinkage of the glomeruli, enlargement of the Bowman space, tubular degeneration and nuclear hypertrophy). Moreover, a semi-quantitative histopathological scoring system (pathological index) confirmed significant alterations in the three organs of all exposed fish. Furthermore, a significant increase of GDI indices observed in gills and liver, for all tested concentrations, indicated a dose-dependent effect. The present study suggests that the release of CeO 2 -NP into the aquatic environment promotes biochemical, genotoxic and histopathological damages in fish. However, the mechanisms underlying the occurrence of such effects require further investigation., Competing Interests: Declaration of competing interest The authors declare that they have no competing interests., (Copyright © 2020 Elsevier Inc. All rights reserved.)