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A better understanding of carotenoid dynamics (transport, absorption, metabolism, and deposition) is essential to develop a better strategy to improve astaxanthin (Ax) retention in muscle of Atlantic salmon. To achieve that, a comparison of post-smolt salmon with (+ Ax) or without (− Ax) dietary Ax supplementation was established based on a transcriptomic approach targeting pyloric, hepatic, and muscular tissues. Results in post-smolts showed that the pyloric caeca transcriptome is more sensitive to dietary Ax supplementation compared to the other tissues. Key genes sensitive to Ax supplementation could be identified, such as cd36 in pylorus, agr2 in liver, or fbp1 in muscle. The most modulated genes in pylorus were related to absorption but also metabolism of Ax. Additionally, genes linked to upstream regulation of the ferroptosis pathway were significantly modulated in liver, evoking the involvement of Ax as an antioxidant in this process. Finally, the muscle seemed to be less impacted by dietary Ax supplementation, except for genes related to actin remodelling and glucose homeostasis. In conclusion, the transcriptome data generated from this study showed that Ax dynamics in Atlantic salmon is characterized by a high metabolism during absorption at pyloric caeca level. In liver, a link with a potential of ferroptosis process appears likely via cellular lipid peroxidation. Our data provide insights into a better understanding of molecular mechanisms involved in dietary Ax supplementation, as well as its beneficial effects in preventing oxidative stress and related inflammation in muscle.

Novel sources of omega‐3 fatty acids (FAs) are essential for the sustainable development of the aquaculture industry. In the present study, we assessed the response of the fish to a novel algal oil as a source of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) for rainbow trout (Oncorhynchus mykiss) diets. Our results show that the palatability of the diets was maintained with high inclusion levels (up to 10%) of algal oil. The digestibility of omega‐3 FAs was compared among diets containing 10% fish oil (control diet) and diets with no omega‐3 lipid sources (0AO) or increasing levels of algal oil (2.5, 5, and 10% for diets 2.5AO, 5AO, and 10AO, respectively). The digestibility of EPA and DHA was above 99% and was only significantly decreased in the 0AO diet. The FA profile of the muscle was found to reflect that of the diets, suggesting that, when high levels of omega‐3 are included in the diet of rainbow trout, they are deposited in the muscle rather than used for metabolic processes. The growth and the blood parameters of the animals were optimal for all the treatments in the safety trial, with algal oil inclusion levels up to 6%. All these results in combination show that Veramaris® algal oil containing EPA and DHA can be used as an efficient source of omega‐3 FAs for salmonids.

Intestinal inflammation in Atlantic salmon was studied by profiling the intestine mucus proteome, employing iTRAQ and 2D LC-MS/MS approach. Two fish groups were fed soy saponin-containing (inflammation inducer) diets (SO and SP) and two control fish groups were fed diets devoid of soy saponin (CO and CP) for 36 days. The CP and SP diets contained a health additive. Inflammation characteristics in the intestine were milder in the SP-fed fish compared to the SO-fed fish. The SO group was characterised by alterations of many proteins. KEGG pathways such as phagosome and lipid binding were possibly affected in the SO group due to the higher abundant proteins like Integrin beta 2 precursor, Coronin 1A, Cathepsin S precursor, Vesicle-trafficking protein, and Neutrophil cytosol factors. On the other hand, the SP group had fewer altered proteins and inflammation characteristics; aminoacyl-tRNA biosynthesis and ribosome in the fish group were plausibly changed due to the higher abundance of many large and small subunit of ribosomes. Elevation of the abundance of ribosomal proteins, aminoacyl-tRNA ligases, and appropriate abundance of Glycogen phosphorylase and Glutamine synthetase could possibly alleviate intestinal inflammation. Data are available via ProteomeXchange with identifier PXD027922 and PXD029849. SIGNIFICANCE: Intestinal inflammation, caused by dietary factors, can be considered as a non-infectious disease. Hence, researchers are gathering clues to avert the associated health issues. The present study was conducted to infer the alterations in the intestine mucus proteome induced by a dietary health additive to counter intestinal inflammation in farmed Atlantic salmon. The reduction in the number of affected proteins and their alterations point to mechanisms evoked by the premix. Our knowledge on inflammation associated proteome in fish is limited and the present study not only highlights the changes, but also opens the possibility to avert the dysfunction of the organ through a dietary approach.

Intestinal inflammation in farmed fish is a non-infectious disease that deserves attention because it is a major issue linked to carnivorous fishes. The current norm is to formulate feeds based on plant-derived substances, and the ingredients that have antinutritional factors are known to cause intestinal inflammation in fishes such as Atlantic salmon. Hence, we studied inflammatory responses in the distal intestine of Atlantic salmon that received a feed rich in soybean derivatives, employing histology, transcriptomic and flow cytometry techniques. The fish fed on soy products had altered intestinal morphology as well as upregulated inflammation-associated genes and aberrated ion transport-linked genes. The enriched pathways for the upregulated genes were among others taurine and hypotaurine metabolism, drug metabolism—cytochrome P450 and steroid biosynthesis. The enriched gene ontology terms belonged to transmembrane transporter- and channel-activities. Furthermore, soybean products altered the immune cell counts; lymphocyte-like cell populations were significantly higher in the whole blood of fish fed soy products than those of control fish. Interestingly, the transcriptome of the head kidney did not reveal any differential gene expression, unlike the observations in the distal intestine. The present study demonstrated that soybean derivatives could evoke marked changes in intestinal transport mechanisms and metabolic pathways, and these responses are likely to have a significant impact on the intestine of Atlantic salmon. Hence, soybean-induced enteritis in Atlantic salmon is an ideal model to investigate the inflammatory responses at the cellular and molecular levels.

Astaxanthin (Ax), the main carotenoid responsible for the distinct red flesh color in salmonids (Oncorhynchus, Salvelinus, Salmo, and Parahucho), is added to the diet of farmed fish at a substantial cost. Despite the great economical value for the salmon industry, the key molecular mechanisms involved in the regulation of muscle coloration are poorly understood. Chinook salmon (Oncorhynchus tshawytscha) represent an ideal model to study flesh coloration because they exhibit a distinct color polymorphism responsible for two color morphs, white and red flesh pigmented fish. This study was designed to identify the molecular basis for the development of red and white coloration of fish reared under the same experimental conditions and to better understand the absorption mechanism of Ax in salmonids. Pyloric caeca, liver, and muscle of both groups (n = 6 each) were selected as the most likely critical target organs to be involved respectively in the intestinal uptake, metabolism, and retention of Ax. Difference in the transcriptome profile of each tissue using next-generation sequencing technology was conducted. Ten KEGG pathways were significantly enriched for differentially expressed genes between red and white salmon pylorus tissue, while none for the transcriptome profile in the other two tissues. Differential expressed gene (DE) analyses showed that there were relatively few differences in muscle (31 DE genes, p

The efficacy and tolerance of a novel microbial 6-phytase were investigated in rainbow trout, Oncorhynchus mykiss, and Nile tilapia, Oreochromis niloticus. Reference diets were sufficient in available phosphorus (P). The test diet limiting in available P was supplemented with phytase at 500, 1000, or 2000 phytase units/kg feed. The enzyme was effective in increasing total P apparent digestibility coefficient in relation to increasing the dose of phytase in rainbow trout and Nile tilapia. Zinc apparent digestibility improved in relation to phytase supplementation in rainbow trout. P release due to phytase supplementation ranged from 0.06 to 0.18% P/kg feed in rainbow trout and from 0.13 to 0.26% P/kg feed in Nile tilapia. A 58-d performance trial was conducted to evaluate tolerance of fish to phytase supplementation. Dietary treatments consisted of a basal diet without phytase or supplemented with 2000 and 200,000 phytase units/kg feed. Results indicate that this novel microbial 6-phytase is well tolerated by fish. Significant improvements for growth as well as feed conversion ratio were observed when the phytase was fed at 2000 phytase units/kg feed. This phytase is proven efficient in releasing P from phytate and could be added when plants are used for fish meal replacement in diets for salmonid and omnivorous fish.

Pigment-depletion in the fillets of farmed Atlantic salmon (Salmo salar) arises after periods of elevated water temperatures with voluntary starving. This study tested the effects of dietary pre-loading with different pigment carotenoids (astaxanthin and/or canthaxanthin) combined with two α-tocopherol levels (normal and high: 500 and 1000 mg/kg, respectively) on pigment-depletion in vivo in Atlantic salmon after four weeks of challenge. We also tested whether oxidative stress manifested as an underlying depletion mechanism. Carotenoid levels in whole fillet homogenates were not decreased significantly post-challenge but fillet α-tocopherol concentrations were increased significantly in contrast to decreased oxidative stress indices. However, image analysis revealed localised fillet pigment-depletion following all dietary treatments. These data imply that localised pigment-depletion was not prevented by pre-loading of the fillet with different carotenoid-types/mixtures and increased of α-tocopherol levels from normal to high, respectively. Further, we suggest that oxidative stress might not facilitate pigment-depletion in vivo.

The effect of dietary cholesterol on astaxanthin (Ax) absorption and transport in the plasma of Atlantic salmon was investigated. Under controlled conditions, three experimental diets, non-pigmented diet (NPD), NPD with 40 mg Ax kg(-1), and NPD with 40 mg Ax kg(-1) and 2% cholesterol, were fed to juvenile salmon reared in sea water. After 12 weeks, blood was collected and plasma separated for analysis of plasma Ax and cholesterol content. In addition, plasma samples from each group of fish were fractionated into lipoproteins using a sucrose density gradient and ultracentrifugation. The apolipoprotein components of VLDL, LDL and HDL from each sample fraction were separated using SDS-PAGE. The addition of 2% cholesterol to the Ax-containing diet significantly increased the concentration of Ax and cholesterol in fish plasma. The protein-rich fraction was found to be the major carrier of Ax in salmon plasma. Cholesterol supplementation significantly increased Ax in plasma and VLDL as well as increasing plasma cholesterol. The VLDL fraction showed the most significant change in fish fed diet supplemented with cholesterol resulting in higher levels of Ax in this lipoprotein. The results clearly show that dietary cholesterol had a significant effect on the Ax transport process in the blood.

Based on the concept of nutritional programming in mammals, we tested whether a short term hyper or hypo vitamin stimulus during first-feeding could induce long-lasting changes in nutrient metabolism in rainbow trout. Trout alevins received during the 4 first weeks of exogenous feeding a diet either without supplemental vitamins (NOSUP), a diet supplemented with a vitamin premix to satisfy the minimal requirement in all the vitamins (NRC) or a diet with a vitamin premix corresponding to an optimal vitamin nutrition (OVN). Following a common rearing period on the control diet, all three groups were then evaluated in terms of metabolic marker gene expressions at the end of the feeding period (day 119). Whereas no gene modifications for proteins involved in energy and lipid metabolism were observed in whole alevins (short-term effect), some of these genes showed a long-term molecular adaptation in the muscle of juveniles (long-term effect). Indeed, muscle of juveniles subjected at an early feeding of the OVN diet displayed up-regulated expression of markers of lipid catabolism (3-hydroxyacyl-CoA dehydrogenase – HOAD - enzyme) and mitochondrial energy metabolism (Citrate synthase - cs, Ubiquitinol cytochrome c reductase core protein 2 - QCR2, cytochrome oxidase 4 - COX4, ATP synthase form 5 - ATP5A) compared to fish fed the NOSUP diet. Moreover, some key enzymes involved in glucose catabolism (Muscle Pyruvate kinase - PKM) and amino acid catabolism (Glutamate dehydrogenase - GDH3) were also up regulated in muscle of juvenile fish fed with the OVN diet at first-feeding compared to fish fed the NOSUP diet. We researched if these permanently modified gene expressions could be related to global modifications of epigenetic marks (global DNA methylation and global histone acetylation and methylation). There was no variation of the epigenetic marks in muscle. However, we found changes in hepatic DNA methylation, global H3 acetylation and H3K4 methylation, dependent on the vitamin intake at early life. In summary, our data show, for the first time in fish, that a short-term vitamin-stimulus during early life may durably influence muscle energy and lipid metabolism as well as some hepatic epigenetic marks in rainbow trout. Statement of relevance Programming at first feeding with different levels of vitamins was successfully tested in fish for the first time. These data proove one more time the importance of the early life on the fish metabolism in adults.

The experiment was designed to investigate the dietary factors that might enhance or interfere with astaxanthin (Ax) absorption in salmon including potentially interfering factors such as certain carotenoids (zeaxanthin and lutein), plant sterols, fibre and enhancing compounds such as cholesterol and vitamin E. Two hundred and eighty-eight salmon (778 ± 78 g) were reared in sea water under controlled conditions and fed practical experimental diets. The experimental diets were supplemented with 40 mg Ax kg-1, in addition to various dietary factors, including cholesterol (2%), vitamin E (450 IU kg-1), wheat bran (5%), lutein (40 mg kg-1), zeaxanthin (40 mg kg-1) and phytosterol (2%). After 26 days of feeding, blood was collected and plasma was separated to determine the plasma Ax concentration. Ax was not detected in the plasma of fish fed the non-pigmented diet. Fish fed diet containing 2% cholesterol significantly improved Ax absorption, which was reflected in the higher Ax concentration in plasma of Atlantic salmon. Other supplements including vitamin E, wheat bran, lutein, zeaxanthin and phytosterols in diet had no significant effect on plasma Ax concentration. Fish fed diet containing 2% cholesterol significantly increased cholesterol concentration in fish plasma. Phytosterol had no benefit to lower cholesterol plasma level in fish fed 2% phytosterol-supplemented diet.

Since mucosal surfaces represent major portals of entry for pathogens, its associated immune system is important to protect the organism. In this paper, we compared at the cellular and molecular levels intestinal leukocyte suspensions with their head kidney (HK) or peripheral blood (PBL) counterparts to highlight characteristics of intestinal immune functions in healthy rainbow trout. These studies show that intestinal phagocytes are less activated by yeast cells but when they are activated they can ingest as many yeast cells as their HK counterparts. A natural cytotoxic activity could be detected which is twice higher in intestinal than in HK leukocyte preparations. This natural cytotoxic activity is correlated with the expression of transcripts encoding the natural killer enhancement factor (NKEF). Intestinal leukocytes did not respond to an in vitro mitogenic stimulation performed under classical culture conditions. And finally, a high expression of CD8α transcripts was observed in gut leukocyte preparations, suggesting that the intestine could contain a high proportion of T cells expressing the αα homodimeric form of CD8. This kind of comparison on nonimmunized fish provides better knowledge on basal immune functions in the intestine to, analyze later on, immune responses induced by an antigenic stimulation.

Immunity encompasses all mechanisms and responses used by the organism to defend itself against bacteria, viruses or parasites. Adequate supply and balance of nutrients are required for proper efficiency of the host defences. Research has identified dietary factors that affect human and animal immune responses like amino acids, fatty acids, minerals and vitamins. Some of these nutrients have been proven to have specific actions on immunity when provided at pharmacological doses. This paper will review these nutrients and their current use in aquaculture. The immune system is an efficient but complex system. Its complexity has made the assessment of the effects of diets difficult. Nevertheless, the standardization of methodology as well as the use of new techniques at the cell or the gene level should help to better understand the mechanisms of immune modulation. This paper will review the major functions of fish and shrimp immune system and the methodologies used. Cellular and humoral functions including cytokines will be discussed in relation to potential means to modulate them and the underlying mechanism. A better understanding of the mechanisms of modulation of the immune functions should help in the discovery of new dietary factors to improve the immune status of the animal, leading to better disease resistance.

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