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Simple Summary: This study investigated the effects of three artificial diets used in aquaculture, two for rainbow trout and one for Atlantic salmon, on the growth rate, organ responses, gene expression and immune responses of parr juvenile Atlantic salmon. The diets differed with respect to their carbohydrate, protein and lipid levels, with the lipid levels being the main focus of this study. We found no significant differences in the growth, feed efficiency, immunity, histology or gene expression of Atlantic salmon parr between the rainbow trout and salmon feed groups. Therefore, rainbow trout feed, which has a relatively low lipid content, could be used as a rearing feed for juvenile parr-stage Atlantic salmon, bringing potential economic benefits. Lipids in fish diets provide energy and play important roles in immunity and metabolism. Atlantic salmon, a species that migrates from freshwater to seawater, requires high energy, especially during smoltification. Juvenile teleosts have low lipid requirements, and a high dietary lipid content is known to have negative effects on their growth and digestion. Therefore, this study evaluated the effect of two commercial rainbow trout feeds (low-lipid, 13.41% and 14.6%) on the growth and immune responses of early parr-stage Atlantic salmon compared to commercial salmon feed (high-lipid, 29.52%). Atlantic salmon parr (weight: 14.56 ± 2.1 g; length: 11.23 ± 0.44 cm) were randomly divided into three groups and fed either one of two commercial rainbow trout feeds (RTF1 and RTF2) or the commercial salmon feed (ASF) for 12 weeks. At the end of the feeding trial, growth, haematology, histology and gene expression analyses were performed. There were no significant differences in weight gain rates or feed efficiency between the groups (p > 0.05). Superoxidate dismutase, glutathione peroxidase, lysozyme and immunoglobulin M activities were not different among the experimental groups (p > 0.05). A histological examination of the liver and intestinal tissues showed no pathological symptoms of inflammatory response or lipid accumulation in any of the groups. In an intestinal transcriptome analysis using RNA-seq, the expression levels of several genes linked to lipids, immune-related proteins, cytokines and chemokines did not differ significantly between the groups (p > 0.05). Commercial rainbow trout feed with low lipid content has no clear negative impact on the development of Atlantic salmon during the early parr stage (14.5 to 39.6 g). This study provides basic information for the development of economical feed for early parr-stage Atlantic salmon. [ABSTRACT FROM AUTHOR]

Simple Summary: The global price of fish oil continued to increase due to a consistent downward production trend. Therefore, research on the replacement of fish oil is growing and the search for sustainable alternative sources in aquaculture. The present study was conducted to evaluate dietary microalgae, Schizochytrium sp. (SC) as fish oil replacer in rainbow trout, Oncorhynchus mykiss. Our results suggested that dietary SC is well-digested and could replace up to 80% of fish oil in the diet of rainbow trout without negative effects on growth and immune responses. The price of fish oil has reached a historical peak due to a consistent downward production trend, and therefore, the search for sustainable alternative sources has received great attention. This research was conducted to evaluate dietary micro-algae, Schizochytrium sp. (SC) as fish oil (FO) replacer in rainbow trout, Oncorhynchus mykiss. In the first trial, apparent digestibility coefficient (ADC) was 92.4% for dry matter, 91.4% for crude protein, and 94.2% for crude lipid in rainbow trout. In the second trial, six diets were formulated to replace FO at 0% (CON), 20% (T20), 40% (T40), 60% (T60), 80% (T80), and 100% (T100) with SC in the rainbow trout (3.0 ± 0.4 g, mean ± SD) diet. After eight weeks' feeding trial, weight gain (WG), specific growth rate (SGR), and feed efficiency (FE) of fish fed the T20 diet were significantly higher than those of fish fed other diets (p < 0.05). However, there were no significant differences in these parameters among those of fish fed CON, T40, T60, and T80 diets. Lysozyme activity of fish fed the T20 diet was significantly higher than those of fish fed other experimental diets (p < 0.05). After 10 days of disease challenge testing with pathogenic bacteria (Lactococcus garvieae 1 × 108 CFU/mL), the cumulative survival rate of fish fed the T20 diet was significantly higher than those of fish fed the CON, T80, and T100 diets. Therefore, these results suggest dietary microalgae SC is well-digested and could replace up to 80% of fish oil in the diet of rainbow trout without negative effects on growth and immune responses. [ABSTRACT FROM AUTHOR]

This study was conducted to investigate the effects of different taurine levels on the conjugated bile acid composition and growth of juvenile rockfish. Five taurine level diets were made by the supplementation of taurine (0%, 0.5%, 1.0%, 1.5% and 2.0%) to a basal diet. Fish meal washed with 70% ethanol to exclude taurine was used for the sole protein source. Feeding experiments were accomplished at 15°C using juvenile fish (initial BW: 13.5 g). Fish were fed the experimental diets for 4 months. At the end of experiments, fish were weighed and stored at −80°C for analysis of free amino acids and conjugated bile acids contents. The growth performance and feed efficiency of Korean rockfish were improved by taurine supplementation in the experimental diets. The taurine contents of the whole body increased with the increase in the taurine supplementation. The primary conjugated bile acids in gall bladder were taurocholic acid (83.5-165.6 mg mL−1) and taurochenodeoxycholic acid (6.3-20.0 mg mL−1). Total bile acids increased with increases in dietary taurine. Taurocholic acid content was more than 95% of the total conjugated bile acids. This indicates that taurine is the sole amino acid to make conjugated bile acid in Korean rockfish. Dietary taurine levels improved the conjugated bile acid composition in juvenile Korean rockfish. [ABSTRACT FROM AUTHOR]

An 11-week feeding trial was conducted to study the effects of the different levels of dietary vitamin C on growth, tissue ascorbic acid concentrations and histopathological changes in parrot fish. Casein and gelatin-based diets were formulated to contain 0, 60, 120, 240, 480 and 2000 mg l-ascorbic acid (AA) per kg diets on AA equivalent basis in the form of l-ascorbyl-2-monophosphate (AMP), 60 and 240 mg AA per kg diet as l-ascorbic acid. However, the analyzed AA levels were 0, 50, 100, 205, 426 and 1869 mg AA per kg diet in AMP supplemented diets; 36 and 149 mg AA per kg diet in l-ascorbic acid supplemented diets. Thus, the diets were designated as AA-free, AMP50, AMP100, AMP205, AMP426, AMP1869, AA36 and AA149. Fish averaging 3.9±0.06 g (mean±S.D.) randomly were fed the experimental diets in triplicate groups for 11 weeks. Weight gain (WG) of fish fed AMP50 and AA36 diets were significantly lower than those of the other groups, and fish fed AMP1869 diet showed a higher WG than did fish fed AMP50, AMP100, AMP205, AA36 and AA149 diets (P<0.05). However, there was no significant difference in WG between fish fed diets AMP426 and AMP1869, and among fish fed AMP100, AMP205, AMP426 and AA149 diets. Fish fed the AA-free diet began to show deficiency signs, such as retarded growth, darkening, anorexia and high mortality, after 3 weeks of feeding trial. After 6 weeks of the feeding trial, liver from fish fed the AA-free diet showed severe atrophy. By the end of the seventh week, all fish fed the AA-free diet were dead. Liver AA concentration from fish fed AMP50 diet was significantly lower than that from fish fed AMP205, AMP426, AMP1869 and AA149 diets, and fish fed AMP50, AMP100, AA36 diets showed a significant lower AA concentration in liver than did fish fed AMP205, AMP426 and AMP1869 diets.Broken line analysis of weight gain indicated that the dietary vitamin C requirement of parrot fish is 118±12 mg AA per kg diet in the form of l-ascorbyl-2-monophosphate for maximum growth. [Copyright &y& Elsevier]

An 8-week feeding trial was conducted to evaluate the effects of dietary probiotics on growth performance and non-specific immune responses in starry flounder, Platichthys stellatus . Fish averaging 46.5 ± 0.65 g (mean ± SD) were fed one of the six experimental diets; one control (Cont), and five other diets were prepared by supplementing single-probiotics 1 ( Bacillus subtilis ; SP 1 , 2 × 10 9 CFU kg −1 diet), single-probiotics 2 ( Bacillus licheniformis ; SP 2 , 2 × 10 9 CFU kg −1 diet), multi-probiotics 1 ( Bacillus subtilis + Bacillus licheniformis ; MP 1 , 2 × 10 9 CFU kg −1 diet), multi-probiotics 2 (commercial probiotics; Bacillus subtills + Bacillus licheniformis + Paenibacillus polymyxa + Aspergillus oryzae + Saccharomyces cerevisiae ; MP 2 , 2 × 10 9 CFU kg −1 diet) and oxytetracycline (OTC) at 5 g OTC kg −1 diet. At the end of 8 weeks feeding trial, weight gain (WG) and specific growth rate (SGR) of fish fed SP 1 , MP 1 and MP 2 diets were significantly higher than those of fish fed control diet (P < 0.05). Superoxide dismutase (SOD) activity of fish fed MP 2 diet was significantly higher than those of fish fed OTC diet (P < 0.05). Nitro blue tetrazolium (NBT) activity and lysozyme activity of fish fed SP 1 , MP 1 and MP 2 diets were significantly higher than those of fish fed OTC diet (P < 0.05). However, there was no significant difference among fish fed SP 1 , SP 2 , MP 1 and MP 2 diets. During the Edwardsiella tarda challenge test, the first mortality occurred on day 2. After the 14 days challenge test, cumulative survival rate of fish fed MP 1 and MP 2 diets were significantly higher than those of fish fed control diet (P < 0.05). However, there was no significant difference among fish fed SP 1 , SP 2 , MP 1 , MP 2 and OTC diets in survival rate at the termination of the challenge test. Although there was little advantage in immunological parameters with fish fed MP diets, single and multi-probiotics were equally effective statistically. These results demonstrated that single or multi-probiotics had equal beneficial effect as an antibiotic replacer in terms of growth performance, non-specific immune responses and disease resistance in starry flounder. [ABSTRACT FROM AUTHOR]

This study was conducted to evaluate dietary myo -inositol (MI) requirement of juvenile parrot fish. A basal experimental diet was formulated and used as a control and four other diets were prepared by supplementing 100, 200, 400 or 800 mg MI per kg − 1 diet (designated as M0, M100, M200, M400 and M800, respectively). Triplicate groups of fish (initial body weight, 11.5 ± 0.01 g) were fed one of the diets to apparent satiation twice daily for 18 weeks. The results showed the significant increase of growth performance at dietary MI level of 100 mg kg − 1 but no further improvement was observed at higher MI levels. Significantly lower feed conversion ratio was obtained in fish fed the M200 and M400 diets than those fed M0 diet. Significantly lower AST and ALT activities were recorded in fish fed 100 and 100–800 mg kg − 1 MI, respectively, compared to those fed the control. Whole-body protein content decreased significantly at all supplementation levels of MI in comparison to control. Liver MI concentration significantly increased by MI supplementation and inversely correlated with liver lipid content. Broken-line regression analysis indicated that MI requirement of parrot fish is 94.3 and 121.3 mg kg − 1 diet based on weight gain and liver MI concentration, respectively. The findings suggest that approximately 100 mg kg − 1 MI can support maximum growth of juvenile parrot fish and prevent a potential abnormal lipid metabolism. [ABSTRACT FROM AUTHOR]

Abstract: Two consecutive feeding trials were conducted to investigate taurine essentiality and requirement for parrot fish (Experiment I) and to determine whether taurine supplementation to high soybean meal (SM) diets would improve its growth performance (Experiment II). In Exp I, a fish meal (FM) based diet was used as a control and supplemented with 0.2, 0.4, 0.8, 1.2 or 1.6% taurine, and fed to triplicate groups of juvenile parrot fish (initial body weight, 13.5g) to apparent satiation for 8weeks. The growth and feed utilization were significantly improved by taurine supplementation up to 0.8% and thereafter plateaued. An optimum dietary taurine level was determined by a broken-line regression analysis based on weight gain and estimated at 0.88% diet. In Exp II, six experimental diets were prepared by supplementation of 0 or 1.0% taurine to a FM-based diet or addition of 0, 0.1% (low), 1.0% (medium) or 2.0% (high) taurine to a basal diet in which 30% of FM was replaced with SM (designated as FM, FM+T1, SM, SM+T0.1, SM+T1 and SM+T2, respectively). Each experimental diet was fed to juvenile parrot fish (initial body weight, 6.4g) twice daily to apparent satiation for 12weeks. The fish fed SM diet showed significantly lower growth performance compared to fish fed FM-based diets. Supplementation of taurine to SM diet significantly affected fish growth and higher performances were observed in fish fed SM+T1 or SM+T2 diets that were comparable to that of the fish fed FM diet. However, no significant changes were observed regarding the inclusion of taurine into FM-based diet. These results clearly demonstrated the positive effects of dietary taurine supplementation on feed utilization and growth performance of juvenile parrot fish when 30% FM was replaced with SM. The optimum dietary level of taurine seems to be approximately 1% in diets. [Copyright &y& Elsevier]

Abstract: Two studies were conducted to investigate the effects of dietary supplementation of three Bacillus spp. on growth performance, innate immunity and disease resistance of olive flounder against Streptococcus iniae and to examine the efficacy of Bacillus spp. on water quality reducing ammonia concentration and increasing fish survival. In the first experiment, a basal diet was prepared and regarded as a control and three other diets were prepared by supplementing one of three Bacillus spp. (B. subtilis, B. pumilus or B. licheniformis) at the dietary level of 0.5%. Triplicate groups of fish (initial body weight, 25g) were fed one of the four diets for eight weeks. Fish fed with B. subtilis containing diet showed significantly higher growth performance and feed efficiency than fish fed with the control diet. Also, significantly higher survival rates were observed in fish fed B. subtilis or B. pumilus containing diets during the feeding trial. Phagocytic activity was significantly increased in fish fed the probiotic containing diets and higher superoxide dismutase activity was observed in fish fed B. pumilus or B. licheniformis when compared to the control. However, serum lysozyme and myeloperoxidase activities did not significantly differ compared to the control. After a challenge with S. iniae, fish fed B. subtilis or B. licheniformis showed significantly higher survival rates compared to fish fed the control diet. In the second experiment, fish (30.1g) were fed a commercial diet for three weeks and then they were distributed to nine tanks at a density of 30 fish per tank (3 replicates per treatment). Fish were fasted for 5days in static water system, while one of two probiotics, B. subtilis or B. licheniformis was treated every 24h into the rearing water at the concentration of 104 CFUml−1. During the trial, significantly decreased ammonia concentration and fish mortality were observed by the supplementation of B. subtilis into the rearing water. The results in these studies indicate that B. subtilis has beneficial effects on growth performance, innate immunity and disease resistance of olive flounder and quality of the rearing water. [Copyright &y& Elsevier]