Insights into the functional properties of a natural free amino acid mix: Effect on growth performance, nutrient metabolism, and immune response in a carnivorous fish, Asian seabass (Lates calcarifer).

Dietary supplements containing a functional feed additive have been shown to be beneficial to fish and shellfish aquaculture. However, the functional properties of aquafeed formulations have rarely been reported in fish. This study aimed to investigate the effects of natural free amino acid mix (FAAM) supplementation as a functional solution on the growth performance and nutrient utilization in a carnivorous fish, Asian seabass (Lates calcarifer). Five isonitrogenous and isolipidic diets were prepared with graded supplementation levels of FAAM at 0 % (control group), 0.25 %, 0.50 %, 0.75 %, and 1.0 %, denoted as FAAM0, FAAM0.25, FAAM0.5, FAAM0.75, and FAAM1.0, respectively. The experimental fish were fed different dietary FAAM supplementations to apparent satiation twice daily for eight weeks. Significant improvements were observed in the growth performance of fish among the five groups (P < 0.05). Fish fed with FAAM0.75 displayed significantly increased activities of lysozyme, myeloperoxidase, catalase, and glutathione peroxidase (P < 0.05). The activities of digestive enzymes, including amylase, protease, and lipase, were enhanced by the supplementation of FAAM in the feed (P < 0.05), especially for the groups that contained more than 0.5 % FAAM in the feed. Furthermore, the morphological profile of the intestinal tract, including the mucosal fold height, width, thickness, and goblet cell, increased in fish fed with FAAM at 1.0 % (P < 0.05). Moreover, FAAM supplementation in diets not only modulated the expression of immune-related genes (glutathione peroxidase (GPx), complement (C)3, C4, and C-reactive protein) in the liver but also positively impacted the growth-ralated genes, including growth hormone (GH), GH receptor (GHR), insulin-like growth factor I (IGF-I), and IGF-II. In addition, the amounts of monounsaturated fatty acids (mainly oleic acid (C18:1n9c)) and polyunsaturated fatty acids-especially γ-linolenic acid (C18:3 n6) and α-linolenic acid (C18:3n3)-increased in fish fed with diets containing FAAMs (P < 0.05). Interestingly, the diets supplemented with FAAMs also had a positive effect on the economic indices in terms of revenue-to-cost ratios. These findings provide a scientific basis for the application of FAAMs as a functional solution that can be used in feed formulations for Asian seabass.

Optimum dietary sources and levels of selenium improve growth, antioxidant status, and disease resistance: re-evaluation in a farmed fish species, Nile tilapia (Oreochromis niloticus).

The objective of this study was to investigate the effects of sources and levels of selenium (Se) on juvenile Nile tilapia (Oreochromis niloticus). A completely randomized design involving a 2 × 3 factorial arrangement of treatments was used in this study. Organic Se (L-selenomethionine; SeMet) and inorganic Se (sodium selenite; Na2SeO3) were each added to the basal diet at 1, 3 and 5 mg Se/kg. The basal diet, without Se supplementation, was used as a control. There was a total of 7 experimental diets, and each was fed in triplicate to groups of fish with an initial average body weight of 13.5 g for 8 weeks. The results showed that growth performance was significantly affected by dietary sources and levels of Se (P < 0.05). Fish fed diets supplemented with SeMet of 1.0 mg Se/kg resulted in higher growth performance compared to basal diet (P < 0.05), but Na2SeO3 supplementation did not affect growth. The feed conversion ratio was significantly decreased as dietary sources of SeMet (P < 0.05). Interestingly, fish fed diets supplemented with both forms of Se had lower cholesterol levels than those fed the basal diet (P < 0.05). Moreover, dietary sources and levels of Se significantly increased (P < 0.05) the antioxidant enzyme activities such as lysozyme, catalase, myeloperoxidase, superoxide dismutase and glutathione peroxidase. Dietary sources and levels of Se significantly could enhance the Nile tilapia resistance against Streptococcusagalactiae infection (P < 0.05). Overall, it can be concluded that the inclusion level of 1.0 mg Se/kg of organic Se in the diet is suggested to be the optimal level for the growth performance and immune response of Nile tilapia. Therefore, dietary supplementation with Se is useful for improving growth, antioxidant status, immune response, and disease resistance.

Impacts of Aegle marmelos fruit extract as a medicinal herb on growth performance, antioxidant and immune responses, digestive enzymes, and disease resistance against Streptococcus agalactiae in Nile tilapia (Oreochromis niloticus).

An experiment was conducted to investigate the effects of Aegle marmelos fruit (AMF) extract on the growth performance, biochemical parameters, immune response, antioxidative capacity, and digestive enzyme activity of Nile tilapia (Oreochromis niloticus). Fish were fed a diet supplemented with AMF at concentrations of 0 (AMF0; control), 5 (AMF5), 10 (AMF10), 15 (AMF15), or 20 (AMF20) g/kg for 8 weeks. The results show that the final body weight, weight gain, specific growth rate, average daily gain, and feed conversion ratio were significantly higher in fish fed AMF15 and AMF20 compared to those fed the control diet (P < 0.05). Moreover, significant increases in antioxidant enzyme activities and non-specific immune responses were observed in groups fed AMF15 and AMF20. Interestingly, the level of cholesterol decreased with increasing AMF concentrations in the diet. As dietary AMF levels increased, digestive enzyme activities significantly improved. After the feeding trial, fish were injected intraperitoneally with Streptococcus agalactiae, and the 14-day cumulative mortality was calculated. A high survival rate after challenge with S. agalactiae was observed in all groups that received AMF-supplemented feed. Therefore, the present study suggests that supplementing the diet of Nile tilapia with AMF at a concentration of 20 g/kg could encourage their growth, improve their immunity and antioxidant status, and provide strong protection against S. agalactiae.