A 60‐day indoor feeding trial was conducted to evaluate the effects of dietary tryptophan supplementation on growth performances, whole‐body chemical composition, expression of muscle growth‐related genes (MyoD, myogenin and myostatin), and haematological and biochemical responses of juvenile genetically improved farmed tilapia (GIFT). Five corn–soy‐based isonitrogenous and isoenergetic diets were formulated to contain graded levels of dietary tryptophan (2.6, 3.2, 3.7, 4.2 and 4.8 g/kg of diet). Each diet was randomly assigned to triplicate groups of 30 fish (5.3 ± 0.1 g) per experimental unit, which were fed thrice a day (9:00, 13:00 and 17:00 hr). Maximum growth performances and feed utilization were observed in fish fed tryptophan at 3.7 g/kg of diet. There was no significant (p > .05) effect on whole‐body composition and amino acid profile by dietary tryptophan supplementation. However, significant (p < .05) differences were observed in plasma metabolites and the mRNA expression of MyoD, myogenin and myostatin. Serum cortisol level was found significantly lowest in fish fed tryptophan at 3.7 g/kg of diet. Second‐order polynomial regression analysis of weight gain and nitrogen gain against dietary tryptophan levels indicated that the optimum dietary tryptophan requirement for maximum growth and feed utilization of juvenile GIFT tilapia was 3.8 g/kg of diet.

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Stocking density is one of the critical factors that influence the production and health status of fish in aquaculture practices. In this 60-day trial, effect of different stocking densities (70, 140, 210, 280 and 350 fish/m 3 ) on growth performance, digestive enzyme activity, body composition and gene expression of Asian seabass, Lates calcarifer, was studied using Recirculating Aquaculture System by following completely randomized design with four replications. Asian seabass (5.20 ± 0.10 g) were randomly distributed in 20 tanks, each of 500-L capacity, and fed four times a day (6:00, 12:00 18:30 and 23.00 h). The study found that growth performance and feed utilization efficiency were significantly decreased with increasing stocking density. A significantly higher survival (95.00 ± 1.25%) was recorded in the low stocking density group (70 fish/m 3 ). On the other side, fish reared in higher stocking densities (140, 210. 280 and 350 fish/m 3 ) displayed lower digestive enzyme activities, such as protease, amylase, lipase and cellulase. There is a significant density-dependent decrease in crude protein deposition in the fish body and the study found significantly higher protein (19.12 ± 0.10%) content in the 70 fish/m 3 . The relative gene expression of GH/ IGF axis and myostatin (MSTN) was significantly down-regulated and up-regulated, respectively, with the increasing stocking density. Overall, the study found that the increasing stocking density produced chronic stress which negatively affected the growth performance of the fish. Therefore, the study suggests that rearing of Asian seabass at a stocking density of 70 fish/m 3 in a recirculatory aquaculture system could improve the growth performance, metabolic and molecular activities of the fish.

Utilization of Bio-methanated Distillery Effluent (Spent Wash)

Background: This experiment was conducted to evaluate the effect of different stocking density on growth performance, survival, water quality and body indices of E.suratensis fingerlings for 90 days at PRFF, Pazhaverkadu. Methods: Three different stocking densities are 100, 200, 300 no of fishes/m3. The fingerlings of pearlspot, E.suratensis with an average body weight of 5.05±0.03 g were stocked at a rate of SD-1 (100/m3), SD-2 (200/m3) and SD-3 (300/m3) culture for a period of 90 days. Result: The growth parameters were found to significantly decrease with increasing stocking density in the biofloc rearing system. Result of Nitrite and nitrate concentrations were significantly lower in the BFT treatment with lower stocking density than in higher stocking density (P less than 0.05). The highest mean body weight gain recorded in SD1 (42.37±0.04 g) followed by SD2 (29.98±0.08 g) and SD3 (20.85±0.06 g). BFT significantly increased fish specific growth rate and net yield. There was no significant difference in hematology analysis (in terms of white blood cell and red blood cell counts, hemoglobin and hematocrit levels), total superoxide dismutase activity of fish between different stocking density (P greater than 0.05). Second-order polynomial regression analysis of weight gain against pearlspot culture under lower stocking stocking density (100/m3) indicate that biofloc technology culture with lower stocking density can improve the growth performance and immune response and also the maintenance of good water quality and improvement of feed utilization of pearlspot.