Effect of stocking density on growth performance, digestive enzyme activity, body composition and gene expression of Asian seabass reared in recirculating aquaculture system

Abstract

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/m3) 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/m3). On the other side, fish reared in higher stocking densities (140, 210. 280 and 350 fish/m3) 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/m3. 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/m3 in a recirculatory aquaculture system could improve the growth performance, metabolic and molecular activities of the fish.