Growth, digestive enzymes activities, serum biochemical parameters and antioxidant status of juvenile genetically improved farmed tilapia (Oreochromis niloticus) reared at different stocking densities in in-pond raceway recirculating culture system

Abstract

The feeding trial was conducted in 80 days to assess the effects of stoking densities on growth, digestive enzymes activities, serum biochemical parameters and antioxidant status of juvenile genetically improved farmed tilapia (GIFT, Oreochromis niloticus) reared in in-pond raceway recirculating culture system (IPRS). Fish (initial body weight: 6.25 ± 0.32g ) were randomly allotted to six in-pond raceways (22 × 5 × 2.5 m) stocked at three different stocking densities: low stocking density (LSD, 0.28 kg/m3), medium stocking density (MSD, 0.57kg /m3) and high stocking density (HSD, 0.85 kg /m3). The results indicated that no significant differences were observed in final body weight, weight gain and specific growth rate of GIFT reared at different stocking densities on day 20 (p > 0.05). Fish reared in the HSD group showed poor growth than those reared in the LSD and MSD groups on day 50, but fish reared in the MSD and HSD groups showed poor growth than those reared in the LSD group on day 80. There were no significant differences found in digestive enzyme activities, serum cortisol, lysozyme and superoxide dismutase (SOD) content, hepatic catalase (CAT), total SOD, total antioxidant capacity (T-AOC) activities and malondialdehyde (MDA) content among fish reared at different densities treatments (p > 0.05). Fish reared in the HSD group exhibited significant higher red blood cell number, haematocrit and glucose (GLU) contents on day 80 (p < 0.05). In brief, under this trial conditions, high stocking densities (0.57 kg/m3) resulted in decrease in growth, and GIFT might have an adaptation capability to crowding stress without a change in antioxidant activity, some physiological and immune parameters.