Growth performance, digestive enzyme activity, non-specific immune response and stress enzyme status in early stages of grey mullet reared in a biofloc system.

Abstract

A 60- day experiment was conducted to evaluate the effect of biofloc on growth per-formance and physiological responses of grey mullet (Mugil cephalus). Grey mullet fry (average body weight of 0.91 ± 0.01 g) were stocked in biofloc treatment (BFT) and clear water (CW) control in triplicates. Grey mullet reared in biofloc- based units attained significantly better (p < 0.05) performance in terms of final body weight (FBW) (5.98 ± 0.08 g), specific growth rate (SGR) (3.15 ± 0.05), percentage weight gain (PWG) (560.7 ± 18.7) and survival (80.00 ± 3.8) with lower feed conversion ratio (FCR) (1.65 ± 0.04) and higher protein efficiency ratio (PER) (1.74 ± 0.04). The proximate analysis of the carcass showed better crude protein and crude lipid values in grey mullet reared in BFT than CW. In line with the growth performance, signifi-cantly higher activities of digestive enzyme such as, amylase (7.46 ± 0.28 U mg pro-tein−1), lipase (1.55 ± 0.07 U mg protein−1) and protease (2.91 ± 0.25 U mg protein−1) were found in the fish reared in BFT. Similarly, significantly higher serum protein (3.60 ± 0.46 mg ml−1), serum albumin (2.69 ± 0.30 mg ml−1), NBT (0.45 ± 0.02) and myeloperoxidase activity (0.98 ± 0.02) were found in fish reared in BFT compared to CW. There were no significant differences in stress indicators like serum cortisol and serum glucose of fish between the two groups, but lower values were observed in BFT. The results of this study demonstrated that biofloc- based culture system is ef-fective in improving nursery rearing of M. cephalus by enhancing growth performance, digestive enzyme activity, immune status and reduced stress response.