Effects of dietary salt supplementation on growth, body composition, tissue electrolytes, and gill and intestinal Na+/K+ ATPase activities of black sea bass reared at low salinity

Abstract

Abstract Two feeding trials were conducted to investigate the effects of dietary sea salt supplementation on growth and survival of black sea bass Centropristis striata reared under sub-optimal salinity conditions at 15 and 10 g L− 1. In experiment 1, six iso-nitrogenous (46% crude protein) and iso-lipidic (10% lipid) test diets containing a mineral premix were formulated to supplement graded levels (0, 2.5, 5, 7.5, 10, and 12.5% dry wt.) of natural sea salt (99.9% NaCl). Diets were fed twice daily to juveniles (mean wt. = 8 g) held in triplicate 75-L tanks at a salinity level of 15 g L− 1 under controlled laboratory conditions for 56 days. In experiment 2, six natural salt-based diets as in experiment 1 and another diet with 0% salt and no mineral mix were formulated. Diets (experiment 2) were fed to triplicate groups of fish (mean wt. = 9.37 g) held at 10 g L− 1 salinity for 70 days. In both experiments, final survival was 78–97%, with no treatment differences. At 15 g L− 1 (experiment 1), no differences in weight gain were observed among dietary salt treatments. In contrast, a 5% salt diet significantly (P   5% salt at 10 g L− 1 showed higher survival when challenged with a further reduction in salinity to 4 g L− 1. Gill Na+/K+ ATPase activities appeared to be higher in fish fed the diet with highest level (12.5%) of supplemental salt, whereas intestinal Na+/K+ ATPase activity appeared to be maximal at lower levels of dietary salt. Irrespective of dietary salt treatment, black sea bass juveniles maintained good growth and survival and normal whole body electrolyte concentrations at rearing salinities of 10 and 15 g L− 1, indicating that these fish are good osmoregulators and could be potentially cultured under these low salinities. The results indicate that dietary salt supplementation at 5% improved growth and averted mortality under low salinity conditions. These findings may enable black sea bass to be grown in recirculating aquaculture systems in low-salinity brackish water. Relevance with commercial aquaculture These results indicate that dietary salt supplementation may be used to avert mortality when a producer is faced with adversely low salinity conditions due to weather and tides as may occur in coastal black sea bass fish farms sourcing brackish water from tidal creeks.