Potassium amendment of inland saline groundwater: Insights into the physiological responses of silver pompano Trachinotus blochii (Lacepede, 1801) at different salinities

A trial was conducted to evaluate the effect of graded levels of potassium (K+) amended inland saline groundwater (ISW) on serum ionic composition, antioxidant and metabolic enzymes [Na+/K+ATPase, Catalase, Superoxide dismutase (SOD), Glutathione peroxidase (GPx), Glutathione S-transferase (GST), Lactate dehydrogenase (LDH), aspartate aminotransferase (AST)] activities of silver pompano, Trachinotus blochii (Lacepede, 1801). The ISW was amended with 100% K+ at 5 ppt (ISW5), 10 ppt (ISW10) and 15 ppt (ISW15) and reconstituted seawater (RSW) with similar salinities (RSW5, RSW10 and RSW15) was employed as a reference medium. Experiment was conducted using completely randomised design. T. blochiijuveniles (1.5±0.5 g) were reared in 300 l capacity circular FRP tanks for 90 days. Fish were fed with commercial extruded floating feed. At the end of experimental period, serum ionic composition, enzymatic profiles and proximate composition were estimated. Results of the study showed that the serum ionic content (K+, Na+, Ca2+ and Mg2+) varied dose-dependently with salinity (p<0.05). Na+/K+ATPase, antioxidant enzymes (Catalase and SOD) and metabolic enzymes (GPx, GST, LDH and AST) showed higher activities at lower salinity (ISW5 and RSW5) compared to fish reared at 10 ppt and 15 ppt ISW. Similarly, proximate composition exhibited significantly (p<0.05) lower protein and lipid content at lower salinity (ISW5 and RSW5) signifying the stress condition at lower salinity. Physiological responses of T. blochii in terms of serum ionic composition, enzymatic profile and proximate composition were optimum at 10 and 15 ppt amended ISW, implying that rearing at 10-15 ppt with 100% K+ amendment of inland saline groundwater is appropriate. Keywords: Antioxidant activity, Inland saline groundwater, Metabolic enzymes, Potassium amendment, Proximate composition