Effects of Salinity and Na+/K+ Ratio on Osmoregulation and Growth Performance of Black Tiger Prawn, Penaeus monodon Fabricius, 1798, Juveniles Reared in Inland Saline Water

A 60-d growth trial was conducted with the black tiger prawn, Penaeus monodon (ca. 0.8g juveniles) at CIFE Rohtak Centre to evaluate the effects of salinity and Na+/K+ ratio of inland saline water on shrimp growth, survival, and osmoregulation. Three different salinities (5, 10, and 15ppt) and five different Na+/K+ ratios (25:1, 45:1, 65:1, 85:1, and 27.9:1), for a total of 15 treatments were prepared by ionic manipulation. The medium with Na+/K+ ratio 27.9 was reconstituted seawater and was used as the reference treatment. At the end of the 60-d trial both salinity and Na+/K+ ratio significantly influenced the survival and growth of shrimp in inland saline water (P<0.05). Final mean individual weight, weight gain (%) (WG [%]) increased with decreasing Na+/K+ ratios. Survival rates were significantly higher (P<0.05) for Na+/K+ ratio 45 and 27.9 at salinities 10 and 15ppt, respectively. Minimum growth and survival (0-24%) were observed in mediums with Na+/K+ ratio 85 at all salinities. Serum osmolality and osmoregulatory capacity were similar across all treatments at identical salinities except for sodium to potassium ratio (Na+/K+) 85. The serum sodium and potassium levels did not show any significant difference (P>0.05) for mediums with Na+/K+ ratio 25, 45, 65, and 27.9 at all salinities. Significantly different (P<0.05) serum sodium levels were observed in mediums with Na+/K+ ratio 85 at all salinities at the end of the trial. The serum potassium levels were significantly low in treatments with Na+/K+ ratio 85. There was no significant difference in the serum magnesium levels between treatments and the serum calcium levels were significantly lower for shrimp reared in the reference mediums. Results of this study confirm that P. monodon can be successfully cultured in low salinity waters with Na+/K+ ratio ranging between 25 and 45:1.