Comparison of growth, osmoregulatory capacity, ionic regulation and organosomatic indices of black tiger prawn (Penaeus monodon Fabricius, 1798) juveniles reared in potassium fortified inland saline water and ocean water at different salinities

Growth, osmoregulatory capacity, ionic regulation and organosomatic indices of black tiger prawn (Penaeus monodon Fabricius, 1798) juveniles (2.6 ± 0.2 g mean initial weight) were studied for 28 days in two water types namely inland saline water fortified with 100% K+ (ISW100) as in ocean water (OW) and OW. Three different salinities (5, 25 and 45 ppt) of each water type were prepared. No water type or salinity affected the survival of juveniles. The highest specific growth rate (SGR) was observed at 25 ppt in OW (4.7 ± 0.2%/day) and ISW100 (4.1 ± 0.1%/day). The serum osmolality was hyper-regulated and hypo-regulated in salinities below and above isosmotic points respectively. There was no significant difference (P > 0.05) between osmoregulatory capacity (OC) of juveniles in ISW100 and OW at any salinity or time, except at 25 ppt. Except exoskeleton moisture content (EM%) of the juveniles reared in OW, there were no significant differences (P > 0.05) among any organosomatic indices of the juveniles reared in ISW100 and OW. At 5 and 45 ppt, in both water types, serum Na+, K+ and Ca2+ concentrations were strongly regulated above and below isoionic points. However, the serum Mg2+ concentration was reduced below the medium Mg2+ concentrations at all salinities. The ability of P. monodon juveniles to regulate these ions in inland saline water (ISW) was improved by fortifying K+ in ISW to a similar level as in OW. The present trial thus augments the importance of fortification of K+ in ISW to a similar level as in OW for P. monodon culture.