The giant freshwater prawn Macrobrachium rosenbergii hatchery operators often face difficulties in seawater transportation. Thus, we aimed to test the locally available crude salt as a suitable alternative to seawater in hatchery operations. For this purpose, seven treatments with different combinations of seawater, brine and crude salt (viz. T1 = 100% seawater, T2 = 100% brine solution, T3 = 100% crude salt, T4 = 80% seawater and 20% crude salt, T5 = 70% seawater and 30% crude salt, T6 = 60% seawater and 40% crude salt and T7 = 50% seawater and 50% crude salt) were tested in the rearing of M. rosenbergii larvae. Water quality parameters exhibited no significant differences, but elemental (Na, Mg, Ca, K, Zn, Cu, Cd and Pb) assemblage (via main effect PERMANOVA) varied across the treatments. Most of the water elements revealed a significant bivariate relationship with the post larvae (PL) production parameters, and this was also confirmed by multivariate RELATE analysis. Among the elements, BEST analysis and the DISTLM model showed that ionic imbalance, especially Na+ concentration, is the main modulator in the hatchery production cycle, productivity and PL survivability. This proves that seawater is the best culture media for larvae rearing but up to 30% replacement by crude salt could be possible at 12 g/L water salinity for giant freshwater prawn PL production.