Effects of Water Hardness and Calcium: Magnesium Ratios on Reproductive Performance and Offspring Quality of Macrobrachium rosenbergii

This study evaluated the effect of specific calcium and magnesium ratios at two hardness values on reproductive performance and offspring quality of Macrobrachium rosenbergii brood-females. Hatchery water containing 110.5mg/L CaCO3 hardness was considered baseline as it has been used successfully to hatch and rear larvae and was used as the control treatment. At each hardness value of 150 and 190mg/L CaCO3, four experimental water treatments were made in triplicate. Each treatment was adjusted using soluble salts (CaCl2H2O, MgSO(4)7H(2)O, and MgCl(2)6H(2)O) to provide the hardness and calcium to magnesium ratios of 0:20, 20:80, 50:50, and 80:20 needed. Each of the experimental tanks (140L) were stocked with six females and one male. The results indicated that both hardness and Ca:Mg ratios affect brood-female reproductive qualitative parameters such as intermolt period, egg hatchability, egg dry weight, and egg-clutch somatic index (ESI) parameters (P<0.05) but not fecundity and eggs per spawn. The results revealed that brood-females at 150mg/L hardness showed greater reproductive performance than at 190 and 110.5mg/L hardness. The findings also demonstrated that the treatment 50Ca50Mg at 150mg/L hardness with 38.8mg/L calcium and 12.9mg/L magnesium had optimum reproductive performance and offspring quality for M. rosenbergii brood-females.