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In this study, we investigated the effects of different Ca2+ and Mg2+ concentrations in the water column on the growth and molting of Macrobrachium rosenbergii. We used three concentrations of both Ca2+ and Mg2+ and tested these in culture experiments over a period of four complete molting cycles. Analyses revealed that increasing concentrations of Ca2+ in the water led to a gradual reduction in the expression levels of MIH and a gradual increase in the expression levels of EcR and chitinase, thus accelerating molting frequency and shortening the molting cycle. However, high concentrations of Ca2+ significantly reduced the survival rate of M. rosenbergii. Increasing concentrations of Mg2+ in the water column led to a significant increase in heart beat count (P < 0.05); in addition, malate dehydrogenase activity during postmolt A and intermolt C tended to increase, and energy metabolism was accelerated. Furthermore, increased Ca2+ concentrations in the water column promoted an increase in the Ca2+ content of muscles and shells. In contrast, as the Mg2+ concentration in the water column increased, the Mg2+ content in the muscles and shells showed different patterns of change. Too low or too high Ca2+ and Mg2+ concentrations in the external environment had differing degrees of negative effects on the gill tissue such as edema and necrosis. In summary, low levels of Ca2+ and Mg2+ in the external environment reduced ion levels in the muscle and shell; inhibited growth, molting, and survival; and exerted negative effects on the gill tissue. Furthermore, high concentrations of Ca2+ and Mg2+ may accelerate molting rate and energy metabolism, but can cause more serious damage to gill tissue and reduce the survival rate. [ABSTRACT FROM AUTHOR]