Effects of Ca2+ and Mg2+ in the water column on the growth and moult of Macrobrachium rosenbergii

Abstract In order to investigate the effect of different Ca²⁺ and Mg²⁺ concentrations in the water column on the growth and moulting of Macrobrachium rosenbergii. In this study, three concentrations of Ca²⁺ and three concentrations of Mg²⁺ were designed to conduct a culture experiment for a period of four complete moult cycles. The results showed that with increasing Ca²⁺ concentration in water, the expression level of MIH showed a decreasing trend, and the expression level of EcR and chitinase showed a gradual increasing trend, which accelerated the moult frequency and shortened the moult cycle. However, high Ca²⁺ concentration significantly reduced the survival rate of M. rosenbergii. With increasing Mg²⁺ concentration in the water column, the heartbeat count increased significantly, the MDH activity during postmolt A and intermolt C tended to increase, and the energy metabolism was accelerated. An increase in Ca²⁺ concentration in water promotes an increase in Ca²⁺ content in muscle and shell. However, as the Mg²⁺ concentration in water increased, the Mg²⁺ content in muscle and shell showed different patterns of change. Too low or too high Ca²⁺ and Mg²⁺ in the external environment will have different degrees of negative effects on the gill tissue, especially the damage of Mg²⁺ to the gill tissue is more serious. In summary, low levels of Ca²⁺ and Mg²⁺ in the external environment reduce ion levels in the muscle and shell, growth, moult and survival are inhibited, while having a stressful effect on gill tissue. High concentrations of Ca²⁺ and Mg²⁺ may accelerate moulting rate and energy metabolism, but will cause more serious damage to gill tissue and reduce the survival rate.