Early life stages of carp (Cyprinus carpio L.) depend on ambient magnesium for their development.

Carp eggs, fertilized in vitro, were allowed to develop in fresh water with magnesium concentrations varying from 0.001 to 0.100 mmol l-1. Magnesium concentrations below 0.010 mmol l-1 seriously impeded carp embryonic development: the incidence of deformed larvae and mortality increased steeply to 100% at water magnesium concentrations of 0.001 mmol l-1. Thus, early life stages of carp require ambient magnesium for survival and successful development. The magnesium and calcium concentrations of the developing eggs were dependent on the ambient magnesium concentration. The uptake of magnesium by eggs decreased and the uptake of calcium increased with decreasing ambient magnesium concentrations. However, the uptake of the sum of these divalent ions seemed to be independent of ambient magnesium concentration. This indicates a competition between magnesium and calcium for (passive) uptake into developing eggs.