1. 1. The dry solids of eggs and larvae are gradually decreased, the most pronounced mass reduction being observed in larvae. In the process of egg development the water content is significantly increased after fertilization and the transition to larva state. 2. 2. In the first two days after fertilization a loss of a minor amount of Na⁺ is observed, K⁺. Mg²⁺ and Ca²⁺ contents vary but slightly. 3. 3. In the course of a week of life in fresh water before passing to active feeding the larvae get from the environment and accumulate Na⁺, K⁺ and Ca²⁺.