Abstract
As a result of studies for 3 years on the roach Ratilus ratilus under natural conditions, it was shown that the Na, K, Ca, and Mg content in the blood plasma, erythrocytes, and muscle tissue as well as muscle water were maintained year after year within definite ranges characterizing normal values for these parameters. Comparison of variations in the Na, K, Ca, Mg blood plasma concentrations in different fish species revealed the presence of common limits for each of these elements. Throughout the year the most essential changes in the roach blood and tissue cation levels were found during reproduction period. During spawning the fish are characterized by the state of acute stress with parameters indicating a decrease in stability and exhaustion of adaptive possibilities in animals. Intensification of defense reactions, including those providing maintenance of the water–salt homeostasis occurs shortly before spawning for a preliminary preparation to the stress situation.
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