Dynamics of the content of H2O, Na, K, Ca and Mg in the eggs of bream, Abramis brama L. in natural conditions and under stress

Abstract

Objective: To study the dynamics of H2O, Na, K, Ca and Mg content in the oocytes of bream, Abramis brama observed in prespawning period on breeding ground and in reply to catching, transportation and subsequent remaining of spawners in a cage. Methods: For research on the dynamics of H2O and cations content in the oocytes of bream females, Abramis brama in the course of eggs transition from maturity Stage IV to Stage V, fishes were caught from breeding ground in the coastal zone of the Volga Reach of the Rybinsk reservoir at the Vereteya Station. For studying the influence of stress, the bream (76 individuals) were caught from breeding ground by hauling the seine during 15 min. Capture, sorting and transportation for 3 h to the ponds were the stress factors. Samples of oocytes from 6-8 fishes were taken immediately after capturing, then two more were taken during transportation. Later fishes were removed from the cage in certain time intervals. Concentration of Na and K in the dissolved samples of oocytes was measured by the spectrometer (Flapho-4, Carl Zeiss, Iena, Germany) and content of Ca and Mg was measured by atomic-absorption spectrometer-1 (the same producer). Results: In natural conditions before spawning in the course of maturation of oocytes from maturity Stage IV to V, H2O content in the ovicells of bream has increased by 3.3% and concentration of Na, K, Ca and Mg has decreased by 24.9%, 38.1%, 56.2% and 65.7%, accordingly. Stress caused by capturing, transportation and the subsequent remaining of bream spawners in a cage did not change parameters of water-salt exchange of the oocytes. Conclusions: In natural conditions before spawning, the maturation of oocytes of bream from maturity Stage IV to V take place. Stress caused by capturing, transportation and the subsequent remaining of bream spawners in a cage prevents the transition of eggs from maturity Stage IV to V. It is suggested that in order to develop optimal technique stimulating oocytes maturation and the process of ovulation in industrial conditions, study of these reactions of spawners of one or another species in natural environment is preferentially conducted. Conditions of incubation and combination of hormonal preparations selected on the basis of these