Dynamics of composition and morphology in oocytes of Eurasian perch, Perca fluviatilis L., during induced spawning

Histological and chemical composition (water, protein, lipids, fatty acid profile [FA]) analyses of gonads and ovulated eggs in various (I–VII) maturation stages of wild Eurasian perch, Perca fluviatilis L., were carried out on females during induced (hCG 500 IU kg− 1) spawning under controlled conditions. The results indicate that the process of vitellogenesis is finalized in the first two maturation stages (I and II). An analysis of the gonad composition and the FA profile indicated that the proper process of the final oocyte maturation (FOM; germinal vesicle [GV] migration and coagulation of oil droplets, GV disintegration) does not begin until stage III and ends with ovulation (stage VII). This follows from the fact that in stages I–II, fat was incorporated into the oocytes and n-3 polyunsaturated fatty acids accounted for the highest share of FA built into the oocytes at that time. Additionally, it was found that in the Eurasian perch the oocytes are hydrated just before the ovulation itself, after proteolytic processing of vitellogenin into a homogenous yolk mass or at the end of this process. On the other hand, the hydration process itself proved the least intensive (only 4%) of the processes previously described in the teleosts. On the basis of the obtained results, it is recommended that hormonal stimulation should not be performed during artificial spawning of the Eurasian perch in the first two specified maturation stages since this could possibly adversely affect the quality of the obtained eggs.

► We investigated maturation process in hormonally stimulated Eurasian perch females.
► Histological and composition analysis were done at different maturational stages.
► Changes in ovaries composition were observed up to the maturation stage III.
► Histological analysis first time showed yolk proteolysis and egg hydration in perch.
► It is not recommended to induce perch females up to the maturation stage III.