Histological and morphological analysis of oocytes of the Prussian carp (Carassius gibelio Bloch, 1782) under the conditions of the Zaporizhzhia (Dnipro) reservoir

Purpose. To conduct histomorphological analysis of the Prussian carp eggs under the conditions of Zaporizhzhia (Dnipro) reservoir. Methods. The research was carried out at two observation stations located in the Samara Bay and the lower part of the Zaporizhzhia (Dnipro) Reservoir. The catches were carried out by standard gill nets with 30-120 mm mesh sizes. The object of the study was Prussian carp. The biological analysis of fish was carried out in accordance with the classical methods in ichthyology. For studying the fertility of fish, ovaries from females were taken at the stage IV of maturity. The stage of gonad maturity was determined visually. Individual absolute fertility was determined by the weighting method. To study the reproductive potential and features of fish reproduction, ovaries were taken from females at different stages of maturity. Samples were preserved in Bouin solution and further processed according to generally accepted histological methods. For the preparation of sections, a "Thermo scientific microm HM 325" microtome was used. The sections were stained with hematoxylin-eosin and by Mallory method. Images of preparations were made using a "Sciencelab T500 5.17M" digital camera, connected to a "MICromed XS-2610" microscope. During the description of the periods and phases of growth and development of gonads, stages of ovarian maturity, we used standard ichthyological definitions and terms. Statistical processing was carried out using the STATISTICA 6.0 software. Findings. The structure of the oocytes of Prussian carp is similar to that of common carp: they do not have a fatty drop, there is a wide radially-shaped membrane and a micropyle. The Prussian carp is characterized by asynchronous trophoplasmic growth of oocytes and intermittent spawning. It has been determined that if the spawning is intermittent, the first portion of eggs contained about 60% of all eggs, and the second and subsequent portions the remaining 40%. The absolute fertility of the Prussian carp ranged from 10.51 to 189.95 thousand eggs. The average fertility index in all age groups was 80.28 ± 16.55 thousand eggs. In spawning population, the proportion of females was 55%, males – 45%. The yield to the fishery from eggs was 0.005%. Scientific novelty. For the first time histomorphological analysis of Prussian carps under the conditions of Zaporizhzhia (Dnipro) reservoir was conducted. Practical significance. The study of fish gonads has a significant applied importance for resolving the issues of commercial fishery and ecological monitoring.