Histomorphological study of the gonads of the Caspian roach in the period 2023–2024

The relevance of histomorphologic study of the Caspian roach gonads is determined by the continuing population decline of this species. The study of the functional status of the gonads in the depressed state of the population is important for assessing its reproductive potential and ability to recover. The absence of a large number of resorbed oocytes ensures normal fecundity, and vice versa, the presence of disorders in gonad development leads to reduced fecundity, worsened survival of eggs and larvae. Decreasing Caspian Sea level, water temperature fluctuations, and lack of suitable spawning substrate may contribute to the destruction of maturing oocytes, suppressing the reproductive potential of the fish population. The material for this study was gonads of females sampled during the spring spawning migration from the Caspian Sea to the Volga River and the prewintering period in the Northern Caspian Sea 2023–2024. The ovaries of female roach were at IV and IV–V stages of maturity during the spawning migration period, and at III and III–IV stages of maturity during the pre-wintering period. It was shown that the maximum level of individual disturbance was 2 times higher during the spring period 2023–2024 than during the fall period. It was determined that the individual proportion of oocytes with abnormalities in 2023–2024 was in the range of 23–28%, averaging 25%. Mass resorption of oocytes, detected only during the spawning migration period, was at 13%. Disturbances in the shell structure, changes in the cytoplasm and single cases of complete destruction of oocytes were recorded. It was noted that the cytoplasm of oocytes was most damaged. Investigation of the condition of gonads and identification of the causes of oocyte resorption is a step towards the conservation of the roach population.