Особливості плодючості бичка кругляка (Neogobius melanostomus) за різних екологічних умов
The specificities of round goby fecundity (Neogobius melanostomus) in different ecological conditions

Summary/Abstract: We conducted a comparative analysis of the absolute and relative fecundity of round goby (Neogobius melanostomus (Pallas, 1984)) females in the Kakhovskyy Reservoir and the Azov Sea. We analysed the indicators of salinity, pH and oxygen levels in the waterbodies investigated. We determined the dependence of fertility of round gobies on body weight, length and age. This article presents the results of a comparative analysis with the works of other authors, including the results of a similar study conducted 40-years ago. We conducted cameral processing of the results by standard methodology. We counted the oocytes at varying stages of maturity. All oocytes were grouped by their diameter. We visually identified four groups of oocytes: 1700–2500 mkm – the large, mature oocytes (ІV stage of maturity); 400–1200 mkm – light yellow oocytes, which are ripening (ІІІ stage); 100–300 mkm (ІІ stage) whitish eggs, and the smallest (I stage) – up to 100 mkm. Stages II–IV were subjected to statistical processing. The differences between the indicators of fertility of fishes from saltwater and freshwater waterbodies show an increase in the relative and the absolute fecundity of fishes from the sea (saltwater) and decrease in the fecundity of the fishes in freshwater. The correlation analysis between the waterbodies and the length of the fishes showed 0.81 at the Kahovskyy Reservoir and 0.62 in the Azov Sea. The correlation analysis between the same waterbodies and the weight of the fishes was 0.63 and 0.74 respectively. This could indicate that conditions for the fishes’ existence were more favourable in the sea. The comparison analysis between our data and the 40-year old data for the Azov Sea depending on length and weight show a significant increase in oocyte numbers. This increase was noted for all size groups of fish. Nevertheless, the greatest differences were between fish in the Azov Sea (all data) and those in the Kahovskyy Reservoir. These results should be studied in the context of the nutrition spectrum and calorific objects of the round goby in these water bodies. It would be interesting to analyse data on gobies of the Azov Sea according to gradation in salinity levels.

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