Roach is a valuable industrial object in the Zaporizhzhian (Dnipro) reservoir, but in the long-term dynamics of fishing, there is a gradual reduction in its reserves and growth lag in certain industrial areas. The purpose of this work was to study the annual linear growth of roach in the two main fishing areas of the Zaporizhzhian (Dnipro) reservoir – the Samara Gulf and the lower part of the reservoir. The fish was catched in July 2024 during industrial fishing. The material for the research was the 5-year-old common roach, which dominates in industrial populations. The linear weighting indicators of fish were determined by generally accepted methods in ichthyology. Features of fish growth were evaluated by linear growth at different ages. The age of the fish was determined by the scales. The distance between the annual rings was measured using a micrometer eyepiece. Individual linear growths of fish were calculated using the equation of E. Lea. The data is statistically processed using the Statistiсa program. According to the results of our research, 5-year-old roach in the Samara Bay ranged from 55% to 68% in nets with an eyepage of 30–35 mm. In the lower part of the reservoir, the proportion of whip in the catches reached 80% in nets with a cell of 40–45 mm. The average values of the standard length of the roach from the lower part of the reservoir were 22.2±1.67 cm, the average weight was 225.3±18.32 g. In the Samara Bay, these indicators were 19.2±1.85 cm and 133.2±21.55 g, respectively. That is, the length of the 5-year-old specimens in the Samara Bay was 14% less, and the mass was 41% less than the lower part of the reservoir, and this difference in the Student coefficient was probable (p≤0.05). The dynamics of annual increases in the length of the body of the roach from the two different sites was identical. The maximum increase in length occurred in the first 2 years of life, then naturally decreased, which is typical for carp fish. A significant lag in the growth of the roach of the Samara Bay begins in the 3rd year of life. If in the 1st and 2nd years the difference between the growth of fish from two sites was 8%, then at the age of three it increased more than three times – up to 27%. A probable cause of inhibition of the growth of roach in the Samara Bay is the intoxication of the body with heavy metals due to their high content in water and the gradual accumulation in the body of fish. The second reason may be the fierce food competition with the Prussian carp, which is the absolute dominant in the bay in terms of number and biomass. Adjusting the number of Prussian carp by coordinating catch regimes would reduce the load on the feed base for the roach. In this work, for the first time, the individual growths of the roach in the two main fishing areas of the reservoir. We have established the age interval within which the growth of fish in the Samara Bay is inhibited. The identified features of growth in the process of ontogenesis of the roach of various industrial populations are of practical importance for the development of a complex for the further improvement of post-militarized water bodies, which requires the latest innovative measures.
Foroshchuk et al. (Fri,) studied this question.
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