University proceedings. Volga region. Natural sciences

Background. The biology of the loach Misgurnus fossilis (Linnaeus, 1758) has been sufficiently studied, while its modern population characteristics in the European part of Russia are rare in the scientific literature. This is especially relevant in the current period, when the occurrence of loach has significantly decreased, and in a number of regions, it is listed in the Red Book. The purpose of this work is to study the characteristics of the loach population living in the Rzhavets Creek basin, a tributary of the Penza river flowing through Penza region. Materials and methods. A sample of 168 loaches was collected from the Nizhniy pond of the fish farm on the Rzhavets Creek. The ichthyological material was processed using generally accepted and original methods. Results. The Rzhavets brook loach corresponds to the European loach in body coloration and the main meristic and plastic features. The sizes in the sample varied: 9.2–24.0 cm and 6–110 g, in the population up to 27.5 cm and 131 g. Its lifespan is about 10 years. In the first year, the average fish growth rate is 5.2 cm, in the following years 2.3 cm. No difference in the growth rates of males and females was noted. The fatness according to Fulton is 0.64 – 0.84, according to Kalabukhov – 0.17–4.62, according to Clark – 0.57–0.72. Sexually mature individuals appear at a length of 15.0 cm at the age of 4+. At the age of 4+ – 6+, all analyzed individuals were males at maturity stage I-II. No males were observed at the age of 6+. Starting from the age of 7+, all individuals were females at the mature stage – IV. The diameter of the eggs in the gonads (in October) was 1.0–1.4 mm. The number of eggs in 1 gram is 940–960 eggs. Individual absolute fertility at the age of 7+ is 13.6 thousand eggs, at the age of 8+ – 21.9 thousand. Relative fertility exceeds 200 eggs/g. Conclusions. According to the main species indicators, the loach population of the Rzhavets stream lives in favorable and stable conditions. Loaches from fish farms can also be used to restore lost populations in the region and populate degraded water bodies deprived of ichthyofauna.