Forming a replacement-brood stock of European grayling Thymallus thymallus (Linnaeus) in artificial conditions

Purpose. To develop methods for forming of a replacement-brood stock of the European grayling. Methodology. In the course of the work, we used the generalized results of the studies performed during 2014-2017. Rearing age-1 and 1+ fish was done 135 m 2 ponds. Water temperature in the winter fluctuated within 2-5ºС. Findings. During three years, we formed a replacement-brood stock of the European grayling of age-3 European grayling with a total number of 15 fish at the State Enterprise “Trout hatchery “Lopushno”. Eight months before spawning, artificial feeds were removed from the diet of brood grayling and they were replaced by natural feeds. Frozen chironomid larvae were used in the study. The feed conversion ratio of the natural feeds during rearing of brood stock was 6 units that corresponded to 12.82 kg. The mean weight of domesticated brood fish used for the spawning was 181.3 g, mean length – 25.0 cm. Weights of males varied from 190 to 260 g, those of females – from 134 to 200 g; lengths of males varied from 26 to 32 cm, those of females – from 24.5 to 29.0 cm. Males exceeded the females by mean weight; a similar result was observed for the mean length, where males exceeded the females by 7%. Working fecundity of females was 2762±491 eggs. Fertilization rate was 60%. Originality . For the first time in Ukraine, a holistic mechanism of scientific principles and methodical recommendations for artificial reproduction of the European graying was developed for the purpose of the following stocking of rivers, aimed at preserving their number in the water network of the Carpathian region. Practical value. The results of the work are the basis for planning, conducting and controlling the results of the artificial reproduction of the European grayling of the Carpathian region.