Some morphological peculiarities of the sterlet (Acipenser ruthenus Linnaеus, 1758) in the conditions of intensive rearing in floating cage systems

Purpose. To study peculiarities of the sterlet in the process of intensive rearing of their replacement and brood groups in floating cages installed in water bodies with natural temperature regime. Methodology. The material for the study were age-3+ and age-5+-6+ sterlet reared at the industrial type fish farm “Oseter” LLC of Kyiv region located in the forest-steppe physical-geographical zone of Ukraine. The experimental groups of fish were reared in 24 m2 (4x6 m) cage chambers submerged in water by 2.5-3.0 m. Measurements of alive fish were performed in different seasons of 2019 using schemes recommended for measuring sturgeons. Twelve plastic features of the sterlet were studied, weights of individual fish and indexes of body built were determined. Fulton's conditions indexes were calculated with the use of standard lengths (l) and total lengths (L). Studies of physicochemical parameters of water medium were performed using generally accepted fisheries and hydrochemical methods. Findings. Individual patterns in exterior features of the sterlet of different ages were detected, where females exceeded males by mean values of absolute and relative fish body depths, thickness and girth. It was found that the mean values of the relative distance from the anal fin to the end of middle rays of the caudal fin were characterized by sufficient stability. It was noted that the gonad maturation stage should be taken into account for a comparative analysis of morphobiological parameters of sterlet females and males when performing studies within one fish generation in the same periods of the year. A complex of methods combined with morphological studies with ultrasonography and other modern techniques is recommended for early vital sex determination in sturgeons. Originality. Some morphological peculiarities of brood groups of the sterlet, rearing of several generation of which was performed in the conditions of intensive aquaculture in a limited space of cages, were studied. Practical value. The results of the studies can be interesting for the development of selective breeding work in sturgeon aquaculture and contribute to the development of methods for early vital determination of the sex in sturgeons.