Effect of stocking density on the efficiency of rearing of sterlet Acipenser rutenus (Linnaeus) and paddlefish Polyodon spathula (Walbaum) in the conditions of Southern Ukraine

Purpose. To determine the effects of specific elements of biotechnologies used for rearing sterlet and paddlefish seeds for the optimization of rearing technology and their rational use in pond fish facilities of Southern Ukraine. Methodology. Rearing of young-of-the-year sterlet and paddlefish was conducted in experimental ponds (2 ha and 3 ha). In order to develop appropriate natural food supply, we added mineral and organic fertilizers (5 tons/ha). Rearing of YOY sterlet was conducted with different stocking densities (65000 and 95000 fish/ha), the control variant had 100000 fish/ha. Rearing of YOY paddlefish was conducted with a stocking density of 500 and 1500 fish/ha. Mean individual body weight while stocking experimental ponds was 69–75 mg (sterlet) and 600–700 mg (paddlefish). Findings. Results of rearing were analyzed and fishery performance of sterlet (Acipenser ruthenus L.) and paddlefish (Polyodon spathula (Walbaum)) reared according to the combined technology were analyzed. We examined pond food supply composition (phytoplankton, zooplankton, zoobenthos), growth and nutrition of YOY sterlet and paddlefish. It was found that a stocking density of 79000 fish/ha and abundant food supply for YOY sterlet can result in mean individual body weight of 3.60–4.40 g, survival rate –– 70.32– 82.78%, fish productivity –– 238.09 kg/ha. Stocking ponds with paddlefish with individual body weight of 600–700 mg and stocking density of 500-1500 fish/ha resulted in obtaining young-of-the-year with mean individual body weight of 278.0-409.8 g, survival rate –– 25.4–31.2%. Scientific novelty. Our experiment allowed better understanding of the correlation between stocking density and results of the rearing of sterlet and paddlefish seeds. We found a clear correlation between mean individual body weight, stocking density and duration of rearing for YOY sterlet. We found an effect for some biotechnological aspects on biochemical indicators of YOY sterlet. Practical value. The obtained data enriches and refines existing representation of the correlation between technological factors and efficiency of rearing viable sterlet and paddlefish seeds in the conditions of southern Ukraine and contributes to finding optimal parameters of rearing in terms of modern aquaculture.