Abstract
Fry of Russian sturgeon ( Acipenser gueldenstadtii Brandt et Ratzeburg, 1833) was an object of research in the course of studying the influence of different concentration of water salinity onto the operation of a closed water supply unit and on the intensity of fish growth. Salt medium (3; 5; and 7‰) was made using sodium chloride solution, whose osmotic force corresponded to water salinity in the Northern Caspian - from 0 to 7‰. Temperature and oxygen condition changed within 20.0-22.0°C and 85.0-100.0% of saturation. Maximum fish growth was registered in salinity of 5 and 7‰, increase made 8.0-21.0%. The intensive growth rate proved that sturgeon breeding in brackish waters facilitated more efficient digestion of food components in the fish gastrointestinal tract. Blood indices corresponded to parameters specific for fishes in the natural habitat: haemoglobin - 30.0-45.0 g/l; cholesterol and crude protein - up to 3.5 mmol and 26.0 g/l. Level of lipids was high - 4.8-6.5 g/l, which is characteristic to fish fed with complete dry feed. Osmolality of fish blood serum was within 219.0 ± 2.41 - 239.0 ± 0.94 mmol/kg of H2O and corresponded to the parameters of sturgeons of different age groups in desalinated area in the Northern Caspian. However, increase of water temperature and salinity up to 7‰ affected operation of biological filter and raised the concentration of ammonium nitrogen in water, which lowered viability to 10.0%. Parameters of hydrochemical condition of a closed ecosystem were within normal values under salinity of aqueous medium up to 5‰, which should be taken as optimal for creating brackish regime in the closed water supply units of sturgeon breeding.
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