OPTIMUM, CRITICAL AND THRESHOLD VALUES FOR WATER OXYGENATION FOR MULLETS AND FLATFISHES IN ONTOGENESIS

Purpose. To determine the optimum, critical, and threshold values of water oxygenation for embryos, larvae and fingerlings of mullets and flatfishes under different temperature conditions. Methodology. Oxygen consumption was studied in chronic experiments with ?interrupted flow? method with automatic fixation of dissolved oxygen in water with the aid of an oxygen sensor and automatic, continuous recording of the obtained results. ?Critical? (Pcrit.), and the ?threshold? (Pthr.) oxygen tension in the water have been determined. Findings. Under optimum conditions, the normal embryogenesis of mullets and flatfish to the gastrulation stage, provided 90?130% oxygen saturation. The critical content was 80?85%, the threshold ? 65?70% of the saturation. At the stage of ?movable embryo? depending on water temperature and fish species, the optimum range of water oxygenation was within 70?127.1%. The most tolerant to oxygen deficiency was flounder (Pcrit ? 25.4?27,5; Pthr. ? 20.5?22.5%), the least resistant to hypoxia was striped mullet (Pcrit. ? 50?60; Pthr. ? 35?40%). The limits of the critical and threshold concentration of dissolved oxygen directly depended on the temperature and salinity, at which embryogenesis occurred. An increase in water temperature and salinity resulted in an increase in critical and threshold values for oxygen tension embryos. Mullet and flatfish fingerlings in all stages of development had a high tolerance to hypoxia, which increased as they grew. They were resistant to the oversaturation of water with oxygen. The most demanding for the oxygen regime are larvae and fingerlings of Mugil серhalus and Liza aurata. Hypoxia tolerance of Psetta maeoticus and Platichthys luscus at all stages of development is very high. The fingerlings of these species can endure reduction of the dissolved oxygen in water to 2.10 and 1.65 mgO2/dm3 respectively for a long time without visible effects. Originality. For the first time, we experimentally established the optimum, critical and threshold values for water oxygenation for embryos, larvae and juveniles of striped mullet, golden mullet, haarder, flounder and Black Sea turbot. Practical value. The obtained data can be used for the optimization of culture conditions and commodity cultivation of mullets and flatfishes.