Hormonal Regulation of Fish Adaptation to Atypical Fluctuations in Temperature and Oxygen Regime of a Water Body

Recently, the water temperature significantly exceeded the climatic norms for the studied region of Ukraine. Water is heated to 30ºC with a decrease in the concentration of dissolved oxygen in shallow water. In this connection, the change in the hormone content in the blood plasma of carp, roach, rudd, perch and ruff in response to these factors has been studied. Most of the fish species studied in June respond by increasing the cortisol content in the blood by 1.2–3.3 times to an increase in water temperature. Fish quite successfully adapts after a month's stay in conditions of high water temperature to 31ºC, and the level of cortisol is reduced. The content of thyroid hormones in the blood of the rudd, roach and ruff is quite high and after a month of adaptation to the existing factors. This indicates an increased activity in their metabolic processes. The content of somatotropin and prolactin in the blood of the studied fish species decreases 2.4–5.0 and 1.9–7.7 times, respectively, in response to an increase in temperature and a decrease in the oxygen concentration in water. This should lead to a decrease in the rate of fish growth and change in the activity of osmotic exchange. However, hormonal reactions are species-specific in nature to the existing factors. Perch and roach are less plastic to increase water temperature. Carp most favorably tolerates an increase in water temperature and a decrease in oxygen concentration.