Changes in Hormonal Status of Aboriginal Fishes under the Impact of Agricultural Runoffs

Changes of cortisol, triiodothyronine, and thyroxine content in the blood plasma of perch, ruff, rudd and bleak under the impact of agricultural runoff from the adjacent territories to the water bodies were studied. Under the long-term exposure to the contaminated water, the weight and size of fish their growth rates specimens significantly decreased. The hormonal responses to the polluted waters impact are species-specific and partly depend on the ecological features of the species. Under the chronic impact of the polluted water, the cortisol content in blood plasma decreases and triiodothyronine content increases as compared to the control. The fishes occurring in the surface water layers create the thyroxine reserve in blood, and fishes which prefer the near-bottom layers use it to increase the triiodothyronine content. After treatment of the fields close to the reservoir with pesticides, the ruff and rudd develop the active stress reaction, the cortisol and thyroxine content in blood significantly increases. According to the considered indicators, the bleak is the most resistant to agricultural runoffs or possesses the ability to avoid toxic water pollution.