Assessment of Fish Physiological State in the Kiliya Delta of the Danube River in Summertime in Terms of Blood Biochemical Indices

Changes in the content of cortisol, triiodothyronine, thyroxine and glucose, the activity of AST and ALT and their ratio in the blood plasma of perch, roach, rudd and silver crucian carp from the Kiliya delta of the Danube River were studied in summertime. Hormone content was determined by enzyme immunoassay, and enzyme activity and glucose content - by standard methods. It has been shown that studies of the biochemical state of various ecological groups of fish make it possible to assess the quality of both surface and near-bottom water layers of the entire water body. The deteriorations of surface water quality and stressful circumstances result in an increase in the content of cortisol and triiodothyronine in the blood plasma of rudd. Under deteriorated environmental conditions, in fish from the near-bottom layers of water (roach and perch), partial liver damage is observed according to the activity of AST and ALT, and the De Ritis coefficient. Basically, all studied species actively use energy resources (glucose) to adapt to existing environmental conditions. For the vast majority of the studied indices, the highest coefficient of variation is observed in silver crucian carp, then rudd, and significantly less in roach and perch.