The influence of different concentrations of the synthetic steroid 19-nortestosterone on the body mass and indexes of internal organs, hematological parameters, testosterone, progesterone and cortisol content, certain links of metabolic processes and enzymatic activity in the tissues of carp (<i>Cyprinus carpio</i> L.) was studied. Under the short-term impact of 50 μg/dm<sup>3</sup>, 19-nortestosterone increased the total protein and albumins content, creatine phosphokinase and aspartate aminotransferase activity, decreased the inorganic phosphorus and iron content, alkaline phosphatase and alanine aminotransferase activity in the blood plasma and did not affect the respiratory rate, external body features, the mass of hepatopancreas and spleen and their indexes, hematological indicators, the steroid hormones concentration in blood plasma and hepatopancreas, content of glucose, triglycerides, creatinine, calcium, inorganic phosphorus in blood plasma.
Under 200 μg/dm<sup>3</sup>, the respiratory rate and ESR increased, as well as the cortisol and testosterone content in blood plasma and hepatopancreas, whereas progesterone in blood plasma decreased and in hepatopancreas increased. High concentration of 19-nortestosterone caused elevated protein and albumin content, creatine phosphokinase and aspartate aminotransferase in the blood plasma activity, whereas glucose, inorganic phosphorus, iron, alkaline phosphatase activity was lower. The 19-nortestosterone did not affect the mass and index of hepatopancreas and spleen, hemoglobin concentration, the erythrocytes, leukocytes and lymphocytes number and ratio of eosinophils, neutrophils, lymphocytes and monocytes, as well as triglycerides, creatinine, calcium content, lactate dehydrogenase and alanine aminotransferase activity in blood plasma.
The conclusion was made about the carp's ability to adapt to low concentrations of the synthetic steroid 19-nortestosterone under its short-term impact by modification of the certain links of metabolism and enzymatic activity. High concentration of 19-nortestosterone significantly affected the hormonal status and metabolism of carp.