EN
The influence of poisoning with nitro-compounds on the immunological system of carp has been assessed under natural conditions using water diversion of the Nitrogen Plant at Puławy. The examinations were carried out on 80 carps weighing 250-300 g each which were maintained for six weeks in the water diversion and in which an increased level of nitro-compounds was found. Twenty fishes transported from a healthy environment served as control animals. After the period of poisoning the fish were placed in aquaria with water free from contaminants and remained under the influence of levamisole (5 mg per 1 1 of water) in order to stimulate immune mechanisms after nitro-compounds immunosuppression. The reaction of the immunological system was assessed on the following basis: the number of leukocytes and neutrocytes in 1 pi of blood, metabolic activity of granulocytes, the level of lysozyme in the serum and in the mucus of the carp. It was found that a chronic poisoning of carp caused irreversible changes in their immune system; the fish could not respond to the immunostimulating action of levamisole. The findings give the reasons to believe that fish kept for a longer time in water with an elevated concentration of nitro-compounds may be more susceptible to various disease-causing factors.