Tests of acute toxicity for rainbow trout fry of chlorfenviphos and bromfenviphos were undertaken in order to establish the Lc 50 values. Studies were also made on the effect of lethal concentrations, corresponding to 24 h LC 50 , upon the activity of selected enzymes and hematological indices. Activity of brain acethylcholinesterase, and blood peroxidase and catalase, was assessed. Hematological studies embraced: content of hemoglobin, hematocrit, number of red and white corpuscles, percentage share of lymphocytes, red/white cell ratio, and MCV, MCH, and MCHC indices.

Comparative studies on effects of CVP and BVP insectici des in sublethal concentrations on young rainbow trout (Salmo gairdneri Rich.) were carried out under laboratory conditions. The insecticide effect was inferred from enzy matic and haematologic analyses. One experiment involved a 14-day exposure to insecticide concentrations corresponding to 5% of 96-h LC 50 , followed by the brain acetylcholines terase, blood peroxidase and catalase activity assessment and determination of haematologic indices. The other experiment involved observing changes in the brain acetylcholinesterase activity over 30 days following the 24-h exposure to concentrations corresponding to 50% of 24-h LC so,