The toxic potential of aldrin and heptachlor on Danio rerio juveniles (Cypriniformes, Cyprinidae).

With the objective of evaluating the effects of organochlorine pesticides (aldrin and heptachlor) on the survival, growth and gill morphology of juvenile zebrafish (Danio rerio), four partial chronic toxicity bioassays were conducted (seven days' duration) with both compounds in a semi-static system with renewal every 24 h. The results did not show any effects on the fish's survival, but did on their growth and gill morphology. Aldrin was more toxic than heptachlor, since the chronic value (CV) for growth was nearly 8.7 times less, a result confirmed by analyzing the histology of the gills, in which the changes detected were considered more severe for the former substance. In general, they were found branchial lesions of first stage, in other words, cell proliferation between the secondary lamellae, hyperplasia, lifting of respiratory epithelial cells; fusion of several secondary lamellae and dilation of blood vessels. Aneurysms (alterations of second stage) they were verified in the exposed organisms to the aldrin, which also presented about 10% of reduction in the standard length and 30% of reduction in the total weight in relation to the exposed organisms to the control. For heptachlor these values were of 8% and 25%, respectively. The intensity of the gill lesions and growth of the fish did not depend on the pesticide concentration, suggesting different modes of action of the products.