Deltamethrin (DM) is a synthetic pyrethroid pesticide highly toxic to aquatic organisms. Because of its lipophilic feature it can be highly absorbed by the fish gills, which partially explains the high sensitivity of these animals to DM exposure in concentrations up to a thousand times lower than in mammals. This study compared clinical, biochemical and haematological observations between DM intoxicated and non-intoxicated fish. The experiment involved five exposure conditions (control and four concentrations of DM) and was executed in triplicates with 4 animals per set (n=60). The first behavior changes represented by rapid operculum movement and irregular or on the surface swimming were observed shortly after exposure to the concentrations of 0.5, 1.0 and 1.5 mg/L of DM. Fish exposed to the DM concentration (0.5 mg/L) for 96 h showed significantly higher leukocyte counts when compared to fish in the other groups. The response of the fish exposed to different concentrations of DM produced an inverted U-shaped curve, so the fish exposed to higher concentrations of DM may have had adaptive behavior alterations or loss of selectivity effects at concentrations high in relationship of leukocytes number. Significant decrease in the activity levels of some of the hepatic enzymes such as aspartate aminotransferase, alanine aminotransferase and alkaline phosphatase result from DM exposure. The results demonstrated that DM environmental pollution can rapidly cause death to Rhamdia quelen as it is a toxic insecticide for this species.

Keywords: Fish, Toxicity, Hepatic enzymes, Leukocytes, Pyrethroids, Rhamdia quelen.

.