MODIFICATION OF THE RHEOTROPIC RESPONSE OF RAINBOW-TROUT (SALMO-GAIRDNERI) BY SUBLETHAL DOSES OF THE AQUATIC HERBICIDES DIQUAT AND SIMAZINE

The rheotaxis and swimming speeds of rainbow trout in response to a water current simulated by moving a striped background past the fish were observed following 24-h exposures to field application concentrations of the herbicides diquat, simazine and their commercial formulations. Fish tissues were subsequently analysed to assess the extent of uptake of the herbicides. Toxicological modification of rheotaxis and swimming speeds was observed in fish exposed to diquat and its formulation Reglone A® resulting in an increased incidence of downstream drift. Simazine residues in fish increased in proportion to treatment levels whereas diquat residues in fish levelled off with increasing treatment levels. The toxicological modification of rheotropism is presented as a sensitive bioassay to assess sublethal effects of biocides. © 1979.