Pesticides and Fishes—A Review of Selected Literature

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Abstract
Pesticides contribute to widespread pollution of the aquatic environment. Physiological and ecological effects after twenty years of accumulation are poorly understood and the critical need for such data is increasing in proportion to the level of contamination. While LC50 (mean lethal concentration) levels producing acute toxicity have been recorded for many fishes and types of pesticides under controlled laboratory conditions little has been done to define those levels which produce chronic toxicity in the natural environment. Intraspecies variation in susceptibility (LC50) is common leading to the reporting of "resistant" populations of every species of fish utilized in comparative bioassays of populations by one investigator. Populations which survive high residue concentrations produce an increased level of environmental contamination through "biological magnification." Physical factors in aquatic habitats, other than temperature, have been little studied in relation to pesticide effects. Silt from agricultural runoff is a transportation vehicle which appears to provide a more important entrance to the aquatic environment than an exit. Argillotrophic nutrition for crustaceans could explain the transitional role of zooplankters in the passage of pesticide pollutants through the ecosystem. The relative importance of ingestion versus respiratory surface absorption appears to be largely dependent on the solubility of specific compounds as contrasted to their tendency to be adsorbed to available surfaces. Histological and physiological effects of pesticides are largely undefined with much of the work completed to date inconclusive. An abundance of contradictory statements and un-supportable generalities together with inconsistencies in the biology of pesticide accumulation must be clarified to provide direction and meaning for future work. Concentration of pesticides in water was proven inadequate in the determination of "safe" levels of habitat contamination. Monitoring programs should be expanded to include histological and ecological studies. Marshes, ponds and reservoirs would be equal if not superior to major river and Great Lakes sampling stations currently being utilized. Research programs necessary for the detection of sublethal damage to fish populations are suggested in the hope that in the near future direct mortality may not be the chief criteria of danger from pesticide contamination.

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