Effects of diazinon on the gills of bluegill sunfish Lepomis macrochirus.

Damaging effects of diazinon, an organophosphorus insecticide, on the gills of bluegills, Lepomis macrochirus, are many. Adult bluegills were exposed to 15, 30, 45, 60, and 75 micrograms/L of diazinon and their gills were microscopically examined. Compared to the gill structure of the control fish, all the diazinon concentrations caused various types of changes, such as lifting of the epithelial layer, hyperplasia and necrosis, shortening of the lamellae and frequent epithelial rupture, lamellar fusion, severe hyperplasia and mucous cells hypertrophy, extensive fusion, and clavate lamellae. Some of the structural changes may serve as a defense mechanism in protecting the fish from the diazinon-contaminated water by increasing the diffusion distance. Increase in the diffusion distance and mucus secretion can adversely affect the respiration of the fish, ultimately leading to its death.