Diet and reproductive success of bluegill recovered from experimental ponds treated with atrazine

In July 1979, 6 ponds (0.045 ha, depth 2.1 m) were each stocked with 50 bluegill sunfish (Lepomis macrochirus), 20 channel catfish (Ictalurus punctatus), and 7 gizzard shad (Dorosoma cepedianum). The ponds were then treated with 0, 20 or 500 ug atrazine per litre. All fish were removed 136 days later, by which time aqueous atrazine concentrations were 70 per cent of initial values. Fish mortality did not differ between treatments. Bluegill was the only species to reproduce during the study. Numbers of young produced in atrazine treated ponds were significantly lower (p less than 0.01) than in control ponds. Analysis of bluegill stomach contents revealed significant dietary differences between fish from treated and control ponds. In fish from treated ponds, there were significantly fewer (p less than 0.001) food items per stomach, and these food items represented a significantly lower (p less than 0.001) number of taxonomic groups. Atrazine treatment reduced pond macrophyte communities by up to 90 per cent, which could explain the observed effects on bluegill diet and reproductive success; macrophytes provided habitat for bluegill prey, and also provided bluegill young with a refuge from predators. Additionally, bluegills short of suitable prey had been reported to eat their own eggs and young.