Effects of malathion on survival, growth, development, and equilibrium posture of bullfrog tadpoles (Rana catesbeiana)

Bullfrog (Rana catesbeiana) tadpoles were exposed to malathion in water in a 28-d static renewal test. The effects of malathion on survival, growth, d evelopment, and loss of equilibrium posture were determined. Survival was s ignificantly decreased at molathion concentrations of 2,500 mug/L and highe r. Development of tadpoles was delayed significantly by malathion exposure as indicated by a dose-related decrease in developmental stage over time. D evelopment of tadpoles in the 1,000-mug/L and higher treatment groups was s ignificantly delayed from that observed in the control. The effects of mala thion on developmental stage suggest that malathion may decrease thyroid fu nction in tadpoles, as it does in other species. Maintenance of equilibrium posture following agitation of the test containers was significantly impai red in tadpoles in all the malathion treatment groups (500 to 3,000 mug/L) relative to the control. Maintenance of equilibrium posture was thus the mo st sensitive end point measured in this study. Loss of equilibrium posture could increase predation losses and decrease feeding in populations of bull frog tadpoles in the field. However, concentrations of malathion that produ ced adverse effects in our study are higher than published, measured concen trations found in wetlands or streams.