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, development, and loss of equilibrium posture were determined. Survival was significantly decreased at malathion concentrations of 2,500 micrograms/L and higher. Development of tadpoles was delayed significantly by malathion exposure as indicated by a dose-related decrease in developmental stage over time. Development of tadpoles in the 1,000-microgram/L and higher treatment groups was significantly delayed from that observed in the control. The effects of malathion on developmental stage suggest that malathion may decrease thyroid function in tadpoles, as it does in other species. Maintenance of equilibrium posture following agitation of the test containers was significantly impaired in tadpoles in all the malathion treatment groups (500 to 3,000 micrograms/L) relative to the control. Maintenance of equilibrium posture was thus the most sensitive end point measured in this study. Loss of equilibrium posture could increase predation losses and decrease feeding in populations of bullfrog tadpoles in the field. However, concentrations of malathion that produced adverse effects in our study are higher than published, measured concentrations found in wetlands or streams.