Effects of cypermethrin chronic exposure and water temperature on survival, growth, sex differentiation, and gonadal developmental stages of Odontesthes bonariensis (Teleostei).

This study assessed the effects of cypermethrin and temperature on the survival, growth, sex differentiation, and gonadal development of Odontesthes bonariensis, a gonochoristic teleost with a strong thermolabile sex differentiation. Two complementary trials were conducted. In the first trial, newly hatched larvae were exposed during six weeks to 0 or 0.1 microgL(-1) of cypermethrin at 17, 22, and 29 degrees C. In the second trial, larvae were exposed at 22 degrees C to 0, 0.1, or 0.125 microgL(-1) of cypermethrin, or 100 microgL(-1) of the non-steroidal antiestrogen tamoxifen. Survival and growth of fish were affected by cypermethrin exposure, water temperature, and the combination of both factors. The survival rate decreased at higher temperatures and cypermethrin concentrations, but the insecticide lethality was inversely related to temperature. Growth was lower at 17 degrees C than at 22 or 29 degrees C, and was significantly increased by cypermethrin exposure. As already described for this species, all females or all males were obtained at 17 or 29 degrees C, respectively, and neither cypermethrin nor tamoxifen exposure caused changes in sex ratios. Slight changes in gonadal development were induced only by temperature. Finally, results showed that the in vitro antiestrogenic effect reported for cypermethrin had no in vivo effects on the sex ratio, the gonadal development, or the germ cell production of O. bonariensis, even at concentrations that affected the growth and survival of the fish.