Effect of bisphenol a on the early life stage in Japanese medaka (Oryzias latipes)

Japanese medaka (Oryzias latipes) were exposed to bisphenol A (BPA) at the sublethal concentrations of 2.28, 13.0, 71.2, 355, and 1,820 μg/L (as mean measured concentrations) in the early life stage from fertilized eggs to 60-d posthatch. Except for the growth and sexual differentiation of the fish at 60-d posthatch, no effects were observed on hatching success and time to hatching in embryological stage and on mortality and abnormal behavior and appearance in hatched larvae. The growth of the fish was suppressed with increasing BPA concentrations, resulting in significant differences in both the total length and body weight of medaka at 1,820 μg/L compared with the controls. When observed for their external secondary sex characteristics, no males were identified in the 1,820-μg/L treatment. In addition, histological examination showed that 32% of fish in the 1,820-μg/L group had testis-ova composed of both testicular germ cells and oocytes. Consequently, the lowest effective concentration for the early life stage of medaka was between 355 and 1,820 μg/L. Since the environmental concentrations of BPA are usually three orders lower than the lowest effective concentration, BPA alone may not affect the early life stage of wild fish populations.