Characteristics of vertebral abnormalities of medaka as a water pollution indicator.

We exposed red medaka at different developmental stages to various levels of cadmium, zinc, oxadiazon emulsion and fenitrothion emulsion to determine whether these fish represent useful biological indicators of water quality. We found that the incidence of vertebral abnormalities was the highest when eggs or newly hatched fry were exposed to the heavy metals or agricultural chemicals, that the chemicals exerted a greater adverse effect on the vertebral structure of medaka than did the examined metals, and that the centrum is the most sensitive vertebral indicator of induced damage. Our results suggest that medaka represent useful biological indicators of water quality.