Abstract
Ethanol and eugenol, which are anesthetics, were applied to Tilapia Oreochromis nilaticus in vivo, and to melanophores on isolated scale of Tilapia in vitro. Fish kept in white background for about 12h were transferred to drug media of the same background. Both ethanol and eugenol caused darkening in white-adapted fish. But some differences in the effect were found between the two drugs. In the case of ethanol, darkening was observed with abnormal behavior of fish, and in the case of eugenol, the total loss of equilibrium usually followed. These drugs, however, showed no effect on the melanophores in vitro. The present results suggest that ethanol and eugenol have an inhibitory effect on the central nervous system. It appears that background adaptation is mainly controlled by sympathetic nervous system in Tilapia.
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