Correlation between body color and behavior in the upside-down catfish, Synodontis nigriventris

Abstract 1. 1. Unlike common fishes and as its Latin name implies, the upside-down catfish, Synodontis nigriventris , possesses dark ventral skin. Microscopic observation reveals that melanophores are present on both the ventral and the dorsal skin but differ in size and density of distribution. 2. 2. The darkness of both sides of the fish changes in accordance with that of the background. 3. 3. At night, the fish are very active and the body becomes pale. The change in color is more noticeable in the dorsal than the ventral skin. 4. 4. When melatonin was added to the bathing water, the fish became pale and swam restlessly even when they were exposed to the black background. 5. 5. It was found that the catfish preferred the black background to the white one.