EFFECTS OF SANDY SUBSTRATE AND LIGHT ON HYPERMELANOSIS OF THE BLIND SIDE IN CULTURED JAPANESE FLOUNDER PARALICHTHYS-OLIVACEUS

Rearing experiments were carried out to clarify the effects of sandy s ubstrate and light irradiation on hypermelanosis of the blind side (th e staining type of ambicoloration) in cultured Japanese flounder. Fish were reared in three experimental conditions: (1) no sandy substrate into which fish could bury themselves and with upward light irradiatin g their blind sides, (2) no sandy substrate and no upward light, and ( 3) sandy substrate (transparent glass sand) with upward light irradiat ion. Pigmented areas on the blind side were measured by an image analy zing system. Flounder from the third condition (sandy substrate with l ight irradiation) showed the lowest pigmentation on the blind side. In contrast, fish from the second condition (no sandy substrate and no l ight irradiation), showed the highest pigmentation coverage. These res ults indicate that sandy substrate on the bottom in culture tanks is m ore important than light irradiation as a factor affecting hypermelano sis of the blind side in cultured Japanese flounder.