The Occurrence of Caligus sclerotinosus ( Caligidae ) Infection in Cultured Red Sea Bream Pagrus major and Involvement of Phototaxis in Fish - to - fish Transfer of the Adults

The occurrences of Caligus sclerotinosus, a parasitic copepod on cultured red sea bream Pagrus major, were surveyed in fish farms and the phototaxis of adult caligid was experimentaly examined. The parasite infection occurred from April to December, in which up to approximately 500 caligids infected the external surface of each diseased fish, covering the whole body surface, eyes and fins. The main disease signs were scale exfoliation, abrasion and ulcerative lesions on the body surface, and chipped fins. Listless swimming near the water surface was also observed. Daily mortalities were usualy below 0.1%. When iluminated at diferent light intensities, most adult caligids showed positive phototaxis and those iluminated at 50 m mol/m/s swam significantly faster than those iluminated at 200 and 800 m mol/m/s. When infected fish were iluminated from one direction in a tank, 2.5% of caligids moved from fish to the iluminated wal of tank. When an infected fish and an uninfected fish were separated with a screen partition in each tank and iluminated from one side, 25% of caligids moved from fish in the shaded side to fish in the iluminated side, but never vice versa, showing that fish-to-fish transfer of C. sclerotinosus adults was afected by light conditions.