Histopathological Effect Of Karenia Mikimotoi Bloom On Gills Of Common Farmed Fishes In The East China Sea

Karenia mikimotoi has been reported to be one of the hemolytic toxin and cytotoxin producers. The toxic effects of K. mikimotoi bloom on fish gills have been carried out in this study. Gills of five cultured fishes - Lateolabrax japonlcus, Miichthys miiuy, Csiaenops ocdlatus, Epinephelus akaara and Pseudosciaena polyatis were collected from the fish farms of Nanji Island, Zhejiang Province, after a mass dead caused by a K.mikimotoi bloom in June 2005.The results revealed that the histopathological effect has been observed in fish gills, including gill arch, gill raker, primary filament and secondary filament. The epithelia cell, capillary vessel and ruin erythrocyte, so that the surface of fish gills was bare. Some terminal of secondary filaments were expanded and curved and some cohere to each other. Some lossed erythrocytes, fragments of proteins mucus and some dye solution have also been observed around the secondary filament, primary filament, gill arch and gill raker. Some structures can not be observed directly by microscope, for example, mucous cell and chloride cell. Because surface of fish gill is bare the mucous cell may be destroyed by the cytolytic effects.The results also showed that exposure time in the K. mikimotoi bloom was a very important factors to decide toxic extent. The longer exposure time in the K. mikimotoi bloom, for example Pseudosciaena polyatis resulted in an more serious gill damage than those in the shorter, such as Lateolabrax japonlcus.