PATHOLOGICAL STUDIES IN THAILAND ON COMMERCIALLY VALUED FISH AFTER EXPOSURE TO CRUDE CYANOTOXIN EXTRACT

Abstract

Pathological changes in four species of Thai commercially valued fish (age 1-1.5 month), Gunther's walking catfish, Clarius macrocephalus (Gunther), Nile tilapia, Oreochromis niloticus (Linnaeus), Striped catfish, Pangasius hypophthalmus (Sauvage) and common silver barb, Barbodes gonionotus (Bleeker), after exposure to crude cyanotoxin extract, at different concentrations, were investigated. The cyanobacterium, Microcystis aeruginosa, was collected from a fish farm in Pathum Thani province and analyzed using HPLC. Skin, liver and gills were histopathologically examined. The skin showed significant, lesions of irritation and epidermal layers were thickened, by an increase of mucous cells, in the scaled species, Nile tilapia and common silver barb, while the non-scaled species, Gunther’s walking catfish and striped catfish showed an increase of club cells. Severe congestion existed in the liver of the non-scaled species, as well as in the gills of all treated groups. It was believed that the fish died due to respiratory failure. The results indicated that microcystins, the endotoxin of M. aeruginosa, in a crude extract, caused the pathological effects seen in the four species of
Thai, commercially valued, fish.