Toxic effects of meothrin on the gill ultrastructure in grass carp, Ctenopharyngodon idellus

The fingerling Grass carp. Ctenopharyngodon idellus. was exposed in differentconcentrations of meothrin nearby 24h LC_(50) and its gill morphology was examined by light and elec-tron microscopy. The results indicate that meothrin caused fish convulsions. cough, ataxia,intermittent paralysis and overtumed. Morphological examination revealved severe alterations to com-pare with control fish. These initially consisted in hypertrophy of the secondary lamellae, andfinally resulted in local telangiectasia, fusion between secondary lamellae.Ultrustiuctural changes in the gills showed the pillar cell system collapse and resulted in largenon-tissue spaces which were invaded by leucocytes. The cytoplasin of the epithelial cells appearedmany myelin figures, electron dense deposits. Chloride cells were severely damaged with a degeneratedmitochondria and nuclear membrane. Higher concentration of meothrin caused a loss of adhesion be-tween the epithelial cells. accompanied by a collapsing of the structural integrity of the primarylamellae and degenerating of epithelial and chloride cells .