Objective:To monitor the response of gills of Cyprinus carpio var. communis to LC50 levels of ammonia over a period of 96 h by bath exposure, using scanning electron microscopy (SEM). Methods: Cyprinus carpio procured from a local fish farm in Vadalore, Cuddalore District, Tamil Nadu, India were acclimatized under laboratory conditions for 20 d. Fish were placed into experimental tanks with 20 L of water and 22 mg/L ammonia. A total of 10 fish were collected from each experimental tank every 24 h for histopathological studies. Results:Histopathological studies showed these changes in the gills:secondary lamellar fusion, haemorrhage, oedema, epithelial hyperplasia, and chloride cell proliferation. Occasionally, multifocal necrosis of inter-lamellar regions of gill filaments but with no apparent haemorrhage was observed under electron microscopy. Conclusion:The present study shows that histopathological and ultrastructural alterations in gills are useful indicators for ammonia toxicity in Cyprinus carpio.
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