Histopathological, serum enzyme, cholesterol and urea changes in experimental acute toxicity of ammonia in common carp Cyprinus carpio and use of natural zeolite for prevention R. PEYGHAN 1, * and G. AZARY TAKAMY 2 1 Veterinary Medicine Faculty, Shahid Chamran University, PO Box: 145, Ahvaz, Iran; 2 Veterinary Medicine faculty, Tehran University, Azadi St. Tehran, Iran; *Author for correspondence Received 24 September 2001; accepted in revised form 22 July 2002 Key words: Alkaline phosphatase, Ammonia, Common carp, Histopathology, Toxicity, Urea, Zeolite Abstract. Common carp, Cyprinus carpio, was exposed to ammonia in a series of acute toxicity tests at 20–22 °C. 24 -h LC50 values were estimated 123 mg/l total ammonia-N (45.5 mg/l molecular ammo- nia-N). In the lethal concentration of ammonia for common carp (150 mg/l total ammonia), the appli- cation of 10 g/l natural zeolite prevented the fish mortalities. In histopathologic study, the most impor- tant lesions that encountered in the gill were hyperemia, edema and aneurysm. In the kidney, degener- ative changes of tubules and glumeruli, expansion of Bowman’s capsules, hyperemia, congestion and hemorrhage were the most prominent lesions. There were hyperemia, degeneration and the presence of some necrotic aria as the only lesions observed in the liver. In the serum the level of alkaline phos- phatase (ALP) and urea of experimental groups were significantly higher than the control. There was no significant difference in other enzymes and cholesterol level between experimental groups and control fishes. Introduction Ammonia toxicity is one of the serious problems in fish culture especially in recir- culation system, aquariums and superintensive fish culture. Several investigations about ammonia toxicity in different fishes have been conducted so far (Alabaster et al. 1979; Cai and Summerfelt 1992; Colt and Tchobanoglous 1976) however no study on histopathology, serum enzyme and urea changes in acute toxicity with ammonia in common carp has yet been reported. Despite the importance of ammonia toxicity and presence of several reports about heavy mortality in different fish species (Spear and Backman 1988; Svo- bodova et al. 1997), there are many problems in diagnosis and prevention of this toxicity. The signs that may be seen in ammonia toxicity do not specifically indi- cate the existence of such toxicity so the diagnosis is usually based on water analy- sis. However, water analysis also is a difficult and complicated task in diagnosis of ammonia toxicity, since the mortality is often recorded after a delay and water con- dition may have been changed meanwhile. Aquaculture International 10: 317–325, 2002. © 2002 Kluwer Academic Publishers. Printed in the Netherlands.