author(s)
Mohammed Abd Kadhim and Jamal K Al-Faragi

abstract
A toxicity test was conducted for 24 hours periods to evaluate the impact of three lethal concentration of un ionized ammonia (UIA) at three levels of water salinity on mortality rate behavior and gill histopathology of Cyprinus carpio. A total of 240 of C. carpio (mean weight of 50±5 g) reared in 24 glass aquaria divided to three groups (A,B and C) according to water salinity levels: ( A:tap water, B:2 and C:4 g/l NaCl) and subdivided to three groups each group exposed to different lethal concentration of UIA (1.0, 1.5 and 2.0 mg/l) with control groups (with no adding of ammonia). The mortality rate significantly decrease (p<0.05) and (p<0.01) at levels B and C respectively compared with level A. Fish exposed to 1.0, 1.5 and 2.0 mg/l (UIA) appeared the following toxicity signs: lost equilibrium in water, moved very rapidly, increase ventilation, convulsions, spiral swimming, gasping, increase in mucous secretion in the gills and on the skin and hemorrhage in the gill, these sings were less in extent in fish groups reared in water at levels B and C g/l of NaCl respectively. Histopathological examination of gills showed different degrees of pathological changes which included various degrees of degeneration cells. These changes became sever with increasing concentration of ammonia. These changes were lesser extent in C. carpio groups reared in water containing 4g/l NaCl. The current study indicated that there is a relationship between the tolerance of ammonia toxicity and the water salinity level.