Some histopathological aspects of chlorine toxicity in rainbow trout (Oncorhynchus mykiss)

Objective: Chlorine is added to municipal (tap) water supplies to kill microorganisms. Toxicity with discharges of chlorine is common because it is used to disinfect effluents, to control fouling organisms in cooling water system, and in the food and paper industries. Rainbow trout are very sensitive to changes in water chemistry and even have been considered as a good experimental model, acting as an indicator for toxicity in aquatic animals. The aim of this paper was to study the histopathological changes due to chlorine toxicity in rainbow trout. Method & Materials: Eight month old rainbow trout were found dead ten days after shot down of a fresh water recirculation system during a blackout. The type of chlorine used by the water department was chloride dioxide and CL 2 (Liquid). Fish were found swimming in a swirling motion or died suddenly. Ten days later mortality rates reached 60%. The cause of death was diagnosed as chlorine toxicity. The fish carcasses appeared pale and anemic and had enlarged gall bladders and mild multifocal dermatitis. Samples were preserved in 10% formalin buffer and were sent to pathology laboratories. Sections of these tissues were prepared. Results & Conclusion: The gill lesions finding in our study resembled a typical irritant response, beginning with epithelial lifting, hypertrophy and hyperplasia. The vacuolation in gills can be related to the haemolytic anaemia caused by hypoxia. Telangiectasis of secondary lamellae is associated with chemical pollution. Our findings in the spleen suggested that in acute hemolytic crises most of the blood pigments accumulate in the spleen rather than the kidney. Although chlorine toxicity has been frequently reported as a cause of mortality in fish, the pathology changes related to this toxicity is treated rather briefly in literature. Thus, the purpose of this study was to ascertain some of these pathological changes in a naturally occurring toxicity. This case study also illustrates the importance of good history taking and how interrelated fish are with their watery environment.

کلیدواژه ها:

Chlorine ، Toxicity ، Fish ، Histopathology ، Rainbow trout