Although formalin is commonly used as a chemotherapeutant in fish culture, ill health conditions in some fish species at therapeutic levels have been reported. The present study was conducted to investigate the effects of short term formalin bath treatments on the health status of fingerlings and sub-adults of Oreochromis niloticus, a culturable food fish in Sri Lanka. Health status of the fish was assessed in comparison to the control fish by monitoring survival, respiratory rates, erythrocytic indices in blood and histology of gill and liver tissues after one hour exposure to different concentrations of formalin followed by transfer to clean water for 7 days. No significant alterations with respect to the parameters studied were observed in the fingerlings exposed to 50 mg L -1 formalin. Upon transfer to freshwater, formalin induced alterations in oxygen consumption rates and erythrocytic indices in the blood returned to normal levels after 7 days and histopathological changes in gill and liver tissues were observed to be restored to some degree. Results revealed that formalin could be used at the level of 50 mg L -1 for 1 hour for therapeutic purposes without undue harm to O. niloticus fingerlings but special caution should be taken when high concentrations of formalin are used in culturing this species.
Perera, H. A. C. C., & Pathiratne, A. (2005). Effects of short term exposure to therapeutic levels of formalin on health status of nile tilapia, oreochromis niloticus. Journal of the National Science Foundation of Sri Lanka, 33(4), 239–245. https://doi.org/10.4038/jnsfsr.v33i4.2113