Pesticide-induced histopathological changes in the freshwater fishes of Kuttanand, Kerala- a tool to assess water quality and the health status of fishes

Kuttanad, the rice bowl of Kerala, is a region where overdose application of pesticide is prevalent during the punja cultivation periods. According to the data compiled by Kuttanad Water Balance Study Project, 485 tonnes of pesticides were applied in Kuttanad on an annual basis of which 370 tonnes were used for the punja crop alone (KWBSP, 1990). In such a degraded aquatic environment, particularly where pollutants occur at chronic sublethal concentrations, changes in the structure and functions of aquatic organisms occur more frequently than their mass mortality. Therefore, one of the possible methods of assessing the effects of pollutants on fresh water fish inhabiting this ecosystem is to examine their organs for morphological changes. In fishes, apart from lethal effects of pesticides and the consequent mortality of eggs, larvae, and adults, their prolonged exposure in sublethal concentration may also result in reproductive abnormality, stock recruitment, deformities of eggs and larvae, retardation of hatchling percentage and body abnormalities. In the present study, a tool developed by Bernet et al. (1999) is used to assess the histopathological conditions; hence, histopathology is used as a tool to assess the health status of two freshwater fishes of Kuttanad, viz., Etroplussuratensis and Anabastestudineus. The organ index calculated based on various reaction patterns of the different organs of fishes exposed to sublethal concentrations of monocrotophos for a period of 30 days showed that gills were severely affected, liver was moderately affected, and kidney was the mildly affected organ, irrespective of fish species. Histopathology provides evidences of adaptation to degeneration, and histopathological alterations can be used as biomarkers of environmental pollution by organic chemicals. Histological changes in fish gill should become a rapid “early warning system” for water quality assessment in sublethal and chronic situations, as the toxicants induce changes at lower levels of biological organization prior to organismic changes.