Agricultural pesticides are nowadays being extensively used for the control of a wide variety of agriculturalpests. The world over, human health is at risk. While on one hand people are dying due to scarcity of food,on the other they are slowly being poisoned by the chemicals used for growing food. Other than targetedpests, pesticides affect a wide range of non-target organisms, such as invertebrates and fin fish inhabitingaquatic environment. The present laboratory study is aimed at assessing the sublethal effects ofmonocrotophos on the gills of Etroplus maculatus, a fresh water food fish as well as an indigenous ornamentalfish of the paddy fields of Kuttanad, the rice bowl of Kerala. Sublethal exposure was done in a static systemand the target organ undergoes histological Hematoxylin-eosin staining procedures. The pathologicalchanges were obviously dose–dependent and maximum severity was noticed in the gills of fishes exposedto the highest sublethal concentrations. The overall changes observed due to the exposure to differentconcentrations of monocrotophos are hypertrophy, hyperplasia, fusion of secondary lamellae, oedematousseparation of respiratory epithelium, lamellar telangiectasis, stasis, filamental blood vessel enlargementand necrosis. Based on the histological lesions observed the index values were calculated. On the basis ofthe index values, No Observable Effect Concentration (NOEC), Least Observable Effect Concentration(LOEC) and Maximum Allowable Toxicant Concentrations (MATC) of monocrotophos to E. maculates werecalculated. The concentration which showed index value less than 10 is taken as NOEC and between 10-20is taken as LOEC. MATC of monocrotophos to E. maculates is estimated as 0.4243 ppm. Based on the MATCthe calculated application factor (AF) was 0.1263. These NOEC, LOEC, MATC and AF so obtained for thisspecies can also be used to assess tentative water quality status for the pollutants in the natural environment,and the AF derived from the laboratory studies can be directly applied to the filed situations, as they are therepresentative sample of Kuttanad. Histopathology is an important biomonitoring tool for the farmers indeciding the concentrations of pesticides before its application into the paddy fields.

High population growth have led to a tremendous intensification of rice production, which in turn has significantly increased the amount of pesticides applied in rice cropping systems. Since pesticides are toxic by design, there is a natural concern on the impact of their presence in the environment on human health and environmental quality. The present study was conducted to assess the nature and extent of pesticide induced pathogenesis in the tissues of gills, liver and kidney of Etroplus maculatus inhabiting the paddy fields of Kuttanad, Kerala, India, which is subjected to long term exposure to sublethal concentrations of a common pesticide, phosphamidon, used in these area. The organ index calculated based on various reaction patterns of the different organs. The study showed that the gills are severely affected, liver is moderately affected and the kidney is the mildly affected organ. As an indicator of pollution, histology represents a useful tool to assess the degree of pollution, particularly for sub lethal and chronic effects.

Histological changes appear as a medium term response to sublethal stressors and histology provides arapid method to detect the effects of irritants, especially chronic ones in various tissues and organs. Pesticidesusage in agricultural fields to control pests is extremely toxic to non-target organisms like fish and affectsfish health through impairment of histological structure, sometimes leading to mortality. The presenthistopathological study reveals the potential adverse effects of monocrotophos, an organophosphatepesticide, on a fresh water fish, Anabas testudineus and it document a dose- dependent reaction of liver andkidney histology. The histological changes observed in liver included fatty-vacuolation and the displacementof nuclei to the periphery of the hepatocytes, congested and constricted liver sinusoids, condensedhepatocytes, destructed hepatocytes and pyknotic nuclei. The major histological alterations identified inthe kidney were melano-macrophage centres, shrunken renal tubules and degenerated renal tubule.Calculation of organ index is used for comparing the severity of lesions in different organs. These organindices are used for calculating total index. In the present study the total index showed the health status offishes in each sublethal concentration “Calculation of organ index is used for comparing the severity oflesions in different organs. These organ indices are used for calculating total index. In the present study thetotal index showed the health status of fishes in each sublethal concentration and the status became worsein the higher sublethal concentrations. “ and the status became worse in the higher sublethal concentrations. Histopathology can be used as a tool for assessing the sublethal conditions of water quality and it gives a“rapid early warning system”.

An array of wide spectrum chemicals and their combinations are now being used as insecticides, fungicides,herbicides, nematicides, rodenticides and molluscicides. Kuttanad, the rice bowl of Kerala, India (Altitude– sea level; Latitude – 9.9 N and Longitude – 76.2 E) is a region where there is over application of pesticideduring the punja cultivation periods. Phosphamidon, Monocrotophos, Henosan and Thymet are the majorcomponents of the pesticides being used in Kuttanad. The exposure of fish to pesticides is likely to inducea number of lesions in body organs like gills, liver and kidney. The gills are the most important and sensitiveorgans of a fish body, which first experience the hazards of, polluted ambient water. As the fish gills areexposed to pesticides, a wide variety of structural changes in fish gills have been reported. They arehypertrophy, hyperplasia, oedematous separation of respiratory epithelium, telengiectasis, stasis,hemorrhage, necrosis, etc. The study shows that the pathological changes are gradually increasing fromthe lowest concentration to the highest concentration. The present study is aimed at assessing the extent ofPhosphamidon induced histological changes in the gills of Anabas testudineus, a fresh water food fish widelyinhabiting the paddy fields of Kuttanad, Kerala, India, and to arrive at a Maximum Allowable ToxicantConcentration (MATC) and an Application Factor (AF) based on the histopathology. This end point givesan ‘early warning’ of the damage caused in the fish at the histological level before their mortality. Hencepreventive measures can be taken to protect the fishery resources. Based on the index value, the MATC is3.1623 ppm and the Application Factor (AF)is 0.0804.