Fish Gills as a Tool for the Assessment of Sublethal Effects of Monocrotophos on a Freshwater Fish, Etroplus maculatus

Abstract

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.