Research Article Alterations in the Gill Filaments and Secondary Lamellae of Cirrhinus mrigala Exposed to (Nuvan,) an Organophosphorus Insecticide Nidhi Srivastava, Usha Kumari, Amita Kumari Rai, Swati Mittal, and Ajay Kumar Mittal Skin Physiology Laboratory, Centre of Advanced Study, Department of Zoology, Banaras Hindu University, Varanasi 221 005, India Correspondence should be addressed to Swati Mittal; drsmittal73@gmail.com Received 30 June 2014; Revised 18 September 2014; Accepted 3 October 2014; Published 27 October 2014 Academic Editor: Victor H. Casco Copyright © 2014 Nidhi Srivastava et al. his is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. he alterations in the epithelium of the gill ilaments and the secondary lamellae of the gills of Cirrhinus mrigala, on exposure to “Nuvan,” have been explored in the present investigation using light and scanning electron microscopy. he ishes were exposed to two sublethal concentrations, 5 mg/L and 15 mg/L, of “Nuvan.” he changes are more rapid and intensive at higher concentration than at lower concentration, suggesting that the changes are dose dependent. Increase in thickness of epithelium covering secondary lamellae, merger of epithelium of gill ilaments and adjacent secondary lamellae, and aneurysm is considered to reduce eiciency of gills for gaseous exchange. A signiicant decline in the density and area of the mucous goblet cells in the epithelium of the gill ilaments and the secondary lamellae of C. mrigala exposed to “Nuvan” could be correlated with excessive loss of the secretory contents of these cells, uncompensated by their production in suicient quantities. he histopathological changes, in general, take longer time to recover in the ishes exposed to 15 mg/L than those exposed to 5 mg/L indicating that the changes in ishes exposed to higher concentration are more severe than those at lower concentration of the insecticide. 1. Introduction he use of chemical insecticides is fairly recognized as a cost efective method of controlling the pests and parasites in agriculture and aquaculture practices, but these chemicals are highly toxic to other species in the environment. hey produce adverse efects on nontarget aquatic organisms living in areas near agricultural ields [1]. Pesticides oten end up in aquatic habitats carried up by wind, rain water, or through uncontrolled waste disposal. Being biodegradable and of short persistence in environment, organophosphorus insecticides are extensively used for the control of pests in agricultural ields, and, therefore, large quantities of these insecticides reach the water bodies [2]. “Nuvan,” an organophosphorus insecticide, is released on surface water as it is a commonly used chemotherapeutant in ish farming to eradicate crustacean ectoparasites [3–7] and to treat culture ponds for the eradication of freshwater ish predators prior to the stocking of spawn—fry, ingerlings, or juveniles of carps [8–10]. In ish, gills are the main site of gaseous exchange [11– 15]. In addition, they are involved in osmoregulation [16– 19], acid base balance [20–23], and excretion of nitrogenous compounds [24–26]. he complexity and constant contact with the surrounding water make the gill the irst target to waterborne pollutants [27]. Several studies have been made in the past on the histological organization and physiology of gills in a variety of ish species under control conditions. Important reviews on the structure of gills in relation to their respiratory function of ish species that have appeared in the literature include those of Hughes (1984) [28], Laurent and Perry (1995) [29], Wilson and Laurent (2002) [30], and Evans et al. (2005) [31]. More recently, Cinar et al. (2009) [15] reported the histology of the gills of the ish Pseudophoxinus antalyae and Tano de la Hoz et al. (2014) [32] reported the surface ultrastructure of the gills of Odontesthes argentinensis. According to Mallatt (1985) [33], gills are the primary sites of toxic action of many waterborne pollutants and the gill lamellae serve as an interface for ion and gas exchange between the blood and the external medium. Studies on the Hindawi Publishing Corporation Journal of Histology Volume 2014, Article ID 190139, 11 pages http://dx.doi.org/10.1155/2014/190139