*Corresponding author; Email address: suralena1974@gmail.com 53 Journal of Theoretical and Experimental Biology (ISSN: 0972-9720), 13 (1 and 2): 53-61, 2018 © 2018 Elias Academic Publishers www.jteb.webs.com Impact of Quinolphos on Enzyme Activities in the Selected Tissues of the Fresh Water Fish, Cirrhinus mrigala (Ham.) Sreeya G. Nair and R. Radha* Department of Zoology, Sree Ayyappa College for Women, Chunkankadai-629003, Tamil Nadu, India. Received: 02 March, 2018; revised received: 22 April, 2018. Abstract Pesticide toxicity is a global problem with most of the poisoning occurring in developing nations. As fish is considered as the most important and vital link in the food chain of ecosystem, a thorough understanding of pesticide effects on fishes would be really vital for fish conservation. Hence, an attempt has been made to investigate the sub lethal effects of quinolphos on enzymatic changes of C. mrigala effect of quinolphos in C. mrigala. Results showed that the LDH activity in the tested tissues like those of the liver, muscle and intestine of C.mrigala decreased when exposed to different concentrations of quinolphos. The SDH level in the tested tissues of quinolphos exposed fish was also considerably reduced with increase in the duration of exposure. But quinolphos exposed C. mrigala showed increase in acid and alkaline phosphatase content in the liver, muscle and intestine. It is clearly evident that exposure of C. mrigala to quinolphos clearly induced the LDH and SDH disorder which may be responsible for the pesticide toxicity. The activity of acid and alkaline phosphatase (AcP and AlP) in the examined tissues of C. mrigala reared in different sub-lethal concentrations of quinolphos was increased considerably. The percentage of increase over the control was maximum in intestinal tissues. In the light of this study comprising enzyme changes, it is clearly evident that quinolphos are toxic chemicals to fishes. Keywords: Pesticide toxicity, quinolphos, C. mrigala , acid and alkaline phosphatase, Succinic dehydrogenase, Lactate dehydrogenase Introduction Increasing human population and consequent need for more food, health services and improved living standards have boosted the development of chemical industry manufacturing pesticides, drugs, cosmetics and other chemicals for human use. These chemicals are neither degraded biologically nor assimilated in the living system as they are not compatible with the living system. Over the past four decades, pesticides have become an indispensable part of world agriculture since these are applied to protect standing crops, stored grain and insect pests (Singh et al., 1998). Pesticides have, no doubt, been a boon to human civilization in sustaining agriculture revolution but at the same time bared its ravaging face on humanity pushing to a point of almost no return (Tilak et. al., 2005). Modern agriculture practices, despite their remarkable contribution to the enhancement of crop production, have also widely polluted the aquatic environment (Pandey et al., 2000). It has been estimated that the use of pesticides has increased the crop’s yield three fold.