Effects of Quinalphos 25 EC and Dimethoate 30 EC on Activities of AchE, Catalase, GOT and GPT in the Freshwater Prawn Macrobrachium rosenbergii

The commercially important freshwater prawn, Macrobrachium rosenbergii post larvae (PL), 1.5±0.2 cm and 0.1±0.03 g were subjected to static renewal type acute toxicity bioassays against two orgnophophate insecticides, quinalphos (Ekalux EC 25) and dimethoate 30% EC (TAFGOR). The 96 hr LC50 values were determined to be 0.774 μgl-1for quinalphos and 0.856 mgl-1for dimethoate. The PL were exposed to lethal (the 96 hr LC50) and sub-lethal (1/2 nd and 1/4th of the 96 hr LC50) concentrations of these insecticides (quinalphos: 0.774, 0.384 and 0.193 μgl -1; dimethoate: 0.856, 0.428, 0.214 mgl-1) for a duration of 4, 8 and 12 days to study their acute and chronic impacts on whole body activities of enzymes, the neurotransmitter, acetyl cholinesterase (AChE), the antioxidant, catalase and metabolic enzymes, glutamate oxaloacetate transaminase (GOT) and glutamate pyruvate transaminase (GPT). The activity levels of AChE and catalase were found to be significantly (P<0.05) decreased in test prawns when compared with control, whereas, there were significant elevations in GOT and GPT levels (P<0.05). Among GOT and GPT, the impact was more on GOT than GPT. The dosage and time dependent manner of inhibition or elevation in activities of these enzymes were recorded. Among these two insecticides, quinalphos showed more impacts than dimethoate on this non-target organism. Introduction Pesticides have tremendous benefits to man by increasing crop protection and thereby increasing food production, and controlling the vectors of man and animal diseases. They are transported over long distances by global circulation, and through run-off, find their way into aquatic systems. At the same time the pollution of freshwater ecosystem by chemical pesticides has become one of the most critical environmental problems (Northoff and William, 2004). This causes extensive damage to the activities of the living resources of food-web due to their toxicity, persistency with half-lives of decades and tendency to accumulate in the organisms (Joseph and Raj, 2010; Joseph et al., 2010; Joseph and Raj, 2011). Quinalphos (C12H15N2O3PS), O,O-diethyl O-quinoxalin-2-yl phosphorothioate, an ester of OP is used as insecticide and acaricide having a quick knock down effect through contact and stomach poisoning (David and Kumaraswami, 1988; Hassal, 1990). It is frequently used in many countries and represents a source of toxicity to humans and vertebrate animals (Kegley et al., 2010). Dimethoate (C5H12NO3PS2), O,O-dimethyl S-[2-(methylamino)-2-oxoethyl] dithiophosphate is a broad-spectrum OP insecticide and acaricide exhibit both contact and systemic activity (David and Kumaraswami, 1988; Hassal, 1990). Its degradation by esterases and amidases are very low in insects as compared with those of mammals (Rose and Hodgson, 2004). The effects of pesticides, such as endosulfan, carbaryl, dichlorvos, lindane, chlorpyrifos, monocrotophos, carbofuran and methomyl have been studied on acute toxicity (Bhavan et al., 1997a, b, 2008; Key and Fulton, 2006; Satapornvanit et al., 2009) and biochemistry (Bhavan and Geraldine, 1997, 2000a, b; 2001, 2002, 2004, 2007, 2009; Geraldine et al., 1999; Bhavan et al., 2011) of freshwater prawns. However, no data is available pertaining to quinalphos and dimethoate toxicity induced changes on the activities of the neurotransmitter, acetyl cholinesterase (AChE), the enzymatic antioxidant, catalase and metabolic enzymes, glutamate oxaloacetate transaminase (GOT) and glutamate-pyruvate transaminase (GPT) in Macrobrachium. Therefore, it was necessitated to generate information on these pesticides in Macrobrachium rosenbergii to establish the potential of predictive biomarkers for use in water pollution monitoring. Materials and Methods The post larvae of freshwater prawn, M. rosenbergii were purchased from Happy Bay Aqua Nova Hatchery, Mugaiyur, Marakanam Taluk, and Kancheepuram District, Tamilnadu, India. They were safely brought to the laboratory in polythene bags filled with hatchery water and well-oxygenated. They were stocked in large cement tank (6’ x 4’ x 3’) and acclimatized for 2 weeks in ground water. During which they were fed with boiled egg albumin, Artemia nauplii and commercially available scampi crumble feed alternatively thrice a day. The excreta, unfed feed and exuvia if any were removed daily, three fourth of the water was renewed daily and adequately aerated. Quinalphos (Ekalux EC 25) and dimethoate 30% EC (TAFGOR) were purchased from local agro service centre. Ten concentrations of each quinalphos (0.250-1.375 μgl-1) and dimethoate (0.060-1.350 mgl-1) were prepared by mixing in distilled water afresh on every day. Post larvae (PL) of M. rosenbergii (1.5 ±0.2 cm and 0.1 ± 0.03g) were transferred to plastic aquaria of 10 l capacity (each with 10 PL) with ground water for 2 days. Out of eleven groups one PL group was served as control and others were exposed to ten different known concentrations (quinalphos: 0.250-1.375 μgl-1; dimethoate: 0.060-1.350 mgl-1) of each insecticide for 96 hours to assess their LC50 value as per the guidelines prescribed by ASTM (1980). The experiment was conducted