International Journal of Scientific and Research Publications, Volume 2, Issue 10, October 2012 1 ISSN 2250-3153 www.ijsrp.org Effect of different sublethal concentrations of Manganese on the levels of cortisol in Garra gotyla gotyla Prof. Kadambri Gupta, Prof. Seema Langer, Jyoti Sharma and Sheetal Sharma Department of Zoology, University of Jammu, Jammu, J&K, India. 180006 Abstract- The objective of this study was to evaluate the possible effects of manganese (Mn) exposure on variations of cortisol levels in Garra gotyla gotyla. LC 50 value of manganese after 96 hours was found to be 3.2mg/l for Garra gotyla gotyla. Three replicates of 10 fishes were subjected to three sub-lethal concentrations of manganese i.e. 0.64mg/l, 1.28mg/l and 1.92mg/l (20%, 40% and 60% respectively of LC 50 value of manganese) for 1, 5 & 9 weeks. Blood samples were isolated from the fish following the exposure to measure the levels of cortisol and compared to the control group. We observed significant increase(p<0.01) in the levels of cortisol of three groups of fish after 1st week of exposure to three doses of manganese as well as significant decrease in the cortisol of three groups exposed for 5th & 9thweek. The rate of decrease in group III (exposed to1.92 mg/l of Mn) was higher than that of group I & II (exposed to 0.64 mg/l of Mn and 1.28 mg/l of Mn). Index Terms- Manganese exposure, Cortisol, Garra gotyla gotyla I. INTRODUCTION he hormone cortisol in fish has been identified as a metabolic hormone (Vijayan et al., 1994) having multifaceted action. It is also considered as an important stress hormone produced in fish (Mommsen et al., 1999). Cortisol is the predominant corticosteroid in most of the teleost group (Handerson & Garland,1980).The secretion of cortisol is dependent on factors such as temperature (Strange, 1980; Davio et al., 1984; Barton & Schreck, 1980 & Barton & Zitzow, 1995), time of day (Davis et al., 1984 & Barton et al., 1986), wave length of light (Volpato & Barreto, 2001), background of color tanks (Gilham & Baker, 1985), nutritional state (Barton et al., 1988), presence of disease (Barton et al., 1986), season (Pickering & Pottingger, 1984), reproduction (Shankar & Kulkarni, 2007). Besides these factors heavy metals are also known to affect cortisol levels in fish (Richard et al., 1998). The catabolic action of cortisol is responsible for the mobilization of energy reserves (gluconeogenesis) and lipolysis (Leach & Taylor, 1982; Sheridan, 1986). Cortisol has also been shown to play important roles in intermediary metabolism, growth, ionic and osmotic regulation, reproduction, immune functions (Wendelaar, 1997 & Mommsen et al., 1999). Undoubtedly, the growing evidence supporting the importance of cortisol in maintaining homeostasis, together with the ease of measuring cortisol and the magnitude of cortisol response to stress, make it convenient measure and the predominantly reported stress indicator. The objective of present study is to evaluate the effect of different sub lethal concentrations of manganese on the levels of cortisol in Garra gotyla gotyla. II. MATERIAL AND METHODS  Animals and experimental conditions Live specimens of Garra gotyla gotyla were collected with the help of cast net and were brought to the laboratory avoiding stress and injury as much as possible. Prior to onset of metal treatment, the fish were acclimatized to the laboratory conditions for approximately a fortnight. During this period fishes were fed with natural diet which included portion of aquatic plants, vegetables, debris and mud as the fishes were herbivores in nature. The 96 hrs LC 50 value of manganese was determined as 3.2mg/l. Manganese stock solution were made from MnSO 4 , added subsequently to dechlorinated tap water in the plastic tubs (capacity of 50L) to obtain test concentrations 0.64mg/l, 1.28mg/l and 1.92mg/l (20%, 40% and 60% respectively of LC 50 value of manganese). The examined fishes were divided in to three groups exposed to three sub lethal concentrations of Mn 0.64mg/l, 1.28mg/l and 1.92mg/l (20%, 40% and 60% respectively of LC 50 value of manganese). Control groups were the fishes maintained in normal, aerated tap water. The water in each plastic tub was replenished daily to keep the metal concentration unchanged. The experiment had three replicates and in each replicate 40L of water was added and 10 number of Garra gotyla gotyla was taken in each experimental tub.  Measurement of the levels of cortisol: Blood was taken from the heart of the fish with non heparinized syringe, collected in plastic Eppendrof tubes. After centrifugation, blood plasma was removed and the samples were then analyzed for measuring the levels of cortisol by Radioimmunoassay following the methodology adopted by Tort et al., 1998.  Statistical analysis of data : The data was statistically evaluated by analysis of varience and paired sample t test using SPSS 17 version. III. RESULTS AND DISCUSSION Exposure of Garra gotyla gotyla to different sub lethal concentrations of manganese (Mn) 0.64mg/l, 1.28mg/l and 1.92mg/l (20%, 40% and 60% respectively of LC 50 value of manganese) caused a significant variation in plasma cortisol level (Table 1). After first week in the manganese exposed (0.64mg/l, T