Effect of an Insecticide Abamectin on Some Biochemical Characteristics of Tilapia Fish ( Oreochromis Niloticus )

: Problem statement: Presence of pesticide in streams and lakes is largely due to the runoff from agricultural fields. Pesticides are not highly selective but are generally toxic to many macrophytes, non-target organisms such as fish. Fish, generally accumulate contaminants from aquatic environments and have been largely used in food safety studies. Approach: The toxic effect of the insecticide abamectin on oxygen consumption and some biochemical characteristics (total protein, carbohydrate and cholesterol in liver, muscle, kidney and gills) of the tilapia fish ( Oreochromis niloticus ) were estimated. Results: The data shows that the rate of oxygen consumption was declined during all the exposure periods. On the other hand, all biochemical’s parameters were found to be decreased in all tissues on comparison with control. Conclusion: The results indicated the toxic nature of the insecticide abamectin.


INTRODUCTION
With rapid industrialization and increase in human population, the pollution of water bodies has become a universal phenomenon in the present day world (Bela and Prasad, 2008). The important sources of water pollution are industrial effluent, domestic, sewage, drainage and pesticides, which pollute the river and major water sources (Maruthanayagam and Sharmila, 2004). Pesticides and related chemicals destroy the delicate balance between species that characterizes a functioning ecosystem (Khan and Francis, 2005). Presence of pesticide in streams and lakes is largely due to the runoff from agricultural fields and outfall from pesticide manufacturing factories (Anandkumar, 1988). Pesticides are not highly selective but are generally toxic to many macrophytes, non-target organisms such as fish (Ayoola, 2008;Franklin et al. 2010).
Fish is highly nutritious, easily digestible and much sought after food. Nutritional value of fish depends on their biochemical composition, which is affected by the water pollution (Prado et al., 2009). Alterations in biochemical components as response to environmental stress are authenticated by many authors. Tilak et al. (2001) studied the toxicity and effect of chloropyriphos to the freshwater fish Labeo rohita (Hamilton); Alkhail et al. (2004) studied the toxicity and sub lethal effects on brain AChE and gill ATPases activity of tilapia fish, Oreochromis niloticus. Arockia and Mitton (2006) investigated the effect of carbamate pesticide lannate (methomy1) on the biochemical components of the freshwater cichlid Oreochromis mossambicus (Peters); Venkateswara (2006) studied the toxic effects of novel organophosphorus insecticide (RPR-V) on certain biochemical parameters of euryhaline Wsh, Oreochromis mossambicus.; Shereena et al. (2009) studied the effect of an organo phosphorous pesticides (Dimethoate) on oxygen consumption of the fish Tilapia Mossambica.; Impact of Cypermethrin and Ekalux on respiratory and some biochemical activities of a fresh water fish, Tilapia mossambica was studied by Logaswamy and Remia (2009); recently Patnaik (2010) studied the biochemical alterations Induced by Sevin in Clarias batrachus.
Saudi Arabia is the largest date producer in the world. Abamectin is used in Saudi Arabia to control motile mites and some other insects (Kamel et al., 2007;Fathi and Al-Fredan, 2007). Abamectin can runoff from the sites of application and becomes an aquatic pollutant (Tatjana and Nevenka, 2006). In addition Fish, generally accumulate contaminants from aquatic environmentsand have been largely used in food safety studies. The aim of this study was to identify the toxicity of abamectin on oxygen consumption and some physiological activities of tilapia fish (Oreochromis niloticus)

MATERIALS AND METHODS
Abamectin (1.8% EC) Arab Industrial Company, Dammam, Saudi Arabia was used in this study. The main structural characteristics and structural formula of Abamectin were presented in (Table 1 and Fig. 1).
For the present study, Fresh water fish Tilapia (Oreochromis niloticus) were collected from Al-Khadoud spring channel and experiment was conducted in the laboratory at Department of Biological Sciences, College of Sciences, King Faisal University during summer 2009. Table 2 shows the means values of the physico-chemical characteristics of Al-Khadoud channel water (Fathi and Al-Kahtani, 2009). The fishes were acclimated to the laboratory temperature (23±0.5) in large glass aquarium. The fish were fed twice daily with 38% protein commercial fish food (CP-Pet; Pokphand Animal Food Co. Ltd., Bangkok, Thailand). The period of acclimation lasted for 2 weeks. Batches of 10 healthy fishes were exposed to different concentrations of insecticide abamectin to calculate the medium lethal concentration LC 50 value using probit analysis method (Finney, 1971).
The fishes (Four groups) were exposed to the sub lethal concentration (20 µg L −1 ) of abamectin for 24, 48 72 and 96 h respectively. Another group was maintained as control. At the end of each exposure period, fishes were sacrificed and tissues such as liver, gill, muscle and kidney were dissected and removed. The tissues (10 mg) were homogenized in 80% methanol, centrifuged at 3500 rpm for 15 min and the clear supernatant was used for the analysis of total proteins, carbohydrates and cholesterol. Total Protein concentration was estimated by the method of Lowry et al. (1951). Total carbohydrate in the tissue was estimated by the method described by Hedge and Horfreiter (1962). Cholesterol was estimated based on enzymatic method using cholesterol esterase, cholesterol oxidase and peroxides (Richmond, 1973). Changes in the rate of oxygen consumption of the fishes were evaluated at different exposure periods. The rate of oxygen consumption was estimated by Winkler's method (Welsh and Smith, 1960), the results were in ml g −1 h −1 . Results were tested by one-way Analysis Of Variance (ANOVA). ANOVA effects and treatments differences were considered significant when p<0.05. Insecticide/miticide Acute toxicity: Abamectin is highly toxic to insects and may be highly toxic to mammals as well Effects on birds: Abamectin is practically nontoxic to birds Effects on aquatic organisms: Abamectin is highly toxic to fish and extremely toxic to aquatic invertebrates

RESULTS AND DISCUSSION
The oxygen consumption and the biochemical constituents of the tilapia fish (Oreochromis niloticus) exposed to sublethal concentration of Abamectin at different exposure periods were observed in the present study. Studies on oxygen consumption form a useful tool in the assessment of toxicant stress on the aquatic organisms and give an index of energy expenditure mechanisms for environmental variation (Sornaraj et al., 2005;Logaswamy and Remia, 2009;Francesco et al., 2008;Franklin et al. 2010).
Toxicants in the environment mainly enter into fish by means of their respiratory system (Tovell et al., 1975). The rate of oxygen consumption (mL g −1 h −1 ) of tilapia fish (Oreochromis niloticus) exposed to the sublethal concentrations of Abamectin for different exposure periods are shown in Fig. 2. The data shows that the rate of oxygen consumption was declined during all the exposure periods. Several authors (Rao et al., 2003;Shivakumar and David, 2004;Vutukuru, 2005;Vineetkumar et al., 2008;Shereena et al., 2009;Logaswamy and Remia, 2009) reported that the disturbance in oxidative metabolism leads alteration in completely animal oxygen consumption in different species of fish exposed to pesticides.
Proteins are important organic substances required by organisms in tissue building and play an important role in energy metabolism (Yeragi et al., 2003;Remia et al., 2008;Pang-Hung et al., 2008). The result of the present study showed significant decrease in protein content in the tissues studied (Table 3). The percent decrease was found to be greater in all exposures in liver tissue. The reduction of protein may be due to proteolysis and increased metabolism under toxicant stress (Remia et al., 2008). Dalela et al. (1981) observed a decrease in protein content in Mystus vittatus under pesticide exposure and reported that the depletion of protein may be due to the excretion of proteins by kidney due to kidney failure or impaired protein synthesis as a result of liver disorders. A number of workers have reported decline in protein level of various organs and tissues under toxic stress of various chemicals. Begum and Vijayaraghavan (1996) have reported that the protein content of muscle tissues of fish Clarius botrachus was significantly depleted during 192 h of dimethoate exposure. Kumar and Saradhamani (2004) observed significant decrease in protein content in all the tissue of the fish Cirrihinus mrigala upon exposure to the pesticide avaunt. Carbohydrate is an essential component of living cells and sources of energy for animals. The results of the present findings showed a significant decrease in carbohydrate content in all the tissues studied (Table 4). Many workers reported a similar trend of decrease in carbohydrate (Venkatramana et al., 2006;Saradhamani and Selvarani, 2009). On the other hand, some other workers (Witold et al., 2007;Francesco et al., 2008;Logaswamy and Remia, 2009) reported that sublethal concentration of certain organophosphate pesticides caused glycogenolysis, which produced hyperglycemia in the African food fish Tilapia mossambica and the Indian catfish, Heteropneustes fossilis.
However, Remia et al. (2008) reported that the elevation of carbohydrates might be due to the stress induced by the insecticides as physiology of organisms with the help of corticosteroids.
Cholesterol is an important normal body constituent used in the structure of cell membranes, synthesis of bile acid and synthesis of steroid hormones. The results presented in Table 5 shows a significant decrease in cholesterol content in the studied tissues of fish Tilapia (Oreochromis niloticus). The decrease was found to be high in gills and less in muscles. Generally, the decreases in cholesterol contents in all tissues were found to be increased with the hours of exposure. The reduced cholesterol level may be due to the inhibition of cholesterol biosynthesis in the liver or due to reduced absorption of dietry cholesterol as reported by Kanagaraj et al. (1993).   75+0.14 ANOVA *** ** *** *** Results of one-way ANOVA indicate; *: p<0.05; **: p<0.01; ***: p<0.001; NS = Non significant Shakoori et al. (1996) reported that the cholesterol decrease may be due to utilization of fatty deposits instead of glucose for energy purpose.
However, Remia et al. (2008) reported that the decline of cholesterol may be due to utilization of fatty dposites instead of glucose for energy purpose.
Various authors studied similar reduction of lipids in various tissues. Ram and Sathyanesan (1984) observed a decreased lipid level in the liver of Channa punctuatus exposed to emisan. Srinivas et al. (1991) has showed decreased lipid content in T. mossambica on exposed to atrazine. Gradual depletion in lipid content of liver and muscle when exposed to Malathion was analysed by Mishra et al. (2004). Arockia and Milton (2006) have showed declining trend of lipid content in the tissues like brain, gill, kidney, liver and muscles upon exposure to carbamate in the fish Oreochromis mossambicus. Saradhamani and Selvarani (2009) showed significant decrease in cholesterol content in the tissues of the freshwater fish, Tilapia mossambica exposed to metribuzin.

CONCLUSION
A toxicant induce its effect at cellular or even at molecular level, but ultimately cause physiological and biochemical alterations. The results of the present study clearly indicate the toxic nature of the insecticide Abamectin on the oxygen consumption and the biochemical constituents of the tilapia fish (Oreochromis niloticus). The changes in proteins, carbohydrates and lipid in the insecticide Abamectin treated fishes will naturally affect the nutritive value of these animals and all the metabolites studied are found to be sensitive changes in the normal indictors, which reflect changes in the normal activities of various functional systems. It is therefore necessary to focus attention on changes in biochemical composition of aquatic organisms, which are under pollutant threat.