Behaviour and Respiratory Dysfunction as an Index of Malathion Toxicity in the Freshwater Fish, Labeo rohita (Hamilton)

The pollution of rivers and streams with chemical contaminants has become one of the most critical environmental problems of the century. As a result of the pollutants transport from industrial areas into the environment and their chemical persistence, many freshwater ecosystems are faced with spatially or temporally alarming high levels of xenobiotic chemicals (Brack et al., 2002; Diez et al., 2002). Some of these chemicals are biodegradable and quickly decay into harmless or less harmful forms, while others are non-biodegradable and remain dangerous for a long time. Now, there is a growing concern worldwide over the indiscriminate use of such chemicals, resulting in environmental pollution and toxicity risk to aquatic organisms (Khan, 1996). Thus, ecological damage of the environment caused by anthropogenic factors as well as the presence of hazardous agents may affect fish. Malathion is a non-systemic, wide spectrum organophosphate insecticide. It was one of the earliest organophosphate insecticides developed (Introduced in 1950). This is used for agricultural and nonagricultural purposes. Once malathion is introduced into the environment, usually from spraying on crops or in wide urban or residential areas, droplets of malathion in the air fall on soil, plants, water or manmade surfaces. While most of the malathion will stay in the areas where it is applied, some can move to areas away from where it was applied by rain, fog and wind. In water, malathion breaks down quickly by the action of water and bacteria in the water. Malathion is broken down in air by reacting with other chemicals formed naturally in the air by sunlight to form a more toxic product called malaoxon. If malathion is present on dry soil or on man-made surfaces such as sidewalks, pavements, or playground equipment, it usually does not break down as fast as it would in moist soil. Once malathion is introduced into the environment, it may cause serious intimidation to the aquatic organisms and is notorious to cause severe metabolic disturbances in non-target species like fish and fresh-water mussels (USEPA, 2005). The physiological condition of the organism during toxic impact must be considered to understand the influence of pesticide. Labeo rohita is edible freshwater fish of great economic connotation and it is used in the composite fish culture. Behaviour is considered a promising tool in ecotoxicology (Drummond and Russom, 1990; Cohn and MacPhail, 1996) and these studies are becoming prominent in toxicity assessments in unicellular organisms (Tadehl and Häder, 2001), insects (Jensen et al., 1997) and fish (Little and Finger, 1990). Most physiologic and environmental changes can induce variations in fish behavior (Israeli-Weinstein and Kimmel, 1998; Almazán-Rueda et al., 2004). Hence the present study was under taken to evaluate the aquatic toxicity of malathion with special emphasis on behavioural and oxygen consumption of the Abstract