Abstract
Sub-lethal studies of chlorpyrifos, O,O-diethyl-O-(3,5,6-trichloro-2-pyridyl) phosphorothioate on mosquito fish, Gambusia affinis were carried out in vivo, for 20 days to assess the locomotor behavior in relation to bioaccumulation and interaction with a targeted enzyme, acetylcholinesterase (AChE, EC: 3.1.1.7). Fish exposed to sub-lethal concentration of 60 microg/L (1/5 of LC 50) were under stress, and reduced their locomotor behavior like distance travelled per unit time (m/min) and swimming speed (cm/sec) with respect to the length of exposure. The alteration in locomotor behavior of fish may be due to an accumulation of acetylcholine (ACh), a neurotransmitter at synaptic junctions, due to the inhibition of AChE enzyme activity (40 to 55%) in brain and also bioaccumulation of the toxicant in different parts of fish. The bioaccumulation values indicated that the accumulation of chlorpyrifos was maximum in viscera followed by head and body. The average bio-concentration values are 0.109, 0.009 and 0.004 microg/g for viscera, head and body with depuration rates of 2.24, 1.69 and 0.39 ng/h respectively. It is evident from the results that the sub-lethal concentration [1/5 of LC 50; equivalent to Lowest Observed Effect Concentration (LOEC)] of chlorpyrifos can able to alter the locomotor behavior of G. affinis in relation to the length of exposure. The findings revealed that the locomotor activity of test organism could be considered as a suitable marker to evaluate the affect of toxicant even at LOEC levels.
Highlights
Pesticides are widely used in agriculture and there is a need for tools to monitor the impact of these pesticides on fish population
Acute toxicity of chlorpyrifos on fish, Gambusia affinis was carried out by semi static method and its LC50 value for 96 h is presented in table 1
It is evident from the results that chlorpyrifos can be rated as highly toxic to G. affinis with an LC50 value of 297.63±21.72 Ag/L
Summary
Pesticides are widely used in agriculture and there is a need for tools to monitor the impact of these pesticides on fish population. Mortality is obviously not the only endpoint to consider and there is a growing interest in the development of behavioral markers to assess the sub-lethal affects of toxicant. Behavior is considered a promising tool in ecotoxicology [6,7,8] and these studies are becoming prominent in toxicity assessments in unicellular organisms [9], insects [10, 11], fish [12] and even rodents [13]. Locomotory behavior is commonly affected by contaminants [14] and the pattern of fish swimming is a highly organized species-specific response. The advanced time-lapse video techniques have been successfully used to facilitate the documentation of behaviors in insects, fish and rats of normal and stressed organisms [15,16,17]. With the recent development of computer-assisted electronics, videocamera tracking systems have been greatly improved (Ethovision, Noldus, The Netherlands) and used extensively in quantification of locomotor behavior with a high degree of precision [10, 18]
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