Investigating the behavioral response of zebrafish larvae after exposure to different classes of insecticides
As only a small amount of all used pesticides reach on their designated target, a large quantity of them runs off and ends up in surface waters, endangering aquatic ecosystems. In this context, it is important to evaluate, on aquatic organisms, the toxicity of these products, especially insecticides. Zebrafish are commonly used organisms that serve as a model in toxicity-evaluation of chemical compounds. To avoid the death of the tested specimen, new methods have recently been developed, such as in vitro or behavioral studies, to which belongs this research project. Attractive or avoidance effects induced by insecticides are studied on larva zebrafish. The six chosen insecticides were all found in strong concentrations in several Swiss streams: diazinon, dimethoate, imidacloprid, methomyl, pirimicarb and thiacloprid. To study and characterize behavioral changes, four solutions (0.1, 1, 10 and 100 μM) are injected in a chamber where the larva can freely move, creating a high concentration zone. Several methods were used: mean velocity and location of extreme velocities, the mean turn angle and the location of extreme values, time spent in the contaminated and in the outer zone, the displacement of the average position as well as a simulation with a random walk. Zebrafish showed attraction signs for the largest concentration in pirimicarb. Two insecticides induced a avoidance behavior, diazinon at 10 μM and all solution of thiacloprid. Finally, the three last insecticides did not lead to observable signs of behavioral changes, although the larvae avoided slightly the injection. Of all the used methods in this study, some were less pertinent, such as the mean velocity or the mean turn angle, which did not lead to clearly interpretable results. However, the extreme value location provided with a better understanding of zebrafish subject to insecticides.
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