An Analysis of Photobehavior of Daphnia Magna Exposed to Tributyltin

Photobehavior of Daphnia magna was examined when individuals were exposed to the antifouling toxicant tributyltin chloride (TBTC). Two separate experiments were performed in different types of containers in order to test the repeatability of the results. The major conclusion of the study is that at concentrations below that which cause mortality, individuals exhibit abnormal photobehavior. At lower concentrations of TBTC, the time to initiation of abnormal behavior was extended due to a possible threshold concentration at the site of action. The threshold concentration for sign reversal of phototaxis is approximately 0.5 ppb (ng/ml) after 96 to 144h exposure. The estimated LC50 value for this same time period is approximately 3.5 to 6 ppb (ng/ml) which shows that the sublethal response is about an order of magnitude below that of the standard acute mortality value. Effects on swimming speeds and ecological consequences are discussed.