The swimming behaviour of Brachionus calyciflorus (rotifer) under toxic stress : II. Comparative sensitivity of various behavioural criteria

Changes in the swimming behaviour of the freshwater rotifer Brachionus calyciflorus, analysed using an automated tracking system, were used as sublethal indicators of toxic stress. Three swimming criteria were measured (speed, sinuosity, and the periods of swimming), and the influence of three chemicals [copper, pentachlorophenol (PCP) and γ-hexachlorocyclohexane (lindane)], on the rotifer locomotory characteristics were examined after 5 minute, 2 and 6 hour exposure periods. For each toxicant used, the 6h-EC50 values calculated from either speed, periods of swimming or sinuosity were comparable to the 96h-, 48h- or 24h-L(E)C50s obtained in conventional acute toxicity tests as well as EC50s of several other rapid-screening bioassays. Additionally, different behavioural alteration patterns were observed which depended on the toxicant tested. The swimming sinuosity of the rotifer was not affected by Cu and only slightly impacted by PCP whereas sinuosity was the only criterion affected by sublethal lindane concentrations. Alterations of both speed and period of swimming induced by short exposures to copper and PCP were not observed when using lindane. Changes in the swimming patterns are discussed in the light of the general mode of action of the respective toxicants.