Validation of multi-well plate toxicity test to assess feeding behaviour of H. attenuata.

The freshwater cnidarian Hydra attenuata has been widely used in small scale bioassays to assess the toxicity of numerous environmental contaminants. Most of these tests concentrate on the (sub)lethal effect of toxicants, measured by characteristic changes on the morphology of the animal. In this study, we validate an experimental protocol using new endpoints based on feeding behaviour in Hydra exposed to the well-known toxicant cadmium chloride. Hydra were exposed to increasing concentrations (nominal) of CdCl2 employing a small scale multi-well format and feeding endpoints (prey ingestion and capture) were compared to those of morphology, reproduction (hydranth number) and attachment impairment. Lethal (LC50) and sublethal (EC50) endpoint values of 1.16 and 0.18 mg/L (after 24h of exposure), and of 0.167 and 0.045 mg/L (after 96 h of exposure) were determined, respectively. More sensitive sublethal endpoints yielded a 96h LOEC of 0.019 mg/L with corresponding NOEC and toxicity threshold (TT) values lying below this concentration. A significant decrease in prey ingestion capacity was seen at concentrations as low as 0.06 mg/L CdCl2, with an 96 h EC50 based on feeding of 0.08 mg/L, while no effect was observed on prey capture at 96 h. Hydra reproduction (increase in hydranth numbers) was significantly impaired at a cadmium concentration of 0.12 mg/L. The previously unreported endpoint of Hydra attachment was found to be very sensitive with a significant reduction occurring at a concentration as low as 0.02 mg/L CdCl2. The potential use of these sub-lethal endpoints to investigate the more subtle effects of complex environmental
pollutants is discussed.