A Miniaturised Protocol for Feeding Measurements in Daphnids

Daphnids, commonly known as water fleas, are freshwater planktonic microcrustacean species used as model organisms in ecotoxicology, particularly in regulatory frameworks that adhere to OECD and ISO standards. Mortality is the most common endpoint in toxicity testing; however, more sensitive indicators are required to assess sublethal acute effects of pollutants. The use of feeding impairment as a toxicity phenotypic endpoint in daphnids is considered a cost-effective approach that aligns with the 3Rs principle (Replace, Reduce, Refine) and is more physiologically and environmentally relevant. Current feeding methods are inefficient due to the large test volumes and extended incubation periods required. In this paper, we present a miniaturised protocol to assess feeding behaviour following exposure to chemicals in daphnids. The method is based on the consumption of algae, which is measured with chlorophyll fluorescence. The optimised protocol is more robust and rapid, and results can be obtained in 30 min and in a 96-well plate. Responses in feeding rate were investigated using this miniaturised protocol following exposure to a range of prevalent pollutants, which include two metals and, as a more realistic sample, a leachate from smoked cigarette filters. All three pollutants were tested at sublethal concentrations. This method provides an efficient approach to assess the toxicity of chemicals and water quality.