SELECTION OF A SUITABLE CLADOCERAN SPECIES FOR TOXICITY TESTING IN TURBID WATERS

Two Australian cladocerans, Moina australiensis Sars and a species of Ceriodaphnia, were evaluated as possible biological indicator organism s to assess the toxicity of irrigation supply and drainage water of th e Murrumbidgee and Coleambally Irrigation Areas. M. australiensis, bei ng large (similar to 2000 mu m) and orange, was initially chosen to ov ercome visibility problems in highly turbid Australian inland waters. However, the organism responded erratically in culture. Mortality was high and neonate production was unpredictable when cultured under reco mmended United States Environmental Protection Agency protocols. Attem pts to improve culture performance by optimizing food (quality and qua ntity), water (control source, hardness, volume) and temperature were only marginally successful. Similar difficulties were not evident when Ceriodaphnia sp. was used as the test organism. Although Ceriodaphnia sp is small (similar to 1000 mu m), grey and more difficult to see in turbid water its responses were more predictable and reliable than th ose of M. australiensis. Results of initial trials comparing the two o rganisms suggest that Ceriodaphnia sp. was a better test organism and more suited to local requirements.