Cyst-based toxicity tests. XI. Influence of the type of food on the intrinsic growth rate of the rotifer Brachionus calyciflorus in short-chronic toxicity tests.

As important members of zooplankton communities worldwide, rotifers are used extensively in ecotoxicological research. Chronic rotifer tests are, however, dependent on live algal food which adds to the complexity, the variability and the costs of these bioassays. To bypass the former problem, experiments have been undertaken with the freshwater rotifer Brachionus calyciflorus, to determine their intrinsic growth rate (r) when fed for 48 h on a mixture of green algae (Raphidocelis subcapitata recently renamed Pseudokirchneriella subcapitata) obtained from algal beads stored for different periods of time, and other inert foods. All tests have been performed in disposable multiwells, in 1 ml cups each inoculated with 1 rotifer freshly hatched from dried cysts. The majority of the growth tests was performed in eight replicates. The investigations revealed that microalgae from algal beads stored for up to one year, in darkness, at 4 degrees C, supplemented with dried blue-green algae (Spirulina) gave satisfactory rotifer reproduction. The intrinsic growth rates of the rotifers, were, however, dependent on the storage time of the algal beads; the highests r's (0.7-0.8) were obtained with algae from beads not older than four months. Growth tests with combinations of P. subcapitata and other inert feeds revealed that the enrichment food Selco used in aquaculture, also gave the same reproductive output as the combination microalgae/Spirulina. A rotifer growth experiment with 18 replicates showed that the variation coefficient is below 20% when the tests comprise eight replicates. This study demonstrated that microalgae from beads, supplemented by other inert food, open the door for a practical and cost-effective short-chronic rotifer test, which is totally independent of the culturing of both the test species and its live food.