Acute LD50 of a Gyrodinium corsicum natural population for Sparus aurata and Dicentrarchus labrax

Between February and March 2000, seven lethal dose assays (48hLD50) were performed during a Gyrodinium corsicum proliferation in Alfacs Bay (Spain), in order to determine the densities that produce acute lethal effects for the main finfish species cultivated in the area. When samples were tested immediately after collection, the 48hLD50 for Sparus aurata ranged between 1268 and 3136 cells ml−1, and NOEC between 366 and 2372 cells ml−1. These consistent LD50 values on different dates suggests the presence of a toxic compound associated with G. corsicum. A progressive increase in toxicity observed during the bloom indicates a possible influence of environmental factors on toxic activity. The relationships between cell densities of natural G. corsicum populations and mortalities of juvenile seabream (S. aurata) and seabass (Dicentrarchus labrax) are reported for use in the prevention of fish kills by this dinoflagellate.