Strong haemolytic activity was observed for extracts of 15 Fibrocapsa japonica strains collected from different global regions. The EC(50) values ranged between 0.4 x 10(4) and 1.9 x 10(4) F.japonica cells ml(-1).The relationship between the haemolytic activity observed in the cell extracts and the amount and nature of polyunsaturated fatty acids (PUFAs)was investigated. Between 7% and 89% of the haemolytic activity could be attributed to the amount and toxicity of the PUFAs C18:4n3 (OTA), C20:5n3 (EPA), and C20:4n6 (AA). However, the higher the haemolytic activity of a strain the more it appeared to be caused by haemolytic compounds other than the PUFA's. The EC(50) of the extracts with the highest haemolytic activity strongly depended on light intensity and was in line with observations made on Chattonella marina.
In the cell extracts of the strains studied brevetoxins were always below detection limits. For strains where 20-35% of the haemolytic activity was not caused by PUFAs, the concentration of these compounds was close to LC(50) values reported for fish. Overall the haemolytic activity of the F. japonica strains was in the range of known harmful microalgae. Therefore, PUFAs in combination with potent light dependent haemolytic compounds could be a major cause of ichthyotoxicity observed during F. japonica blooms. (C) 2009 Elsevier B.V. All rights reserved.