Chemical characterisation of three haemolytic compounds from the microalgal species Fibrocapsa japonica (Raphidophyceae)

The molecular structures of the three main haemolytic compounds (Fj1, Fj2 and Fj3) isolated from the ichthyotoxic microalgal species Fibrocapsa japonica have been investigated by NMR, LC–ESI–MS, ESI–MS–MS, IR, GC–MS and GC–HRMS methods. They are polyunsaturated fatty acids which we identified as: 6,9,12,15-octadecatetraenoic acid (OTA, C18:4ω3), 5,8,11,14,17-eicosapentaenoic acid (EPA, C20:5ω3) and 5,8,11,14-eicosatetraenoic acid (arachidonic acid AA, C20:4ω6). The identity of the latter two was confirmed on the basis of commercial standards (C20:5ω3 and C20:4ω6). Both displayed the same spectroscopic and chromatographic characteristics as Fj2 and Fj3 and had a similar strong haemolytic effect. We propose that when F. japonica cells accumulate in fish gills during blooms these compounds could be the cause of icthyotoxicity.