Parasites are ubiquitous in aquaculture and can have devastating effect with serious socioeconomic, ecological and welfare consequences. Of these, monogenean parasites are of particular problem as currently there is no effective and permitted treatment for this disease in aquaculture therefore, raising a need for alternative treatments. Previous research has laid a foundation for use of Phaeodactylum tricornutum, a marine diatom, as potential treatment against monogenean infection. P. tricornutum is a potent photosynthetic diatom, which is commercially produced for high value nutraceuticals, such as LC-PUFA and fucoxanthin. To further develop a sustainable and cost-effective treatment for aquaculture, the use of residue material from commercial P. tricornutum production was explored.
For this development, monogenean infection by Gyrodactylus turnbulli affecting guppies (Poecilia reticulate) was used. The residue material was treated by a range extraction protocols to liberate free fatty acids (FFA) and produce fatty acid ethyl esters (FAEEs). Several extracts and preparations were tested, including Ethanolic residue extract (RE), FFA produced from this RE and FAEEs produced from the original P. tricornutum residue powder. These preparations were initially tested in situ, using infected tail clips, followed by in vivo testing. All extracts and preparations were effective against the parasite, but the FAEE fraction was the most effective, both in situ and in vivo. The active ingredients included FAEE of the omega-3 EPA (20:5), palmitic acid (16:0), 16:1 and Myristic acid (14:0). The research presents the potential utilization of the commercial biorefinery P. tricornutum residue as a source for natural treatment against G. turnbulli and potentially other monogenean parasites.