Unusually high levels of non-saponifiable lipids in the fishes escolar and rudderfish: Identification by gas and thin-layer chromatography

Analysis of the non-saponifiable lipids of the fishes Lepidocybium flavobrunneum and Ruvettus pretiosus (escolar), and Centrolophus niger and Tubbia spp. (rudderfish) was performed. The analyses were used to clarify the cause of recent reports of illness (diarrhoea) in Australia from consumption of purported rudderfish. Both escolar and rudderfish contained very high levels of oil (generally between 14 to 25%, as % wet mass) in the fillet and the oil compositions were different to most seafood. Escolar oil contained mainly wax ester (>90% of oil). The oil from five specimens of rudderfish contained mainly diacylglyceryl ether (DAGE, >80% of oil) or hydrocarbon (>80% of oil, predominately squalene). One rudderfish specimen contained mainly polar lipid. Major differences in oil content and composition, including fatty alcohol and glyceryl ether diols (derived from DAGE), were observed between purported individuals of the same species or related species of rudderfish, raising the possibility of geographic or seasonal differences affecting the oil composition. The oil composition of fish fillet samples associated with the health issues were consistent with the profiles for escolar, rather than rudderfish species. These findings, in particular the lipid class and fatty alcohol profiles, were supported by general protein fingerprinting results and were consistent with the samples originating from individuals of the escolar species L. flavobrunneum. The high wax ester content of the escolar group clarifies the reported diarrhoeal effects to consumers. Purgative properties of high wax ester containing fish oils have been reported for escolar and other species. The results highlight the potential for non-saponifiable lipid profiles to be used for identification of fish fillets and oils to at least group level.