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Illness associated with minor fish species

Communicable Diseases Intelligence 26 2002 436 carries reports of recent outbreaks in Victoria, New South Wales and South Australia of oily diarrhoea associated with the consumption of certain species of ocean fish. The three outbreaks are commented on in the editorial of the same issue.

In each outbreak, the oily diarrhoea was caused by indigestible wax esters in the fish. While there is some confusion about the naming, or at least the labelling, of these fish, common names associated with these outbreaks are rudderfish, butterfish, oilfish, ruddercod and escolar. These fish are normally presented in a restaurant or catering setting, but they are also marketed at retail level under different labels.

The editorial, citing a Sydney Fish Market source, indicates that outbreaks from escolar have been occurring in the restaurant and catering area for a number of years. The editorial writers believe there is probably a significant under-reporting of illness associated with consumption of these fish as the symptoms can be mild and short-lived.

Data from CSIRO Marine Research, cited in one of the incident reports, show that two species of fish, escolar (Lepidocybium flavobrunneum) and oilfish (Ruvettus pretiosus), contain approximately 20 per cent by weight of indigestible wax ester oil. Both species are caught incidentally from tuna longlines on the east and west coasts of Australia. While not a major catch, the fish are caught in quantities sufficient to make them commercially important. Rudderfish (Centrolophus niger) also contain a high level of oil but not the indigestible wax ester seen in escolar and oilfish. It is reported that many fishermen appeared to be landing and selling escolar as rudderfish. Butterfish (Scatophagus sp.) is mistakenly used as a marketing name for rudderfish or escolar particularly in Victoria.

Since these outbreaks and the problem of misidentification and mislabelling , a working group comprising Commonwealth and State Health authorities, the fishing industry and CSIRO Marine Research has been set up. A priority of this group has been to confirm the identification and correct labelling of implicated species and to have this information distributed throughout the fish supply chain.

The majority of consumers affected by oily diarrhoea after consuming these fish suffer only mild symptoms. However some people have experienced more severe symptoms including diarrhoea, nausea, headaches, abdominal cramp and vomiting. It is also unclear why in the reported incidents some people who consumed fish became ill and some did not. The authors suggest this could be due to variability in wax ester content of different fillet cut depths and mixing of fillets from different fish species sold as 'rudderfish' at the wholesale and retail levels.

Further information on the species discussed can be found in the Australian Seafood Handbook, CSIRO Marine Research, 1999.

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Prepared by Keith Richardson and Rachel Jackson
Food Science Australia
PO Box 52, North Ryde 1670. Tel +61 2 9490 8397 Fax +61 2 9490 8499
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