Marine Life
Dr Julian Pepperell
April 2007

Another mystery fish and the curse of the oilfish

Seamount Fish

In November last year I made a trip out to the sea mount off Cairns. We had good success in tagging one marlin and catching a heap of wahoo and with the weather being unusually calm, decided to stay the night anchored on the mount. We started fishing for what we thought were red emperor but were bitten off quite a few times before we finely landed several of the fish that you see in the photo. Not knowing what they were they went back to fight again. Could you possibly identify it? So far, I have had no luck in finding out what it is.

Brett Innes
Airlie Beach, QLD

Even though this is a very pretty and distinctive fish, I have to admit it had me stumped for a while. I like to think I have a pretty good library of fish ID books, but after thumbing through most of them, nothing was jumping out at me as an obvious candidate. When in doubt, ask a real expert, so following my own advice, I forwarded the pic on to my ever helpful colleague at the Australian Museum, Mark McGrouther. As usual, Mark was right on the money, straight away identifying this lovely looking fish from its distinctive orange eye colour, head markings and fin placement as the midnight snapper (or midnight seaperch), Macolor macularis. This is a member of the large and diverse Lutjanid family of fishes which also includes the mangrove jack, fingermark bream, jobfish and red emperor. As suggested by this list, pretty well all of the lutjanids are great eating fish, so it looks like Brett tossed back a nice feed.

The midnight snapper is found on steep slopes of seaward tropical reefs, and obviously from this account, on seamounts as well. Interestingly, the juveniles look nothing like the adult fish pictured, being patterned in black and white stripes along the sides and with a black back interspersed with white spots. A closely related and similar looking species which is sometimes caught with the midnight snapper is the black and white snapper (Macolor niger). This fish can be distinguished by its dark grey coloration and black eyes. And why is the midnight snapper so named, I hear you ask? Because it is a nocturnal feeder which is nearly always caught at night.

Tummy troubles

I came across a fish related story from Hong Kong which I thought might be of interest. Apparently, some oilfish was sold as 'cod', and many people became ill with stomach upsets and diarrhoea after eating it. When the fish was identified as oilfish, it was removed from sale, and apparently it is not permitted to be sold in several countries. I know however that oilfish is sold in Australian fish markets so I was wondering why that might be the case? Is it dangerous to eat or is it safe?

Bernard Yau
Croydon NSW

Interesting story which was apparently big news in Hong Kong at the time. To begin with, the oilfish, Ruvettus pretiosus, is a large (up to 100kg), distinctive looking fish identified by its black colour, its tuna-like shape and its rough scales with very sharp, bony tubercles between the scales. It a member of the family Gempylidae, members of which go under the common names of either snake mackerels or gemfishes. Other commercially important members of the Gempylid family are the barracouta, the deep water gemfish and the escolar. The latter species, Lepidocybium flavobrunneum, is also a black tuna-like fish which looks very similar to the oilfish, but can be distinguished by its prominent wavy lateral line and lack of those nasty spiky processes between the scales.

The oilfish has been given that name for very good reasons. Its flesh, which is beautifully white and dense when cooked, has a very high oil content, and like many other deep water fishes, also contains waxy esters. The fish is perfectly edible - in fact, delicious - but the waxy ester is a highly effective purgative, or laxative, so the message is, don't eat too much at one sitting, or else you will be sitting in the smallest room of the house shortly after! Even though the oilfish has this rather unpleasant reputation, it is still keenly sought by those who consider the flavour of the flesh worth the risk of the aftermath. The flesh of the escolar, described above, is not as oily as its relative, which may explain why both species are often marketed under the name 'escolar', perhaps to hide the fact that one might be buying oilfish. It is likely that this is the same reason that the fish in Hong Kong was labelled as 'cod'. Oilfish is certainly not banned from sale in Australia, and in fact, has been marketed in increasing quantities in recent years since it is a relatively common bycatch of longlining for tuna and swordfish (I understand that it is particularly popular among the Greek community of Melbourne). There is a general recommendation that only small portions of oilfish are eaten at any one time, but the general public would not necessarily be aware of that advice. It appears that some people are more sensitive than others to the purgative effects of the oilfish. I know I have eaten it with no apparent side effects. Bon appetit!