The yellow margin moray eel is a rather common species in the Maldives. The front of this fish is speckled yellow on dark brown. You often only see the head of a moray eel, what is a pity in the case of G. flavimarginatus. The tail is less speckled, with a bright orange fringe. You could think the spectacular tail belongs to a different animal.
This moray eel was described by the German naturalist Wilhelm Peter Eduard Simon Rüppell in 1830. He called it Muraena flavimarginata. Five years later he described the Napoleon wrasse, which I wrote about earlier.
Like more than half of all moray eel species, the yellow margin moray eel belongs now to the genus Gymnothorax. That makes around 100 Gymnothorax species, because 200 out of approximately 1000 species of eels in the order Anguilliformes belong to the family Muraenidae, the moray eels.
Published was Rüppells work in a German book called ‘Atlas zu der Reise im nördlichen Africa. Fische des Rothen Meeres’. I was able to find a digital copy online, and it is a great read. Rüppell was accompanied by Michael Hey, and both went on a five years long journey to North Africa in 1822. The Senckenberg society founded a part of the journey, but obviously did Rüppell also spend a fortune on this journey. Hey and Rüppell went on shorter separate trips during their stay in Africa, and both, but especially Hey, fell sick several times.
Four years later P. J. Cretzschmar, Med. Dr. described their troublesome journey, where brutal conflicts, and resistance from locals crossed some of their plans. They went on hunts for hippopotamus, as well as for giraffes, crocodiles and all kinds of other animals.
On Page 119 Muraena flavimarginata from the Red Sea is described. It is only one page, and he talks a lot about the fishes intestines. The size is described simply as ‘big’, ‘like M. tegrina’ (now known as Myrichthys maculosus, the tiger snake eel), and interestingly he says ‘the flesh is tasty’. That made me laugh, because of what I found before. I’ll come to that soon. He’s using that word tasty a lot for several fishes in his publication. Today it feels a bit awkward. I want to believe that in recent times not many biologists have a culinary interest in their objects.
Our moray eel has a wide distribution range. They can be found anywhere near the equator, except for the Atlantic. Compared to other species of moray eels, G. flavimarginatus is medium sized, in my experience 1m is a average length.
A well known curiosity about moray eels (and also Cichlids) is their second pair of jaws, called pharyngeal jaws, which help to swallow prey. You wouldn’t usually see those extra jaws, but you might want to Google it, and give yourself a scary moment!
Have you ever wondered if moray eels were edible? Of course people eat moray eels. Rüppell for sure did. The funny thing about Rüppells comment ‘schmackhaft’ (tasty) is this:
G. flavimarginatus is nowadays said to be one of the most poisonous species of moray eels. Eating a moray eel might reserve you a spot on the toilet for a few days or even weeks. Obviously our traveller did not have issues, or did he not link his issues to the creatures he ate? There are some reports of people falling seriously ill after eating morays.
The reason is interesting. There’s no poison or venom in a moray eel. It’s a dinoflagellate that lives in fishes, and they cause Ciguatera fish poisoning. The name Ciguatera comes from the Cuban word cigua for a snail, Cittarium pica (the Magpie snail), which was falsely acclaimed to cause poisoning.
The tiny organism is called Gambierdiscus toxicus. It’s a protista, belonging to the supergroup SAR (Stramenopiles, Alveolates & Rhizarians). There seems to be an endless number of SAR species, but this single one is known to accumulate in carnivorous reef fish like barracuda, groupers, and moray eels. As the name ‘toxicus’ indicates, this dinoflagellate produces CTX, ciguatoxins, which comes in several varieties. Moray eels won’t catch microscopic dinoflagellates, but tiny creatures will, and G. toxicus climbs up the food chain. It seems that each round of digestion increases the chance to modify the CTX to a more toxic molecule (by addition of hydroxyl groups).
We had Dinoflagellates before in a nicer context. Noctiluca scintillans causes this wonderful blue beach with its bioluminiscence. It can cause deadly red tides as well, when overpopulation causes a lack of oxygen in the water, which harms other animals.
Gambierdiscus toxicus causes let’s say the brown tide, diarrhea, and worse. It produces toxins while living in fish, and theses toxins are stable in heat. So there is always a risk of food poisoning when eating moray eels, and cooking does not help. Who would have thought that dinoflagellates are so busy?!
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