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To EEL or not to EEL? Are you a big fan of EELS?

To EEL or not to EEL? Are you a big fan of EELS?

Written by Juli Cole, 22 April 2024.

I love Moray Eels, even the big guy who came out of his hole on top of my head on one dive in Thailand, giving me a metaphorical heart attack. I like snakes too so maybe that is the attraction. I like how fierce they seem with their heads sticking out of their holes, their mouths open, showing off their teeth. They make look fierce, but actually it is how they breathe; they have to manually move their jaws up and down to pump the water through their gills as they don’t have gill covers like fish do. Though usually pretty chill with divers if left unprovoked, they are aggressive hunters; I have seen them in action on night dives, actively poking their head into crevices, trying to catch their prey taking a nap.

I was delighted the first time I saw a Ribbon Eel (Rhinomuraena quaesita – also referred to as Leaf Nosed Eel or Bernis Eel), a smaller species of the moray family, at the South Miniloc dive site, El Nido, PH. The brilliant blue color is striking and like one author noted, they look like little Chinese style dragons. And on this dive, there were two of them together. I was really jazzed!   Then in Bali, I noted one by itself, only this one was black. Cool, I thought, another type of ribbon eel, will look that one up. Only I couldn’t identify it that evening when I went through my books – they only showed one species.  A couple months later, I was diving off Mabul Island, Semporna, at Seaventure, and I saw a yellow one. Same thing as with the black, my faithful books were letting me down. What was going on – did I discover some new species, get to name it after me haha?

Nothing like that but something equally as strange as I discovered when I dug deeper and learned about the interesting lifestyle of these sea dwellers. So let me tell you about Ribbon Eels, just yet another fascinating creature of the sea (play opening theme song, joke).

They are endemic from East Africa, throughout Asian waters and into Australia, preferring more shallow water < 50m, to be found in corals reefs, lagoons and some sandy areas. Unlike their bigger cousins, they are diurnal lie-in-wait predators , waiting for the small fish or crustacean to happen by rather than actively hunting. Its rare to see them out of their holes, but if you do, they are beautiful swimmers, thus their names.

Eels from the order Aguilliformes, to which ribbon eels belong, lay eggs which are fertilized by expelled sperm, similar to many fish species. When they first hatch, the pre-larvae still have the yolk from the egg attached and use that up (nothing goes to waste in the sea – except what mankind dumps into it) then they become this ghost like larva and, from what is said, can only be described as bucktoothed – wish I had a close-up image to go with it!  These larvae are called Leptocephalus “Slim Head” – a ghost like gelatinous ribbon looking thing, greenish in color – check out this website for a very cool video of one on the move:

As they mature, the see-through gelatinous mass is replaced by muscle tissue, their “buckteeth” are replaced by rows of small short teeth, and they form into a proper eel shape, jet black with a yellow dorsal fin. This then was my black eel I spotted in Bali, a juvenile Ribbon eel. And they are all male. Dudes only. As they mature yet more, they become the typical electric blue with yellow nostrum and stripes down the length of its body. They will stay this way for the rest of their lengthy life – about twenty years! And they are home lovers – unless disturbed for some reason, they will stay in the same hole. Sometimes they will share it with a roommate, like the pair I saw in El Nido. And they will continue to be all male.

Except, for unknown reasons, they might become female.

Yes, for arbitrary reasons unknown to scientists (maybe funding is not high for Ribbon eel research) they will become female. They turn yellow, they grow longer and bigger, produce eggs, live for one month, lay the eggs and die.  It was unclear what triggers this radical metamorphosis: is it environmental triggers, an abundance of food, lack of females as one author suggested, I guess assuming the females die off so quickly? Among anemone fish, Clownfish – Nemos , they are similarly all males. The biggest fish among the colony transforms into the sole female until she dies, then the next largest one will become the female.  However, yellow female ribbon eels are rare so there must be some other contributing factor to initiate the change. Perhaps it is not just being the largest but maybe age as well: the last gift to the species in their old age before they expire. 

Photo courtesy of AnimalSpot

They are the only eels known to do this. One author suggested that the mechanics of this development is possible as the male/female tissue of hermaphroditic creatures tends to be simpler and less complicated than say human sex tissue for instance. So because of its simpler structure, it is easy then to stop producing sperm fluids and begin producing eggs instead. Some hermaphroditic creatures retain both male and female tissue throughout their lives such as the anemone fish; however this does not seem to be the case for the ribbon eel.

So as it turned out, I did see something rare in Semporna – the yellow ribbon eel was female and doomed to not live there much longer. I am not sure how I feel about that being a female …

AND HERE is BONUS MATERIAL: As I was looking up websites, trying to find answers to my many questions (most remained unanswered), I came across this crazy photo:

Yes that is a seal with an eel up its nose! This is a Monk Seal from Hawaii, endangered, with a marine spotted eel (not endangered) up its nose. This photo is from 2016. The seals were monitored for four decades previous, and this was the first occurrence observed. However, after this, there were several more cases. Not sure why? The by then dead eel was removed safely from the seal. Not recommended to try this at home! Ouch and YUCK!

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