In this round of „Take a Minute“, we present you with the Giant moray eel (Gymnothorax javanicus). Granted, at first glance, it neither looks relaxed nor relaxing. However, it opens and closes its mouth simply for breathing. Moray eels have relatively small oral cavities with the gills sitting behind them. The constant gaping pumps oxygen-rich water with fresh oxygen through. That is why morays often swim with their mouth open.

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If a moray wanted to make a thread display, it would hold its mouth wide open to show off its sharp pointy teeth. There is a second row of teeth in the upper jaw, assisting in grabbing prey and holding it tight. By the way, all of these teeth are pointing backwards. But not to worry, same as with all of our aquatic friends, they rather flee from humans if given the chance than attack. Only cornered animals with no way out, e.g. in the case of people hunting for crayfish and sticking their hands into cracks on the reefs, will attack. Okay, and some species attack when nesting and guarding their young. Surely, we can all relate to that.

Gymnothorax javanicus is the biggest of all moray eels in terms of body mass. It can weigh more than 30 kilograms and can grow up to three meters in length (Wikipedia). However, the longest moray eel is the slender giant moray (Strophidon sathete). Juveniles are still light brown with large black spots, while adults turn darker brown with leopard-like spots behind the head.

Giant moray eel (Gymnothorax javanicus) the model alien

Giant morays are carnivorous and hunt their prey along the reef – often but not exclusively at night (Sea unseen). They go after fish as well as crustaceans or octopuses. Sometimes, groupers such as roving coral groupers invite giant morays to hunt with them by shaking their head in the direction of the prey. While the moray can get into the reef and this way may scare prey up and out, the grouper hunts above the reef and might scare prey to seek refuge in the reef (Biology dictionary). Either way, the other predator is waiting. Similarly, Yoeri observed giant morays hunting together with jacks and napoleon wrasses. If the giant moray can‘t get the prey down in one go, it either wraps itself around it to crush the victim until it is small enough to be swallowed, or it tears pieces from the prey and eats it bite-by-bite.

When researching the giant moray I found some pages and videos referring to it as alien-like. I think they got it wrong: The alien from the movie Alien is clearly moray-like. Moray eels have a second set of jaws with teeth in their throat called pharyngeal jaws (Animal corner). Morays first latch onto their prey with the outer jaws. Then they actively use the pharyngeal jaws to pull it deeper down into the throat and stomach. They are the only fish using pharyngeal jaws to capture prey. When hunting by themselves they rely on their excellent sense of smell instead of their rather poor eyesight.

From fish to fish

Moray is a fish with a dorsal fin that runs along the full length of its body (Animal network). They don‘t have pectoral or pelvic fins and swim in an undulating motion, pretty much like snakes. Morays don‘t have scales but thick skin with many cells secreting lots of mucus. In some species the mucus contains toxins. While sand-dwelling morays use the mucus to stabilize the sides of their burrows, eels such as the giant moray living in cracks and crevices in the reef might just glide through the habitat with more ease this way. Possibly, it helps the giant moray to stay clean. Divers can often observe cleaner wrasses and shrimps taking care of the set of teeth as well as the rest of the muscular bodies of giant morays.

This giant moray was filmed by Yoeri at the house reef of Wakatobi Dive Resort in Indonesia with a Panasonic GH5s in a housing of Nauticam and with lights of Archon. However, the species is widespread not only in the Indo-Pacific but all the way from the Red Sea and the eastern coast of Africa via Polynesia, the Pitcairn group and Hawaiian islands to the west. North to south, giant morays can be found from Japan to New Caledonia, Fiji and Australia. Giant morays live in lagoons and on the outer slopes of coral reefs. During the day, they mostly stay inside reef crevices between 1 and 50 meters deep.

Down to sex

Giant moray eel (Gymnothorax javanicus) reaches sexual maturity when they are around 2,5 years old. For mating, giant morays wrap their bodies around each other and release eggs and sperm simultaneously (Sea unseen). Morays as so many other ocean creatures are hermaphroditism. Some are sequential, meaning they change their sex over the time of their lives, and others are synchronous, having both reproductive organs. Courtship usually happens when water temperatures are high. After the larvae have hatched, it floats through the ocean for a year or so. As soon as the larvae are big enough, they swim down to the reef and hide there while slowly turning into the next generation of moray eels.

It clearly pays off to know about (marine) animal behaviour.

From giants via reef impressions to tiny critters: Take a Minute has it all

For more visual meditation and marine information, watch the whole playlist on our YouTube channel or browse through the different clips on our designated page „Take a Minute“ on this website.

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