Eels Marine Biology

Eels Marine Biology2011-02-07T10:50:07+08:00

Moray Eels – Muraenidae

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Eels tend to sometimes over-crowd their living spacesFound in Tropical and Sub Tropical Oceans and ranging in length from 30cm to 4m, Moray Eels represent an abundant and diverse group of approximately 10 genera and perhaps as much as 200 species. They can be seen on reefs, hiding between rocks and in holes, as displayed in image 1. Often with their head and about a quarter of their body visible. They have small circular gills, so must maintain an open mouth in order to breath, which makes them look quite menacing.

Moray Eels bodies are scale-less, dorsal fin begins behind the head & stretches the length of the bodyTheir bodies are scale less with the dorsal fin beginning behind their head and continuing the length of the body where it ends at the caudal and anal fin, see image 2. Some produce and discharge slimy mucus on the skin which can be toxic, different patterns and skin coloration usually represents a different species.

Venturing from their daytime hiding places most come out to hunt at night as seen in image 3. Feeding on a variety of fish and invertebrates, cephalopods and occasionally other moray eels.

Venturing from their daytime hiding places most come out to hunt at night Some have very sharp teeth as seen in image 4, used for tearing flesh from their prey, others, whose diet consists more of crustaceans have blunt teeth. Their poor eyesight is compensated with a highly developed sense of smell and they are able to knot their body whilst attacking for agility and power.

They can also survive out of water for up to four hours at a time, in fact we observed one hunting in the shallows for quite some time with the majority of its body out of the water.

These beautiful creatures really don’t deserve the aggressive reputation gained from their opened mouth appearance, as with the majority of marine life they will only attack if provoked or disturbed whilst mating.

Moray Eels are prone carriers of Ciguatera, a naturally occurring poisonThey are actually quite shy but inquisitive. Generally speaking, they are not suitable for Aquariums, as they can grow too large for inadequate tanks. They are also fantastic escape artists owing to their strong, slippery and agile body.

Little is known of their mating habits, they are ocean spawners and appear to share territory with the opposite sex during the mating season. They are also known to congregate in groups when spawning

Moray Eels are prone carriers of Ciguatera, a naturally occurring poison that passes up the marine food chain and although some humans do eat certain species their flesh can be poisonous.

People have died after eating them.

Ribbon Eel – Rhinomuraena quaesita

Ribbon Eels 2 in a holeA prized find, although generally quite rare they are plentiful in the Celebes Sea, enjoying reef crests, slopes and sandy bottoms at a depth range of 1 -65m. Unlike most Morays they live in sandy burrows.

A diver approaching a black Ribbon Eel stretching from its holeThey are quite secretive usually only showing their head and their distinctively large flared nostrils – image 5. Should a diver get to close, they will hide away in their hole and probably stay hidden for a few minutes.

Image 6 shows a diver approaching a black Ribbon Eel stretching from its hole. Sex can be determined through coloration although remembering the guidelines is quite difficult. Juveniles and sub adults are black with a yellow dorsal fin. Females are yellow with a black anal fin, eventually becoming entirely yellow as they mature. Males are electric blue but can be black or yellow. They feed on fishes and crustaceans.

Snake Eels – Ophichthidae

This ambush predator is rarely observed and often missed by diversA noticeable difference between this species and the Moray Eel is their pointed nose and muscular, bony, pointed tail used to bury itself deep into the substrate. A large family of eels with almost 300 species worldwide, probably many more undiscovered due to their secretive behaviour.

This highly successful ambush predator is rarely observed and often missed by divers, inhabiting silt and sanding areas adjacent to coral reef.

The structure of the hole is supported by a mucus lining, excreted from the body of the snake eel.

When sighted divers usually only see the creatures head peering out of the burrow as shown in image 8. If disturbed they retreat slowly down into the substrate, disappearing infront of your eyes. Banded species are more active hunting in the open, displaying aposematic mimicry of the venomous seasnake (for defence).

Photographing Ophichthidae requires patience and care, for after they retreat they rarely show themselves again for some time.

Garden Eels – Heterocongridae

Frequently abundant yet not discovered until the advent of Scuba DivingFrequently abundant yet not discovered until the advent of Scuba Diving, these fascinating creatures live on flat sandy bottoms just off the reef slope. They live in vast communities never leaving their burrows. In order to mate they will extend their bodies and reach into a neighbours burrow and entwine their bodies.

Feeding on passing zooplankton they reveal only about a third of their body relying on their keen eyesight rather than sense of smell. If disturbed they retreat into their burrow simultaneously creating a wave effect extending about 3m ahead of the intruder which is quite fun to see but makes for a very difficult photo subject. Vast fields of Garden Eels are a spectacular sight to behold, an excellent place to experience this is Mabul Island.

How have Garden Eels managed to stay hidden from Man for such a long time ? They do not take bait from a hook and line and because they rarely venture from their burrows they were not netted, so were never caught by fishermen. The advent of recreational scuba marked their discovery but even then they were rarely seen as they generally inhabit vast sandy areas off the reef where divers do not frequent.

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