Eels: Mysterious and Majestic
Eels: Mysterious and Majestic
You might have heard the song performed by the American singer, actor, comedian and film producer Dean Martin among others that goes:
There’s a thing on the reef, with big shiny teeth — it’s a moray;
If he’s big and he’s mean, and he’s slimy and green — it’s a moray;
Put your hand in a crack and you won’t get it back; it’s a moray….
Given the aforementioned descriptions, it is no surprise that over the course of human history eels have often been portrayed as sea monsters. Others, however, think of eels as nothing short of beautiful, shy, and collectively speaking, a feature attraction of the underwater world. No doubt, many photographers actively seek out eels, and many other divers are thrilled to see them.
Worldwide there are approximately 800 species of eels described in 19 families, but as is so commonly the case, the accuracy of these figures is being debated as various species continue to get studied and reclassified. Surprising to some, all eels are types of bony fish, but not all eels are moray eels. The term “true eel” is often used to mean the species described in the order Anguilliformes. The term “true eel” (there is no such thing as a “false eel”) is used to distinguish anguilliform from species described in other orders that have a misleading common name in which the word eel is used.
Several significant differences between most bony fish and eels are readily apparent. While no one would argue against the statement that bony fish occur in a wide variety of shapes and sizes, anguilliforms have a more serpentine-like shape and swim in a more serpentine-like fashion than most other bony fish.
Worldwide there are approximately 200 species of eels described in the family Muraenidae. These species are known as moray eels. Among the eels, it is the morays that have gained the most notoriety for their menacing appearance and supposedly fierce demeanor.
Occurring throughout temperate and tropical seas worldwide, morays are characterized by wide, powerful jaws that fill a protruding snout. Their large mouths are filled with numerous fang-like teeth. The relatively small, round openings to their gills are located on the side of the head. A long continuous fin runs on the top of the body from just behind the head all the way to the end of the tail as the dorsal, caudal and anal fins join together. Moray eels have a keen sense of smell and relatively poor vision.
Many fish cannot go backward quickly, but that is not the case with moray eels. The absence of the paired pectoral and pelvic fins helps morays back up without getting hung up in the tight confines of reef communities. In addition, the lack of large scales and having skin covered by a lubricating layer of mucous help morays maneuver in tight quarters.
The heads of moray eels appear too small for the eels to consume some of the large bony fish, crustaceans and cephalopods that these nocturnal hunters prey upon, however, a second set of toothed jaws known as pharyngeal jaws located in the throat help morays “grip and rip” prey as they transport their food into their digestive system. Moray eels are believed to be the only animals that use pharyngeal jaws to help capture and immobilize prey.
During the day, morays tend to hide in crevices, holes and under ledges. Often only their head is visible as it extends into or past the opening. If you spot a moray eel, look closely and you might notice a variety of cleaner shrimps, gobies or other fish on the eel and even venturing into the eel’s mouth, as they clean the eel helping to rid the host eel of unwanted fungi, bacteria, dead skin and ectoparasites.
Garden Eels And Conger Eels
Collectively speaking, the eels commonly known as garden and conger eels are described in the family Congridae, a grouping comprised of approximately 150 species (some sources list as many as 180 species) described in three subfamilies. Commonly shared congrid features include a laterally compressed body, short snout with the mouth at the front of the snout, large lips, single, long continuous fin on the top of the body, lack of scales and the possession of paired pectoral fins. In most cases, congrid eels can be distinguished from moray eels by noting that most congrids possess the pectoral fins lacking in morays and have noticeably more rounded heads.
Residing in burrows of their own construction, garden eels are shy colonial “now you see them, now you don’t” sand dwellers that can embarrass you when you eagerly pull your diving buddy away from one subject to point them out as these eels are quick to disappear into their burrows when disturbed or feeling threatened. When undisturbed, garden eels raise their head and much of their body out of their burrow and they face into the current so they can pick planktonic organisms out of the water column.
When approached, garden eels withdraw tail first into their burrow. Their tail is pointed, and the skin in the tail is hardened. When creating a burrow garden eels tighten their muscular body to make themselves rigid, and then they drive their tail into the sand. When a garden eel is satisfied that its burrow is deep enough, the animal wiggles its dorsal fin to push sand out of its new home. Mucus from the skin of the eel cements the sidewalls of the burrow to prevent cave-ins.
The family Ophichthidae, a name derived from the Greek ophis meaning serpent and ichthys meaning fish, contains the species commonly called snake eels and worm eels. This family, known as the snake eels, is comprised of approximately 250 species. Occurring in a wide range of habits including shallow coastal areas, rivers and pelagic ecosystems, family representatives are found worldwide in temperate and tropical seas. The bodies of most snake eels exhibit strong, sharply defined tails that help them rapidly bury themselves in soft substrate by “wriggling in” while moving backward. Snake eels tend to remain buried during daylight hours. They emerge at night to forage along the bottom in pursuit of a variety of crustaceans and bony fish.
Snake eels are equipped with highly prominent nostrils that protrude from the front of the head and that serve as a good identifying characteristic when trying to distinguish snake eels from sea snakes. The bodies of many snake eels are spotted or striped. Some specialists contend that this patterning is intended to help the non-poisonous snake eels mimic poisonous sea snakes in order to deter predators, however, other specialists question this belief because similarly patterned snake eels are common throughout the Caribbean and other bodies of water in which sea snakes do not occur.