Eels

True eels (Anguilliformes) on Wikipedia 

Ribbon Eel (Rhinomuraena Quaesita) on Wikipedia 

The ribbon eel, Rhinomuraena quaesita, is a species of saltwater eels, the only member of the genus Rhinomuraena of the Muraenidae (Moray eel) family of order Anguilliformes. What is now known as Rhinomuraena quaesita also includes the former Rhinomuraena amboinensis. R. quaesita was used for blue ribbon eels and R. amboinensis for black ribbon eels, but these are now recognized as the same species. The ribbon eel is native to the Indian and Pacific oceans.

The ribbon eel is an elegant creature with a long, thin body and high dorsal fins. Many feel that it resembles a brightly colored party streamer. The ribbon eel can easily be recognised by its expanded anterior nostrils. Juveniles and sub-adults are jet black with a yellow dorsal fin, while females are yellow with a black anal fin with white margins on the fins. The adult male can be black, fluorescent blue with yellow highlights, blue-green, or brilliant yellow.

The ribbon eel grows to an overall length of approximately 100 cm (36 in), and has a life span of up to twenty years. The ribbon eel is the only moray eel that is not gonochoristic.

Behavior:

Like many eels, the ribbon eel is sometimes thought to be angry or aggressive, because its mouth is often open, appearing ready to strike. In reality, the eel is simply breathing.

In the wild, the ribbon eel buries itself in sand or hides in rocks or reefs, dashing out to feed on small fishes. The ribbon eel is known as one of the most sociable and peaceful of all moray eels, and does not bother humans or get easily irritated. As the eel grows and gets older, it changes sex from a male to a female. The ribbon eel also changes its colour from blue to yellow when it becomes fully mature (& female).

In the aquarium:

Because most ribbon eels do not live longer than a month in captivity, some feel that this species should never be purchased. Ribbon eels have been observed in nearly every case to stop eating after being captured. Although there are reports of ribbon eels surviving and eating in captivity for 2 years or more. But most don't survive over a month.

Moray Eel on Wikipedia 

Moray eels are large cosmopolitan eels of the family Muraenidae. There are approximately 200 species in 15 genera. The typical length of a moray is 1.5 m (5 ft), with the largest being the slender giant moray, Strophidon sathete, at up to 4 m (13 ft).

Anatomy

Muraena helena showing typical moray eel morphology: robust anguilliform shape, lack of pectoral fins and circular gill openings.The dorsal fin of the moray extends from just behind the head, along the back and joins seamlessly with the caudal and anal fins. Most species lack pectoral and pelvic fins, adding to their snake-like appearance. Their eyes are rather small; morays rely on their highly developed sense of smell, lying in wait to ambush prey.

The body of the moray is patterned, camouflage also being present inside the mouth. Their jaws are wide, with a snout that protrudes forward. They possess large teeth, designed to tear flesh as opposed to holding or chewing.




Moray eel jaw anatomy:

Moray eels' heads are too narrow to create the negative pressure that most fish use to swallow prey. Moray eels have a second set of jaws in their throat called pharyngeal jaws, which also possess teeth. When feeding, morays launch these jaws into the oral cavity, where they grasp struggling prey and transport it into the throat and down to the rest of the digestive system. Moray eels are the only known type of animal that uses pharyngeal jaws to actively capture and restrain prey.[1][2][3] Morays are capable of inflicting serious wounds to humans.

Morays secrete a protective mucus over their smooth scaleless skin which contains a toxin in some species. Morays have much thicker skin and high densities of goblet cells in the epidermis that allows mucus to be produced at a higher rate than in other eel species. This allows sand granules to adhere to the sides of their burrows in sand-dwelling morays[4], thus making the walls of the burrow more permanent due to the glycosylation of mucins in mucus. Their small circular gills, located on the flanks far posterior to the mouth, require the moray to maintain a gape in order to facilitate respiration.

Morays are carnivorous and feed primarily on other fish, cephalopods, mollusks, and crustaceans. Groupers, other morays, and barracudas are among their few predators. There is a commercial fishery for several species, but some have been known to cause ciguatera fish poisoning. Morays hide in crevices in the reefs, and wait until their prey is close enough for capture. They then jump out and clamp the prey in their strong jaws.





Behavior:

Cooperative hunting

Ribbon moray,
Rhinomuraena quaesitaIn the December 2006 issue of the journal, Public Library of Science Biology, a team of biologists announced the discovery of interspecies cooperative hunting involving morays. The biologists, who were engaged in a study of Red Sea cleaner fish (fish that enter the mouths of other fish to rid them of parasites), discovered that a species of reef-associated grouper, the roving coralgrouper (Plectropomus pessuliferus), often recruited morays to aid them while hunting for food. This is the first discovery of cooperation between fish in general. [5] [6]

Fimbriated moray,
Gymnothorax fimbriatus
[edit] Reputation
Morays have sometimes been described as vicious or ill-tempered. In fact, morays are shy and secretive, and they only attack humans in self-defense. They also accidentally bite human fingers when being fed, because they cannot see or hear very well, although they have an acute sense of smell. Morays hide from humans and would rather flee than fight. Morays, however, do inflict a nasty bite, because, although not poisonous, their backward-pointing teeth are covered with bacteria which may infect the wound. Another danger that morays present is when they are eaten. If the eels have eaten algae, or fish that have eaten algae, they will cause ciguatera fish poisoning if eaten. Morays rest in crevices during the day and are nocturnal predators, and although they may ensnare small fish and crustaceans that pass near them during the day, they mostly come out at night.

Congo Eel on Wikipedia 

Description:

Amphiumas have an elongated body, generally grey-black in color. They do have legs, but they are very small - while amphiumas can be up to 1 m long, their legs measure only up to about 2 cm. Therefore, they can resemble eels. They have many teeth and can cause extreme pain if they bite.

Larvae have external gills. After about four months these external gills disappear and the lungs begin to work. One pair of gill slits is retained and never disappears, so the metamorphosis remains incomplete.

Distribution:

Amphiumas inhabit the southeastern part of the United States. They share much of the same distribution with the sirens, although they are not closely related.

In the past amphiumas have been further distributed. Fossils from the Pleistocene epoch show that they once were distributed in Europe as well.

Behavior:

During the day amphiumas hide in vegetation, and at night they become active and go hunting. Their prey include frogs, snakes, fish, crustaceans, insects and even other amphiumas. They rarely bite larger animals, like humans, but if provoked they can become aggressive. They can be found in most wetlands in the coastal plain of the southeastern U.S., even ones which periodically dry, as they are able to aestivate in the moist mud below drained marshland and other ephemeral wetlands. Amphiuma are rarely encountered on land, but it is possible.

Garden Eel on Wikipedia 

Electric Eel (Electrophorus Electricus) on Wikipedia 

Anatomy:

A typical electric eel has an elongated square body, a flattened head, and an overall dark grayish green color shifting to yellowish on the bottom.[1] They have almost no scales. The mouth is square, placed right at the end of the snout. The anal fin continues down the length of the body to the tip of their tail.[2] It can grow up to 2.5 m (about 8.2 feet) in length and 20 kg (about 44 pounds) in weight, making them the largest Gymnotiform.[1][2] 1 m specimens are more common.[citation needed]

They have a vascularized respiratory organ in their oral cavity.[2] These fish are obligate air-breathers; rising to the surface every 10 minutes or so, the animal will gulp air before returning to the bottom. Nearly 80% of the oxygen used by the fish is taken in this way.[citation needed]. Despite its name, the electric eel is not related to eels but is more closely related to catfish.

Scientists have been able to determine through experimental information that E. electricus has a well developed sense of hearing. They have a Weberian apparatus that connects the ear to the swim bladder which greatly enhances their hearing capability.

Physiology:

Electric eel at the New England Aquarium.The electric eel has three abdominal pairs of organs that produce electricity. They are the main organ, the hunter's organ, and the sachs' organ. These organs take up 4/5 of its body. Only the front 1/5 contains the vital organs.[1] These organs are made of electrocytes lined up in series. The electrocytes are lined up so the current flows through them and produces an electrical charge. When the eel locates its prey, the brain sends a signal through the nervous system to the electric cells. This opens the ion channel, allowing positively-charged sodium to flow through, reversing the charges momentarily. By doing that it creates electricity. The electric eel generates its characteristic electrical pulse in a manner similar to a battery, in which stacked plates produce an electrical charge. In the electric eel, some 5,000 to 6,000 stacked electroplaques are capable of producing a shock at up to 500 volts and 1 ampere of current (500 watts). The organs give the electric eel the ability to generate two types of electric organ discharges (EODs), low voltage and high voltage. The shock could be harmful for an adult human.

The Sachs organ is associated with electrolocation.[1] Inside the organ are many muscle-like cells, called electrocytes. Each cell can only produce 0.15V, though working together the organ transmits a signal of about 10V in amplitude at around 25 Hz. These signals are what is thought to be used for communication as well as orientation; useful not only for finding prey, but also in finding and choosing a mate.

High-voltage EODs are emitted by the main organ and the Hunter's organ that can be emitted at rates of several hundred Hz. [1] These high voltage EODs may reach up to 650 volts. The electric eel is unique among the gymnotiforms in having large electric organs capable of producing lethal discharges that allows them to stun prey.[2] There are reports of animals producing larger voltages, but the typical output is sufficient to stun or deter virtually any other animal. Juveniles produce smaller voltages (about 100 volts). Electric eels are capable of varying the intensity of the electrical discharge, using lower discharges for "hunting" and higher intensities for stunning prey, or defending themselves. When agitated, it is capable of producing these intermittent electrical shocks over a period of at least an hour without signs of tiring. The species is of some interest to researchers, who make use of its acetylcholinesterase and ATP.

The electric eel also possesses high-frequency sensitive tuberous receptors patchily distributed over the body that seem useful for hunting other gymnotiforms.[1]

Distribution:

The electric eel may be found in northern South America, primarily in the basins of both the Amazon River and Orinoco River, as well as the surrounding areas.[2]

Ecology and life history:

Habitat:
They tend to live on muddy bottoms in calm water. They are also found in swamps, coastal plains, and creeks.[1] It can be found in South American rivers.

Feeding ecology:

Juvenile eels feed on invertebrates, while adult eels feed on fish and small mammals. First-born hatchlings will even prey on other eggs and embryos from later batches.[1]

Taxonomic history:

The species is so unusual that it has been reclassified several times. Originally it was given its own family Electrophoridae, and then placed in a genus of Gymnotidae alongside Gymnotus.[2]

Importance to humans:

Electric eel.In captivity, although the eels are common in their range and popular draws for public aquaria, the eel's habit of delivering shocks, even when gently handled, means that they are too dangerous for most amateurs to try to keep at home. Moreover, the animals grow very large, and are impossible to maintain for all but the most dedicated of keepers. It is necessary to wear rubber gloves when handling them. Some countries such as Australia strictly forbid the keeping of electric eels, for fear that they could escape into the wild and become a public hazard.

Freshwater Eel on Wikipedia 

Siren on Wikipedia 

Behavior:

The Lesser Siren is nocturnal, spending its days hidden in the debris and mud at the bottom of slow moving bodies of water. They feed primarily on aquatic invertebrates, including various kinds of worms, snails, and crustaceans. They will also eat the tadpoles and eggs of other amphibians.

Reproduction occurs in the spring months, with eggs being laid in a shallow depression at the bottom of a calm area of water. Usually surrounded by vegetation. Though little is known about their courtship, it is believed to be quite violent, as many specimens collected have scarring from healed bite marks from other sirens. 12-300 eggs are laid at a time, and several clutches may be laid over the course of the year. Hatchlings are only about 0.4 of an inch (1.1 cm) in length, but grow quickly. Maturity is reached in 3-4 years.

The Lesser Siren is vocal, unlike most salamanders, and will emit a series of clicks when they approach others of their species, or a short screeching sound if handled.

If the habitat dries up during the summer months, Lesser Sirens are capable of excreting a substance from their skin which protects them from dehydrating, and enables them to stay buried in dry mud for months until the water returns. Their small legs enable them to move on dry land for short periods of time.

Geographic distribution:

The Lesser Siren is found in the United States, primarily from Virginia to Florida, and west to Texas (ranging into northeastern Mexico as far as Veracruz), and north to Illinois, Indiana and Michigan.

Taxonomy:

Sources disagree on the number of subspecies are within Siren intermedia, most agree that there are at least two, an eastern and a western variety. Many sources also include a third subspecies, the Rio Grande Lesser Siren, Siren intermedia texana, but researchers disagree whether the Rio Grande variety belongs as a Lesser Siren, within Siren intermedia, or as a Greater Siren, within Siren lacertina, and some others even consider it to be its own species, as Siren texana.

Eastern Lesser Siren, Siren intermedia intermedia (Goin, 1942)
Western Lesser Siren, Siren intermedia nettingi (Goin, 1942)
Rio Grande Lesser Siren, Siren intermedia texana (Goin, 1957)

Conservation status:

The Lesser Siren is quite common through most of its range, but rarely seen due to its secretive nature. Like almost all species of amphibian, it is believed that their numbers are declining due to general reductions in water quality, believed to be caused by agricultural pesticide and fertilizer runoff. They are frequently collected and used as bait for fishing. The species is believed to be extirpated from the state of Michigan, and the S. i. texana subspecies is listed as a threatened species in the state of Texas.

Wolf Eel on Wikipedia 

Rubber Eel on Wikipedia 

Deep-sea Spiny Eels (Notacanthidae) on Wikipedia