Anguilliformes

(Eels and morays)

Class Actinopterygii

Order Anguilliformes

Number of families 15

Evolution and systematics

Fossil Anguilliformes are known from the Upper Cretaceous (about 93 million years ago) until the Pliocene (about two million years ago) and have been found in Africa, Europe, North America, the East Indies, Australia, and New Zealand. The Anguilliformes also are called Apodes ("limbless"), because of their lack of protruding fins, and true eels, because there are many other fishes (about 45 families) that do not belong to this group but have similar burrowing habits, and an eel-like shape as a result of convergent evolution. Anguilliformes are related to the Elopiformes (tarpons), the Albuliformes (spiny eels and halosaurs), and the Saccopharyngiformes (snipe and gulper eels) because they all have a leptocephalus, or ribbonlike, larval stage during development. The larval stage groups them into the subdivision or superorder called Elopomorpha. Some researchers, such as Filleul and Lavoué, have questioned this phylogenetic relationship based on molecular studies. Nelson divided this order into three suborders and 15 families (Anguillidae: 15 spp.; Heterenchelyidae: 8 spp.; Moringuidae: 6 spp.; Chlopsidae: 16 spp.; Myrocongridae: 2 spp.; Muraenidae: 200 spp.; Synaphobranchidae: 26 spp.; Ophichthidae: 250 spp.; Colocongridae: 5 spp.; Derichthydae: 3 spp.; Muraenesocidae: 8 spp.; Nemichthydae: 15 spp.; Congridae: 150 spp.; Nettastomatidae: 30 spp.; Serrivomeridae: 10 spp.). Much more work is needed in this area to determine the exact phylogenetic relationships within this group.

Physical characteristics

In addition to their eel-like bodies, anguilliform species have widely varying coloration that ranges from black or dark gray in deep-sea species to rich colors and complex patterns in tropical reef species. Adult sizes range from about 4 in (10 cm) to 11.5 ft (3.5 m), as in the moray species Thyrsoidea macrura. Systematists have emphasized numerous other morphological characteristics that have been found useful for phylogenetic purposes, including the lack of pelvic fins and the continuous dorsal, anal, and caudal fins that can have up to 650 soft rays, giving some individuals the appearance of having a pointed tail. Most species do not have pectoral fins, but when they are present, they lack bony connections to the skull. Most species also lack scales; in those species that have them, they are cycloid in type and embedded under the skin. The gill openings usually are narrow, with the gill region elongated and the gills displaced posteriorly. These species also have lost gill rakers. The skeleton is reduced, but the vertebrae may number as many as 700. They lack both pyloric caeca and oviducts but have retained the swim bladder. In summary, this order has many morphological simplifications or losses as a result of their evolutionary trend toward a worm-like configuration; the increased number of vertebrae is the result of the same phenomenon.

Distribution

Both the current distribution and the fossil record indicate that the members of this order always have occupied the same geographical areas, that is, tropical and temperate ocean. Anguilliformes are found in rivers draining into the North Atlantic, Baltic, and Mediterranean. They also have been introduced into Asia, South America, and Central America, but for the most part they have not reproduced in those areas. However, Anguillidae have a more restricted distribution, and do not inhabit the eastern Pacific and South Atlantic.

Habitat

The order Anguilliformes can be found in a wide variety of marine, brackish, and freshwater habitats, including streams,

lakes, deep-sea waters, and coral reefs. Some representatives of this order are catadromous, meaning that adults spend most of their lives in estuaries and freshwater and then move to the sea to spawn. The same species can be found in marine, estuarine, and freshwater environments. While some are pelagic, most are found living in small openings in coral reefs and rocks or burrowing in soft substrates. In general, morays and congers inhabit coral reefs and rock crevices, whereas certain congrids of the subfamily Heterocongrinae form vast colonies of up to several hundred individuals in tropical reef areas. Despite the fact that they favor these specific habitats as adults, all of the leptocephalus larvae form part of the marine plankton at one time or another in their life cycle.

Behavior

One of the most extraordinary aspects of their biology is their ability to migrate, yet they are slow swimmers. They swim by means of sinuous lateral movements of the body and median fins. Another interesting aspect of their swimming behavior is the ability of burrowing species to swim backward, which allows them to retreat rapidly into their burrows while still being able to look at any potential enemy. Although they can congregate in large numbers under specific circumstances, both larvae and adults do not form schools and thus can be considered to be solitary.

Feeding ecology and diet

The species of this order can be labeled generalists and opportunistic feeders, to the point that virtually any animal species they encounter can become a source of food for them, from aquatic insects in freshwater to crustaceans and many other species of fishes. This flexibility toward food items and even feeding habits is evident during development: depending upon the stage of development, they will shift toward the most appropriate food source and capturing tactics. Extreme cases include the parastic snubnosed eel, Simenchelys parasitica, which burrows into the tissues of other species of fish. They can attach themselves to the heart of their host, from which they consume the blood. Other species feed on dead animals that lie on the bottom, including whales. This has led to a renewed interest in the ecological role played by some anguilliforms in benthic habitats, including the recycling of nutrients. Anguilliformes are preyed upon mostly by other types of fish. When they are in larval form, small fish and even some invertebrates will prey on them. As they grow larger, the size of their predators also increases.

Reproductive biology

The migratory and reproductive biological characteristics of anguilliforms are intertwined closely; thus, one cannot be explained without explaining the other. Although the life cycle of every anguilliform species has yet to be studied, it is believed that all of them undergo the same complex path of development, regardless of the final habitat they occupy. Fertilization among these fishes is external, and the eggs are relatively large (about 0.98 in, or 2.5 mm), which allows them to undergo extended development even before being able to

feed. The eggs hatch, producing a prolarva, which in turn transforms into the leptocephalus larva.

The leptocephalus larva is so singular that biologists have studied it closely since the nineteenth century, when many researchers thought these larvae were actually adult fishes, given their complex morphologic features and behavior. They are elongated and laterally compressed while being transparent and gelatinous, which could make them difficult to detect. Although there is a great deal of morphological diversity among leptocephalus larvae, they all have a small and round caudal fin that is continuous with the dorsal and anal fins. This gives them varied shapes that are leaflike in appearance. In fact, the diversity of larval morphological features even within the same species is such that it is difficult to tell which larva belongs to which adult form. A couple of important characteristics of these larvae is their W-shaped myomeres (muscle packages) and prominent sharp teeth. These two features, together with their size, usually 2–4 in (5–10 cm) in length, make them sustained swimmers and powerful predators of other planktonic organisms. Some, like the slender snipe eel, Nemichthys scolopaceus, can reach 18 in (45 cm) in length, undoubtedly very large for fish larva.

Leptocephalus larvae can be found at varying depths, from the surface of the ocean to 1,600 ft (500 m). As opportunistic feeders, they eat anything that is available, from diatoms to small crustaceans and other fish larvae. By the same token, they are preyed upon by different species of fish. It has been calculated that, on average, of six million eggs released by the European eel, Anguilla anguilla, only one survives to reach adulthood.

Leptocephalus larvae undergo metamorphosis in the open ocean after a period that ranges from six months to three years. In general, it can be said that the colder the waters, the longer the larval stage. The juveniles usually look like smaller versions of the adults. These juveniles are the product of many changes that can be summarized as follows: (a) reduction in the total body mass (up to 90% of weight) and body length, making the initial juvenile smaller than the larva itself; (b) transformation of the leaflike shape into a cylindrical shape;

(c) loss of larval teeth; (d) loss of larval melanophores (pigment cells); (e) loss of pectoral fins; and (f) change in the position of the dorsal fin to much farther back.

The juveniles use oceanic currents to disperse; once they have occupied what is going to be their habitat as adults, they continue to grow and mature. This process can be quite lengthy, up to 10 years for some species. The complexity of this process also involves their sexual maturation, which includes phases of neutrality, precocious feminization, and juvenile hermaphroditism before they become adult males or females. As in some reptiles and other species of vertebrates, the sex ratio (proportion of males to females) can be the result of environmental factors (the more stressful the environmental conditions, the higher the proportion of females). Once true eels become fully adult, they undergo either a short-distance or a long-distance migration to a spawning area.

Conservation status

No anguilliform species have been listed by the IUCN under any category. With freshwater habitat modification and the threat posed to coral reefs all over the world, however, several species could be considered threatened in one way or another.

Significance to humans

Eels, whether "true eels" or otherwise, have been mentioned in mythology from ancient Greece to Polynesia. Today, only the freshwater eels (family Anguillidae) are of major economic importance in areas in which they are abundant, because of their value as food at both juvenile and adult stages. Some morays and congers are popular in public aquaria and among marine aquarists.

Species accounts

List of Species

European eel

Anguilla anguilla

family

Anguillidae

taxonomy

Muraena anguilla Linnaeus, 1758, "Europe." Tucker (1959) suggested that the European eel and the American eel, A. rostrata, are the same species.

other common names

English: Common eel; French: Anguille; German: Aal; Spanish: Anguila.

physical characteristics

Specimens have been reported to reach 52.36 in (133 cm) in length, with a weight of 14.548 lb (6.599 kg). Distinguished from other types of freshwater eels mostly by the number of vertebrae, which range from 110 to 119. Color greenish-brown to yellowish-brown. It has small vertical gill openings that are restricted to the sides. The lower jaw is slightly longer and projects. The dorsal fin originates far behind the pectoral fins, whereas the anal fin originates slightly behind the anus and well back from the origin of the dorsal fin.

distribution

Rivers of the North Atlantic, Baltic, and Mediterranean, along the coasts of Europe from the Black Sea to the White Sea. Its spawning area is the western Atlantic, specifically the Sargasso Sea. It has been introduced successfully into Finland and Romania. Introductions in Norway, Israel, Japan, Taiwan, Brazil, Indonesia, California, Eritrea, and Jordan have not been successful.

habitat

Waters where the temperatures range from 32–86°F (0–30°C). Young eels grow in freshwater where they stay for 6–12 years (males) or 9–20 years (females). After becoming sexually mature, they migrate to the sea, where they can be found in deep waters living on the bottom, under stones, in the mud, or in crevices. Spawning takes place in the Sargasso Sea. The larvae are brought by the Gulf Stream to the coasts of Europe. They evolve into small eels before moving into freshwater basins.

behavior

The European eel spawns in the Sargasso Sea in the subtropical northwestern Atlantic Ocean. Their larvae, leptocephali, are transported by the Gulf Stream and North Atlantic current system to Europe. Despite being an individualistic species, large groups of elvers and young eels can be observed from time to time in estuaries and rivers. An elver is a small cylindrical young eel, more advanced in development than a leptocephalus larva but less developed than an adult eel. Those congregations of elvers and juveniles are not fish schools in the real sense of the word (active assembling for selective advantages such as protection against predators or reproduction) but rather a mass response to environmental conditions. When elvers and young eels are observed in mass from time to

time in estuaries and rivers, it is because they are responding individually to particular ecological conditions and not because they are actually forming schools.

feeding ecology and diet

Opportunistic feeders. They include among their food items almost any species of aquatic fauna, freshwater as well as marine, that they encounter. Adults do not feed during migration to sea. Other eels, herons, cormorants, pikes, and gulls prey upon them.

reproductive biology

The American eel (A. rostrata) and the European eel (A. anguilla) spawn in Sargasso Sea, located in the subtropical northwestern Atlantic Ocean, between January and May. Their larvae, leptocephali, are transported by the Gulf Stream and North Atlantic current system to North America and Europe, respectively.

Before entering the continental coastal zones and estuaries, the leptocephali transform into elvers. Once there, and before entering the freshwaters, they develop into small (juvenile) eels. The young eels spend their growing period in freshwater, where males stay for 6 to 12 years; females spend from 9 to 20 years there. While in freshwater, they live on the bottom under stones or in the mud or rock crevices. At the end of their growth period, the eels become sexually mature and migrate to the sea, where they inhabit deep waters.

There is a significant differential in time in the life cycle span between both species. The overall mean age of European elvers is 350 days at metamorphosis (from leptocephalus to glass eel) and 448 days at estuarine arrival, with 98 days between metamorphosis and estuarine arrival. These ages were all significantly greater than those of American elvers 200, 55, and 255 days, respectively. Also, growth rate of the American eel (0.008 in [0.21 mm] per day) is greater than that of European eel (0.006 in [0.15 mm] per day). This is a result of delayed metamorphosis in the European species, which allows the European eel larvae to be transported from North America to Europe by the oceanic current. Thus, the European eel evolves the strategy to delay metamorphosis by reducing growth rate, enabling it to segregatively migrate with the American eel. The differences in leptocephalus stage duration and growth rate are the principal factors determining the segregation of migrating American and European eels.

conservation status

Not listed by the IUCN.

significance to humans

The European eel is consumed fresh, dried or salted, or smoked, and it can be fried, boiled, and baked. It is particularly popular among Mediterranean Europeans. This species has been raised by the aquaculture industry, particularly in Japan and Taiwan, with some success.

American eel

Anguilla rostrata

family

Anguillidae

taxonomy

Muraena rostrata Lesueur, 1817, Cayuga Lake, New York.

other common names

English: Common eel; French: Anguille américaine; German: Amerikanischer Aal; Spanish: Anguila Americana.

physical characteristics

Males grow to 59.84 in (152 cm) and females to 47.24 in (120.0 cm); these eels weigh as much as 16.16 lb (7.330 kg). The major difference between the European eel and the American eel is the number of vertebrae, which is 110 to 119 and 103 to 111, respectively. Otherwise, the species are almost identical.

distribution

Western Atlantic from Greenland and the Atlantic coast of Canada and the United States to Panama and throughout much of the West Indies south to Trinidad. The range includes the Great Lakes, the Mississippi River, and the Gulf basin. It has been introduced to Guam and Japan.

habitat

At sea they are found over rather deep waters; in freshwater they are inhabit permanent streams with continuous flow.

behavior

Individuals of this species are solitary and nocturnal. While in freshwater, they hide during the day in undercut banks and in deep pools near logs and boulders and sometimes bury themselves in the substrate, whether mud, sand, or gravel. At night they typically swim near the bottom in search of food. They can breathe through the skin along with their gills and are able to live for several hours outside water.

feeding ecology and diet

Like the European eel, food items vary with the stage of development and location. The leptocephalus larvae, for example, is planktivorous; the elver feeds on aquatic insects, small crustaceans, and dead fish; and the adult eats insects, crustaceans, clams, worms, fish, frogs, toads, and dead animal matter. Sharks are their main predator.

reproductive biology

Despite many attempts to conduct direct observations, knowledge of reproductive behavior can only be inferred, based on circumstantial evidence. We know that during the autumn adults migrate to the Sargasso Sea to spawn, with spawning taking place in January. At that time, females lay up to four million buoyant eggs, dying shortly after. After fertilizing the eggs, the males also die. With the help of ocean currents, the leptocephalus larvae drift toward coastal waters for as long as 18 months. After becoming an elver, American eels undergo a slow transformation that includes increases in their size, eye diameter relative to body size, and in the amount of eye pigments. They also become darker along the body. They spend most of their lives (up to 20 years) in freshwater before returning to the sea for spawning.

conservation status

Not listed by the IUCN. It has been listed as "rare" by a number of U.S. counties and states, but lacks specific legislation to protect it. Nonetheless, fishery authorities in the United States are taking measures to decrease the impact of fisheries, particularly at the larval and elver level. The Atlantic States Marine Fisheries Commission is preparing a Fishery Management Plan (FMP), requesting that the U.S. federal government include this species under some protection status under the supervision of the U.S. Fish and Wildlife Service.

significance to humans

They are consumed as food and prepared in many ways. Larvae and elvers (considered a delicacy) are captured using fine mesh fyke nets and dip nets; adults are caught with eel pots and trot lines. Although they can be caught in considerable numbers, their handling can be difficult, because the adults exude a noticeable layer of slime over the entire body. Moreover, large eels actively bite when caught on a hook and line.

Froghead eel

Coloconger raniceps

family

Colocongridae

taxonomy

Coloconger raniceps Alcock, 1889, Bay of Bengal.

other common names

Japanese: Fusa-anago.

physical characteristics

May grow to 19.7 in (50 cm). The body is stubbier (particularly in the anterior region) than the bodies of most true eels. They have numerous pores in short tubes.

distribution

Indo-West Pacific area, from East Africa and Madagascar in the west to the western Pacific in the east to southern Japan in the north.

habitat

Deep-sea species usually found at depths between 980 and 3,720 ft (300–1,113 m).

behavior

Because of its deep-water habits, it is rarely observed except very occasionally by deep sea submersibles.

feeding ecology and diet

Apparently feeds on other fishes.

reproductive biology

Nothing is known.

conservation status

Not listed by the IUCN.

significance to humans

None known.

American conger

Conger oceanicus

family

Congridae

taxonomy

Anguilla oceanica Mitchill, 1818, Atlantic.

other common names

English: Conger eel, sea eel; French: Congre d'Amérique; Spanish: Congrio americano.

physical characteristics

Specimens may reach 90.6 in (230 cm) and 88.2 lb (40 kg). The species has a long snout and a very large dorsal fin that originates much closer to the pectoral fins. It is gray on the dorsum and white on the venter.

distribution

Western Atlantic from Cape Cod, Massachusetts, to northeastern Florida in the United States as well as in the northern Gulf of Mexico westward to the Mississippi delta. In the eastern Atlantic it has been reported around Saint Helena Island, South Carolina.

habitat

Usually inhabits shallow inshore waters to depths of 1,565 ft (477 m).

behavior

Chiefly nocturnal feeder in shallow waters (60 ft [18 m] or less).

feeding ecology and diet

Feeds mainly on fishes but also on shrimps, worms, and other small benthic organisms.

reproductive biology

Spawning occurs from June through August. The leptocephalus larva reaches a maximum length between 5.9 and 6.3 in (15–16 cm). Metamorphosis consists of thickening of the head and body and development of the swim bladder, permanent teeth, and pigment in the skin.

conservation status

Not listed by the IUCN.

significance to humans

Anglers along piers, docks, and jetties in the mid-Atlantic states commonly catch this species. It is caught in baited fish and crab traps as well as on hook and line but seldom in nets, because the fish can squirm through them. It is difficult to remove them from hooks. They are marketed fresh and salted in the Chesapeake Bay region, but today the species is not subject to commercial fishing in the United States and is rarely eaten. American congers are much more appreciated in parts of Europe, Africa, and Asia, where they are smoked.

Splendid garden eel

Gorgasia preclara

family

Congridae

taxonomy

Gorgasia preclara Böhlke and Randall, 1981, Sumilon Island, Philippines.

other common names

English: Orange-barred garden eel.

physical characteristics

Individuals may reach 15.75 in (40 cm) in length. They have slender and elongated bodies with short mouths, anterior nostrils on the snout tip between restricted labial flanges, and small pectoral fins. The number of vertebrae ranges from 144 to 156.

distribution

Indo-West Pacific region from the Maldives in the west to Papua New Guinea in the east and from the Philippines and Ryukyu Islands in the north to the Coral Sea in the south.

habitat

Found in colonies on sand slopes exposed to current at depths usually below 90 ft (30 m).

behavior

Live individually in burrows, forming large colonies. They hover above their sand burrows and retreat tail first when disturbed.

feeding ecology and diet

They feed on plankton that they capture while standing in their burrows.

reproductive biology

Nothing is known.

conservation status

Not listed by the IUCN.

significance to humans

None known.

Rusty spaghetti eel

Moringua ferruginea

family

Moringuidae

taxonomy

Moringua ferruginea Bliss, 1833, Island of Mauritius.

other common names

English: Slender worm-eel; Gela (Solomon Islands): Poli ni tahi.

physical characteristics

May reach 55.1 in (140 cm) in length. It has a wormlike, very elongated body with yellow to reddish coloration. The dorsal and anal fins are reduced to low folds. It lacks scales and has greatly reduced eyes. The gill openings are low on the body. The rusty spaghetti eel has about 73 lateral-line pores before the anus.

distribution

Indo-Pacific, from East Africa in the west to Easter Island in the east and from the Ryukyu Islands in the north to Australia in the south. It is distributed throughout Micronesia as well.

habitat

Found in sandy bottoms.

behavior

Fossorial in that it can burrow headfirst. The physical attributes, such as an elongated body and reduced eyes, allow for this behavior.

feeding ecology and diet

Feeds on small prey found either on the bottom or burrowed in the sand.

reproductive biology

Little is known, except that rusty spaghetti eels seem to show sexual dimorphism in size and coloration.

conservation status

Not listed by the IUCN.

significance to humans

None known.

Green moray

Gymnothorax funebris

family

Muraenidae

taxonomy

Gymnothorax funebris and Lycodontis funebris Ranzani, 1840, Atlantic Ocean.

other common names

English: Black moray; French: Murène verte; Spanish: Culebra morena.

physical characteristics

Grows to 98.5 in (250 cm) in length and weighs up to 64 lb (29 kg). It is considered the largest Atlantic moray. Individuals of this species are uniformly greenish to dark gray-greenish. The green moray's color is a result of a yellowish mucous over the animal's dark blue skin.

distribution

Distributed throughout the western and eastern Atlantic (from Nova Scotia, Canada, to Brazil, including the Gulf of Mexico and Bermuda) and the eastern Pacific.

habitat

Benthic and solitary species commonly seen along rocky shorelines, reefs, and mangroves, including dirty harbors, in waters shallower than about 90 ft (about 30 m).

behavior

Cleaned by some species of gobies and other fish species, as observed on the coral reefs in Bonaire and the Netherlands Antilles and at the Fernando de Noronha archipelago in the western South Atlantic.

feeding ecology and diet

Feeds on fishes and benthic crustaceans.

reproductive biology

Little is known about reproduction, except that green morays have external fertilization and, like any other anguilliform, they have a leptocephalus larval stage.

conservation status

Not listed by the IUCN.

significance to humans

Green morays are consumed as food and are marketed both fresh and salted. Large individuals are ciguatoxic, however. Ciguatera is a type of food poisoning caused by the consumption of tropical marine species that harbor a heat-resistant, acid-stable toxin known as ciguatoxin. The green moray consumes certain species of microorganisms that form this toxin. This natural toxin can concentrate as it moves up the food chain, but its adverse effects appear to be limited to humans. Because of its large size and aggressiveness, the bites of this moray are particularly dangerous.

Ribbon moray

Rhinomuraena quaesita

family

Muraenidae

taxonomy

Rhinomuraena quaesita Garman, 1888, Marshall Islands.

other common names

English: Ribbon eel, black ribbon eel; French: Rhinomurène noire; Samoan: Pusi.

physical characteristics

May reach 51.2 in (130 cm) in length. It has a very elongated body. Mature males are mostly blue, whereas mature females

are almost completely yellow. They have three fleshy tentacles on the tip of the lower jaw; a single fleshy, pointed projection at the tip of the snout; and tubular anterior nostrils ending in gaudy, fanlike expansions.

distribution

Indo-Pacific from East Africa in the west to the Tuamotu Archipelago in the east and from southern Japan in the north to New Caledonia and French Polynesia in the south, including the Marianas and Marshall Islands in Micronesia.

habitat

Lagoons and associated seaward reefs as deep as 180 ft (60 m).

behavior

Secretive, nonmigratory species that normally hides in sand or rubble, sometimes with only its head protruding.

feeding ecology and diet

Feeds on small fishes.

reproductive biology

Fertilization in this species is external. This may be the only moray that undergoes abrupt changes in coloration and sex. It is classified as a protandrous hermaphrodite, that is, functioning males reverse sex to become females.

conservation status

Not listed by the IUCN.

significance to humans

It is acquired for display in aquaria because of its striking coloration and unusual morphological features.

Slender giant moray

Strophidon sathete

family

Muraenidae

taxonomy

Muraenophis sathete Hamilton, 1822, Ganges River.

other common names

English: Gangetic moray, giant estuarine moray; French: Murène fil géante; German: Süsswassermuräne; Spanish: Morenilla gigante; Tagalog (Philippines): Payangitan.

physical characteristics

Specimens as large as 157.5 in (400 cm) have been recorded. Individuals of this species have a very elongated body. This species is brownish-gray dorsally and paler on the venter.

distribution

Indo-West Pacific Ocean, from the Red Sea and East Africa to the western Pacific.

habitat

Benthic muddy environments of marine and estuarine areas, including inner bays and rivers.

behavior

The most interesting behavioral feature of this species is their ability to stand vertically from a burrow with the head kept horizontally beneath the surface, rising and falling with the tide.

feeding ecology and diet

Feeds on a wide variety of crustaceans and fishes.

reproductive biology

Almost nothing is known about reproduction.

conservation status

Not listed by the IUCN.

significance to humans

This species is consumed in India, the Philippines, Sri Lanka, South Africa, and other southeastern African countries as well as in Oceania.

Slender snipe eel

Nemichthys scolopaceus

family

Nemichthyidae

taxonomy

Nemichthys scolopacea Richardson, 1848, type locality not available.

other common names

English: Atlantic snipe eel, glass snake, threadfish; French: Avocette ruban; Spanish: Pez agazadicha.

physical characteristics

Grows to 51.2 in (130 cm). They are extremely long eels whose posterior end is exceptionally narrow, to the point that it ends as a long filament. They have exceptionally long jaws that curve outward and do not close together except among fully mature males. They are also unusual because of their proportionally very large eye. In color they vary between dark brown and gray, often darker ventrally, with the anal fin and tips of the pectoral fins almost black. Males are quite different from females in that once they fully develop, their jaws shorten, and they lose their teeth. This feature led some researchers to believe that each sex was a separate species.

distribution

Worldwide in tropical and temperate seas. In the western Atlantic they range from Nova Scotia in Canada to the northern Gulf of Mexico and all the way south to Brazil. In the eastern Atlantic they are found from Spain to South Africa, including the western Mediterranean, although there are some reports from Iceland. In the northwestern Pacific they inhabit Japanese waters and the Arafura Sea. In the eastern Pacific they occur from Alaska to Chile, including the Gulf of California.

habitat

Pelagic, found mostly in middle to deep waters between 295 and 6,560 ft (91–2,000 m). The depth varies with the latitude—they occur in shallower waters at higher latitudes.

behavior

As with many planktonic organisms, it is possible that their extremely elongated bodies are used to increase drag and therefore buoyancy in midwaters.

feeding ecology and diet

Feed on crustaceans while swimming with their mouths open.

reproductive biology

They are oviparous, with external fertilization, buoyant eggs, and planktonic leptocephalus larva. The leptocephalus larva is very elongated, with a filiform tail. The strong sexual dimorphism in the direction of degenerative changes in males and females suggests that they may display semelparity, that is, that they breed only once and then die immediately.

conservation status

Not listed by the IUCN.

significance to humans

None known.

Tiger snake eel

Myrichthys maculosus

family

Ophichthidae

taxonomy

Muraena maculosa Cuvier, 1816, Mediterranean Sea.

other common names

English: Ocellated snake eel, spotted snake eel; Afrikaans: Swartogies-slangpaling; Tahitian: Puhi popooru.

physical characteristics

Specimens may reach 39.4 in (100 cm). The young have black saddles. Adults are pale cream in color, with large and small black spots. All have a stiffened, pointed tail.

distribution

Indo-Pacific region from the Red Sea and East Africa in the east to the central Pacific in the west. The species does not occur in the Hawaiian islands, where it has been replaced by M. magnificus.

habitat

Sandy areas of reef flats, lagoons, and seaward reefs. Lives buried in the sand.

behavior

The most interesting behavioral characteristic of tiger snake eels is their ability to burrow tail first and then move equally forcefully forward and backward through the sediment. They may aggregate in large numbers under a light at night.

feeding ecology and diet

Feeds on small fishes and invertebrates.

reproductive biology

Nothing is known.

conservation status

Not listed by the IUCN.

significance to humans

None known.

Pignosed arrowtooth eel

Dysomma brevirostre

family

Synaphobranchidae

taxonomy

Nettastoma brevirostre Facciolà, 1887, Sicily, Italy.

other common names

None known.

physical characteristics

Individuals reach 11.8 in (30 cm) in length. Like most deep-sea fishes, they are pale in coloration. This species lacks pectoral fins as well as scales. The lower jaw is shorter than the upper jaw. It has between 193 and 204 vertebrae.

distribution

North Atlantic, from Madeira to the Gulf of Guinea, including the western Mediterranean. It is found all the way to Messina in Sicily. It also occurs off the coasts of Florida in the United States and has been recorded in Hawaii.

habitat

Muddy substrates of waters at a depth range between 1,150 and 2,130 ft (350–650 m).

behavior

Burrowing, solitary species.

feeding ecology and diet

Probably feeds on small benthic fish and invertebrates.

reproductive biology

Nothing is known.

conservation status

Not listed by the IUCN.

significance to humans

None known.

Snubnosed eel

Simenchelys parasitica

family

Synaphobranchidae

taxonomy

Simenchelys parasitica and S. parasiticus Gill, 1879, Massachusetts.

other common names

English: Slime eel; French: Anguille à nez court.

physical characteristics

Specimens may reach 24 in (61 cm). This species has a slimy body with a blunt, thick, round snout and a small mouth. The gill slits are broadly separated, and the scales are embedded in the skin. Coloration is gray to grayish-brown; it is darker on the fin edges and along the lateral line.

distribution

Worldwide species, particularly in tropical and subtropical waters.

habitat

Individuals of this species are found at depths of 1,200–8,700 ft (365–2,650 m), over muddy, deep-sea bottoms. They also parasite on other fishes.

behavior

Little is known besides their feeding behavior. They are capable of homing in on dead animals.

feeding ecology and diet

Feeds on benthic invertebrates and fish, including dead tissue. It is parasitic on some fishes. Large, dead fishes may look as if they are alive as these eels feed inside their carcasses.

reproductive biology

Nothing is known.

conservation status

Not listed by the IUCN.

significance to humans

No significant economic importance but are of scientific value because their unusual ecological characteristics and feeding habits.

Resources

Books

Bertin, L. Eels: A Biological Study. New York: Philosophical Library, 1957.

Berra, Tim M. Freshwater Fish Distribution. San Diego: Academic Press, 2001.

Forey, P. L, D. T. J. Littlewood, P. Ritchie, and A. Meyer. "Interrelationships of Elopomorph Fishes." In Interrelationships of Fishes, edited by M. L. J. Stiassny, L. R. Parenti, and G. D. Johnson. New York: Academic Press, 1996.

Lee, D. S., C. R. Gilbert, C. H. Hocutt, R. E. Jenkins, D. E. McAllister, and J. R. Stauffer, Jr. Atlas of North American Freshwater Fishes. Raleigh: North Carolina State Museum of Natural History, 1980.

Moyle, Peter B., and Joseph J. Cech, Jr. Fishes: An Introduction to Ichthyology. Upper Saddle River, NJ: Prentice Hall, 2000.

Nelson, J. S. Fishes of the World. 3rd edition. New York: John Wiley and Sons, 1994.

Page, L. M., and B. M. Burr. A Field Guide to Freshwater Fishes: North America North of Mexico. Boston: Houghton Mifflin, 1991.

Randall, J. E., G. R. Allen, and R. C. Steene. Fishes of the Great Barrier Reef and Coral Sea. Honolulu: University of Hawaii Press, 1990.

Robins, C. Richard, and G. Carleton Ray. A Field Guide to Atlantic Coast Fishes of North America. Boston: Houghton Mifflin, 1986.

Tesch, F. W. The Eel: Biology and Management of Anguillid Eels. New York: John Wiley and Sons, 1977.

Periodicals

Bruun, A. F. "The Breeding of the North Atlantic Freshwater-Eels." Advances in Marine Biology 1 (1963): 137–170.

Costa, J. L., C. A. Assis, P. R. Almeida, F. M. Moreira, and M. J. Costa. "On the Food of the European Eel, Anguilla anguilla (L.), in the Upper Zone of the Tagus Estuary, Portugal." Journal of Fish Biology 41, no. 5 (1992): 841–850.

Deelder, C. L. "Synopsis of Biological Data on the Eel Anguilla anguilla (Linnaeus, 1758)." FAO Fisheries Synopsis 80, rev. 1 (1984): 1–73.

Filleul, A., and S. Lavoué. "Basal Teleosts and the Question of Elopomorph Monophyly: Morphological and Molecular Approaches." Comptes Rendus de l'Académie des Sciences, Paris 324 (2001): 393–399.

McCleave, J. D., P. J. Brickley, K. M. O'Brien, D. A. Kistner-Morris, M. W. Wong, M. Gallagher, and S. M. Watson. "Do Leptocephali of the European Eel Swim to Reach Continental Waters? Status of the Question." Journal of the Marine Biological Association of the U.K. 78 (1998): 285–306.

Romero, A., and J. Gimeno. "Las Anguilas, Eternas Pasajeras de las Aguas." Algo 286: 23-25.

Tucker, D. W. "A New Solution to the Atlantic Eel Problem." Nature 183 (1959): 495–501.

Wang, C.H. and W.N. Tzeng. "The Timing of

Metamorphosis and Growth Rates of American and European Eel Leptocephali: A Mechanism of Larval Segregative Migration." Fisheries Research 46 (2000): 191-205.

Other

"Anguilliformes: Eels." (13 Nov. 2002). <http://www.floridasmart.com/subjects/ocean/animals_ocean_eels.htm>

Aldemaro Romero, PhD