Eelpout

Quick Take

• One eelpout species does something for its offspring that no other fish on Earth does, and it has nothing to do with laying eggs. Live birth details →
• Some deep-sea eelpouts evolved a bizarre internal adaptation specifically to hide evidence of what they eat. Black stomachs explained →
• When a predator closes in, certain eelpouts use a disguise that has nothing to do with camouflage or speed. How eelpouts evade predators →
• Eelpouts routinely escape commercial fishing nets, though not for the reason you would expect. Limited fishing history →

The term eelpout refers to around 300 species of marine fish in the family Zoarcidae. As the name implies, eelpouts roughly resemble eels with their elongated bodies. You can find eelpouts around the world, although most live in the Northern Hemisphere. Eelpouts are bottom-dwelling fish that live in a wide range of depths. They vary in size and shape, but all sport characteristic, thick, fleshy lips. 

5 Facts About Eelpouts

• The ocean pout ranks as the largest member of the eelpout family. 
• The female European eelpout gives birth to live young and is the only fish known to suckle its offspring. 
• They occur at depths ranging from 0 feet to over 13,900 feet below sea level. 
• Some actively guard their eggs until they hatch. 
• Certain deep-dwelling eelpouts have evolved black stomach linings to hide the light emitted by consumed bioluminescent prey. 

Classification and Scientific Name

All marine eelpouts belong to the order Perciformes. This diverse order of ray-finned fish includes over 1,320 species. Some of its members include sculpins and lionfish. The word Scorpaeniformes translates roughly to “scorpion-shaped.” It stems from the Greek word skorpios, or “scorpion,” and the Latin word forma, or “shape.” Due to the shape of the sub-orbital stay in many of its members, some people refer to them as “mail-cheeked” fish. In Scorpaeniformes fish, one of the bones below the eye socket (the suborbital stay) extends noticeably backward. 

They are members of the family Zoarcidae. In total, the family contains over 300 known species. The family name is formed by the Latin words Zoarces and –idae (meaning “resemble” or “appearance”), or “resembling Zoarces.” The term Zoarces refers to a genus of the same name in the subfamily Zoarcinae. In Greek, Zoarces means “that gives life,” and refers to the fact that species in the genus are ovoviviparous. 

Eelpouts remain little studied due to their elusive habits and bottom-dwelling nature. As a result, experts continue to discover new species every year. Presently, scientists classify them into one of four subfamilies: Gymnelinae, Lycodinae, Lycozarcinae, and Zoarcinae. Some of the most well-known species belong to the genus Zoarces in the family Zoarcinae. Its members include the ocean pout (Zoarces americanus), eastern viviparous blenny (Zoarces elongatus), and viviparous eelpout (Zoarces viviparus). Other notable species include the halfbarred pout (Gymnelus hemifasciatus), twoline eelpout (Bothrocara brunneum), and limp eelpout (Melanostigma gelatinosum).

Appearance

Eelpouts vary in appearance by species, yet all share similar characteristics. They feature large, fleshy lips that extend outwards. These lips give eelpouts a “pouting” expression, hence their common name. Eelpouts sport long, elongated bodies that are much longer than they are wide. They frequently have small, ovoid heads and few or no scales. Nearly all eelpouts sport long dorsal and anal fins. In many species, one or both of these fins connect to the caudal fin. 

Most eelpouts measure under 20 inches long, and some measure as little as 5 or 6 inches in length. However, some species can grow significantly larger. For example, the ocean pout ranks as the largest eelpout. At maximum size, ocean pouts can reach up to 46 inches long and weigh around 12 pounds.  

Eelpouts also vary widely in color. Although most species tend to look brown or tan, they can range from white to gray or pink to orange. Some sport uniform coloring, while others feature light banding or dark markings down the length of the body. 

Distribution, Population, and Habitat

You can find eelpouts all over the world in a wide range of marine habitats. That said, most eelpouts reside in the Northern Hemisphere in the Arctic, the Northern Atlantic, and the Northern Pacific. Eelpouts tend to prefer colder water, as evidenced by the fact that at least 40 species reside in the Arctic Ocean. The remaining species almost exclusively live in subarctic waters. However, a few live in warmer waters. These species — such as Pyrolycus jaco — live around hydrothermal vents. Hydrothermal vent fluids can reach temperatures over 752 degrees Fahrenheit (400°C), but eelpouts like Pyrolycus jaco live in the much cooler waters surrounding these vents, not in the superheated fluids themselves. 

Eelpouts are bottom-dwelling fish. They live on a variety of substrates, including soft, sandy, or muddy substrates and hard, rocky bottoms. You can often find them near cracks, crevices, holes, or other structures that provide them with cover. Some species will dig burrows in sand or mud to hide from predators. In terms of depth, they range from shallow waters measuring a few feet deep to depths over 13,900 feet below the surface. Overall, the majority of species live in mid-to-deep waters. 

Predators and Prey

Several animals prey on eelpouts. Common predators include seals and seabirds, as well as larger fish such as cod, skate, sculpin, or halibut. To protect themselves from predators, eelpouts tend to hide in burrows, cracks, crevices, or caves. Additionally, some attempt to mimic the appearance of aquatic jellies by curling themselves into an “O” shape. 

As a general rule, eelpouts are opportunistic carnivores. They are predators and benthic scavengers that will eat just about anything they can catch. While some larger species prey on small fish, eelpouts are not optimized for hunting fish. They move rather slowly, which makes them ill-equipped to actively hunt faster prey. The few species that prey on faster fish typically do so using ambush or stalking tactics. Most eelpouts prey on crustaceans and invertebrates. Common prey includes bivalve mollusks, such as clams, mussels, and oysters. They also frequently prey on sea squirts and sea urchins, starfish, and sand dollars.  

Reproduction and Lifespan

Most eelpouts in the Northern Hemisphere mate during the fall between August and October. Many eelpouts will migrate to breeding or spawning grounds, including areas of brackish water. Like other fish, most eelpouts lay eggs, with most laying eggs in shallow nests, on gravel beds, or attached to some other sediment. The number of eggs varies by species and can range from a few dozen to several thousand. Interestingly, eelpout eggs tend to incubate longer than the eggs of other fish. For example, ocean pout females lay their eggs in a gelatinous mass and then guard the eggs for 2 or 3 months until they hatch. 

Meanwhile, a small minority of eelpouts give birth to live young. These ovoviviparous eelpouts develop embryos inside their bodies and then give birth to live offspring. For example, viviparous eelpouts carry their eggs for up to 6 months, one of the longest-known pregnancies in any fish. Additionally, the viviparous eelpout represents the only known fish that suckles its young embryos using specialized ovarian follicles. 

The lifespan of eelpouts varies by species. Due to their slow rate of growth, eelpouts are relatively long-lived, with some species able to live up to 20 years. 

Food and Cooking

Historically, eelpouts have not been heavily fished by commercial fishing industries. Due to their bottom-dwelling lifestyle, they tend to avoid industrial nets and traps. Additionally, captured specimens can easily slip out of nets due to their slimy bodies and lack of a rigid skeleton. That said, some anglers and commercial fisheries do target larger eelpouts as a food source. Despite their somewhat unappetizing appearance, eelpout meat is edible. Their firm flesh and relatively few bones make the meat easy to prepare. Common methods of cooking include baking, frying, roasting, and stewing. 

Population

Little data exists concerning the population of different species. Some species have only been spotted a handful of times, which makes sense given that they can live at extreme depths. Additionally, eelpouts face few threats from overfishing or competition with other species. their greatest threats likely come from climate change and broader environmental degradation. However, experts still don’t know what effects these issues may have on them. Well-studied species, such as the ocean pout and viviparous eelpout, exhibit relatively stable populations. The IUCN lists the viviparous pout as a species of Least Concern, while the ocean pout is currently Not Evaluated.