Eelpouts are primarily marine, ray-finned fish that belong to the family Zoarcidae. They get their name from their eel-like bodies and distinctive pout-shaped lips.
These fish are most abundant in the Arctic, the North Pacific, and the North Atlantic oceans of the Northern Hemisphere.
Around 300 species of eelpouts are found worldwide, all of which are opportunistic carnivores that typically feed on bivalves, amphipods, echinoderms, and sea squirts.
These fish are primarily bottom dwellers, with most species laying eggs on the ocean floor in shallow nests or gravel beds.
On average, these fish measure between 21 and 26 cm (0.68 to 0.85 ft). However, the largest species, the ocean pout (Zoarces americanus), reaches about 1.1 m (3.6 ft).
Smaller eelpouts, like Gymnelus hemifasciatus, typically measure only about 10 cm (0.3 ft) in length.
They have an elongated, laterally compressed body with large, fleshy lips that protrude outwards in the shape of a pout. The dorsal and anal fins extend all along their body length to the caudal fin.
In adults, the heads are small and ovoid, compared to juveniles, with a more rounded snout. Depending on the species, these fish have tiny, almost invisible scales or lack them altogether. Their body color ranges from brown, white, and gray to pink and orange. In some species, like Gymnelus hemifasciatus, the body is speckled with light bands, including some other markings.
In 1839, the English naturalist William Swainson proposed placing these fish in the family Zoarchidae. However, the spelling was altered to Zoarcidae by Theodore Gill in 1861.[1]
According to the 5th edition of Fishes of the World, this family was initially placed under the suborder Zoarcoidei within the order Scorpaeniformes. However, they are currently placed in the order Perciformes.
Currently, around 300 species of eelpouts are grouped under 4 subfamilies and 61 genera.
Though eelpouts have a global distribution, they have the highest species concentration in the Arctic, the North Pacific, and the North Atlantic oceans. Around 40 species of eelpouts are found in the Arctic waters, while the remaining are primarily found in the subarctic waters. A few species, like the viviparous eelpout (Zoarces viviparus), are also found in brackishwater environments.[2]
While some species, such as the viviparous eelpout, usually live in shallow waters (between 2 and 20 m), others have been spotted as deep down as 13,900 ft below the surface.[3][4] At the bottom, they live on various substrates, from soft and sandy beds to hard and rocky surfaces.
These animals are opportunistic feeders and consume a wide variety of prey depending on their availability. They feed on bivalves, like clams, mussels, oysters, as well as other marine invertebrates, including amphipods, sea urchins, starfish, sand dollars, polychaete worms, and sea squirts.
Large eelpout species may also feed on smaller fish varieties if readily available.
They often hide in sand or mud or even near cracks, crevices, and holes to dodge the eyes of predators. When threatened, some species, like midwater eelpouts, curl into an O-like shape, mimicking jellyfish, which most predators find highly repulsive.[5]
Eelpouts undergo slow growth and are typically long-lived, with some individuals surviving up to 20 years in the wild.
In the Northern Hemisphere, these fish mate in the fall (between August and October), sometimes after migrating to particular spawning grounds. The females typically lay demersal eggs (laid on the seafloor), either in shallow nests or gravel beds. The egg clusters range from 9.2 mm to 9.8 mm in diameter, the largest among all marine animals. Some species, like ocean pouts, lay their eggs in a gelatinous mass and guard them for about 2 to 3 months, after which they hatch.
However, the viviparous eelpout is the only eelpout species that gives birth to live young. It carries the young for almost 6 months (one of the longest pregnancies in fish) and is the only known fish that suckles its young with a nutrient-rich fluid, just like mammals.
Their natural predators include seals, sea birds, and predatory fish, like cods, skates, sculpins, and halibuts.
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