Inshore Hagfish

The inshore hagfish (Eptatretus burgeri) is a jawless fish in the family Myxinidae found in the northwestern Pacific along the coasts of Japan, Korea, and eastern China. Unlike many hagfish that live on the deep continental slope, this species is notable for occurring in comparatively shallow inshore waters, giving it its common name. Like all hagfish, it lacks a true backbone, jaws, and paired fins, and is regarded as one of the most ancient surviving vertebrate body plans, having changed little over hundreds of millions of years. It is a bottom-dwelling scavenger that burrows into soft mud, emerging mainly at night to feed. The species has been widely studied by biologists as a model for primitive vertebrate physiology and slime production.

• Long, scaleless, worm-like body, grey-brown to pale pink in color
• No jaws or paired fins; only a low, rounded tail fin
• Slit-shaped mouth surrounded by short sensory barbels
• A single row of external gill openings along each side of the body
• Numerous slime pores visible as small dots along the flanks

The inshore hagfish is best separated from other regional hagfish species by its shallower habitat and the number and arrangement of its gill pores, a key trait ichthyologists use to distinguish Eptatretus species. Its eel-like shape and lack of visible eyes or jaws distinguish it immediately from bony fish and lampreys, which have a circular sucker mouth.

Inshore hagfish live along the coasts of Japan, South Korea, and parts of the East China Sea, favoring soft mud or fine sand bottoms in relatively shallow water, typically from a few meters down to around 100 meters, shallower than many deep-slope hagfish relatives. They dig burrows in the sediment where they shelter during the day, emerging at night or when carrion is present. Water temperatures in their range are temperate, and the species tolerates seasonal changes better than strictly deepsea hagfish. Because of their accessibility close to shore, inshore hagfish are one of the more frequently studied hagfish species in fishery and physiology research in East Asia.

Inshore hagfish are nocturnal, burrowing scavengers that remain buried in soft sediment through the day and emerge after dark to feed on dead and weakened animals on the seafloor, using a rasping tongue-like structure to tear tissue. When disturbed, they release copious slime from pores along their body, deterring predators by clogging their gills. They can knot their bodies to work slime off their skin or brace themselves while feeding on a carcass. Inshore hagfish are simultaneous hermaphrodites and lay a small number of large, tough, yolky eggs directly onto the seafloor, skipping any larval stage. They play an important ecological role recycling nutrients from dead organic matter on the seabed.