The family Pholidae, commonly known as gunnels or rock gunnels, consists of elongated marine fishes that primarily inhabit temperate waters of the Northern Hemisphere, especially the North Pacific and, to a lesser extent, the North Atlantic. The scientific name Pholidae comes from the Greek ‘pholeos‘, meaning ‘burrow‘ or ‘hole‘, referring to the behavior of many species that hide among crevices, rocks, and underwater structures. They are coastal fishes associated with rocky bottoms, algal beds, or debris-covered substrates, where they find protection and food. They are typically found from the intertidal zone down to depths of about 200 meters.
Members of the Pholidae family are characterized by elongated, eel-like bodies that can reach lengths of 15 to 50 cm depending on the species. The head is small and lacks scales, while the body may be covered with very small scales or be completely naked. One of their most distinctive features is a continuous dorsal fin that runs from just behind the head to the base of the caudal fin, composed entirely of soft rays. The anal fin is also long, and the caudal fin is small or poorly differentiated. In many species, the pectoral fins are well-developed, while the pelvic fins may be absent or reduced. Their coloration ranges from brown to greenish, often with patterns of spots or bands that provide camouflage among rocks and seaweeds.
Gunnels are opportunistic carnivores, feeding mainly on small benthic invertebrates. Their diet includes crustaceans such as amphipods and isopods, polychaete worms, and small molluscs. Occasionally, they also consume fish larvae or eggs. Their elongated shape allows them to easily probe crevices and cracks in search of prey. They feed both during the day and at night, although many species are more active during twilight hours. Their excellent camouflage and stealthy movements enable them to approach prey undetected.
Currently, around 20 genera and more than 45 species are recognized within the Pholidae family. Representative genera include Pholis, Gunnels, and Apodichthys. One of the best-known species is Pholis gunnellus, known as the rock gunnel, found in the North Atlantic. A curious feature of this group is their ability to survive out of water for short periods, thanks to their moist skin and partial cutaneous respiration, which allows them to move between tide pools or seek shelter in intertidal areas. In several species, parental care has been documented, with one parent guarding the eggs until they hatch. Although they have little commercial value, gunnels play an important ecological role as predators of invertebrates and as prey for larger fish, seabirds, and marine mammals.
