Gobiesocidae

Lore & Background

Clingfishes are primarily found near the shore in the Atlantic, Indian and Pacific Oceans, including marginal seas such as the Mediterranean, Gulf of Mexico, Caribbean and Gulf of California. The greatest species richness is in tropical and warm temperate regions, but the range of a few extends into colder waters, like Diplecogaster bimaculata (north to Norway), Apletodon dentatus, Lepadogaster candolii and L. purpurea (all three north to Scotland), Gobiesox maeandricus (north to Alaska), Gobiesox marmoratus and Sicyases sanguineus (both to southernmost South America), and Gastrocymba quadriradiata (from New Zealand's subantarctic islands). Clingfishes mainly inhabit shallow rocky reefs and shores, coral reefs, seagrass meadows and algae beds. They often live in places exposed to strong currents and wave action, and some are amphibious. As long as the strongly amphibious, intertidal-living species are kept moist by splashing waves, they can survive for up to three–four days on land, gaining oxygen from the air by the branchial surfaces (gills), skin and perhaps the mouth. At least a few species even tolerate a relatively high degree of water loss when on land. A relatively small number of species shelter in sea urchins or crinoids. Whether this relationship is obligate or facultative varies with species. In some, only young clingfish are obligate and gradually move away as they become adult. Three clingfish species, the Australian Cochleoceps bicolor and C. orientalis, and the warm East Atlantic Diplecogaster tonstricula, are cleaner fish that will cling onto the bodies of larger fish. Although several species can occur in brackish water, only seven Gobiesox species from warmer parts of the Americas are freshwater fish that live in fast-flowing rivers and streams. Most known clingfish species are from relatively shallow coastal waters, but several inhabit the mesophotic zone and a few even deeper, with Alabes bathys, Gobiesox lanceolatus, Gymnoscyphus ascitus, Kopua kuiteri, K. nuimata and Protogobiesox asymmetricus reported from depths of 300–560 m. Because of their small size and typical habitat, it is however suspected that still-undiscovered deep-water species remain. Even in shallow coastal waters many clingfish are highly cryptic and easily overlooked, mostly staying under cover, although there are species that are active and will swim in the open. As a consequence their abundance is often not well known. Several species are only known from a single or a few specimens. Species that appear uncommon or rare based on standard methods can actually be common if using methods that are more suitable for detecting them. Studies of better-known species have shown that they can be locally abundant. As many as 23 individuals of Lepadogaster lepadogaster have been documented from a single square metre. As of 2018, the IUCN has evaluated the conservation status of 84 clingfish species. The majority of these are considered least concern, 17 are considered data deficient, 8 considered vulnerable and a single endangered. The vulnerable and endangered species all have small distributions, restricted to islands or a single bay. Three Gobiesox species that are restricted to fresh water in Mexico have not been rated by the IUCN, but are considered threatened by Mexican authorities.

Reader's Guide

Clingfishes are notable for their remarkable sucking disc, which is located on the underside at the chest and is formed primarily by modified pelvic fins and adjacent tissue. In some species it is divided in two, resulting in a larger front and a smaller rear sucking disc. The sucking disc is covered in tiny hexagons and each of these consists of many microscopic hair-like structures (setae), similar to the structures that allow geckos to cling to walls. The sucking disc can be remarkably strong, in some species able to lift as much as 300 times the weight of the clingfish. Gobies can have a similar sucking disc, but unlike that family the single dorsal fin in clingfish is not spiny. In a few clingfish species the disc is reduced or even absent, notably Alabes, which are quite eel-like in their shape and aptly named shore-eels. The sucking disc is also reduced in some deep-water clingfish species. Most clingfish species have a cryptic colouration, often brown, grey, whitish, black, reddish or green shades, and in some cases they can rapidly change colour to match their background. Species of deep water are often orange-red. Diademichthys lineatus, Discotrema species, Lepadichthys caritus and L. lineatus are strongly banded, which may function as a disruptive pattern when among sea urchin spines or crinoid arms, but may also be warning colours, as some members of these genera have poisonous skin and mucus. The skin of clingfishes is smooth and scaleless, with a thick layer of protective mucus. In at least Diademichthys lineatus and Lepadichthys frenatus, the mucus production increases if the fish is disturbed. The taste of their mucus is highly bitter to humans and it can kill other fish, due to a grammistin-like toxin. Another defense appears to be present in a couple of Acyrtus and Arcos species, which have a spine at their gill cover that appears to be connected to a venom gland, strongly suggesting that the world's smallest venomous fish is Acyrtus artius, which is less than 3 cm long. Feeding varies depending on exact clingfish species. Most primarily feed on tiny crustaceans or gastropods. Other small animals recorded in their diet include chitons, bivalves, medium-small crustaceans like crabs and barnacles, sea urchins, worms, insect larvae, fish and fish eggs. In some species, cannibalism where a large clingfish eats a smaller clingfish is not uncommon. Limpets and other shelled invertebrates are well-protected and often strongly attached to the rock surface. Clingfish species that feed extensively on them have developed specialized teeth and techniques to dislodge them, including rapidly inserting their relatively large, fang-like front teeth under the edge of the prey to flip it, or jamming the teeth on or under the shell's edge to make a small break.

Did You Know?

• The sucking disc of some clingfish species can lift as much as 300 times the weight of the fish.
• The world's smallest venomous fish is likely Acyrtus artius, a clingfish less than 3 cm long.
• Three clingfish species are cleaner fish that cling onto the bodies of larger fish.