Gobiesocidae

Family of fishes

Clingfishes are fishes of the family Gobiesocidae, the only family in the order Gobiesociformes. These fairly small to very small fishes are widespread in tropical and temperate regions, mostly near the coast, but a few species in deeper seas or fresh water. Most species shelter in shallow reefs or seagrass beds, clinging to rocks, algae and seagrass leaves with their sucking disc, a structure on their chest. They are generally too small to be of interest to fisheries, although the relatively large Sicyases sanguineus regularly is caught as a food fish, and some of the other species occasionally appear in the marine aquarium trade. 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. 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 cephalus, G. fluviatilis, G. fulvus, G. juniperoserrai, G. juradoensis, G. mexicanus and G. potamius) 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 Because of their small size and typical habitat, it is however suspected that still undiscovered deep water species remain. 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 (more than two individuals per square foot). as of 2018, the IUCN has evaluated the conservation status of 84 clingfish species (roughly half the species in the family). The majority of these are considered least concern (not threatened), 17 are considered data deficient (available data prevents an evaluation), 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.

[[File:FMIB 45581 Cheilobranchus rufus. jpeg|thumb|Alabes are eel like, unlike other clingfish Males typically grow larger than females. Another defense appears to be present in a couple of Acyrtus and Arcos species. They have a spine at their gill cover and it appears to be connected to a venom gland. Although the evidence presently is circumstantial, this strongly suggests that the world's smallest venomous fish is Acyrtus artius, which is less than long.

thumb|upright=0.75|Sucking disc of Sicyases sanguineus (viewed from below with mouth at the top)

Clingfish are named for their ability to firmly attach themselves to various surfaces, even in strong water currents or when battered by waves. This ability is aided by their 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 also reduced in some deep water clingfish species. Species of deep water are often orange red (these long wave length colours are the first that disappear with depth, making them suitable for camouflage). 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. This includes 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. In the opposite extreme of the species with relatively few large teeth is Nettorhamphos radula. This species has 1,800–2,300 microscopic teeth (about ten times more than known from any other clingfish), but its feeding behavior is unknown. No clingfish species is known to be exclusively herbivorous, but some are omnivorous and will feed extensively on a range of algae (brown, green and red), whereas ITIS place them in the suborder Gobiesocoidei of the order Perciformes, under superorder Acanthopterygii. ITIS lists Gobiesociformes as invalid. The 5th edition of Fishes of the World places the Gobiesociiformes in the clade Percomorpha as part of the series Ovalentaria. Mostly being very small and often cryptic, new species are regularly discovered and described. A major authoritative work on the family is a monograph that was published in 1955 by J. C. Briggs, but in the half century after its publication, up until 2006, fifty six new clingfish species were described, or on average more than one per year. as of 2020, there are 182 recognized clingfish species.