Green Rat Clingfish
Miniature marine fish off coast of Australia
Barryichthys algicola
Teleostei: Gobiesocidae
Not exactly euphonious, the common name “green rat clingfish” trips over the tongue, but does pique one’s curiosity. Besides, as the Bard might have said, a green rat clingfish would be just as fascinating by any other name.
Less than an inch long, 17-21 mm to be exact, the green rat clingfish is — you guessed it — green, with a lighter green stripe on the side of the head, from the tip of the snout to the upper part of the gill, passing through the eye which has an orange iris. It is so far known from sites along the northern and northeastern coast of Tasmania, and two locations on the coast of mainland Australia, in Victoria and New South Wales. Most specimens were collected from subtidal fields of macroalgae, up to two meters deep.
The Green Rat Clingfish, Barryichthys algicola, by Barry Hutchins. CC BY-NC-SA 4.0
This is one of two new species assigned to a newly named genus Barryichthys. It is easy to sort out the meaning in its scientific name. The genus name honors Barry Hutchins who first discovered examples of the lineage in the 1980s. And the specific epithet points to the fish’s natural history, the fact that it dwells among algae.
Miniaturization — the evolution of a very small adult body size — is common among animal taxa, with numerous examples found in teleost fishes. Like many miniaturized species, this fish shows certain reductions compared to the anatomy of its larger relatives. This includes absence of a good deal of the cephalic sensory system, and the lower gill-arch skeleton. It also has some unusual features, such as elongate papillae on the adhesive disc.
The new species belongs to Gobiesocidae, the family of clingfishes. Members of the family are found in the Atlantic, Indian, and Pacific oceans, from the intertidal zone to depths of 500 meters. Most species live in tropical or warm temperate regions, but some are found in colder waters. Their habitats are primarily shallow, rocky reefs and shores. Some are closely associated with macroalgae or seagrass beds, and may be obligately associated with them. Some species are amphibious, able to live out of water for a few days, taking oxygen from the air by means of gill surfaces. Mostly marine, a number of species may be found in brackish water, but only seven freshwater species are known.
Most clingfishes are small, less than two inches in length. A few are larger, including a couple of species that can grow to about a foot. Most have narrow, tapering bodies and flattened heads, giving a visual impression of an elongated tadpole. Their skin is smooth, without scales. Some species are known to excrete a mucus when threatened that is said to taste extremely bitter — a fact I am happy to take their word for — and to be toxic to other fish.
Clingfishes are famous for their adhesive discs. These ventral structures are formed from elements of the paired fins and fin girdles, and are used by the fish to firmly attach to the substrate. The attachment is so strong that a disc can lift up to 300 times the weight of the fish. As a result, they are able to hang on to a rock or other substrate, even in very strong currents or while being dashed by waves.
Diets of most clingfishes consists of small-sized invertebrates. None are known to be strictly herbivorous, but some are omnivores and will consume quantities of algae. A few are associated with other species, such as living in or among sea urchins, or acting as cleaner-fish, eating parasites from larger fish.
To date, more than 180 species of clingfishes have been named in fifty genera. But their small size and cryptic habits suggest that more species remain to be discovered.
Further Reading
Conway, K. W., Moore, G. I., and A. P. Summers (2019) A new genus and two new species of miniature clingfishes from temperate southern Australia (Teleostei, Gobiesocidae). ZooKeys 864: 35-36.