Unique discovery: the 'big little fish'

Researcher Bram Couperus of WMR is pleasantly surprised by the spontaneous discovery: "Discovering a new fish species in the Northeast Atlantic is a rare event. It has not occurred before in the history of our institute, founded in the 1950s. This fish was caught in an area where there is a lot of fishing, especially by Dutch fishers. One would therefore expect the species to have been caught before. If this is the case, at least it escaped attention - until last year."

Search for unknown fish

The new fish species was noticed last year in the catch during the blue whiting survey, a survey conducted annually to assess blue whiting stocks in European waters. Couperus: "Blue whiting lives in the so-called meso-pelagic or twilight zone. At that depth you will find striking species, such as lanternfish and deep-sea angler fishes. Among those, there was suddenly an unknown fish."

For the Wageningen researchers, the search for the fish's identity led via a Russian taxonomist to the Natural History Museum Stuttgart in Germany, where the fish taxonomist Ronald Fricke already had experience with this group of fish, the deepwater cardinalfishes (Epigonidae). Fricke: “Deepwater cardinalfishes of the genus Microichthys are known from three other species that live in the Mediterranean Sea and eastern Atlantic. They are free-swimming in deep water and only a handful of specimens is known to science. The discovery of the new species off Ireland is very exciting, as it seems closer related to a Mediterranean species from Sicily, than to the other Atlantic species from the Azores.”

New fish, new name

One reason the fish had not been noticed before is that it measures only 5.5cm, making it easy to slip through the meshes of a net or be overlooked when caught. The previously known species of this group of fish are even smaller than the specimen caught. The Latin name of this genus is therefore Microichthys, meaning 'small fish'. The new species gets the addition 'grandis'. That makes its full name Microichthys grandis, literally 'big little fish'.

Habitat

The location where the big little fish was caught is the Porcupine Bank Canyon, an underwater canyon with cold-water coral along the western edge of the Porcupine Bank. The fishing technique used by the researchers did not involve bottom trawling. This is because blue whiting is a so-called pelagic species that swims in schools in the water column and is not bound to the seafloor. Fishing vessels targeting blue whiting in the area also fish with a pelagic net. The researchers suspect that the newly discovered species is naturally very rare, and also so small that it usually passes through the meshes of the net, making the chances of catching it very low.