It is only five and a half centimeters long, making it the largest in its family: researchers report on the discovery of Microichthys grandis - the big little fish. Accordingly, there are still new species to be discovered even in the heavily fished waters off Ireland. It is possible that the deep-sea dweller rarely ends up in nets and has therefore been overlooked so far, the scientists explain.
For biologists, every new insight into the biodiversity of nature is a highlight. There are particularly promising "hunting grounds" in the world for the search for previously unknown creatures - such as remote rainforest areas or special sea regions. Europe and its adjacent waters, on the other hand, have been intensively explored biologically. This is what makes the current discovery so special, emphasize Bram Couperus from the Wageningen Marine Research Institute and Ronald Fricke from the State Museum of Natural History in Stuttgart. “Discovering a new species of fish in the Northeast Atlantic is a very rare event. This has never happened before in the history of our institute, which was founded in the 1950s,” says Couperus.
What kind of fish is that?
The newcomer was caught by the marine biologist and his colleagues as part of the annual survey of blue whiting cod stocks off the west coast of Ireland. Its purpose is to define catch recommendations for this edible fish at European level. “The blue whiting lives in the so-called mesopelagic or twilight zone. At that depth, you'll find conspicuous species like lanternfish and deep-sea frogfish," says Couperus. Among them, the researchers discovered this mysterious little fish. Apparently it was a representative of the widespread group of deep-sea cardinal fish (Epigonidae). But to find out more, the Dutch researchers turned to an expert on these sea creatures at the Natural History Museum in Stuttgart.
Ronald Fricke was then able to assign the find to the genus Microichthys and describe it as a new species. The Latin name of the genus means "small fish". With a length of just over five centimetres, this also applies to the newcomer. "These deep-sea cardinal fish are known from three other species that live in the Mediterranean and the eastern Atlantic," says Fricke. However, these previously known species are even smaller than the new species. That is why the fish was given the name Microichthys grandis – “big little fish”.
Interesting family relationship
As Fricke emphasizes, the new species now reveals an interesting speciation history in the "small fish". "Now two pairs of species are known - one in the Atlantic, the other in the Mediterranean". However, the new species off Ireland seems to be more closely related to the Mediterranean species from Sicily than to the other Atlantic species. According to Fricke, there could be a plausible explanation for this surprising finding: the two species from the Atlantic could have migrated into the Mediterranean when the Strait of Gibraltar opened up about six million years ago. "Due to the much warmer deep sea water in the Mediterranean, they then adapted to these conditions and developed into their own species," the scientist suspects.
But how could the “big one among the small fish” remain undiscovered for so long? The researchers suspect that the new species is naturally rare. In addition, this fish is so small that it can easily slip through the meshes of nets, making the chances of catching low. Or maybe it's just that no one was looking closely. “This fish was caught in an area where there is a lot of fishing, mainly by Dutch fishermen. One would therefore expect the species to have been caught before. If that's the case, it simply went unnoticed before," says Couperus.
Source: State Museum of Natural History Stuttgart, specialist article: Ichthyol Res, doi: 10.1007/s10228-023-00909-1