The "Baltic flounder" is the first fish found to be native only to the Baltic Sea.
Researchers at the University of Helsinki have named the first endemic fish discovered in the Baltic Sea.
The Baltic flounder, Platichthys solemdali, is the only known fish species native to the Baltic Sea, said professor Juha Merilä from the university in a press release.
According to the university, finding a new vertebrate in the Baltic Sea is significant, because the area has a scarcity of marine fauna and biological research has been conducted there for more than a century.
Merilä said the Baltic flounder has not been recognised before as it appears to be nearly identical to the European flounder. Currently, the two species can be distinguished only with genetic methods, or by studying their eggs and sperm, he added.
Whereas the Baltic flounder lays sinking eggs on the sea floor in coastal areas, the European flounder spawns buoyant eggs in deep areas in the open sea.
In addition, the new species is more abundant in the Gulf of Finland that the European flounder, which is largely found in the central and southern Baltic Sea, the university said.
According to the researchers, the process where the new species was formed occurred at a record speed, in just 2,400 generations, which is a short period in evolutionary time scales.
Now that the new species has been formally described, the two flounders can officially be considered separate species.
The Latin name of the new species is dedicated to the late Per Solemdal, who was the first researcher to study the flounder’s eggs and sperm in connection to salinity, the university said.
The only other species native to the Baltic Sea is a brown algae,Fucus radicans.