There are two cryptic (i.e. morphologically very similar) species of flounder in the Baltic Sea: the European flounder (Platichthys flesus), which spawn pelagic eggs in high-salinity offshore basins, and the recently described Baltic flounder (Platichthys solemdali), the only endemic fish of the Baltic Sea.
The latter lays demersal eggs and is well adapted to the low salinities of the coastal waters of the Gulf of Finland and northern Baltic Proper. It was long assumed that only the demersal-spawning species occurs in the Gulf of Finland, where salinity is too low for P. flesus's reproduction.
Researchers - University - Helsinki - Test - Species
Researchers from the University of Helsinki developed a simple genetic test to distinguish the two species. By analyzing the DNA from flounders' ear bones collected over the past four decades, they discovered that European flounders were in fact once the most abundant species in the Gulf of Finland. However, they have almost completely disappeared.
"We discovered that the decline in fishery landings closely mirrors in time the near-complete disappearance of the pelagic-spawning European flounder -- a species that was not supposed to occur here. This species -- not the Baltic flounder -- dominated local assemblages until three decades ago, but has since disappeared as a result of worsening environmental conditions," says researcher Paolo Momigliano from the University of Helsinki.
European flounders cannot reproduce...
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