European flounder can complete whole life cycle in freshwater
Most flounders sampled in Lake Pulmanki in northern Finland had spent their entire lives in freshwater. The study provides the first evidence of the species living entirely in freshwater. The work is published in Evolution.
A recent study has revealed that European flounders can complete their entire life cycle in freshwater. Generally, these marine fish migrate to river mouths to feed and return to marine or brackish water to reproduce. However, a population of these flounders in Lake Pulmanki, a former Arctic Ocean fjord now connected to the sea, challenges this norm.
Researchers from Italy, Hong Kong, Australia, Portugal, and Finland analyzed the otoliths - small bony structures in the fish's inner ear - of flounders in Lake Pulmanki. The otolith records showed that most of these flounders had spent their entire lives in freshwater, suggesting that this population can recruit without a marine phase. The genetic analysis further supports this, indicating that the shift to freshwater reproduction is likely a complex genetic process involving variants on several chromosomes.
This finding is significant as it provides insights into how a predominantly marine fish can reproduce in freshwater. It also presents an opportunity to explore the genetic changes associated with this transition, which may lead to speciation.
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