How a small fish coped with being isolated from the sea

[Still Waters]

The last ice age ended almost 12,000 years ago in Norway. The land rebounded slowly as the weight of the ice disappeared and the land uplift caused many bays to become narrower and form lakes. Fish became trapped in these lakes.

Sticklebacks managed to adapt when saltwater became freshwater, and they can still be found in today's coastal lakes along the Norwegian coast.

Saltwater gradually changed to brackish water and later to freshwater. This environmental change naturally led to a total replacement of the animal and plant life.

The exception is the tiny stickleback, which successfully adapted as saltwater became freshwater and can still be found in today's coastal lakes along the Norwegian coast. How in the world did this little fish manage to adapt to such big changes, even in several places at the same time?

https://phys.org/news/2021-05-small-fish-coped-isolated-sea.html