Evolution of landlocked/ freshwater fish? ?

Question

I'm wondering if anybody can tell me some popular evolutionary theories for landlocked fish. Especially, fish in regions where the lakes were recently created by the glaciers of the last ice age, which was around 10,000 years ago (not a long time for evolutionary mutations).

Answer 1

Inland lakes plus alpine lakes & streams can be isolated remnants of old  water courses from before the glaciers retreated.

Fresh water fish recolonized all of the rivers and lakes that were under ice during the Ice Age. Many lake dwelling fish will enter streams to spawn, just like the Yellowstone cutthroat trout still does. Many salt dwelling fish enter streams to spawn.

So fish move through and between river systems downstream or upstream to lakes. As the ice retreated the land rose closing off some water courses & isolating the fish that had migrated to those lakes.

Most marine sticklebacks have body armor but the fresh water versions trapped after the ice ages have a rare version of the gene Ectodysplasin and have reduced bony plates. This genetic variation still exists in the marine population at a very low frequency and it is recessive so is rarely expressed. The sticklebacks isolated inland carried this rare allele and survived so the frequency in the population increased. This is repeated in a number of inland lakes showing parallel selection.

http://www.sciencemag.org/cgi/content/ab...

http://judson.blogs.nytimes.com/2008/01/...