When the last Ice Age ended, about 10,000 years ago, pockets of migratory ocean threespine sticklebacks colonized newly formed lakes and streams in coastal regions, and then evolved independently in response to their new local environments. As a result, many of these populations show significant differences in body structure. Marine sticklebacks, for example, have a hind fin with a large spine projecting down from their pelvic structure. In contrast, dozens of freshwater populations have lost that hind fin; its absence likely reduces their need for calcium and chances of being nabbed and eaten by hungry insects.

So, when the Ice Age ended, fish began to inhabit the newly formed bodies of water, in the +120m hydrosphere. Okay, fine. Not even going to question the evolutionary pressures against inhabiting disconnected bodies of water or swimming into a nation whose rivers almost all lead out.

As you can tell, I do question how they arrived in such abundance all over Canada, since it was covered in 2 miles of ice and after its removal their appearance seems immediate.

I also question the implication that they evolved so much over 10,000 years, when we have not observed even a rudimentary change in a single mouse for over 500 years (which is quite literally millions of generations of mice).

Not to mention the reproductive risk of evolving and thus subliminal pressure not to - I mean, who would fuck something with half a fin - or a half-formed eye sticking out of its head (think about the poor first fucker to be born with an eye. Aren't we lucky someone reproduced with them?)

Once again, I could be wrong - but I'm not intentionally misleading, trying to find the truth of the ice-age and fish and mice just sort of fit in.