Just to add a related anecdote to your post….

My family has owned property on Manitoulin Island (world’s largest freshwater island, in Lake Huron) for over a century. The island is home to more than one hundred individual lakes…all formed at roughly the same time and in the manner described above.

However, each lake had its own individual speciation. Brown trout were only found in this lake. Whitefish were only in that lake. Walleye in these two lakes over there…. Smallmouth bass and yellow perch, for some reason, could be found in pretty much any of the lakes, although the perch from the largest lake had begun to diverge in their appearance from normal yellow perch; they were darker in color, had a pronounced dorsal hump, and would reach sizes way beyond normal perch. Locals just called them giant perch.

Unfortunately, cormorants, careless people and government-run stocking programs have caused major changes to fish stocks in the last twenty years.