For fish living in the sea, migration is easy because all the oceans are connected. But what about fish that spend their whole lives in lakes. How did they spread from lake to lake. I imagine that the first fish probably developed in the seas and some species evolved that could swim up rivers and eventually to lakes. What I want to know is what is the mechanism for fish to spread to other “land locked” lakes other than by stocking by humans.
Birds perhaps?
Yes, birds eat fish eggs and then shit them undigested into other lakes.
They take advantage of floods.
I’ve always heard the bird story too. I’ve never heard it corroborated, but something’s gotta do it, especially where minnows are concerned. Nobody stocks a pond with minnows/shiners, but any pond of a sustainable size will eventually have some.
I’ve always understood that the primary vector of transmission of fish to new bodies of water was via the feet of waterfowl. But, apparently the digestive tracts of said feathered friends is also a first class mode of travel—at least for the crustaceans(and, like I always say, what’s good enough for crustaceans is good enough for ichthyoids*).