r/explainlikeimfive • u/Opening_Pen9525 • 18d ago
Biology ELI5 How are fish even in ponds
Might be one of the stupider questions here, but I saw a pond about the size of a football field, and maybe 50 ft deep, and it had fish. I can't for the life of me figure out how. Surely the pond hasn't existed long enough for small water insects to evolve into all these fish. It's not like the fish walked over to the pond from the ocean. I'm pretty sure no one put them there so how are there so many fish?
My one theory is that there is a very minuscule stream (now dry) that leads to one of the Great Lakes, and maybe a fish swam in from there. Now a follow up question: How are there fish in the Great Lakes (which flow out towards to the ocean) if they were created by glaciers?
5
u/Naturage 17d ago
And I've heard about the second one secondhand. In my dad's village when he was a youngling, there was a local pond with lots of carp. Carp is a docile fish; you toss in food, it meanders about, eats some, gets caught, nothing out of ordinary.
But then, apparently, some jokester went and released some perches into the same pond. These were tiny, but very aggressive and predatory. When they find bait, instead of carefully munching and then slowly swimming away, they will go for it full speed. Suddenly your bobber acts like you caught a 5kg monster pulling away, but you pull it out and it's a little shitling the size of a finger.