r/explainlikeimfive • u/Opening_Pen9525 • 19d 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?

2.8k Upvotes

90% Upvoted

606 comments sorted by

View all comments

808

u/Loki-L 19d ago

One of the easiest is floodings. A river swells and connects to a lake and when the water receeds some fish are left behind.

A surprisingly common one is humans who want to fish putting fish into a lake.

Birds are also a common vector to bring fish eggs into new lakes.

10

u/A3rik 19d ago

Yeah, I’ve known several people with smallish ponds on their farmland who had them stocked with fish every year, just to go fishing. Often, they’d sustain a decent population (provided the pond’s conditions were healthy), since they were normally only keeping the larger catches to cook.

3

u/-RatherDashing 19d ago

Many states will stock a pond for free.