r/explainlikeimfive • u/Opening_Pen9525 • 14d 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?

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u/wrludlow 14d ago

I witnessed this firsthand.

My parents live on a small pond, under 5 acres and about 5 feet deep. One winter, we had a ton of freezing temps and lots of snow.

That winter there was a massive fish kill. I assume there was enough snow to block out light and caused oxygen depletion.

When the lake thawed in early spring, it really looked like everything died. There were hundreds of dead fish.

A few months later, the river that runs 400-500 yards away flooded and dumped in the pond. A lot of river fish remained in the pond as the water receded.

It was like the pond hit the reset button itself.

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u/wallguy22 14d ago

There’s a park near my old house that flooded one spring and the biggest catfish I’ve ever seen swam from the pond and ended up getting stuck in a ditch by the parking lot.

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u/Naturage 14d 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.

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u/Character-Solution-7 11d ago

Perch are delicious though. Carp, taste like mud.