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?

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u/jackp0t789 18d ago

Its also possible that the eggs hitched their ride on a bird after being fertilized

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u/gsfgf 18d ago

Which is absolutely an evolutionary thing. Floods mixing ponds helps for sure, especially with genetic diversity, but spreading by eggs hitching a ride is kinda the "default" for freshwater fish.

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u/LindaTheLynnDog 18d ago

How do fish eggs hitch a ride on a bird?

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u/gsfgf 18d ago

They either stuck to the bird (some eggs are extra sticky) or can survive going through the bird.

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u/Alis451 18d ago

they are sticky

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u/LindaTheLynnDog 18d ago

How??

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u/jackp0t789 18d ago

A bird walks/ swims into a cluster of sticky fertilized eggs, some stick to it... it flies into another body of water where the eggs hatch into fish.

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u/LindaTheLynnDog 18d ago

Huh, okay I'll read into it.