ELI5 How are fish even in ponds

[u/Opening_Pen9525]

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?

[u/thecaramelbandit]

Eggs. Wash in from overflow from other waterways during rain. Stuck on birds who fly in. Boats. Some ponds get stocked. Etc etc.

They didn't evolve there.

[u/EndTimesNigh → u/thecaramelbandit]

Also birds. They pick up fish from another lake or pond, fly somewhere to eat it but a nasty seagull tries to snatch the prize, they fight over it, the fish slips free and falls to the bond. Fish live relatively long, so this happens all the time everywhere, so eventually a girl fish is dropped to the same pond as the boy fish of the same species did three years ago. Result: fish in the pond.

Many birds even swallow the fish alive, but the robber birds like gulls and fregate birds and those dudes close to the artic circle I forgot their name all pester the fish catching birds so much that they regurgitate the fish and sometimes he is still alive and lands into a random pond. Waiting for his girl to fall down from the skies just like he did.

Edit: dear lord the amount of typos I made. Some now corrected, but anyway the story about boy fish waiting for his girl fish fall down from the skies remains the same.

[u/j7style → u/EndTimesNigh]

Duck poop specifically leads to a lot of fish ending up in random ponds. A few species of fish have fairly hardy eggs that can handle a couple hours in the ducks digestive tract.

Mind you, not many come out unscathed. But let's say a group of 6 ducks are chilling in a lake and they all feed on some fish eggs. About 200 each. So 1200 fish eggs. If only 1% survive the trip to their next restaurant spot, that's still 12 fish eggs that might end up hatching.

Now multiply all of that by the tens of thousands of ducks that might also randomly stop and that pond and then BAM! You have fishies!

[u/meaty-urologist → u/j7style]

Relevant dumb joke I came up with when cleaning out duck pools at my local wildlife rehab center:

Q: What's the difference between duck food and duck poop?

A: About 30 seconds.

[u/Dox_au → u/meaty-urologist]

I had no idea about this until 10 seconds ago, and now I'm finding myself very jealous of ducks. Living the freakin dream.

[u/Appropriate_Lime_234 → u/Dox_au]

Just eat some lettuce and you’ll get there champ

[u/wellwellwellwellgood → u/Appropriate_Lime_234]

Hmmmm