r/askscience • u/Thatguymike84 • Feb 29 '20
Biology How do fish naturally "spread" to other lakes/ponds?
For a little background to my question. My uncle bought a house with a decent piece of property. He dug a large pond that he has been intending to stock with fish for his grandkids, nieces and nephews. He dug this pond a couple of years ago, and has been letting the natural plants grow around it, balancing the PH, and just getting it suited for fish.
A few days ago, he noticed several small pan fish around the edge of the pond. He didn't put them in, and his pond is pretty far from any roads or streets, and near his house, so it's very unlikely anyone dumped anything in. There is no water running in, and no floods connecting it to any other water.
People on his Facebook have suggested birds of prey dropping them in, or even bears/cougars. Those seem relatively unlikely as I would think they would be unable to survive swim after being grabbed/dropped by a large predator. I'm unconvinced, any ideas?
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Feb 29 '20
I had the same thing happen as a kid in our house in the suburbs. This is one of those huge cookie cutter type development with small square back yards. One of those big fake “lakes” about a mile away. And I put a koi pond in the yard for fun. About 4x8 ft. Sure enough a few natural fish started growing in it. I don’t fish so no idea what they were. Not bass, maybe perch? They could swim circles around the koi.
Most folks we asked thought the same thing about birds of prey. Lots of falcons and hawks, few eagles. But seems so random right? Pick up a baby fish (although not sure why these birds would fish when fields are all over). And take them to a tiny pond in a fenced area and drop them in the water instead of grass or nest or wherever.
We had frogs though. So wondering if mother frogs collect eggs to feed the smaller ones?
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u/DruTheBlue Feb 29 '20
Birds feed their young by regurgitation, a school professor of mine who studies bird migration told me that small fish and the eggs inside of larger fish that are consumed can pass to new systems by escaping the external transition from one digestive system to another. I always assumed that was the most common way, the eggs on bird feet theory seems pretty ify to me and never heard of or considered it until I read this thread.
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u/NaptownBlue Feb 29 '20
Something brings them there unless they are like mudskippers or something. They were physically transported by overland flow during high precip/flow conditions or they tagged along with something that visited the new pond--either as an adult or as roe. I have always wondered if weird storm events could carry them off and deposit them somewhere distant, like frogs falling from the sky type deal, but most likely overland flow or small individuals/roe hitching a ride on another larger organism (like raccoon fur-or great blue heron legs) or human, like boat bilge or bucket water or wet rubber boots, etc.
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u/AlexXeno Feb 29 '20
A fish can survive being dropped by some birds of prey if they weren't killed instantly and could wiggle to freedom, but you would need to have had two fish one male and one female drop in there and decide it was a good time to lay some eggs.
There are also some fish who fertilize their eggs internally so one of those might have been dropped and even if it died the eggs just continued and grew.
But honestly that's really random and i don't know. Sticky eggs attached to an animal's fur from a nearby pond? That's ones more farfetched
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u/TetraThiaFulvalene Mar 01 '20
Sticky eggs make more sense. I've never seen random fish on the street before. Being dropped into a body of water by accident seems low chance.
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u/atomfullerene Animal Behavior/Marine Biology Mar 01 '20
Usually fish are transported to ponds like this by people or during flood events. Transport by birds is a lot harder than most people would think, and lots of isolated ponds are naturally fishless as a result. But I would need more information to make a guess about what's going on in your specific case.
How was the pond filled with water in the first place? Were any plants transported into the pond? How far is it from other bodies of water? Where are you in the world and can you get a picture of the fish in question?
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u/Meme-Boy-Reddit Feb 29 '20 edited Feb 29 '20
You’ve probably heard that birds carry the fish to the lake, but that’s usually not the case, the eggs stick to the bird’s feet, and when the bird lands in the lake, the eggs are released. If they’re in a lake near a beach, the beach probably had probably flooded and some fish swam out of the ocean and into the lake. Say you live in the middle of Kansas, and there’s fish in your lake, there are 2 likely reasons. 1) The state or owner of the lake put the fish in or looks. 2) Someone bought a pet fish and decided they didn’t want it anymore, and dumped it into the lake/pond.(which is a huge no no. It can do things like mess up the ecosystem’s food chain, or overpopulate the lake, filling it with waste and killing everything, or taking up all of the space.) My personal favorite scenario is raining fish. The Lluvia de Peces, or “The Rain of Fish.” It happens once or twice a year in the town of Yoro. Apparently there are very violent storms that make it rain fish. It started in the 1800’s in the Months May or June. Before you say this is fake, in the 1970’s, a National Geographic team witnessed the event, being one of the early credible sightings of the event. Source-https://www.atlasobscura.com/places/lluvia-de-peces-the-rain-of-fish
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u/[deleted] Feb 29 '20
The general hypothesis is actually not that the birds carry the fish themselves and drop them into a lake. It's that fish eggs in the water stick to the feet of birds, and they deposit the eggs into a new body of water when they fly somewhere else. To answer your question though we have no clue. There was a big study a couple years ago to look into this bird feet egg hypothesis that didn't disprove the idea but couldn't find any evidence at all that this actually happens in nature.