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GreenStrong t1_ism07e5 wrote

The answer to this question was only recently discovered. It was always understood that water birds played a role, but it was assumed that they transferred fish eggs on their feet. New research suggests that a small percentage of fish eggs survive digestion by ducks. And ducks eat a large number of fish eggs, which are tiny.

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Pizza_Low t1_ism13yx wrote

And humans are a major factor in bringing fish to isolated lakes and rivers. Particularly the kind we like to eat or fish. For example brown and rainbow trout have been brought into lakes and rivers all over the world for centuries. In modern times by airplane and helicopter, but even in buckets on horseback or hand carried.

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Fiskerr t1_isp08c5 wrote

Millennia, according to Norwegian research. See e.g. Mjærum, A., & Wammer, E. U. (Eds.). (2016). Fjellfiske i fortiden: årtusener med svømmende rikdom. Portal forlag.

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craigery_t t1_ism29va wrote

This is new? I've been told this as long as I can remember.

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PhotoJim99 t1_ismc8cu wrote

Perhaps you were told it as speculation, and now it's been scientifically verified.

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antij0sh t1_isnr3dj wrote

It’s still not “scientifically verified” that bird feces is the vehicle for this phenomenon, it’s only been shown in this study that it’s possible for some eggs to survive digestion.

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PhotoJim99 t1_isqnsy4 wrote

Fair enough, but that's still a significant step forward from "speculated".

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cacomyxl t1_ist1hnx wrote

I think people have mentioned it, but this seems pretty conclusive to me.

Experimental Evidence...

And just like the raft theory of island population by land animals, it only take one incident over a period of many thousands or millions of years.

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katiekat122 t1_isp9s0j wrote

Alot lot are stocked by humans. I can only speculate but humans also fish with love bait etc. shiners. Im sure there are others that are used this may add thought to your question.

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amaurea t1_isxc6ui wrote

Are you sure you're not confusing it with the old "brought along with feet and feathers"-hypothesis? The abstract of this recent paper (2020) says the gut hypothesis was only suggested recently:

>Fish have somehow colonized isolated water bodies all over the world without human assistance. It has long been speculated that these colonization events are assisted by waterbirds, transporting fish eggs attached to their feet and feathers, yet empirical support for this is lacking. Recently, it was suggested that endozoochory (i.e., internal transport within the gut) might play a more important role, but only highly resistant diapause eggs of killifish have been found to survive passage through waterbird guts. Here, we performed a controlled feeding experiment, where developing eggs of two cosmopolitan, invasive cyprinids (common carp, Prussian carp) were fed to captive mallards. Live embryos of both species were retrieved from fresh feces and survived beyond hatching. Our study identifies an overlooked dispersal mechanism in fish, providing evidence for bird-mediated dispersal ability of soft-membraned eggs undergoing active development. Only 0.2% of ingested eggs survived gut passage, yet, given the abundance, diet, and movements of ducks in nature, our results have major implications for biodiversity conservation and invasion dynamics in freshwater ecosystems.

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noob_user_bob t1_isox6z2 wrote

Would this also explain how frogs/tadpoles randomly turn up in my garden water fountain????

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zmilts t1_isoxfu4 wrote

I mean, frogs can move on land, so I would imagine they just walk (hop?) there and lay their eggs.

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noob_user_bob t1_isoyahk wrote

Like it makes sense but I've just never seen a migrating frog before :p

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cacomyxl t1_ist0zhp wrote

Oh, I've seen that. I've had both tree frogs and pond frogs find their way into buckets on my porch and lay eggs.

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motofabio t1_ist1vcq wrote

I bought a house in Simi Valley, up in the hills. It’s basically a desert. Somehow little brown frogs made it under my house. I went down there to get them out because they were constantly croaking, and I found a broken drain pipe that was their source of moisture. How they managed to get from wherever they were to my place is astounding to me.

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GreenStrong t1_isoy32i wrote

Possibly, but frogs are pretty industrious about hopping around and finding breeding pools. Many species prefer these transient pools where there won't be aquatic predators. I would guess that they can smell water. If you don't see frogs hanging around and signing during the day, tree frogs are a strong possibility.

I'm in North Carolina, and I get both green frogs and grey tree frogs in my pond if I don't have goldfish. The green frogs definitely hang out and sing for mates when there are no goldfish or only young ones, but they go elsewhere when the goldfish are bigger than an inch or two.

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