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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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DeusKyogre1286 t1_ism2veo wrote

As a person who did their Honours thesis on a related question, I can only put most of my thoughts on the first question and its relation to North American fish ecology, though I can imagine that given how long evolution/speciation takes, that barring the specific case of African cichlids, most lakes have not really existed for very long. In North America, especially Canada, most of our lakes were formed from glaciation a mere 10 000 years ago - a great glacier quite literally scraped away holes in the land, and these became filled by meltwater, forming lakes and rivers, many of which were once far more interconnected than they are now so there was once an opportunity to disperse where none now seemingly are.

Given this scenario, we can then think about how fish get into these lakes, and eventually begin to speciate, but the fact is that, there just hasn't been a great deal of time geologically speaking for fish to even start diverging, because although these lakes may have formed 10 000+ years ago, the fish probably didn't get there 10 000+ years ago. Some of the fish are of highly conserved lineages, and spread out from refugia in the southwest and southern parts of North America, but many more, especially the most important varieties are actually the product of human activity - people literally dumping lakes with fish to stock them in the 19th century. Think about that - even if these lakes are quite isolated, there hasn't been all that much time for speciation (200+ years), and most of these lakes aren't actually fit for habitation and only have fish as they are cyclically restocked, usually on an annual basis.

Lastly, as u/GreenStrong has provided, there has recently been some suggestion that ducks are acting as zoochoric agents, and spreading out fish eggs, but although this is a plausible practical vector of dispersal under lab conditions, it's still unclear (as far as I've heard!) if this actually could have happened enough times for it to have been a meaningful mechanism of dispersal.

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TinKicker t1_isnxad5 wrote

Just to add a related anecdote to your post….

My family has owned property on Manitoulin Island (world’s largest freshwater island, in Lake Huron) for over a century. The island is home to more than one hundred individual lakes…all formed at roughly the same time and in the manner described above.

However, each lake had its own individual speciation. Brown trout were only found in this lake. Whitefish were only in that lake. Walleye in these two lakes over there…. Smallmouth bass and yellow perch, for some reason, could be found in pretty much any of the lakes, although the perch from the largest lake had begun to diverge in their appearance from normal yellow perch; they were darker in color, had a pronounced dorsal hump, and would reach sizes way beyond normal perch. Locals just called them giant perch.

Unfortunately, cormorants, careless people and government-run stocking programs have caused major changes to fish stocks in the last twenty years.

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Frammingatthejimjam t1_iso8uef wrote

Somewhat off topic but doesn't Manitoulin have the world's largest island on a lake on an island on a lake?

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TinKicker t1_iso96k3 wrote

Yep! Lake Kagawong on Manitoulin is home to Kakawaie Island, which has a small unnamed body of water in its interior.

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weirdclownfishguy t1_ismrnwh wrote

African Cichlids are a really cool example of evolution producing more or less that same result multiple times. Lakes Malawi and Tanganyika have so many species that look so similar to each other

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atomfullerene t1_ism6xxg wrote

>How do fishes get into isolated inland lakes in the first place?

For random small ponds and lakes, there are two main ways that fish get into seemingly isolated bodies of water: people, and flood events.

I cannot emphasize this enough, people are absolutely obsessed with putting fish in all sorts of bodies of water. Fishermen want fish to fish for, and nobody wants mosquitoes. People go to extreme lengths to get fish into everything from their farm ponds to remote lakes in the middle of nowhere in the mountains. In the old days, this meant packing milk cans full of trout fry out on mules, nowdays it means airdropping them.

If the fish you see is any sort of trout, bluegill or other freshwater sunfish, a bass, common carp or goldfish, golden shiners, fathead minnows, mosquitofish, or tilapia, there's a very good chance it was stocked in the body of water by a person. These fish have all been spread all over the place outside of their native range by people. (this is a North America-centric list, other places will have their own commonly stocked fish)

The second method of fish dispersal is flood events. When there's a big flood, all the water flowing into an "isolated" pond has to flow out. The exit may not be obvious most of the time, and it may not have water in it most of the time, but during floods there's a lot of water moving on the land and that lets fish move around to places you wouldn't expect. There are relatively few isolated bodies of water that are truly isolated. This is even more true if you take the long view...there were enormous floods at various points toward the end of the last ice age, and as recently as the 1800's we've had megafloods in the central valley of California, for instance.

Now, I know people always bring up birds, but I'm not at all convinced that is a major method of fish dispersal. The first option is a bird carrying an adult fish and dropping it in a new lake. I find this an extremely unlikely method of fish dispersal, because nearly all fish are external fertilizers. Which means you need a male and a female to be present, you can't just have a pregnant female carrying fertile eggs. The odds that birds would happen to drop two separate fish in the same pond, after carrying them (and you'd have to carry them alive a long way) are just too small for it to happen regularly.

There's a better case for birds consuming fish eggs, but it's still only proven for a few fish species that the eggs can survive passage through a duck digestive tract, and a great many fish don't lay eggs in places where birds might eat them anyway. Probably happens sometimes.

But it doesn't happen very often, and we know that because historically there have been a lot of lakes without fish in them. Especially in high mountains or areas in the north, lots of lakes just...didn't have fish. These often housed unusual or unique ecosystems with amphibians and insects found in few other places. And also it's very common for fish to be found in one watershed and not neighboring watersheds, even if other fish lived in those other watersheds. So it's clear that most fish aren't getting airlifted to nearby streams or lakes, because we know they just weren't in those streams or lakes.

Of course, as I mentioned before, people are absolutely mad for moving around fish so nowadays nearly all of those previously fishless lakes have fish in them thanks to historic stocking efforts.

>and why don't we see more divergent evolution / speciation given the separation of each group of fishes from each other?

Ponds and lakes are usually very short lived, on a geological or evolutionary time scale. Ponds usually come and go over the course of a few hundred or few thousand years, they just don't stick around long enough for speciation to happen. Lakes come and go too, the Great Lakes only appeared at the end of the last ice age, for example. And of course many of the "lakes" people know about are actually reservoirs built by humans in the past hundred years or so and stocked with a mix of human chosen fish.

Old lakes do have a bunch of unique species: the rift lakes in Africa and Lake Baikal are two excellent examples of this phenomenon. And in general, freshwater does cause a bunch of speciation...there are almost as many freshwater fish species as marine species, despite the total volume of freshwater habitat being enormously smaller. This is because isolation in different watersheds causes speciation. But you won't necessarily see that diversity because if you are fishing, you are probably catching and seeing the very handful of fish species that people have stocked in ponds and lakes all over the place.

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czyivn t1_isogyvc wrote

I know some people seem skeptical of birds as a means of dispersal, but unless mistakes are happening with fish stocking or someone is secretly sneaking onto our land to do it, it's the only explanation possible for certain fish getting into ponds on my family ranch. We have ponds stocked with bass, perch, and blue catfish. Suddenly flathead catfish started appearing in some of the ponds and eventually took them all over. We definitely didn't stock them, and the ponds aren't in locations capable of flooding from other nearby ponds. The only reasonable explanation is that either people did it somehow (it wasn't any of my family) or birds are doing it. Ducks aren't that common either, so it would have to be something more like an egret/heron.

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atomfullerene t1_isom395 wrote

How long ago were they stocked with the other fish? My bet is that you had a few juvenile flathead sneak in with the other fish when they were stocked. It takes them 4-5 years to mature, and it might take a few generations before the ponds had enough in them for them to be noticeable.

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czyivn t1_isoyjvy wrote

The only point it really makes sense is during the stocking with blue catfish. Those got big much sooner, though. We were catching 2-3 lb blue cats while the flatheads were still a quarter pound or less. So having it happen from that single stocking event doesn't make a ton of s ense to me, but I guess it's possible if they grow much slower than blue catfish.

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HunterDHunter t1_islw0ts wrote

There has to be a river/stream system feeding the lake. And at some point or another that system was connected to other bodies of water. Entire parts of every continent used to be under water. There are flood events that can spread wildlife. They can also be spread by migratory birds.

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JeegReddit44 t1_islwsfp wrote

So it's swallows then... African or European?

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LaughCatalyst t1_ism02k8 wrote

I know a cave up a hill that's only fed by the drops from its ceiling (which are from hill run off making the cave pretty much a spring) and the cave has little fish living there that people throw food in for.

My guess is birds like you said, or some mischievous humans.

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DarkMuret t1_ism0hib wrote

Depending on the source of the cave, it may have been a flooding event, or a water table connection

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tworutroad t1_isn62o3 wrote

Interesting speculation. The lake I live on is spring fed. I never thought of fish egg transport through water tables.

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stewpideople t1_isn8w43 wrote

Not entirely true. After the glaciers receded in the last ice age. Round lakes were formed. Current studies show those small pools ponds and lakes, removed from flood planes, rivers or other such events, even in lack of man. Birds, storms and land mammals long extinct would be carriers for fish eggs from one pool to another.

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SecretNature t1_ism7d3p wrote

A couple other ways I have personally witnessed. Spring flooding can create creeks between lakes and I have witnessed fish swim between them. I have also watched osprey catch full grown fish and accidentally drop them into other lakes. It seems like a freak accident but I have witnessed it multiple times.

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Flash635 t1_ismy39u wrote

During extreme flood events the water trap at the Carbrook Golf Course in Australia connects to a nearby river.

That's why there are bull sharks in the water trap.

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pandc0122 t1_iso9fxd wrote

I wonder if it’s possible that this behavior is a kind of survival mechanism - spreading food stock to new habitats, increasing the likelihood of good hunting in future seasons.

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SecretNature t1_isqd7od wrote

It is an interesting thought but for the sake of brevity I did not include all of the details in my post. Every time I have seen this happen it was when an osprey was being chased by a bald eagle. They did not want to drop the fish but they had to in order to use their talons to defend themselves. So, I don’t think it was intentional to drop them in the lake. At another location I have found fish in the middle of a baseball field presumably dropped by osprey as well under similar situations.

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pandc0122 t1_it2a0t8 wrote

Ah. And to clarify, I don’t think anything about it is “intentional” - more instinctive. In any case, dropping prey in order to escape an eagle is definitely a survival mechanism. 🙂

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PeaEyeEnnKay t1_isnlcmy wrote

On the speciation side of this question... Speciation typically won't just happen in the short term solely because a population is separated from its ancestors. If there are no environmental pressures for selection to work on then any evolutionary mechanisms (mutation, sexual reproduction, ...) are most likely going to keep selecting for the same features. Given enough time there would likely be some divergence but without pressures to evolve it would be a very slow process, and as others have noted the timeframes for most examples of isolated inland fish we see are pretty small.

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Jonherenow t1_islzgi9 wrote

Glaciers advancing and retreating during the ice age put very large areas under water, connecting what are now separate lakes and streams. But it’s still hard for me to get my head around this one especially at lower latitudes.

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akodo1 t1_ismir4k wrote

Most lakes and ponds have streams flowing into and out of them. Body of waters all tend to flow together. Think of the vast network of rivers, streams, brooks, lakes, and ponds that all flow into the mississippi. While the water all runs in one direction, fish can of course swim up current.

Even when bodies of water are not directly connected, when there's a huge rainfall and floods in one area that water carries fish for miles and miles. There can be divides where normally all water flows eastward, but when there's a flood at a divide, water can flow out both directions, and species that only had access one way find themselves in a different interconnected network.

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Freevoulous t1_isnqztk wrote

Aside from all these great responses, I would also add that there are few species of fish that simply can crawl out of the water and reach another body of water on their own.

Eels are notorious for it, but some species of catfish can do that too.

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SmootZ10 t1_isp8m72 wrote

Some catfish also can burrow to put her places, obviously not far and the conditions have to be just right.

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Furrypocketpussy t1_isnb7li wrote

Not sure about other places, but in many of the remote lakes in the Washington mountains there are a bunch of fish and from what I heard from a park ranger is that they were dumped by helicopters in there. No clue why though

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Metaphant t1_isnu5is wrote

A lot ofvwater ways and watery connections are gone due to ditching out mosses and marschlands. And some waterways have grown over in bogs and swamps. If one look at older maps one can often see connections between lakes not seen today. Only in Sweden 6000 lakes and ponds are gone since the beginning of the 20th century.

I don't know about this idea of mine but might there be older cultures planting fishes in lakes for future fishing?

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SirGlenn t1_ismi9rk wrote

I have friends who own a fish hatchery, you can't inspect every little minnow, every egg cluster in the river for even a couple "invasive species" birds and animals can even excrete eggs or recently hatched eggs from miles and miles away. Is every person exactly the same? No, some come from other places.

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DarkestDusk t1_isly48z wrote

Because breeds of fish are already one thing, but they can adapt to their environment, since I found out that Humans without Leadership would destroy all their environments, and NONE could be saved if things couldn't continually improve.

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