The Freshwater Paradox

Even though less than 1% of Earth's water is freshwater, it's the home for 50% of fish species. This is the Freshwater Paradox.
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- Speciation: The formation of new and distinct species.
- Sympatric speciation: The evolution of new species from ancestral species while both continue to inhabit the same geographic region.
- Allopatric speciation: Speciation that occurs when a population becomes separated by a geographic barrier.
- Adaptive radiation: The diversification of a group of organisms into forms filling different ecological niches.
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REFERENCES
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Thank you to Dr. Elizabeth Miller for lending their time and expertise to this video.
Betancur‐R, Ricardo, Guillermo Ortí, and Robert Alexander Pyron. "Fossil‐based comparative analyses reveal ancient marine ancestry erased by extinction in ray‐finned fishes." Ecology Letters 18.5 (2015): 441-450. pubmed.ncbi.nl...
Bowen, Brian W., et al. "The origins of tropical marine biodiversity." Trends in ecology & evolution 28.6 (2013): 359-366. pubmed.ncbi.nl...
Burress, E. D., et al. "Phylogenomics of pike cichlids (Cichlidae: Crenicichla): the rapid ecological speciation of an incipient species flock." Journal of evolutionary biology 31.1 (2018): 14-30. pubmed.ncbi.nl...
Carrete Vega, Greta, and John J. Wiens. "Why are there so few fish in the sea?." Proceedings of the Royal Society B: Biological Sciences 279.1737 (2012): 2323-2329. pubmed.ncbi.nl...
Dawson, Michael N. "Species richness, habitable volume, and species densities in freshwater, the sea, and on land." Frontiers of Biogeography 4.3 (2012). escholarship.o...
Deutsch, Curtis, Justin L. Penn, and Brad Seibel. "Metabolic trait diversity shapes marine biogeography." Nature 585.7826 (2020): 557-562. www.nature.com...
Elmer, Kathryn R., and Axel Meyer. "Sympatric speciation without borders?." (2010): 1991-1993. pubmed.ncbi.nl...
Hendry, Andrew P. "Ecological speciation! Or the lack thereof?." Canadian Journal of Fisheries and Aquatic Sciences 66.8 (2009): 1383-1398. cdnsciencepub....
McCune, A. R., and N. R. Lovejoy. 1998. The relative rate of sympatric and allopatric speciation in fishes. Pp. 172-185 in D. J. Howard and S. H. Berlocher, eds. Endless forms: species and speciation. Oxford Univ. Press, New York, NY. www.google.com...
McDermott, Amy. "Inner Workings: Reeling in answers to the “freshwater fish paradox”." Proceedings of the National Academy of Sciences 118.36 (2021). www.pnas.org/c...
McGee, Matthew D., et al. "The ecological and genomic basis of explosive adaptive radiation." Nature 586.7827 (2020): 75-79. www.nature.com...
Miller, Elizabeth Christina. "Comparing diversification rates in lakes, rivers, and the sea." Evolution 75.8 (2021): 2055-2073. onlinelibrary....
Seehausen, Ole, and Catherine E. Wagner. "Speciation in freshwater fishes." Annual review of ecology, evolution, and systematics 45 (2014): 621-651. www.aqua.iee.u...
Seehausen, Ole. "Process and pattern in cichlid radiations-inferences for understanding unusually high rates of evolutionary diversification." New Phytologist 207.2 (2015): 304-312. nph.onlinelibr...

[@MinuteEarth]

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[@j-core2895]

first to comment

[@samueltrusik3251]

All of the ocean fish drowned in the great flood from the bible, but the freshwater ones didn`t.

[@lonestarr1490]

@@samueltrusik3251 Pah, the bible! Never will I believe that a man as old as Moses can hold the water that long.

[@niklasd3668]

@@j-core2895 /;. ẞẞ।

[@minute-ai]

@MinuteEarth I add 1!

[@rugvedkulkarni1593]

One question I have: does this paradox apply only to fish or all aquatic species? I would imagine a coral reefs has much more diversity of invertebrates than any lake. If so could invertebrates be taking ecological niches filled by fish in freshwater environments?

[@Infernoraptor]

This is a good point! Plus, if we look at the size of the body of water instead of just salinity, how does that skew things? I mean, just because Lake Tanganyika and Lake Baikal are fresh water, doesn't mean they aren't more ecologically akin to oceans than most rivers or shallower lakes.

[@nickcosimano5028]

This is an amazing point and I would like to know if the numbers do change.

[@PloverTechOfficial]

Very good question.

[@thetobyntr9540]

I think water hardness and acidity seem like important factors for that, since the ocean has a lot of stuff dissolved in it that freshwater being fed mainly by rain is going to be deficient in (to explain acidity, I've heard some streams are really acidic, but I only know of people saying it's a problem for crustaceans in reference to ocean acidification). Intermittent availability of minerals in fresh or brackish water makes bones useful batteries for calcium and phosphate as modern bony fish partially use them, we even metabolize our bones when we have calcium deficiencies, though bone-tooth skin coverings seem to have started in the oceans. Bony fish just seem better tuned for freshwater from the perspective of adaptation since crustaceans have weaker armor if they don't use a lot of minerals, and using a lot means the animal is vulnerable to periods of low nutrients from downpours while it gets the material for the new skin. They're really effective at being plankton sized in freshwater and everywhere else more than fish have been though.

[@linusyootasteisking]

@@thetobyntr9540 are you saying that the innovator of bones was a freshwater fish? i would've assumed oceanic but i don't know. freshwater habitats are a hell of a lot older than bones so quite possible.

[@NotSoDaftGamecraft]

Having kept both I would say that it's the variable conditions in freshwater (seasonal run-off, evaporative chemistry etc) and oceanic conditions are much more stable (hence coral die-off from minute calcium changes) leaving freshwater fish more resilient, and better able to weather environmental changes thus leading over time to more freshwater diversity.

[@fejfo6559]

I don't find this counter intuitive at all. I wouldn't expect more water to automatically give rise to more species. Each species has to fill it's own ecological niche and I don't expect there to be more niches if you just have more of the same environment. What I would expect is that the species in oceans are "more evolved"/better adapted since there is more space for benificial mutations to happen

[@silversurfer8818]

I would say they are less evolved, because they are adapted to a static habitat where no variation exists. There would be no reason to evolve into something, when all abiotic factors remain the same both spatially and temporally.

[@fejfo6559]

@@silversurfer8818 Good point, "more evolved" wasn't the right way to put it. I meant something like "their fitness is closer to a local maximum because they had more opportunities to take a convergence step".

[@HughOBrien]

Also, the deep water is less habitable than the shallow areas near the coast, so measuring habitable area versus water volume may make more sense.

[@skundaihoy]

Couldn't agree more. The equation starts looking a whole lot simpler when you look at how many rivers and lakes there are versus the number of oceans. There are just so many more variations in the environment when you compare rivers and lakes rather than oceans.

[@destroyercrush1052]

skundaihoy 👊

[@captaincrypto8960]

Alternative theory: it’s actually scaled. (Pun intended) there really is a lot more fish in the ocean than the rivers. We just haven’t discovered most of them. Reasons being, it’s much much easier to explore rivers and lakes than oceans. In a River the individual fish is more unique and noticeable so it’s easier to track them. In an ocean one fish is easier to mistake for another, even in different species, making the illusion of less fish. Its also probable that it’s a combination of all these theories that cause this

[@thesqrtofwhy758]

Freshwater Fish are not more unique and noticeable though. Have you ever tried to identify a minnow species?

[@lechking941]

@@thesqrtofwhy758 the point i think the fellow is trying to make is space differances.

[@ericolens3]

My idea is not to say fresh vs salt but to compare Inland bodies of water vs open bodies of water. Also where do brackish species fall? Since they can technically inhabit both? Seas, gulfs, and oceans are open bodies. And obviously rivers, lakes, streams are open bodies. To me there are more "fresh" or inland species due to more inland species can interact with the fish. In the ocean fish swim (run away from) fish. In the streams, EVERYTHING is out to get you. I mean yeah there are exceptions like aquatic mammals and diving birds. But in-land bodies of water means that any bird can swoop down, any mammal can dive in, any reptile can tolerate the non-frigid waters of and in-land body of water. As such the need to adapt is even higher. There are a few ways to adapt in the ocean but the in-land waters have so much more variables. You cant deep dive like you could in the ocean, you can evolve to adapt to frigid temps to avoid the reptiles, you cant grow super large like you could in the ocean. The rules for adapting are more constrained. Yes there is PLANT LIFE due to less salinity as such thats a key stone species. Then river naturally have BEAVERS, another keystone species, so theres so much more competition from every frontier. The ocean had its protections that in land bodies of water cant provide.

[@Predated2]

I think you're ignoring the vast scale of where freshwater fish can be. There are cave systems, filled with fresh water, that we have been unable to explore due to limitations. Exploration devices need to be small and flexible enough to manouvre through a lot of odd gaps, while the device needs a cable attached due to wireless transmission being blocked/interfered with the sheer amount of rocks and minerals between places. Thats not considering small ponds or marshlands where there can be any fish hiding between mosses, under sand, between twigs, looking extremely similar to another already identified species, or simply being transparent. I mean, just look at how many different new species of bugs are discovered on a yearly basis. And how many of these new species look extremely similar to already known species or how difficult they are to find. Thats humans actively being able to get up close to either catch a specimen or to take a sample for DNA testing. Thats not even considering that while freshwater and saltwater fish are very seperate habitats right now, they werent always that seperated. Its not unlikely for a lot of rivers and lakes to have been salt water, and since coast lines are to this day a huge source of biodiversity, its not unlikely that a majority of these fish followed salt water and went into the lands, and then were slowly forced to adapt to water containing less and less minerals. Since this could mean that a lot of aquatic biodiversity went land inwards, millions of years ago and that the biodiversity we see out there today is artificially lowered due to that migration too. There are a LOT of reasons why we cant narrow it down, and it is probably multiple of those reasons combined. Lakes, rivers and ponds have a lot more diverse environments overall, but the ocean would have more room for artificial diversity through more fish sharing the same environment. A mudskipper doesnt have to fear the interference of a goldfish for example, but a seabass does have to fear the interference of the eel.

[@martinkasse1932]

I would also suggest, that’s because of the fact that in a smaller habitat, there is more competition which always is the motor of evolution. To be successful the individuals have to come up with different strategies to sustain them self. Also, in the Oceans there is a bigger variety of size, there are big mammals like Whales, Dolphins and also bigger fish like Sharks. We know that bigger animals have a bigger need of territory which leads to less animals per space unit. Also, they have a slower reproduction time, I think. Both effects add up to lower reproduction rate and therefore fewer times a mutation could appear. I think a big factor is also that in fresh water there’s a bigger variety than in salt water in terms of the habitat. On the one hand we have swamps, lakes, rivers etc. and on the other hand we have the ocean (and some lakes of cause but they often end up so salty no fish can survive at all in it). This makes more different challenges for fresh water fishes which have to adapt to it in different ways. So yeah, there are a lot of different things that add up to this effect. Correct me if my logic fails at some points

[@dundee6402]

Not to mention the climate affects rivers and lakes far more than the ocean! A lake in Northern Europe would be a totally different environment from a river in the Amazons.

[@martinkasse1932]

@@dundee6402 Yes you are right! the ocean woud never freeze shut!

[@kilominum]

he literally brought up that fact and debunked it

[@DBT1007]

Again, YOUR OPINION THERE ALREADY COVERED IN THIS VIDEO. This video also talk about ISOLATIONISM. But... Man.. Just watch the video again. I dont need to explain it again

[@martinkasse1932]

@@DBT1007 you clearly dont get my points, they named some of the Ideas I was talking about in the Video but didn't explain them really andalso not everything I mentioned. So this comment has its right to exist as it's providing new information

[@RicardoMorenoAlmeida]

Thank you for having the courage to say that, as of now, we don't know! It seems that many people are really uncomfortable with "we don't know"! We need more of this as "we don't know" is the driving force of MORE science!!!

[@Struhsie]

I appreciate all of the small Pokémon references in your videos!

[@skeepodoop5197]

Maybe it's just easier to monitor rivers than oceans, due to far less area? Meaning there could very well be far more ocean species we have no idea about?

[@quintinbassett9467]

I can’t remember the specifics, but when counting fish or species of fish it’s often more statistics than anything. Instead of counting every species we can find we instead create as accurate a model as possible and we guess to fill in the gaps. Assuming we actually have a good understanding of ocean ecology these kinds of models give us a general idea of both how much we do and how much we don’t know. Your point still stands, but it is something that people are aware of and try to work around.

[@ncuco]

Most land animals drink fresh water to survive, so I'd assume the transition from sea to land happened in a fresh water environment. Which could help explain the diversity paradox! Living in fresh water is more energy efficient. Consequently, this can allow for faster rates of speciation when competing for new ecological niches that appear after each extinction. Also can explain why lakes have less species, as it being a closed environment, it'll have a smaller amount of ecosystems to emerge after any given extinction. Smaller amount of niches to compete for.

[@CarlosE213]

Excellent, that's how science works, perfect example of how science left to different options and discuss itself watching for a better explanations.

[@Luxalpa]

Freshwater, particularly rivers have way more niches for life to find, as they span different biomes, temperatures, minerals, etc. The ever changing rivers allow for very different compositions and environments, there's a much more diverse amount of predators (bird, mammals, lizards, insects, etc) and plants because all the land-based animal and plant species interact with it. More niches allow more species to co-exist at the same time. Coasts on the other hand are mostly the same in most places. Lakes are too small and too static to give serious competition between the species that would require tight niches; they'd cause species to be stuck on local optima for quite a while.

[@jasonreed7522]

I wouldn't say lakes are too small to have many niches, even small lakes can be over 100ft deep which creates more of a vertical separation than a horizontal one. Granted a lake with a long diameter of 2 miles is not going to have as diverse of environments as a river starting life as a mountain pond/marsh and running over 200 miles to the ocean through mountains, hills, forrests, plains and even cities.

[@hairymcnipples]

This is exactly my thought. Freshwater habitats - and especially non-lacustrine habitats - are incredibly heterogeneous and diverse! So many unique niches to fill. Add in that they are also often very isolated and not only do you have a lot of niches to fill, you often have a different species filling each niche in different systems. Coming from Australia where basically everything is highly diverse for exactly these reasons the fish paradox just doesn't seem that odd to me I guess? I'm only a 2nd year undergrad so if this is the state of the science I'll have to defer to those better equipped but even if the numbers are odd the cause just seems pretty obvious from my perspective.

[@SofaKingShit]

Pretty smart of you. My brian isn't so good.

[@nevermind824]

There's more energy available in the rivers. More light hits the bottom, more minerals in the water, plant life means more variability

[@thePronto]

Maybe the answer lies in analyzing the difference between (mostly) land locked seas (Black, Caspian, Baltic, Red, Mediterranean) and open oceans.

[@cyruskhalvati]

Divergent evolution relies upon two or more populations of a species being for one reason or another unable to mate with eachother, and eventually over millions of years becoming their own unique species. One major driving force behind divergent evolution is physical separation, which is nonexistent in the ocean.

[@georgplaz]

Its so refreshing to see your videos where you roughly show the scientific dialog and also were things are unexplained. its just so much more interesting and authentic than these overly polished stories about how science just knows it all

[@RipleySawzen]

I would say the varied environments of the rivers allow for more niches. It could also be that oceans, which have more species overall, have more niches filled by other animals.

[@sarcasmo57]

Today's fish is trout à la carte. Enjoy your meal.

[@trstmeimadctr]

My hypothesis is that since rivers are liminal ecosystems separating muiltople bodies of water over large distances that means that at least some part of their population will always be insulated from negative environmental factors that push forward evolution in other parts of the population. Therefore there many more opportunities for branching from the same node in an evolutionary line. I hope I was able to convey what I'm thinking very well

[@everythingigothere1304]

The solution to the paradox is simple it’s a lot easier to discover fish species in small lakes and rivers then the humongous ocean

[@drewmur]

This is a great example that you have to look at all the details, not look at one statistic and make a conclusion

[@ridleycombs]

...first? wow I feel like it's 2008

[@MinuteEarth]

You're the first! So old school... - Ever

[@Dragrath1]

Interesting one thing which could potentially be related to this is the evidence that the ancestor of all extant cyanobacteria particularly including the lineage which gave rise to chloroplasts were or still are freshwater specialists with the oldest extant pelagic cyanobacteria dating to the Neoproterozoic suggesting the first colonized the open ocean around the same time as the first Eukaryotic algae. That said as the evidence for cyanobacteria goes back much further than the last common ancestor of extant cyanobacteria it is likely a bit more complicated (especially since the timing for the last common ancestor of Cyanobacteria matches up fairy closely with the Sudbury impact Additionally the closest archaeal relatives to Eukaryotes are also being found from metagenomic sampling of shallow estuaries freshwater environments or soil building up the case that complex life as we know it likely originated on or around the continents back in the paleoproterozoic. If this is the case it is possible that there is just been more time for freshwater speciation relative to marine speciation. Of course fish are pretty recent in evolutionary terms compare to all this but the fossil record does support the first fish being relatively limited to shallow lagoons and estuaries potentially only colonizing the open waters during the Devonian so maybe a continent first model could work there too?

[@arcosprey4811]

I feel like there’s far more niches in freshwater ecosystems. Whereas the ocean is one big ecosystem, freshwater has rivers and lakes and ponds and wetlands that each are near forests, or near grasslands, or near deserts or near the ocean. Many opportunities for niche partitioning.

[@olwiz]

I think a big missing comparison, related to isolation, is the less diverse (and less isolated) qualities of the ocean. Theres plenty of diversity in enviroment, temperature, local flora but by comparison waaay less then lakes and rivers where pretty much each one can count as its own biome with nuances. That lesser number of variety+lack of borders make it so winning species spread more and any changes in the enviroment affect much larger populations at once- all contributing effects to more extinctions. Another missing aspect on the video i think is some quota between new species rate and 'thrive'(how long they last). I feel the oceans are like globalized markets- early capitalism had extreme variety and plenty of oportunities for new ventures, but as companies grow more sucessfull they buy out the competition, stiffle newcommers... similarly a new species variant in the ocean have to face a very fit and sucessfull species with huge population; Unless theyre extra more fit or really lucky id say '9 out of 10' they will disapear waaay earlier then they likely would in different conditions I think a great example is invasive species in freshwater- we have LOTS of cases where invasive fish(introduced by humans) became dominant driving local species to extinction, i think carps being one of the infamous invasive species. Both invader and native are freshwater fish yet naturally such 'super fit' species become local from isolation... Well, given how the ocean is... imagine ALL 'invasive' species going everywhere. Thats the ocean id say. Heck the more i think about it the more it makes sense- the Ocean is SO HARSHER it PUSHED species to freshwater, any that could doing so would thrive... pushing the EVOLUTIONARY MOVEMENT from early sea lifeforms to land species. Compared to land rivers are also harsher, if you need to look for better waters you could be out of luck while on land migration is much easier. Land on the other hand is similar to the sea in some aspect but much different- you cant travel as fast or easily and biomes vary much more... on the sea any species that unlocks 'good/fast swimming' can theoretically travel around the globe, so the most fit dominating happen. In a comparison humans, even if we werent so much smarter, if we were dumber but still adaptive would be like an ocean species- capable of spreading 'everywhere' in their enviroment and so we did.

[@iTrapa]

Maybe ocean is just simply a harder environment, like a higher level area in videogames. Only most optimized fish species are able to compete and flourish in the ocean, while the safer environment of freshwater area allows some obscure build to thrive? Basically, difficulty setting.

[@timbalmer3840]

I like how the last hairstyle was Misty the water pokemon gym leader to go with the theme. Not to sound less intellectual than everyone else's comments 😜 Great questions and theories everyone!

[@stewiex]

1. The environment for fish in fresh water is constantly changing from flooding, rainy seasons and dry seasons for example. 2. There are a lot more predators to escape from when you're in rivers or ponds that are easily accessible from shorelines. I think it's clear that fresh water fish have to be more adaptable to survive. A fish in the ocean that is being stalked by a predator at the shore line needs only to swim to deeper water.

[@jimpinkowski3394]

It may simply be that the relative constancy of the ocean environment does not favor evolutionary change as much as the typical fresh water environment with drastic seasonal changes in temperature oxygenation, food supply, etc.

[@joshuacook2]

There are more niches in rivers because its a complex habitat, and isolation makes it harder for one species to dominate the same niche between different rivers. Each niche tends to be denominated by one species, more niches in more isolated environments means more species. Of course, more scale also creates new niches, but at a much slower rate, hence oceans having about the same number of species despite its huge advantage in size. And this is of course assuming we aren't undercounting deep ocean species, etc, etc.

[@toms169]

I found the numbers at the beginning quite odd. Initially, the statement is that

[@helxis]

"Wait and see" is a depressing end to a video that raises such a curiosity. Don't encourage people to "wait and see". Encourage people to go out and discover.

[@bradleon1926]

There is also the fact we are only accounting the species we've discovered. There could be plenty of undiscovered species we don't know about in the ocean.

[@skaramicke]

Why would anyone assume that the 50% of fish species we’ve seen in the ocean is anywhere close to the total amount of species in the ocean?

[@tobymax10]

Maybe it’s because freshwater fish get extra food from the land like flies and worms and even dead seagulls. There are also more plants along the sides of rivers whereas the ocean can support plants. All of this could help freshwater fish live long enough to reproduce and eventually lead to more longer living species. Just my thought on this

[@dinkusstinkus4396]

It's worth considering how relatively unexplored the ocean is too

[@SalreixVonOtsuu]

1:22 "both pop out new species at *similar rates* " 1:45 "lakes have the perfect combination of all those things and pump out new species up to *five times faster* so which is it

[@kankawabata3398]

Does the salinity of their environment have any effect? I know for example that freshwater fish have more parasite, higher/lower level of different minerals, etc. Maybe one of these factors make diversification more advantageous.

[@potatoheadpokemario1931]

How can you tell if a fossil lived in freshwater or saltwater?

[@Typhyr]

It’s less counterintuitive then it seems when you factor in that the ocean permits a lot larger individuals like whales or whalesharks who feed on larger groups animals like krill or schools of fish. The prey they feed on then need larger numbers for the species to survive, leaving less biomass left for new species to arise.

[@ClaimingKarma]

My guess is fresh water rivers just have more diverse environments that allow many different species survive but they wouldn't call it a paradox if it was that simple

[@thomasolson7447]

Rivers often go for hundreds of km's, maybe even thousands in some cases. A duck will take an issolated species of fish eggs and drop the fertilized eggs in the river. The fish eggs could hatch and might even make it to reproduction.

[@chadleach6009]

Id be interested to find out how fish species separate between areas with strong ocean currents and those without hardly any. I'm thinking that perhaps the ability of nutrients to flow throughout the environment is key, allowing for species to more easily survive in these areas. Lakes and rivers will get runoff from the surrounding land that are full with many elements simply not found commonly found at sea but are vital for life. Another issue might simply be the size, the ocean is so much bigger that what available nutrients there are would be spread out that much further. With lakes and streams smaller sizes they would be able to concentrate these elements where life could much more easily take advantage of them.

[@KungFooActionJesus]

My bet is on food types and source. All animals, us included, adapt to our environment based on available food. With lakes and rivers being close enough to land to account for more insect, amphibians, and even mammal life it makes sense that species would adapt to hunt more or specific prey found in those areas. The ocean is diverse but also very empty. Most of the species in the ocean follow specific currents or flock to specific areas of the ocean limiting their food supply to mostly each other meaning adapting in the ocean would typically make similar traits advantageous. So I think it could be a matter stagnation in exponential growth. While rivers and Lakes had the advantage of diverse food and thus an explosion of new species was to be expected I think it's reached it's bubble point where it's starting to get more familiar throughout the evolution of species diets or rather the food is similar enough for long enough that rivers explosive increase in diversity has settled into the steady pace the ocean has. Just a theory though.

[@Francis-ce1qb]

The ocean is large, has currents and a whole lot of other factors , maybe researching and cataloging fish in the ocean is just that much harder.

[@Timmering]

Love your videos.

[@Great_Olaf5]

Is it possible there's something about freshwater that impacts the bottom of the food chain in such a way as to increase their abundance without harming things higher up in the chain? If the producers are more abundant for any reason, and because of the tighter spaces are more concentrated, that means more energy available up though the whole chain, and that increased energy availability, regardless of nutrient availability (kind of, water is still important, but these are lakes we're talking about) lends itself to greater competition and diversity. Tropical rainforests are extremely energy dense, and despite their dearth of nutrients are notable as the most diverse areas on earth.

[@BuckFieri]

I’m wondering it’s the fact that the ocean is relatively homogenous in composition where lakes can be vastly different

[@foysalkhan4214]

It's mostly because we haven't done that indepth research in the ocean compared to the size of the entire world's ocean. It's very difficult to search every square inch at a depth of a thousand meters

[@yodaiam1000]

I thought that they were going to talk about the variations in water chemistry in freshwater. Ocean water is more consistent in its chemistry. Fresh water varies substantially in PH, hardness, turbidity, nutrients etc. There also seems to be more variation in environments in fresh water. Soft sand, mud, river rock, fast flow, slow flow, temperatures, ice formation. You would think that the more variation in environment, the more variations in species you need to survive.

1:21 Because there's more fish on the ocean, no? So it balances

[@louibeale2387]

I think this has much more to do with how little we actually know about what's in the ocean

Man this video has so many twists and turns. It definitely is a river

[@strings1984]

Brine... The transition between fresh and salt causes extra niches as well as forced mutation to transition... Might help with nailing down some of the complicated reasons this disparity exists... Like you said it's complicated.

[@LuizaVarela-i4j]

it seems pretty obvious to me that the number of biologists discovering species in rivers and lakes is also much higher than biologists doing so in the ocean, at least proportionally. that's probably why, i think

[@FranklyNorman]

Everybody else: MaYbE tHiS hApPeNeD 🤓 Me: Lol “wait and SEA” 🥴

[@gnebulon]

What if we just haven't explored the ocean as well because the rivers and lakes are near where we live and are easier for us to explore?

[@groundedhippo9356]

Sounds like it could be an interesting topic for microbial ecologists

[@cardinalthewarden888]

Well the hostility of oceans is that the species are made at similar rates but die off more in seas

[@Asak999]

Could be because of other predators? wouldn't lakes and rivers have others predators beyond other fishes? perhaps rivers have a more complex food system that generates a more dynamic adaption.

[@TheOGSpartanNinja]

What about all the fishing that’s occurred in the ocean. Aren’t the number of fish at sea like 1% from a hundred years ago, which were itself 1% from a hundred years earlier?

[@darcash1738]

Seems more like an anomaly than a paradox

[@daviddempsay4930]

It is much easier for humans to explore lakes, streams and rivers than it is for humans to explore the vast oceans. Therefore, in comparing the number of freshwater species of fish to the number of ocean species of fish, some allowance must be made for the considerable possibility that there are many more as yet undiscovered species of fish in the oceans than there are in freshwater.

[@ahetzel9054]

Is it fair to point out that there could be a lot of undiscovered species that exist in the ocean, we just haven't discovered them yet? So the paradox is only a paradox because of our limited knowledge? I'm not a scientist so idk if this is a valid point but I feel like no one has mentioned it thus far.

[@pawelabrams]

Those migrations might also play a role - if the adaptation to fresh water is easier than to higher salinity, it would also skew the numbers.

[@alexanderx33]

The devs just wanted freshwater and saltwater fishermen to have equal variety so they would be equally happy.

[@NeinDao]

2:50 if we could explain it, would it still be a paradox?

[@eeveefan987]

I love your Pokemon references!

[@cgm778]

Or maybe it's easier to find and classify species in lakes and rivers because they closer to us than it is in the oceans where whales and sharks live but no human calls home.

[@ValStinks]

lmao I was immediately like "well cuz isolation leads to differentation duh" and was just about to close the video when he said that's not actually the leading theory

[@gearhead1302]

In each lake you can have a different species to fill the same ecological niche = lots of species in fresh water.

[@edoardocherubin6783]

no one talking about how the oceans have truly still been little explored? 'we have explored the lunar surface more than the depths of our oceans' who knows how many other species have yet to be discovered

[@StefKomGeekru]

No paradox, the answer is simple. The condition for new species is based on initial species over time. It is not about the size of their area, nor about the possible dangerous environments. They all have dangerous environments, they all have food. The amount of initial copies of species won't make a significant difference because the variants in a species are developed based on the set of possibilities with in their DNA, not based on how many there are. If you have green and red species, regardless of how much green and red you have, the only colors you make are between red and green, that including yellow, but there is no blue, and there will be no blue. The species also tied by the number of offspring, which since fishes in the ocean and the freshwater are of the same origin, they had the same initial spread thus making the same number of offspring that adapted to their space, but remain constant with the number of variants they develop. Unless a new species has a mutation to mutate more rapidly, their rate will be same. It is not the environment, nor the size of the environment, nor the amount of food, nor the quality of food. Unless one environment compleately erradicates a species, the results will be the same, but in most cases the extinsion of species is not tied to environmental causes, but about their environmental competitors, the whole natural selection, which is proportional to their population size. I'm sorry if this sounds confusing, in the simplest terms as I said, it is based on initial settings over time. The condition that counts is the species themselves. Genetics are not changed by food or disasters, they can be filtered, but not changed, the change is with in, so, it should be equal species if they start with the same number and have had the same time.

[@Kirhean]

I'd have thought it's a matter of available niches. Rivers provide a wide range of possible niches due to having a wide range of conditions even along a single river, lakes and the oceans do not lack variety, but just can't measure up to the sheer volume of available niches. Particularly since rivers, by their nature, have more interaction with terrestrial animals and plants than the ocean does.

[@Chris.Davies]

Ocean life way more dangerous than lake life. I don't know how I can make it any simpler for you.

[@wknight8111]

It's easier to find a mate in the relatively small confines of a river or lake especially if the mating population of your species is relatively small. Large mating populations are going to have an easier time finding each other in the ocean. Likewise there's not enough space in a single river or ocean for a single population to grow too large, but several smaller species may thrive if they can settle into non-overlapping niches and draw from different sources of food.

[@jankrnac3535]

Is weird that rivers would have less extinction, literally anything can wipe whole river. Can come more predators or something like the landslide gets dirty water, algaes can be toxic and get extinction of plants fishes eating ... While in the ocean this things also can happen but it is much bigger place, events must be much bigger to make same extinction as in the river.

[@lool8421]

maybe it could be the fact that it's harder to evolve to live in ocean water because of the amount of salt ocean fish constantly have to spend energy on drinking and separating water from salt, because the salt in the environment keeps sucking out the water, and the less energy you have at disposal, the harder it is to find a better build to survive

[@kevinkane1405]

Evolution is a non random phenomenon. There are reasons for this and I believe it’s a combination of all your explanations

[@futairimasu]

it's like the ocean isn't even trying

[@thibs2837]

Very interesting thanks !

[@willyreeves319]

given how we see invasive species wipe out established ecosystems and that without humans moving them around it's far easier to travel across an ocean than between river systems or lakes (for fish) it seems a likely candidate. also, it's most likely a combination of a few factors

[@salomonhernandez792]

Maybe because more animals are hunting them in Rivers and lakes like birds and bears and in other to pass their genes they make more kids.

[@MxMstrStve]

Well, it's pretty easy... Lakes, rivers etc are formed by oceans. Each time the ocean raises and lowers (yes it happens all the time) new fish get trapped inland and turn into fresh water species. Lake Titicaca has freshwater seahorses. Many African lakes contain very salty water. Science just likes to be pedantic about this type of stuff.

[@wihatmi5510]

Maybe as much new species emoerge in the ocean but there are only so many ecologic niches for animals so there can never be too many species at any given time like in rivers where most of them never met. For me the question seems to be easy to answer.

[@ericolens3]

Doesnt speciation happen more likely when environmental pressures occur. Oceans are somewhat a temperature buffer. I live in Louisiana and from what i learned south Louisiana has less temperature fluctuations than northern Louisiana. Comparing Shreveport to lake Charles (i dont have the stats so sadly its only amecdotal but IT CAN BE VERIFIED) But basically the thermal fluctuations of oceanic species can be a bit less ranged. The shark and some oceanic fish have kept their morphology for even millions of years. Yet inland bodies of water have more opportunities to have diversity. Burrowing into coastal bodies is not the same as Burrowing on the ocean floor. There's more of an arms race when you factor in land based and semi aquatic wildlife. Oceanic animals are mostly fish. (I might be wrong but ocean and fish go hand in hand) But rivers and other inland bodies of water can provide homes for land animals. Like beavers, and all the biodiversity that can come from that keystone species. Fresh water is just inherently better suited for so much biodiversity if not for its lower salinity content then for its hydration that other animals can easily drink. Ironically now im curious if beach animals drink ocean water then just pee out the excess salinity. Or do they go inland to find a fresh water creek? Circling back. Fresh water just has a better bio mass support system due to being an in-land body of water. So that terrestrial animals also play a part in fish needing to evolve. What would an archer fish do to a bug that isn't even on land? The Archer fish's gimmick is that he can eat land bugs by sniping them. What would a mudskipper do without land. (Im not sure if these are fresh water fish or not, but the LAND aspect of in-land bodies of water has more variables in the need for adaption. Land based animals, water based animals, and semi aquatic animals all live on this frontier. Even most human societies were built on a good river source, so its naturally more likely to have more biodiversity. As such a greater need for adaption. The ocean has a few rules to survive 1) get super big 2) be very invisible And some others But any one trick you try to come up with in an in-land body of water. There will always be a counter part to nullify that adaption. Platypus dont even need to see due to electro reception and several other fish have that ability too in the amazon river. All in all, i cant give any single answer. But inland water just has a higher level of competition and the easy tricks of the ocean just dont work there. There too many animals who can nullify pretty much any niche. I think the salmon were smart to use predator satiation. And live in dual environments to ensure safety for their young.

[@bijoychandraroy]

"wait and sea" i sea what you did there

[@LCCWPresents]

To be fair the ocean is mostly unexplored by scientists, so while this is a paradox it could change with further exploration. Though great video.

[@andrewkvk1707]

There's probably more undiscovered species in the oceans than rivers as well.

[@larryeaton4263]

Really it's very simple. Fresh water is divided up into thousands of isolated ponds, lakes, river systems, etc. This allows species to evolve differently in each system if it's isolated long enough. For an extreme example, cave fish. However this isolation is not true for salt water. There are very few isolated saltwater systems. In large oceans fish migrate and have to compete with other species, so evolution doesn't offer as many natural possibilities.

[@neelroy2918]

Everytime narrator said "freshwater fish species" i could almost hear him making a mistake but recovering _just before_ that mistake. If you dont believe me , try saying "freshwater fish species" 10 times in a row.

[@avideosomeday3913]

When I hear paradox I expect some confusion. But in this case there is no confusion, and that make me confused. I guess that is what I expect from paradox..

[@David-lp3qy]

There are probably more niches available in rivers than in oceans because of the differences in environmental dynamics or whateva

[@iancowan3527]

Technically... You sort of answered the question within the video... Ocean would have Larger species and Apex predators that reduce whole environments before they die off! And the ponds and rivers produce species but don't cross over enough to survive dry seasons where animals eat the dead fish! Which is why fossil records are much harder to find.

[@NotABadBear]

has the simple answer not been considered that its easier for a fish to transition from ocean species to freshwater than it is for freshwater to sea

[@jhibbert6627]

Well qouting a certain former sailor that makes spaceship videos "Salt water HATES EVERYTHING"

[@orionphalynx6192]

Check out Tier Zoo. It's neat.

[@holechek]

Fish be messin round that’s all

[@ericjones9487]

Gosh, it's like natural process are not all or nothing and a combination of factors makes up the existing world.

[@Vearru]

My instinct on this was the oceans don’t have as many species as we’d expect because the successful ones are simply able to be successfully over a much greater area. Sure the ocean is huge but if the ecosystems and species range for fish in the ocean is just as huge we should only expect enough species to where the niches in those ecosystems can be filled and do to greater travel range the same fish can fill a niche in many different parts of the ocean at the same time.

[@Andosier]

Interesting how there are underlying assumptions made, that don't hold up when any verification is done. Each iteration of research is based on evolution as being the answer and the fundamentals don't seem to be questioned.