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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To learn more about this topic, start your googling with these keywords:
- 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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CREDITS
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Julián Gustavo Gómez | Script Writer and Narrator
Henry Reich | Director
Lizah van der Aart | Illustration, Video Editing and Animation
Aldo de Vos | Music

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REFERENCES
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Thank you to Dr. Elizabeth Miller for lending their time and expertise to this video.

[rugvedkulkarni]

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?

[EricLopushansky]

Is it also possible that we have just discovered a comparatively smaller percent of ocean species? It's a lot easier to find freshwater species. One you can wade to, the other requires fishing lines, nets, or scuba gear.

[StephenRoseDuo]

I'm pretty sure biologists don't know the definition of paradox

[Dracon]

this man sounds like he's constantly about to drop into a kermit impression

[jaycie]

The common factor with every option you proposed is the fact that the ocean is 1 habitat but every river or lake is it's own. A single Tuna can range a third of the world. Not so with a lake trout.

[captaincrypto]

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

[fejfo]

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

[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.

[julianaquascaped]

Easily one of my favorite video topics to have researched! Especially learning the wildly rapid speciation of African rift lake cichlids. 🤯

[TenorCantusFirmus]

As a fishkeeper, it's amazing to see how overlooked actually is by laymen the huge biodiversity of lakes and rivers - When setting up a freshwater aquarium, the variety of fish of any size, colour, shape and biological niche is absolutely stunning.

[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!!!

[martinkasse]

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

[Struhsie]

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

[skeepodoop]

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?

[patsk]

Rivers would have the most oxygenated water, among other things. But even if that somehow doesn't matter, it sounds like the problem was the initial premise.

[ComicalRealm]

Fun fact: Nearly 97% of the world’s water is salty or otherwise undrinkable. Another 2% is locked in ice caps and glaciers. That leaves just 1% for all of humanity’s needs — all its agricultural, residential, manufacturing, community, and personal needs.

[CarlosE]

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

[Commenter]

I watched a video by _Real Science_ called _Why Hybrid Animals May Take Over the North._ At around the 11:00 mark they were discussing how the hybridization of fish dramatically increases the rate of speciation.

[sphinxtheeminx]

I love the sea but it terrifies me - and I suspect that creatures feel the bad vibes, too. All that emptiness carries a resonance of fear that stops exploration.

[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.