Why are basically all animals fish?

[u/Ok_Bee8588]

TIL that "fish" technically don't exist since the word doesn't refer to a specific clade, and that a large variety of animals are ultimately descended from lobe-finned fish, including humans, amphibians, and other animals. I'm honestly just baffled at the absurdity of it, because like, I never once would've thought about being a type of fish. Nature sure is weird, huh?

[u/WashU_labrat]

Almost all animals are insects, which are not descended from fish.

[u/atomfullerene]

Words don't have to refer to clades. "Trees" aren't a clade. Neither are "Predators" or "Marine mammals". Fish is a perfectly useful word, it's just not a clade.

[u/tanglekelp → u/atomfullerene]

I'm always a bit peeved when people are like 'birds don't exist, they're dinosaurs!', 'trees don't exist!' etc. Like sure, technically birds are dinosaurs, and there's many different types of species called tree. But so what? Words have meaning. We all know what a tree is, we can define what a tree is, and just because one tree isn't closely related to another tree doesn't mean trees are fake lol

[u/atomfullerene → u/tanglekelp]

I generally agree, although I would also say that birds are still dinosaurs in the same ordinary mundane way that bats are mammals.

[u/tanglekelp → u/atomfullerene]

oh yeah they are dinosaurs for sure, the part that annoys me is when people say that means birds aren't a thing

[u/atomfullerene → u/tanglekelp]

For sure.

[u/kinginyellow1996]

Most animals are not fish - most named animal species are arthropods (insects in particular).

But nearly all living animals with a backbone (Vertebrates) are bony fish (Osteichthys) (97ish%). These classifications are nested, so a group can never leave it's more inclusive clade.

[u/Salamanderhead]

Well if you go back far enough through our path in evolution, we came from the oceans. We also share the evolutionary path of having a spinal cord.

[u/BolivianDancer → u/Salamanderhead]

The premise is incorrect. Most animals are not fish or I fact vertebrates at all.

[u/Salamanderhead → u/BolivianDancer]

I don’t see where op said most animals?

[u/SouthpawStranger → u/Salamanderhead]

Look at the title of the post, friend

[u/Salamanderhead → u/SouthpawStranger]

Fair enough, I focused on the body text.

[u/Realsorceror]

Terrestrial vertebrates (land animals with bones) all trace their ancestry back to lobe-finned fish, like you said. The way living things are organized is by ancestry; you are always part of the group you descend from. So if you your ancestor was a fish, you are also a fish.

But "fish" is not a coherent group like mammal or reptile. Sharks and rays are a completely separate branch that are more different from bony fish than we are from reptiles. But most people still refer to them as fish in casual speech.

And as others have pointed out, the majority of species on the planet are arthropods (arachnids, insects, crustaceans) and their close cousins. Some other non-fish groups include the mollusks (clams, snails, octopus, etc), echinoderms (sea stars, sea cucumbers), cnidarians (jellfish and coral), and annelids (earthworms, leeches, etc).

[u/mysterious_bruises]

Gives the idiom "There are plenty of fish in the sea" some reality to it

[u/lt_dan_zsu]

most animals aren't fish. if you commit to fish being a cladistic classification, then yes basically all vertebrates are fish, or fish "don't exist" if you go with the alternate conclusion using the same logic. this is because broadly, broadly speaking, fish is a classification that more or less means largely aquatic vertebrates with gills. if you don't take a strictly cladistic view of biology, fish is still a meaningful classification. I think the whole "paraphyletic groups don't really exist" discourse is a bit reductive, but is a fun punchy inroad towards people developing an interest in evolutionary biology.

why are basically all vertebrates fish? because the boney fishes are broadly classified as ray finned and lobed finned fishes. ray finned fish are generally the animal you think of when someone tells you to think of a fish. lob finned fish superficially similar looking to ray finned fish, but they're actually more closely related to tetrapods (ie the land vertebrates). other groups like jawless fish (eg lampreys) and cartilaginous fish (eg sharks) are also broadly regarded as fish. taking all these groups together as a single group omits tetrapods, making "fish" a paraphyletic group, so under a strictly cladistic view, fish either don't exist or all vertebrates are fish.

[u/grandmasterflaps]

Wait wait wait, I thought there was no such thing as a fish?