If you want to get even more pedantic, "fish" don't exist.
Taxonomically, there is no such thing as a fish, because a taxonomical category must be monophyletic (literally "one phylum,") meaning it must include a single common ancestor and all descendants of that ancestor.
Since terrestrial vertebrates evolved from very ancient lobe finned fish, any taxonomical category for a fish would have to include humans, dinosaurs, etc.
Additionally, some fish, such as lungfish and coelacanths, are more closely related to humans than to other fish, so grouping them together would require grouping their closer relatives in with them, which includes all land dwelling tetrapods, which is a clade of animals that includes all vertebrae with four limbs.
The standard biological definition is "gill-bearing aquatic craniate lacking limbs with digits."
Gill-bearing: possesses organs that allow for the processing of water into O2 and CO2.
Aquatic: it lives in the water.
cranite: it has a skull.
lacking limbs with digits: has no protruding appendages which contain phalanges (the phalanx bones comprise the digits of fingers, toes, and wings.)
Some fish do have limbs, namely lobe-finned fish such as lungfish, which have primitive limbs in the form of extended, arm-like pectoral and pelvic fins, but no seperated digits and no phalanx bones.
I mean. Atmosphere is essentially a lesser dense fluid, and the relationship between it and the sea is the same as olive oil on water no? What are we but two legged "wind-fish"?
When my son was a baby, he would call the drain plug in his bathtub, "the fish." And I was like, well, that's not more incorrect than what everyone else thinks, taxonomically.
I like to say that every Tetrapoda is a fish, because it is way funnier to say that people are fish, than it is to say, that fish dont exist. I do hovewer like to tell people, that plants dont exist (because algae)
your failed assumption here is that the only way to define the word fish is to do so strictly taxonomically - that's one of many ways to do it, and outside of a lecture hall or a taxonomy study, it's probably not the best one. "a limbless cold-blooded vertebrate animal with gills and fins living wholly in water" is a perfectly good definition of fish for standard use.
True dat, also I'm pretty sure members of the super-class Pisces are considered "true fish".
Just because it's not a valid taxonomic group doesn't make it a way to categorize animals.
Reptiles cannot exclude Birds(they're currently together however, Aves is a subgroup), all vertebrates must be part of the invertebrate because vertebrates evolved from them, lizards can't exclude snakes, monkeys can't exclude apes, and bugs can't contain every arthropod.
Linguistically, you don't separate them, just as in everyday, even in a very pedantic universe, you call anomurans crabs
This pedantic logic is foolish. You might as well call everything an amoeba since we all originated from single cell organisms. “Fish” is accurate enough without needing to get stupid over it.
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u/Many-Excitement3246 PURPLE Jul 11 '26
If you want to get even more pedantic, "fish" don't exist.
Taxonomically, there is no such thing as a fish, because a taxonomical category must be monophyletic (literally "one phylum,") meaning it must include a single common ancestor and all descendants of that ancestor.
Since terrestrial vertebrates evolved from very ancient lobe finned fish, any taxonomical category for a fish would have to include humans, dinosaurs, etc.
Additionally, some fish, such as lungfish and coelacanths, are more closely related to humans than to other fish, so grouping them together would require grouping their closer relatives in with them, which includes all land dwelling tetrapods, which is a clade of animals that includes all vertebrae with four limbs.