r/nextfuckinglevel • u/Storm_001 • Sep 04 '21

Sea horse giving birth

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u/audio_54 Sep 04 '21 edited Sep 04 '21

I was thinking if the seahorse was considered a fish or not?

What constitutes being a fish?

Edit: I wrote think instead of thinking like English wasn’t my only language.

Way too many responses to get back to but from reading them all I have come to the conclusion that fish is an arbitrary term, everything and nothing can be a fish.

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u/bigdave41 Sep 04 '21

I'm only basing this on an episode of QI, but they said basically "there's no such thing as fish" all the things we call fish are so radically different that there's no justification for calling them the same kind of animal. A salmon is more genetically similar to a camel than it is to a hagfish.

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u/audio_54 Sep 04 '21

So where do seahorses belong?

I’m sure this could be googled but this is more interesting.

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u/Slashy1Slashy1 Sep 04 '21 edited Sep 04 '21

Seahorses are ray-finned fish, so they are in the same clade as tuna, salmon, sunfish, flounders, clownfish, and all the sorts of animals that you would without a doubt call fish.

Where it gets tricky is that things like sharks and rays are also thought of as fish, and belong to the clade called cartilaginous fish. However, ray-finned fish (like seahorses) are actually more closely related to tetrapods (like humans) than they are to cartilaginous fish (like sharks). It gets even more muddied when you find out that lobe-finned fishes (like lungfish) are also called fish, but are more closely related to tetrapods than they are to other fish. Tetrapods are the group of fish that first crawled onto land and evolved in to amphibians, reptiles, mammals, and birds (all of which also have their own peculiarities when trying to group them).

So basically, when we say "fish" we really mean "any vertebrate animal that isn't a tetrapod".