So, there is a legitimate complaint here. It’s true that sailors in the ancient world had a legitimate reason to want a word in their language whose extension was {salmon, guppies, sharks, dolphins, ...}. (And modern scholars writing a translation for present-day English speakers might even translate that word as fish, because most members of that category are what we would call fish.) It indeed would not necessarily be helping the sailors to tell them that they need to exclude dolphins from the extension of that word, and instead include dolphins in the extension of their word for {monkeys, squirrels, horses ...}. Likewise, most modern biologists have little use for a word that groups dolphins and guppies together.
Ok, but salmon and guppies are more closely related to dolphins than sharks. Like I get where you are going with this, but “fish” is barely a natural category and it isn’t obviously more of one than all descendants of the last common ancestor of the actinopterygians. Even if you limit it to marine descendants it still lets you predict bone vs cartilaginous skeletal system.
Ok, but salmon and guppies are more closely related to dolphins than sharks. Like I get where you are going with this, but “fish” is barely a natural category and it isn’t obviously more of one than all descendants of the last common ancestor of the actinopterygians. Even if you limit it to marine descendants it still lets you predict bone vs cartilaginous skeletal system.