It's 2019 can we please stop the stupid?

[arewethereyet]

I can swim in the sea, am I a fish??

Not the point. Huge difference between nomenclature and scientific classification.

Fish and mammals both swim in the ocean, but fish are always fish and mammals are always mammals.

If you have gills you are a fish, if you have a blowhole and lungs, you are a mammal, regardless of nomenclature.

Umm, no.

Both are referred to as dolphins.  Deal with it.

BTW - that difference isn't so different.
nomenclature
[ˈnōmənˌklāCHər]


NOUN

1. the devising or choosing of names for things, especially in a science or other discipline.
   "the Linnean system of zoological nomenclature" ·
   [more]
   
   • the body or system of names in a particular field.
     "the nomenclature of chemical compounds"
     
   • formal
     
     the term or terms applied to someone or something.