Why Is Fish Not Considered A Meat?

It depends how you  define meat. The usual definition is that meat is the flesh of an animal used for food - in which case, fish is certainly meat. I have heard that it was originally classed as non-meat to get just around certain religious restrictions, which makes sense - or it might have arisen because fish generally tastes different from "typical" meat. Anyway, from a protein point of view it is meat all right.

Debates on this subject can get quite heated - you might like to see some comments here.