I have eaten fish (and no other meat) on Good Friday my entire life. Will continue to do so until I sleep with the fishes.

I also don't eat Easter eggs until Easter Day and usually avoid hot cross buns until Good Friday.

I'm a stickler for a tradition.

Eta - the reason it is considered that fish isn't flesh/meat is that they are not 'carne' which, in Latin, means warm blooded, land mammal/bird. So, technically, using this definition, fish aren't meat. (Not saying that this is the case by other definitions).