it obviously depends on how you view it. Many religious groups have fasts where they say you can not eat 'meat' but you can eat fish, but others include fish in the sacrifice. Religious texts are also very old and the view's and meanings of things change over time.

If you pull out a currant dictionary the meaning of meat reads: 'The flesh of animals (esp. mammals) as food. (it says especially, which does not exclude other animals)
The meaning of fish reads: 'a vertebrate cold blooded animal with gills and fins living wholly in water. When i read those definitions a fish is an animal therefore fish is meat. I don't understand why vegetarians eat fish as they are living, breathing, they have a heart and a brain and muscles to function as land animals do, and recent studies show that it is most likely that fish do experience pain! Anyway it's obviously not a clear cut answer it all depends on your religion or just your personal belief.