We have=possess. Polish "mieć" does not have the 'eating' meaning.
In case you're interested, the literal translation of 'possess' is "posiadać", so "Posiadamy dobre ryby". Rather a strange thing to say, though.
So "We have good fish" (Isn't it almost always "We are having good fish" in this meaning?) gets translated simply as if it was "We are eating good fish", so "Jemy dobre ryby".
Jellei - (Isn't it almost always "We are having good fish" in this meaning?) In answer to your query, I'm quite sure that the answer is 'no'! You could say something like 'We are having good fish TONIGHT' (because the fish was bad yesterday ) but we don't generally use the present participle (-ing) when expressing possession. I can say 'I am having a good time' but 'a good time' is not something you possess. I'm sorry I can't explain the complexities of the English language as clearly as you express the complexities of the Polish language to us, but I hope that helps.
But that's what I meant, that if I express possession, I say "We have good fish", but English can also say "We are having good fish" and it means that we are eating them. "we are having" doesn't make much sense to a Polish person.
Hmmm, I guess that the last paragraph of my message is rather confusing... well, I believe that in theory you could use Present Simple "to have" in the 'eating' meaning, it's just a lot less common, right? And in Polish, "mieć" doesn't have anything to do with eating.