we ordered 3 fish-es?

Fishes is rarely used; just say fish. The sentence is OK informally, but put a comma after Shanghai and one before the second and.

I think it should be 'When I was in Shanghai, my friends and I went to a restaurant and we ordered 3 fish.'

is there any better way to say it? I was always taught that fish is uncountable and it's so hard for me to say 3 fish

Perfect Stranger I was always taught that fish is uncountable

You were taught wrong. What is odd is ordering 'three fish' in a restaurant. We order a menu item, which never in my experience has read 'Three fish with tartar sauce', for instance. It would be natural to use something like this:

When I was in Shanghai, my friends and I went to a res

I don't disagree with anyone. I'd just like to mention that "fishes" is possible in special circumstances, like when one syllable is needed in a song:

Your love means more to me than
All the fishes swimming in the sea and
Like those fishes, my heart begins to swim be