"We eat fish steak."
Translation:Noi mâncăm friptură de pește.
Can you give an example of when it was marked wrong? Normally, you can safely omit it, but there might be situations when you need to specify it so that you can stress something. For example, there was a sentence here "They eat fish and we eat chicken"(or something alike). In this case you need to "ei" (they) and "noi" (we) because you are specifically making a point about who is eating what.