Translation:We do not eat fish.
Hi! Its more accurate that 'We are not eating fish' is '我们不在吃鱼'. For example, it can be that you and some friends are eating chicken now. Another person walks past and asks if thats fish you are having. And you reply 'we are not eating fish, we are eating chicken'. So its '我们不在吃鱼，我们在吃鸡'. As 'eating' is a verb, and 'are' is present tense, its kinda like 'not eating fish now' = '不在吃鱼', where the '在'is derived from '现在' meaning 'now', thus doing that action now. '在' is a little like '-ing' of english words that mean performing the action now, like playing (在玩), eating (在吃), calculating (在算). Its ok to use what you have answered too but its not as accurate, and depending on situation, it might put across another meaning.
Here, '我们不吃鱼' is as if you are telling another person that you do not eat fish. It could be telling a waiter that your table of people do not eat fish at all, or are just not ordering fish. It could also be telling others that you do not eat fish, with many reasons that can include dietary restrictions, preference, etc that can be further explained after that phrase.
Chinese is not easy to explain, hope this didn't confuse you further:/
* bú shì shíwù ;)
And if you care for additional information: 鱼们 is slightly debatable here. Firstly, the suffix 们 can usually only be used for people, not for animals or inanimate objects. However in the context of the movie fish are in fact people, so I think it should be acceptable to say 鱼们. Maybe a native speaker can comment on that^^
However, I still wouldn’t use 们 in this particular sentence because it usually tends to imply a definite noun (i.e. “the fish”, not just “fish”). So 鱼是朋友 (without 们) is better in this context. However from the point of view of sentence melody, a two-syllable word would indeed sound nicer than just 鱼. So I looked up how they actually translated it in the Chinese version of the movie and found: 鱼类是朋友，不是食物。 (鱼类 yúlèi literally means “fish being(s)”, parallel to 人类 “human being(s)”). So you were actually quite close, all but 类 and the missing 是 were exactly like the professional translation. Good work!