I disagree with Anjman I read these as meaning the same thing and all are fine. If there could be any difference, it would be only in a very formal, logical context. The third say absolutely that he doesn't eat meat AND he doesn't eat fish. The first one could mean that or it could mean he doesn't eat one of them. The second one could mean the same as the first or emphasize that either he doesn't eat meat OR he doesn't eat fish. I highly doubt the question is this technical so consider them to mean the same thing.

Yes they do. The first and third sentences are correct but the second sentence is incorrect. One of the correct ways to write it would be. Meat or fish. He doesn't eat either. Hope that helps! :)