It's foolish to assume that fish will have absolutely no impact on the economy. I've seen food items in the beta that are named after fish. I can say with some degree of certainty (speculation only of course) that fish will remain an ingredient in cooking, therefore there will still be a demand for fish in the markets.

As someone from another thread pointed out, I think that he was addressing it in terms of FFXI where you could catch fish and make decent money just vendoring them. That apparently won't be the case here.