You'd have to think that the land hunters would have been the ones with both the incentive and the means to enforce a cultural taboo on fishing. They might not

You'd have to think that the land hunters would have been the ones with both the incentive and the means to enforce a cultural taboo on fishing. They might not want a whole other profession of people training with weapons all day. I could also imagine there might have been a time when there was a group who fished which where eventually wiped out. The non-fishing group may have demonized them so much that when they got rid of them, they just weren't able to overcome the view that fishing was inherently evil. This is, of course, just speculation.