because theres a tribal war

It depends on the type of fish and which tribe it is from. It can mean anything from being very fertile, to being a brave warrior.

Well, in the tribal stage there should be a fish icon on the map, nearby the water. That's where you may fish. It's better if you get the fishing spears, too.

I think they eat deer,fish,fruit,corn,squash and beans

By law; both by Treaty and Classical Federal Court ruling, no tribal member has to purchase a license to hunt or fish on tribal lands (or lands under tribal jurisdiction). However the State of Oklahoma is refusing to recognize these Federal Laws or their related treaties (so a legal battle is likely to ensue).