The Luos generally seem to live along the river nile - and it's major tributeries - they definitely learnt to eat fish - in addition to main activity that most sudane/nilotes did - mostly agro-pastoralism. I think most nilotes wont touch fish considering same class with snakes. I think Dinka-Luo branch initially speared fish before they started to build canoes & learnt to catch smaller fish etc.
What seperate the shilluk Luos with Uganda-Kenya-sudan Acholo-Luos is the large SUDD swamp that was lybranith that made it almost impossible to cross except on few times - like heavy flooding - that washed away the overgrowth making it passable.
The Sudd also prevented the Arabs from coming down - it's huge swamp - about 200Km wide & long - and impossible to navigate without getting lost forever. I think it was only the British later with more navigational device that evenutally conquered it and help Sudan colonize South Sudan.
It's amazing how scattered they are. These folks are essentially the same tribe, but find themselves all over the place. It's like finding Kikuyus in Ruwenzori and their closest cousins somewhere in Baringo. I wonder why they ended up scattered like that. Is it documented anywhere? I have heard of Muslim raids in Sudan, but what about Uganda?