I too have been thinking about making fishing arrows, but I was considering using cane or bamboo. These come in sufficient weights and lengths, and are generally more water resistant than wood shafts. As far as the points go, I have seen some awesome barbed bone fishing points, both online and in museume displays. As soon as I get the time, I am going to try carving some bone points. As far as fletchings go, I would think that they aren't entirely necessary. Modern fishing arrows don't have feathers, so I would think that an extra long, heavy, cane fishing arrow wouldn't need fletching either, especially if it is being shot into the water. Also, for primitive bowfishing, what would be used for a line? Or is a line even necessary? I suppose it depends on where you are doing your fishing. In some places a line might be needed, while in others it might not. I know Don Thomas goes bowfishing without a line in shallow water.
Just my thoughts on the matter. I have yet to actually attemp any of this.