A few years ago I was interested in making a primitive set for shooting alligator gars. Because of the razor sharp scales surrounding the gars body my weak link in the chain was cordage that would withstand the abuse. I found lots of primitive toggle type heads in my research, mostly from the seal and whale hunters. Their soft bodies weren't abrasive to the cordages, only brute strength.
A wooden toggle with a bone tip or a sharpened bone toggle will work with most fish.