In 1962, offshore of Lwanika, a fishing village forty kilometres southeast of Jinja, Uganda, fisherman Lawrence Makhoha hauled a surprise into his canoe. It was a fish that he had never encountered in twenty years on the lake. He was surprised, then curious. What was this fish, and where had it come from? Was it dangerous, or was it safe to eat?l The fish was mputa, Nile perch (mbuta to Luos; Table 1), and Makhoha's experience was to be replayed hundreds oftimes around the shores of Lake Victoria.