Some of the species of "Brachyplatystoma" migrate long distances for reproduction. This is known in "B. vaillantii", "B. platynemum", and "B. rousseauxii", but data about the migratory habits of other species are scant. This migration is associated with white-water rivers, as black water does not contain enough food for migrating Pimelodids. Maturation is timed to the increase in river level. Migration begins as the river level begins to rise with the coming of the rainy season. "B. rousseauxii" has the longest reproductive migration of any freshwater fish; from the mouth of the Amazon, migration may stretch , a trip which may last five to six months, before they spawn in the western tributaries of the Amazon. It is hypothesized that "B. rousseauxii" is homing, that is, it will return to the tributary in which it was born. Before spawning, the stomachs of these fish are empty, due to high digestive efficiency.