They're blind and fat and they are insatiable. They will eat anything – guano, black worms, dead and decaying fish – and they will keep eating until all the food is gone. Unlike other fish, which eventually get full, these fat fish just keep going. They are Mexican cavefish, which adapted to living in the dark by losing their eyes – no need to see – and adapted to living in a place where food is only available twice a year when the river floods by getting as fat as possible. They also have a slow metabolism so they keep the fat on.