Ripsaw catfish

Ripsaw catfish, like many fish species, engage in an annual fish run known as the piracema.  At the onset of the dry season, they begin a massive migration upstream, over distances varying from 100 to 400 km.  The phenomenon is not yet fully understood, but one theory is that these displacements would allow for species dispersal as well as compensate for the gradual downstream movement of the fry.  Biologists fear that the building of hydroelectric dams in the Amazon basin will have a negative impact on migratory species.