Louis Agassiz (1807–1873) was a young student at the University of Munich when Johann von Spix and Carl Friedrich von Martius returned from their expedition to Brazil. Among the many items and specimens the German naturalists brought back were fish. The methodology they had followed on their journey through what was then part of the Portuguese Empire was typical of naturalists in the field: They observed, collected, and in some cases classified. Then, back in Europe, they studied the amassed material. Their journey through the exuberant and unfamiliar natural environment had lasted three years (1817–1820). In this geographical and temporal context, the fish and marine species were rarities that few scientists could address with authority within the framework of European natural history. The observant naturalists were nonetheless able to classify species unknown in Europe while also learning about these species’ natural environments.