The Scientific Explorations for Deep-Sea Fishes in Brazil: The Known Knowns, the Known Unknowns, and the Unknown Unknowns

The deep sea is the largest and one of the most extreme environments on Earth. It is estimated that 10–15% of all fish species are dwelling in the deep sea, most of which have unique morphological and physiological adaptations. Biological expeditions to sample the deep ocean off Brazil started with the British HMS Challenger Expedition (1872–1876), followed by a few fishery stations made by the German RV Ernst Haeckel (1966) and the North-American MIV Oregon II (1957–1975), the cruises of the French RVs Marion Dufresne (1987) and Thalassa (1999, 2000), the Brazilian RV Atlântico Sul (1996–1999), the FV Diadorim and FV Soloncy Moura (1996–2002), OSB Astro Garoupa (2003), and, more recently, the American RV Luke Thomas and Seward Johnson (2009, 2011), the French RV Antea (2015, 2017), and the Brazilian RV Alpha Crucis . A total of 712 species of deep-sea fishes were recorded, including five species of Myxini, six species of Holocephali, 81 species of Elasmobrachii, and 620 species of Actinopteri. As in other parts of the world, the Brazilian deep-sea ichthyofauna struggles under severe anthropogenic impacts caused by the commercial fishing, and the extraction of oil and gas. The deep ocean is a delicate environment and its recovery is considerably slower than an equivalent in shallow water habitat. Therefore, increasing the research efforts is needed to avoid that part of its diversity disappear without our accurate knowledge.