Knowledge about fish diversity in Isla de los Estados is relatively limited and outdated compared to the well-documented biodiversity of the nearby Isla Grande de Tierra del Fuego. This lack of data may lead to an underestimation of the number of species inhabiting this remote region of the southern Atlantic Ocean. This chapter reviews the fish species found in freshwater, coastal, and surrounding marine areas of Isla de los Estados. Research on the island’s freshwater fish diversity is scarce, with one native species identified to date. In contrast, 16 species have been recorded in coastal marine zones, some of which were described more than 120 years ago. Additionally, 25 species have been reported in the surrounding marine areas, with several species obtained from commercial fishing vessels. This study highlights the urgent need for new sampling efforts to produce a comprehensive checklist of fish biodiversity. An updated inventory, along with basic biological information, such as local distribution, reproduction patterns and interactions with other taxonomic groups, is essential for the development of effective conservation and management policies.