I study the origins, interrelationships, and conservation of freshwater fishes, with an emphasis on the fishes of eastern North America and tropical South America. Freshwater ecosystems occupy less than one percent of Earth's surface, yet are essential to human well-being and the persistence of most other species with which we share our planet. Unfortunately, freshwater biodiversity is disappearing several times faster than terrestrial or marine biodiversity due to human activities that disproportionately impact streams, rivers, and lakes. Still, conservation is hindered by the vast number of freshwater species that remain unnamed or poorly known to science, with knowledge gaps especially prevalent in the tropics. My research seeks to better delineate and identify species, understand how and what they eat, and map where they occur in nature and the evolutionary tree of life. Natural history museums are the foundation for this research. My work helps improve and expand these libraries of life through the collection and taxonomic identification of specimens, genetic samples, and photographs. To date, I have conducted over 25 expeditions to 11 countries in the Americas and Africa, yielding over 15,000 specimen lots and 10,000 genetic samples. This work regularly yields the discovery and description of new fish and invertebrate species, new insights into the ecology and evolutionary origins of threatened fish assemblages, and baseline data needed to help businesses, governments, and NGOs develop conservation strategies.