mercatoris
Mercatoris is a small, poorly known genus of freshwater fish that was first described in the late 19th century based on limited specimens collected in the basins of the Paraná River system in Brazil. The sole species that has been placed in this genus, Mercatoris sphaericus, is a slender, silvery fish that grows to a maximum length of approximately 12 cm. Morphologically, the fish is characterized by a long, streamlined body, a terminal mouth, and a distinctly compressed dorsal fin that runs almost to the tail. The caudal fin is forked, providing the fish with swift swimming capabilities adapted to moderately fast-moving streams.
Falco and colleagues originally proposed the genus to accommodate the species due to its unique combination
Despite the limited information, Mercatoris sphaericus is considered of potential conservation concern due to its restricted