Redescription of the Сommon but Poorly Known Piranha Dulce Serrasalmus hollandi (Serrasalmidae) from the Upper Madeira River

The piranha Serrasalmus hollandi was described in 1915 by Eigenmann based on a single specimen from the upper Madeira River basin in the southwestern Amazon and the holotype was later lost. Because morphological variation is absent from the description, species identification is somewhat difficult. Misidentification with S. eigenmanni, another poorly known but morphologically similar species, may have been common in ichthyological inventories. This last species was described in 1929 by Norman, based on a single specimen collected from the Essequibo River, which drains the Guyana Shield, northeast of the Amazon Basin. The present study redescribes S. hollandi, a species commonly known in the Iténez basin of Bolivia as piraña dulce, based on morphological and genetic (mtDNA-COI) information. A neotype was designated from the Paraguá River, a tributary of the Itenéz River which is close to the type locality. A diagnosis to differentiate among S. hollandi and species reported in the Bolivian Amazon and La Plata basins, and S. eigenmanni is presented.