Myloplus arnoldi

Myloplus arnoldi is a medium to large omnivorous fish of the family Serrasalmidae from South America, where it is found in the Amazon, Xingu and Tocantins River basins. It can grow to a length of 33 cm. They are also called the silver dollar and are one of the fish referred to as "silver dollars". These fish are capable of delivering serious bites to humans.

Etymology
The fish is named in honor of German aquarist Johann Paul Arnold (1869-1952), who donated the type specimens to the Zoological Museum of Berlin.