What is "rivulus"

n. found in small streams of tropical America; often kept in aquariums; usually hermaphroditic

Rivulus is a genus of freshwater fish in the Rivulidae family of Cyprinodontiformes. It was formerly considered to be the largest genus in its family; however, the genus's size is currently in dispute. Wilson J. E. Costa split this genus into several new genera (including Anablepsoides, Atlantirivulus, Cynodonichthys, and Laimosemion) in 2011 leaving only a few species left in Rivulus itself. A year later, J.H. Huber released a second paper refuting the proposed split, placing the above genera back in Rivulus and again making the genus the largest in the family Rivulidae. Members of Rivulus and its disputed sister taxa are sometimes kept as aquarium fish.