Karyological Evidence for a Cryptic Species of Piranha within Serrasalmus rhombeus (Characidae, Serrasalminae) in the Amazon

Cytogenetic data obtained for Serrasalmus rhombeus revealed two cytotypes (cyto- type 1 and cytotype 2) at four sampling sites. Cytotype 1 consists of 2n 5 60, 20M 1 24SM 1 6ST 1 10A and was detected in specimens from Negro River (Anavil- hanas Islands), Solimoes River (Camaleao Lake), confluence of Negro and Solimoes Rivers (Catalao Lake), and UatumaRiver. Cytotype 2 consists of 2n 5 58, 22M 1 24SM 1 2ST110A and was detected in specimens from Catalao and Camaleao Lakes. In Cytotype 2, the first chromosome pair was almost twice the size of second pair, and the constitutive heterochromatin pattern of each cytotype is distinct. The two cytotypes occurred sympatrically at Catalao and Camaleao Lakes, and no inter- mediates between the cytotypes were detected, suggesting each cytotype represents a different fish species.