Karyological evidence for a cryptic species of piranha within Serrasalmus rhombeus (Characidae, Serrasalminae) in the Amazon

Abstract

Cytogenetic data obtained for Serrasalmus rhombeus revealed two cytotypes (cyto type 1 and cytotype 2) at four sampling sites. Cytotype 1 consists of 2n = 60, 20M + 24SM + 6ST + 10A and was detected in specimens from Negro River (Anavilhanas Islands), Solimões River (Camaleão Lake), confluence of Negro and Solimōes Rivers (Catalão Lake), and Uatumā River. Cytotype 2 consists of 2n = 58, 22M + 24SM + 2ST+10A and was detected in specimens from Catalão and Camaleão 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 Catalāo and Camaleão Lakes, and no intermediates between the cytotypes were detected, suggesting each cytotype represents a different fish species.