In teleost fishes, 11-ketotestosterone (11KT) is a critical androgen regulating primary and secondary sex characteristics. In the sexually dimorphic Lythrurus fasciolaris (Cyprinidae), dominant nuptial males display heavy tuberculation on the head and nape, dark dorsolateral vertical bars, and dramatic red coloration in the fins, venter, and operculum area. This study aimed to quantify 11KT circulating levels in males and females, and determine any correlation with key male reproductive status indicators such as nuptial coloration, size, and gonadosomatic index (GSI). Thirty-one wild-caught L. fasciolaris were divided into three groups according to reproductive status: dominant males (D), non-dominant males (ND), and females (F). Physical measurements, digital imaging, and blood samples were used to quantify body size, GSI, nuptial coloration, and 11KT circulating levels. Dominant males had higher 11KT levels and nuptial coloration traits compared to ND males and females (red area, hue, saturation), and a higher GSI than ND males. Non-dominant males had more 11KT and coloration than females. Increased 11KT levels corresponded to increased coloration, size and GSI.