Length–weight and length–length relationships, gonadosomatic indices and size at first maturity of E ugerres mexicanus ( S teindachner, 1863) ( P ercoidei: G erreidae) from the U sumacinta R iver, M exico

Summary This study examines the length‐weight ( L ‐ W ) and length‐length ( L ‐ L ) relationships, gonadosomatic indices, and size at sexual maturity for individuals of the endemic Mexican mojarra, E ugerres mexicanus ( S teindachner, 1863) from the U sumacinta R iver B asin, T abasco, M exico. From A pril 2008 to J anuary 2010, 360 specimens were examined, including 151 (41.9%) male, 179 (49.7%) female and 30 unsexed (8.3%) individuals. Overall female:male ratio was 1.2 : 1. Gonadosomatic index ( GSI ) values indicate increased reproductive activity during F ebruary, with significant differences between males ( GSI  = 2.07) and females ( GSI  = 5.48). The mean size at first maturity ( L 50 ) was 17.3 cm TL for males and 20.5 cm TL for females.