We describe gonad development and spawning time and size at first sexual maturity of Graus nigra, at Northern Chile, using fish collected by spearing from July 1998 to July 1999. We used macroscopic characterization and histological sections to describe states of gonadic development and we calculated time of spawning, gonadosomatic index (IGS), gonad index (IG) and condition index (K). We estimated size at first maturity using relative increment of IGS and size at 50% maturity. We found that spawning occurs in spring and size of maturity for females was estimated to be between 39 and 41 cm (Lt) and for males between 42 and 49 cm (Lt), depending on the method of analyzis used.