From February 1993 through January 1994 a total of 890 individuals<span name="style_bold"> </span>of <span name="style_italic">Bairdiella ronchus</span><span name="style_bold"> </span>(Cuvier) were captured in the Ciénaga Grande de Santa Marta (CGSM). Most were caught with casting nets, using the "corral" (pen) artisan method. The fish sizes and weights varied between 66 and 231 mm total length (TL), and between 3.5-156.2 g respectively. The species is typically estuarine, distributed in salinities between 7.3 and 37.3. Female gonadosomatic index (GSI) was 2.97-5.09 (males: 0.32-1.09). The serial correlation method did not find a direct relationship between salinity and GSI. Mean eggs size was 198.65 µm, mean fecundity was 188 964 eggs/individual and is directly related to total length and total weight. The condition factor (K) presented an annual mean of 0.013, and its variation seems to be related to that of the GSI. Mean maturity size is 158 mm TL for females and around 154 mm TL for males. The sex rate was 2.7 females per male.(Cuvier) were captured in the Ciénaga Grande de Santa Marta (CGSM). Most were caught with casting nets, using the "corral" (pen) artisan method. The fish sizes and weights varied between 66 and 231 mm total length (TL), and between 3.5-156.2 g respectively. The species is typically estuarine, distributed in salinities between 7.3 and 37.3. Female gonadosomatic index (GSI) was 2.97-5.09 (males: 0.32-1.09). The serial correlation method did not find a direct relationship between salinity and GSI. Mean eggs size was 198.65 µm, mean fecundity was 188 964 eggs/individual and is directly related to total length and total weight. The condition factor (K) presented an annual mean of 0.013, and its variation seems to be related to that of the GSI. Mean maturity size is 158 mm TL for females and around 154 mm TL for males. The sex rate was 2.7 females per male.