During 1994, the catfish "chivo mapalé" (Cathorops spixii) was the second most abundant fishing resource in the "Ciénaga Grande de Santa Marta" and the "Complejo de Pajarales", the main lacustrine-estuarine system of Colombia. Using commercial catch statistics and fishing explorations, the population parameters were determined reproductive cycle, growth, mortality, yield and biomass per recruit. Mature individuals were present all year around with peaks of ripeness and spawning from June to August during periods of little rain and dry, respectively. The mean maturity size was estimated at 23 cm. The growth parameters of the Von Bertalanffy function were: Loo = 32.5 cm and K = 0.38 year1, with a growth performance index of 2.6. Total (Z), natural (M) and fishing (F) mortality rates were estimated as 2.83, 0.96 and 1.87 year1, respectively. The exploitation rate E = 0.66 indicates that the resource is overfished. Therefore it is recomended a fishery regulation by decreasing the mortality rate to F = 1.0 year1 and increasing the cath mean size to 23 cm.