Observations on the biology of Cichlasoma macracanthum (Jordan & Evermann, 1896) from the Chiquimulilla Channel, on the Pacific coast of Guatemala, were made from March to August 1980. Stomach contents suggest that this species is a benthic omnivore. The principal food items were plant and animal detritus and secondarily fishes, crustacea, macrophytes and insects. Size fluctuated between 70 and 189 mm TL with three age groups for males and females.