Ecology of Cichla (Cichlidae) in two blackwater rivers of southern Venezuela

We investigated the ecology of peacock cichlids (Cichla spp.), diurnal piscovores and important gamefishes, in the Rio Cinaruco (Rio Orinoco drainage of the southern Venezuelan Ilanos) during-the dry seasons of 1992-1993 and the Rio Pasimoni (Rio Negro-Amazonas drainage) during early 1993. In the Cinaruco, three Cichla species partitioned available habitats: C. intermedia near structure in primary river channel within or near swift current, C. orinocensis in shallow water along the shoreline of lagoons or slow channel reaches, and C. temensis in deeper waters along sandbanks and steeper rocky banks of lagoons and the river channel. During the dry season, C. orinocensis and C. temensis fed heavily on small characiform fishes, and C. intermedia consumed a variety of fishes, including loricariid catfishes. Only two peacock cichlids, C. orinocensis and C. temensis, were found in the Pasimoni, a more acidic and less seasonal ecosystem. These two species were larger in the Pasimoni compared with Cinaruco conspecifics; however, conspecifics from the two locations conformed to similar mass-length relationships. In both river systems, C. temensis were significantly larger than congeners, and C. temensis consumed larger prey than congeners in the Cinaruco. Examination of gonads and sizes of intraovarian oocytes indicated that reproduction by all five populations probably is initiated during the late low water period and mag continue into the flooding period.