Riverine characteristics dictate composition of fish assemblages and limitfisheries in reservoirs of the Upper Parana River basin

A qualitative comparative approach has been used to review whether fish ass emblage characteristics, such as paucity of lacustrine-adapted fish species , long food chains, and disproportionate number of piscivorous species, lim it fishery yields in reservoirs of the Upper Parana River basin. The paucit y of lacustrine-adapted species appears to limit fishery yields, but attemp ts to introduce lacustrine species have been generally unsuccessful. The fo od chains of species targeted by the fisheries are relatively long, but sho rt food chains seem to be an adaptation of lacustrine species. Because rese rvoirs with many piscivorous species sustain high fishery yields elsewhere in the world, the hypothesis that an excessive number of piscivores limits yields is not supported. Instead, inadequacies of fish assemblages in reser voirs of the Upper Parana River basin appear to be symptomatic of an unsuit able environment for lacustrine fish species. The physical characteristics of reservoirs in the Upper Parana River basin, exacerbated by climatic patt erns, may preclude the emergence of successful reservoir species from withi n the extant pool of riverine species. The resulting assemblages have chara cteristics that are neither riverine nor lacustrine, and are maladapted to support fisheries in the reservoirs. The introduction of lacustrine species is destined to failure because environmental characteristics are not lacus trine, except in reservoirs positioned high in the watershed, where increas ed retention times allow lacustrine conditions. Published in 2001 by John W iley & Sons Ltd.