Ecology and Status of Piscivores in Guri, an Oligotrophic Tropical Reservoir Academic Article uri icon


  • Guri Reservoir in Venezuela supports sport fisheries for two cichlid species (pavn venado or speckled pavon Cichla temensis and pavn mariposa C. orinocensis) and payara Hydrolycus scomberoides. The lake receives acidic, hyperoligotrophic black waters from the Caron River and experiences water level fluctuations associated with seasonal precipitation and hydroelectric operations. During the early 1980s, piscivore populations expanded in the new reservoir, but the quality of sportfishing declined during the 1990s. During 199394, we studied the ecology of the two Cichla species, H. scomberoides, and a fourth piscivore, Plagioscion squamosissimus (curvinata or silver croaker) and compared our data with those from similar surveys performed 79 years earlier (02 years after attainment of the reservoir's current crest height). Seine and gill-net samples from the lake's northern region produced 50 fish species from 18 families. Seine samples were dominated by a small characid, Hemigrammus micropterus, whereas gill-net samples were dominated by a large detritivorous characiform, Prochilodus rubrotaeniatus. Gill-net catch rates were low in all three surveys. All four piscivores from our recent survey had better body condition than in a 19851986 study, an indication of possible growth compensation. Diet breadths of all piscivores were low, and diet overlap was low for H. scomberoides with the two Cichla species and for P. squamosissimus with C. orinocensis. Hydrolycus scomberoides and C. temensis consumed significantly larger prey than P. squamosissimus, and differences in the relative proportions of specific characid and cichlid fishes consumed by the two Cichla species indicate that they forage at different depths within the littoral zone. The combined effects of hyperoligotrophic waters entering the reservoir, reduced inputs of dissolved nutrients from submerged terrestrial vegetation, low retention time of the reservoir, and harvest probably influence the low abundance of the two Cichla species in Guri Reservoir. 1998 American Fisheries Society.

published proceedings

  • North American Journal of Fisheries Management

author list (cited authors)

  • Williams, J. D., Winemiller, K. O., Taphorn, D. C., & Balbas, L.

citation count

  • 38

complete list of authors

  • Williams, John D||Winemiller, Kirk O||Taphorn, Donald C||Balbas, Luis

publication date

  • May 1998