Effects of Semaprochilodus kneri on benthic algae biomass of the Cinaruco River System

Jennifer Snider

Jose Montoya

Dr. Dan Roelke

Department of Wildlife and Fisheries Sciences

Texas A&M University

        Semaprochilodus kneri (Charachiformes: Prochilodontidae) is a detritivorous fish that feeds on the benthic algae and detritus in the Rio Cinaruco during the dry season and migrates to the Rio Orinoco when the water rises.  This highly migratory fish is believed to induce a trophic cascade in the Rio Cinaruco by creating a seasonal stress upon major primary producers (benthic algae).  This study used several experimental cages (1.control (OS), 2.total fish exclosure (TE), 3.large fish exclosure (LFE), and 4.Semaprochilodus kneri enclosure (SK, March only)) in both the floodplain lakes and the main river channel of the Rio Cinaruco to demonstrate the effect of Semaprochilodus kneri on the benthic algae biomass of the system.  The experiment was run in March, (low-water) and in May (rising-water) to demonstrate effects of the presence/absence of the Semaprochilodus kneri during different water levels on the benthic algae biomass.  Exclusion of the Semaprochilodus kneri (TE, LFE) in March resulted in significantly higher levels of benthic algae biomass than the enclosure (SK). May data expressed no significant difference between the experimental cages in either the river or floodplain lakes.  The study suggests that abundant non-migratory fishes do not significantly influence the benthic algae biomass, and that the Semaprochilodus kneri does significantly affect the abundance of benthic algae biomass during the low-water season. This information supports the theory that Semaprochilodus kneri causes a seasonal stress upon primary production in the Rio Cinaruco, possibly causing a trophic cascade.

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