Impacts of A Herbivorous Fish, Campostoma Anomalum (Central Stoneroller), on Nitrogen Fixation by Benthic Algae

Herbivorous fish negatively impact algal biomass and promote the growth of cyanobacteria. In nutrient poor conditions that sustain high levels of productivity nitrogen fixing cyanobacteria can supply up to 28% of the available nitrogen (Higgins et al. 2001) We investigated the role of grazing fish in sustaining high levels of productivity in nutrient poor conditions. We used the grazing minnow, Campostoma anomalum, and the acetylene reduction technique in a controlled environment to analyze rates of nitrogen fixation and primary production by the periphyton. Fish grazing reduced algal biomass and promoted the growth of cyanobacteria but had no impact on overall rates of primary production and nitrogen fixation. Previous research on the impact of fish grazing on nitrogen fixation is minimal but contradicts our results, showing a need for future studies (Wilkinson and Sammarco 1983)