A small omnivore fish (Acheilognathus macropterus) reduces both growth and biomass of submerged macrophytes: implications for shallow lake restoration

Transplantation of submerged macrophytes has been widely used to improve water quality in restoring shallow lakes in China. However, in some lakes, small omnivorous fish predominated the fish assemblages and fed mainly on submerged macrophytes. Despite significant research examining grazing selectivity in herbivorous fishes, macrophyte feeding preferences of small omnivorous fishes are poorly understood. We conducted a mesocosm experiment to examine the effects of a prolific small omnivorous bitterling fishAcheilognathus macropteruson the relative growth rate (RGR) and biomass of submerged macrophytes (Ceratophyllum demersum, Myriophyllum spicatum, Vallisneria denseserrulata,andHydrillaverticillata). Our results showed that the presence ofA. macropterussignificantly increased nutrient concentrations (e.g.total nitrogen and total phosphorus). The RGR ofC. demersumin the bitterling-present treatment was significantly lower than the controls, in the presence of other macrophyte species. Further, total biomass of the four species of macrophytes in the fish-present mesocosms was markedly lower than in the fish-absent treatment, suggesting considerable consumption of macrophytes by bitterling. Moreover, the percent biomass ofV.denserrulataandH. verticillatawere significantly enhanced by the presence of bitterling. Our findings suggest thatA. macropterusmay increase nutrient concentrations through excretion and reduce the biomass and RGR of certain submerged macrophytes which may shift macrophyte community structure via selective grazing.