Effects Of Acheilognathus Macropterus(Bitterling Fish) On Water Quality And Growth Of Submerged Macrophytes:Implications For Shallow Lake Restoration

Omnivorous fish are pervasive in warm waters and may have strong impacts on water quality by excreting nutrients and disturbing sediment.It may also inhibit submerged plant population growth through grazing.Removal of omnivorous fish and add mussel have been considered as an important manner in the restoration of shallow lakes mainly via re-establishing the submerged macrophytes community.However,mussels may also facilitate the population growth of small omnivorous bitterling fish?Rhodeinae?that they have to rely on mussels for reproduction.The role of these small omnivores on lake ecosystems were not,so far,well studied.In the present study,we conduct mesocosms experiments to examine?1?the effects of bitterling fish?Acheilognathus macropterus?on water quality?nutrients,suspended solids?,plankton and submerged plants,and?2?the interaction effects of bitterling and mussels?Anodonta woodiana?on nutrients and plankton communities.The main results are as follows:?1?Density-dependent effects of bitterling were found on nutrients and suspended solids.The concentrations of total nitrogen?TN?,total phosphorus?TP?,total suspended solids?TSS?in low bitterling density treatments(3.8 ind m^-2)were substantially enhanced 30%,11%,and 66.1%.The concentrations of TN,TP,TSS in high bitterling density treatments(7.6 ind m^-2)were substantially enhanced 73%,24%and 821%.However,these bitterling induced impacts were largely eliminated by the presence of mussels.Compared with high bitterling density treatments,the concentration of TSS and Chla in bitterling fish+mussels treatments were reduced by 52%and 81%.?2?Bitterling has weak or no effects on sediment resuspension,as indicated by the similarISS levels between the fish-absent and fish-present treatments,thus fish excretion is the main pathway enhancing the concentrations of nutrients and Chla concentrations which is different from that of other benthic omnivorous fish?e.g.,common carp and crucian carp?.?3?The presence of the bitterling inhibited the biomass of large zooplankton species,promoted the growth of cyanobacteria population,and enhanced the biomass increase of phytoplankton.Eventually,the biomass of phytoplankton in high bitterling density treatments increased to 10 times the control.However,the presence of mussels reduced the biomass of phytoplankton.?4?Submerged macrophytes were selectively grazed by bitterling.In our experiments,bitterling can directly feed on Vallisneria natans,Ceratophyllum demersum and Myriophyllum verticillatum,and showed a higher grazing preference on C.demersum and M.verticillatum.Reduced the total biomass of submerged macrophytes by 16%.Therefore,A.macropterus showed a negative impact on the water.It can increase nutrient concentration of the water column through excretion,especially at high density;It can feed on large size zooplankton,which lead to an increase in phytoplankton?e.g.cyanobacteria?;It can graze submerged macrophytes,affected the reconstruction of submerged macrophytes.The mussels can counteract the negative effect of bitterling fish on the water.When restoring lakes by stocking mussels,reproduction of a small number of bitterling fish has no obvious impact on the lake system.However,it's still necessary to pay attention on to and control the population of the omnivorous fish.