Study on Algal Control Effects of Different Fish Combinations in Changkeng Reservoir

CHEN Haopeng; XIE Jinxiong; LIN Ying; LIN Junkai; FU Xiaojing; LIN Kaite; YIN Chengjie

doi:10.19672/j.cnki.1003-6504.1826.24.338

Abstract：Phytoplankton overgrowth due to eutrophication in lakes(reservoirs)is one of the most serious problems facing freshwater ecosystems at present,and biological manipulation is considered to be an effective nature-based method to control algal overgrowth.A field mesocosm simulation experiment was established in Changkeng Reservoir to study the effects of different fish assemblage patterns on nutrient,phytoplankton densities and biomass in the experimental water body were observed and recorded.The results showed that different fish combination modes had no significant effect on TN and TP of the water body in the reservoir area,while the effects were more obvious on dissolved oxygen and chlorophyll a concentration,which were mainly reflected that the combination mode of silver carp and small-sized fish could significantly increase the dissolved oxygen concentration and decrease the concentration of chlorophyll a.Further analysis revealed that there were significant differences in the control effects on phytoplankton density and biomass between different fish combination pat-terns.Among them,the algal biomass of cyanobacteria,diatoms,and green algae in the combination of silver carp and small omnivorous fish was significantly reduced(P＜0.05),while the densities of cyanobacteria and diatoms were slightly increased,which probably suggests that the fish combination pattern effectively reduced the densities and biomasses of large-sized phytoplankton in the reservoir,and led to the miniaturization of the phytoplankton.Additionally,it was found that algal densi-ty and biomass increased significantly in the treatment group with only small omnivorous fish,mainly in algal abundance of Cyanobacteria,as well as algal biomass of Bacillariophyta and Pyrrophyta at the end of the experiment(P＜0.05),which may be due to the fact that the excess of small omnivorous fish enhances the predation pressure on zooplankton and attenuates its top-down effect.Therefore,when restoring or managing the water bodies in the reservoir area,the ecological regulation of small-sized fishes' population should be carried out at the same time of carrying out filter-feeding fish breeding and releasing,which in turn has an important role and significance in mitigating the outbreak of algal blooms in the reservoir.