Effects Of Crucian Carp(Carassius Auratus)on Water Quality In Shallow Aquatic Ecosystems: An Experimental Mesocosm Study

The expansion of omnivorous fish is known to affect aquatic ecosystems,including the water transparency and the water quality.Mesocosm experiments were conducted to evaluate the effects of crucian carp(Carassius auratus)on water quality by comparing water field indicators(temperature,p H,dissolved oxygen,total dissolved solids,conductivity),nutrient concentrations in water(total nitrogen,total dissolved nitrogen,ammonia nitrogen,nitrate nitrogen,nitrite nitrogen,total phosphorus,total dissolved phosphorus,soluble reactive phosphorus),phytoplankton biomass(chlorophyll a),periphyton biomass(chlorophyll a),benthic algae biomass(chlorophyll a),total suspended solids(TSS),loss on ignition(LOI),light intensity on sediment surface and zooplankton abundance in the crucian carp treatments and the controls.Results showed that: relative to the controls,the presence of crucian carp caused a significant increase in total nitrogen(TN)in the water column by 44%,total phosphorus(TP)by 82%,and phytoplankton biomass by 142%,but crucian carp significantly decreased by 58% periphyton biomass,measured as chlorophyll a.Crucian carp also significantly increased the TSS concentration by 131% and significantly reduced the light intensity on the sediment surface by 141%.Thus,omnivorous fish deteriorates the water quality.Removal of omnivorous fish,such as crucian carp is likely to improve water quality in aquatic ecosystems by reducing the nutrient concentrations in water,inhibiting the growth of phytoplankton,decreasing TSS and improving water transparency.The results of this study are helpful for management and protection of aquatic ecosystems,especially the management of omnivorous fish.