5. Conclusions
This study demonstrated, via a 7-year monitoring program, the influence of dredging operations on the fish assemblage structure in a farm pond. Before dredging, extensive aquatic macrophyte stands covered the pond, dissolved oxygen levels were low and only two Cobitidae species, which have a tolerance to hypoxic conditions, were recorded. Conversely, after dredging, the number of fish species increased with increasing dissolved oxygen levels, and a significant change to the cyprinid assemblage was also observed. Although aquatic macrophytes are thought to contribute to fish species richness, our results suggest that excessive vegetation growth can have a negative impact on fish assemblages. While fish are considered to have a major effect in lentic ecosystems, dredging operations, which are widely used to maintain the function of lakes and ponds, can significantly change the structure of pond-dwelling fish by altering the dissolved oxygen level.