3. Results
Coverage of aquatic plants in the pond increased since the survey started in 2005 and the surface of the pond was almost totally covered by aquatic vegetation in the year before dredging (Fig. 1). Dissolved oxygen (DO) displayed relatively low values during 2007–2009 (i.e. before dredging) (Fig. 2), with the measured lowest value in 2009 of 4 mg/l. DO levels increased after dredging (Fig. 2), with a significant difference between before and after dredging operation (U-test, P < 0.05).
A total of eight fish species were recorded during the monitoring program (Table 1). Only two species of Cobitidae (Misgurnus anguillicaudatus and Cobitis biwae) were recorded immediately before dredging. Species of Cyprinidae and