THE BUDGET OF DISSOLVED OXYGEN IN HIGH DENSITY PONDS MAINLY STOCKED WITH CTENOPHARYNGODON IDELLA

To increase the efficiency of dissolved oxygen (DO) management in high density ponds mainly stocked with grass carp (Ctenopharyngodon idella), the present research aimed to characterize the budget of dissolved oxygen in nine fish ponds in Zhongshan, Guangdong province, China. The water depth was 1.5-2.0 m. Photosynthesis of phytoplankton and water respiration rate (WR) were determined by the clear and dark bottles method. The sediment respiration rate (SR) was measured by in situ respirometry. The fish respiration rate was determined by the respiratory chamber method. The mechanical aeration was calculated by predicting models. Atmosphere diffusion was estimated by the subtraction method. The results showed the gross oxygen production (GOP) of photosynthesis showed a decreasing trend as the water depth increased, and the value in the bottom was negative, which was the common oxygen debt phenomenon. There was no significant difference between the WR under the surface, middle layer and bottom (P0.05). The GOP of photosynthesis in the surface was significantly higher than the WR (P0.05), but the GOP of photosynthesis was significantly lower than the WR both in the middle layer and in the bottom (P0.05). The photosynthesis of phytoplankton and the mechanical aeration were the main contributors to the total oxygen production in high density ponds mainly stocked with C. idella, which accounted for 44.7% and 42.3% of the total oxygen production, respectively, but the contribution of atmosphere diffusion was the lowest and accounted for 13.0%. Among the oxygen consuming factors, the WR was the largest oxygen consumer, which accounted for 45.9% of the total oxygen consumption of water column, followed by fish respiration rate which accounted for 45.0% of the total oxygen consumption, and the proportion of SR was the lowest which accounted for 9.1%.