Nitrogen and phosphorus loading from fish cage culture in Zhelin Bay

This study assessed the sum,sources,and forms of nitrogen and phosphorus loading produced by cage-cultured fish in Zhelin Bay.The results showed that in 2006 fish cultured with the feed of trash fish produced 2 760.39 tons of nitrogen loading,which included uneaten nitrogen 1 695.24 tons-accounting for 61.4% of nitrogen loading,and 679.11 tons of phosphorus loading,441.36 tons of which were uneaten phosphorus,accounting for 65.0% of phosphorus loading.The analysis of the sources of uneaten food indicated that 768.62 tons nitrogen in the soft tissues of trash fish accounted for the largest proportion in the uneaten nitrogen,while 241.73 tons phosphorus in the bones of trash fish accounted for the largest proportion in the uneaten phosphorus.The amounts of different forms of nitrogen and phosphorus loading were estimated.Solid nitrogen,dissolved nitrogen,solid phosphorus,and dissolved phosphorus were 1 717.38,1 043.01,595.15,and 83.96 tons,respectively,accounting for 62.2% of ni-trogen loading,37.8% of nitrogen loading,87.6% of phosphorus loading,and 12.4% of phosphorus loading,re-spectively.