POPULATION CHANGE OF CULTER ALBURNUS IN XINGKAI LAKE

Our investigation showed that the natural population composition of Culter alburnus showed apparent variation in Xingkai Lake in recent years.In 1982,about 56% of fishing output was mature adults(4—11 years).But,in 1998,the proportion of 4—11 year-old fish was reduced dramatically to 12.8% and the adult fish could be captured only in the first ten-days of May.Meanwhile,about 38.7% of captured fish were 1-year young fish.Small young individuals increased and their growth became slow.The variation of growth can be described as following growth equations and body equations. The growth model of Culter alburnus in Xingkai Lake. 1982: L=103.1567 (1-e-0.1173(t+1.36826)) W=13266.1252 (1-e-0.1173(t+1.36826))2.9974 where L is body length (25.02—80.67cm) W is body weight (0.189—6.20kg) t is age (1—11 year-old.) 1998: L=105.3910 (1-e-0.1262(t+0.597065)) W=15049.8555 (1-e-0.1262(t+0.597065))3.10611 where L is body length (19.23—80.99cm) W is body weight (0.076—6.64kg) t is age (1—11 year-old) The relationship between body weight and body length of Culter alburnus in Xingkai Lake. 1982:W=0.01223L2.99743(r=0.9757,n=226,F=2495.93>F0.01(1,225)=6.82) 1998:W=0.007843L3.10611(r=0.9764,n=258,F=5224.17>F0.01(1,257)=6.74) The female Culter alburnus matures at 5 years old in Xingkai Lake.It lays floating eggs and the breeding date is about from the last ten-days of June to the middle ten-days of July.Mature adults migrate to spawning field in breeding season and spawn when continual wind and wave appears.Xingkai Lake is a boundary lake between China and Russia.On the side of China,Baiyutan beach was once the spawning field.But the breeding stock of Culter alburnus was not found from 1998 to 2002.