STUDIES ON BIOLOGICAL CHARACTERISTICS AND CHANGE OF RESOURCE OF COILIA NASUS SCHLEGEL IN THE LOWER REACHES OF THE YANGTZE RIVER

Studies on biological characteristics,change of catch per boat and maximal sustaining yield(MSY) of Coilia nasus schlegel in the lower reaches of the Yangtze River were carried out during the period from 1993 to 2002.The result showed that average body-length and body-weight were 29.19 cm and 94.33 g in fishing season.The correlative equation between bodylength and body-weight could be expressed as Y= 0.004 8X~2.906 9 and the coefficient of fullness was 0.379.The average value of absolute fecundity and relative fecundity were 23 695 eggs/fish and 229 eggs/g body weight respectively,and the diameter of matured egg was 0.77 mm.The correlative equationY= 0.017 2X~4.101 might be used between absolute fecundity and body-length and it was Y= 305X-5 410.1 for absolute fecundity and body-weight.Most of the fish were two years old in fishing season.The average value of the total catch per boat was 393.14 kg.Average annual catch was 891.51 t and MSY evaluated by model of Schaefer was 2 061.81 t in the lower reaches of the Yangtze River.Compared with historical data,the miniaturization of the fish was evident and the community age structure tended to be onefold and low-aged,at the same time,the resource of C.nasus had decreased significantly.