AGE DETERMINATION AND POPULATION STRUCTURE OF SPAWNING CHINESE STURGEON (ACIPENSER SINENSIS GRAY)

Chinese sturgeon is a migratory fish. After the construction of the Gezhouba dam near Yichang, Hubei Province, in 1981, the mature individuals of this anadromous fish can no longer reach their original spawning grounds located in the upper reaches of the Changjiang River. As a result, they are accumulated in the river from just below the dam to the section near Shishou County. In order to investigate the structure of the spawning population of this fish, altogether 242 specimens were collected in 1981 and 1982. Age of each fish was determined through the sections of first ray of the pectoral fin and flate bone (cleithrum). Data concerning length, weight, sex and mature stage were also recorded. The relationship between the radious in the sections from middle part of the flate bone and the body-length is linear. The back-calculated length of corresponding age by applying the linear formula are given in tables 6 and 7.Among the spawners examined, the males were measured to be 180—220 cm in bodylength and mostly less than 150 kg in weight, while the females were larger, being 240—290 cm in body-length and over 160 kg in weight. The number of both sexes were nearly equal, being 114 males and 128 females.With the exception of some specimens of which ages are still undeterminable, the ages of the spawners were found to be 9—26 years (ca. 14 in average) for males, 14—33 years (ca. 22 in average) for females. The males attain sexual maturity at the age of 9—18 and the females, 14—26.Aspects concerning spawning periodicity of this fish are discussed as well.