STUDY ON AGE, GROWTH, REPRODUCTION AND THE STATUS OF RESOURCE DEVELOPMENT OF CULTER OXYCEPHALOIDES (KREYENBERG ET PAPPENHEIM) IN THE XIAO RIVER

Culter oxycephaloides (Kreyenberg et Pappenheim), which belongs to genus Culter, subfamily Cultrinae, family Cyprinidae, order Cypriniformes. They are a unique species in China and mainly live in the rivers and lakes of the Yangtze River Basin. Due to the impoundment of the Three Gorges Reservoir, the ecosystem of the upper Yangtze River basin especially the tributaries of the Three Gorges Reservoir has been profoundly changed. The Xiao River is an important tributary of the Three Gorges Reservoir, and the habitat of a variety of organisms especially fishes. According to the data collected in 2013, some sections of the Xiao River have become major spawning grounds of Culter oxycephaloides. Hence it is critical to investigate the age structure and the growth characteristics of Culter oxycephaloides, in order to better manage and protect this fish resource. In April-July and October-December of 2013, we collected 1741 individuals from the Xiao River of the Three Gorges Reservoir and conducted the fish biology and ecology study. Our 245 samples could be divided into 5 age groups, and 23 year-old individuals accounted for 78.75% of the total samples. The relationship between the body length (L) and the body weight (W) could be fitted as W = 0.000007L3.10 (R2=0.9, N=789). The Von Bertalanffy growth function was Lt=519.631-e-0.22(t+0.12),Wt=1806.08 1-e-0.22(t+0.12)3.10. The growth inflexion point of the body weight was 5.02 years, and the corresponding body length was 348 mm and the body weight was 558.8 g. The absolute fecundities ranged between 20382 and 88430 eggs per fish, and the relative fecundities were between 54 and 161 eggs/g. The eggs of mature females were 0.030.14 cm in diameter, with an average of 0.11 cm. Based on the frequency distribution plot of egg diameters, we deduced that the development of oocytes in the ovaries of Culter oxycephaloides was in a successive process and the female could spawn twice within a reproductive period. We compared the coefficients of the linear equation, the logarithmic equation, the quadratic equation, the Cubic equation, the compound equation, the power equation and the exponential equation, and found that quadratic equation best described the relationship between the body weight and the absolute fecundity (R2=0.49, sig.= 0.020.05, N=31). The exploitation rate of Culter oxycephaloides in the Xiao River was 0.51/year in 2013. The Beverton-Holt dynamic model indicated that Emax (the exploitation rate for the maximum yield), E10 (the exploitation rate at which the marginal increase of relative yield-per-recruit is 1/10th of the value at E=0) and E50 (the exploitation rate at which the stock is reduced to 50% of the original biomass) were 0.40/year, 0.32/year, and 0.25/year respectively. The comparison between Emax and the exploitation rate in 2013 demonstrated that Culter oxycephaloides in the Xiao River were excessively exploited in 2013. Therefore, the future fishing activity in the Xiao River should be strictly supervised in order to maintain and enlarge the population of Culter oxycephaloides.