Age,Growth,Mortality And Reproduction Of Hemiculter Bleekeri In He-wang-miao Oxbow

The Hemiculter bleekeri ?Warpachowski, 1887?, a small-sized fish, belongs to genus Hermiculter ?Bleeker, 1860?, subfamily Culterinae, family Cyprinidae, order Cypriniformes. It is widespread in most freshwater bodies of China, and is one of the dominant species in the Yangtze River. The research on characteristics of age, growth,and mortality and reproduction of H.bleekeri were conducted based on 591 specimens collected from April 2016 to December 2016 in He-wang-miao Oxbow. In addition, to learn more about the life history strategy, the comparative analysis on growth and reproduction of H.bleekeri in different waters were carried out. The study aimed to improve the understanding the causes why H.bleekeri become the dominant species in the middle reaches of the Yangtze River. The main results are as follows:The age, growth of H.bleekeri were determined by using scales of 591 specimes.Two kinds of annuli were observed on the scales including loose-close and cutting-over pattern. The interpretation rate of annual rings reached 100%. The agreement between two times age readings by the same reader reached 91.37% and the total coefficient of variation ?CV? was 3.08%. It was demonstrated that one annulus was formed per year mainly during May to August, based on marginal increment analysis. The age structure of H.bleekeri was simple with only three age groups and 95.78% was 1 to 2 years old individuals for both sexes.For females, the standard length ranged 7.5 to 13.9 cm and length group from 9.0 to 13.0 cm accounted for 84.69%, body weight ranged from 4.13 to 30.53 g and the 12.0 to 24.0 g body weight group accounted for 75.17%. And for males, the standard length ranged 7.5 to 13.2 cm and length group from 8.0 to 12.0 cm accounted for 80.89%, body weight ranged from 3.86 to 30.76 g and the 9.0 to 24.0 g body weight group accounted for 85.78%. The length-weight relationships of female and male were significantly different. For females, the length-weight relationships showed a negative allometric growth, which could be described as W=0.02649×SL2.7185,respectively. While for males, the length-weight relationships showed an isomeric growth, which could be expressed as W=0.00972×SL3.1208, respectively.The Von Bertalanffy ?VBGF? growth equations which were fitted on the standard length data were: L₁=188.02(1-e^{-0.4652?t+0.7753?}W_t=188.02(1-e^{-0.4652?t+0.7753?2.7185};?=L₁=17.48(1-e^{-0.4118?t+0.8553?}),W_t=153.8(1-e^{-0.4118?t+0.8553?})^3.1208.The growth performances were ???? =2.27, ???? =2.1. The natural mortality rate were M?-0.84 per year and Ms,0.79 per year, which were much higher than the modal mortality ?M=0.2?0.3 per year?. The exploitation rate for females and males was E?=0.76 and E?-0.57,respectively, which showed the population of H.bleekeri was overexploited.The total sex ratio ?? : ?? was 1.44:1, significantly different from 1:1. Females were dominated during spawning period with sex ratio 2.5:1, while in the non-spawning season the sex ratio is 0.91:1, which had no significant difference from 1:1. The age structure of reproductive stock range from 1 to 3 years old, and the recruitment stock ?1 years old? was dominant in the spawning stock, which indicates that the spawning stock belongs to type II . The size at first sexual maturity for females and males were 8.08 cm and 8.47 cm, and the observed minimum mature individual for females and males were 7.5 cm and 8.2 cm, respectively. According to monthly variations of gonadosomatic index ?GSI?, the spawning season might last from April to June, probably to July. Size-frequency of eggs in the ovaries staged ?collected during April and June exhibited the single peak mode, which indicates that H.bleekeri may be a kind of total spawner. The absolute fecundity ?F? ranged from 1703 to 9601 eggs ?5876.6 ± 1837.8 eggs? per fish. The relation between F and weight?W?, gonad weight ?GW?, standard length ?SL? is in linear, linear and power function,respectively. Relative fecundity ?FW? ranged from 204.7 to 406.5 eggs/g ? mean322.3± 49.7 eggs/g ? and was related to GSI in power function. Relative fecundity ?FL?ranged from 212.0 to 827.6 eggs/cm ? mean552.4± 136.1 eggs/cm? and was in power correlation with W and in linear correlation with GSI, respectively.Comprehensive analysis shows that reasons why H. bleekeri became the dominant species in He-wang-miao Oxbow may be attributed to its specific life-history traits. First, simple age structure and early maturation with rapid development and short generation time. Because of those characteristics, it was well adapted to high fishing intensity. Second, its long spawning season and relatively large oocytes size, which could help to increase the survival rate of offspring and recruitment of the population.