Age, Growth, Mortality And Reproduction Of Pseudobrama Simoni (Bleeker) In Tian-e-zhou Oxbow Of Yangtze River

The Tian-e-zhou oxbow is located near Shishou City in Hubei Province. Originally a natural course of the middle reaches of the Yangtze River. It was separated from the main channel when the river was regulated in1972. Two national nature reserves had been founded, including the Lipotes vexillife reserve and the Elaphurus davidianu reserve due to the convenient location and good environmental conditions. This oxbow was approved as Baiji National reserve for the freshwater dolphins Baiji Lipotes vexillife and finless porpoises Neophocaena phocaenoides in1992. It has been the important habitat for finless porpoises. About thirty dophins live in the oxbow at present. As the main diet of the dophins, resources and biomass of the small fishes are directly related to the survival and development of finless porpoises. Pseudobrama simoni belongs to genus Pseudobrama, subfamily Xenocyprininae, family Cypriniade, order Cypriniformes. It is widespread in most water of China. Pseudobrama simoni is one of the dominant species of the small fishes in Tian-e-zhou oxbow. This research will analyze the characteristics of age, growth, mortality and reproduction of Pseudobrama simoni. The result will be helpful to the resource management and protection of Neophocaena phocaenoides. The main results show as follow:The age, growth and mortality of Pseudobrama simoni were studied using scales of596specimens collected in Tian-e-zhou Oxbow from March2011to January2012. It showed that two kinds of annuli were observed in the scales including loose-close and cutting-over pattern. Monthly change in the marginal increment ratio indicated that an annulus formed in one year, from March to May. The interpretation rate of annual rings reached97.3%. The agreement between two times of aging by the same reader reached85.5%and the total coefficient of variation was4.88%. For age determination, scale was a high-quality material. The age structure was simple for87.4%was1to3years and the maximum age of population was5years old for both sexes. Standard length of all specimens ranged from3.8to15.7cm. The length group from7.3to11.3cm accounted for89.12%of the total sample. Body weight ranged from1.38to75.8g. The5.5to40.5g body weight group accounted for90.13%. The relationship between standard length and body weight could be described as BW=0.01SL3.2488, showing no significant differences for the male and female. The relationship between standard length and scale length was described as L=39.55R+2.64. The growth parameters of the von Bertalanffy equation were L∞=19.98cm, W∞=170.52g, K=0.1692, t0=-1.2118for female, L∞=17.99cm, W∞=115.28g, K=0.1766, to=-1.3982for male, respectively. The growth performances index (φ)for female and male of Pseudobrama simonii was1.83and1.76. The fishing mortality rate was0.47a-1for female,0.63a-1for male, respectively. Exploitation rate was0.57.The total sex ratio (female:male) was2:1,showing that the female was much more than male except that on July and the sex ratio reached at7:1on March. Females dominated in sizes larger than10cm and only one was male in eight specimens larger than14cm. The standard length at50%maturity (L50) were8.3cm for females and8.2cm for males, respectively. The minimum standard length and body weight at maturity was7.4cm,8.1g for female and7.7cm,7.9g for male, respectively. The monthly changes of gonadosomatic indices began to increase on March and reach the maxinum value on August. The value of gonadosomatic indices declines on October sharply, and maintained the low value till to January of next year.The gonad stages analysis for female also confirmed the result. The gonad developed to stage Ⅲ and Ⅳ on May and the stage IV maintained till August. When the spawning was terminated, the gonad returned into stage II on October. At the time of March in next year, gonads started growing, and was mature in May gradually. By gonadal histological sections analysis of female gonads from Yangtze River, we could find the POF (post-ovulatory follicles). At the same time,different stages of the oocyte coexsisted in the ovaries. Pseudobrama simoni is a multiple spawner with indeterminate fecundity. The daily rings of otolith for juveniles of speciesmans collected on September5th and6th, confirmed that the juveniles were produced in mid-July.The average absolute fecundity (with±SD) was13460±4883oocytes per female, and the relative fecundity was984±533eggs per gram wet weight of female.Our study indicated that the population of Pseudobrama simoni in Tian-e-zhou oxbow was suffering from over-exploitaton and the population depends on the recruitment from the Yangtze River for the oxbow has no suitable spawning environment for Pseudobrama simoni. So we should follow the following two measures to manage this fish resource, First,we must limit the use of destructive nets,such as purse net to reduce the fishing pressure, Second,we should reconnect the oxbow with the main channel of Yangtze River by opening the control gate during the spawning season and let the fry and juvenile produced in the main channel of the Yangtze River into the oxbow.