| Xenocypris Microlepis,belonging to bleeker family,is a medium-sized commercial fish inhabiting in middle and low levels of water body,and widely distributes in Heilongjiang River,the Yangtze River and Zhujiang River of China.A total of 337 individuals monthly collected from Daoguanhe Reservoir from September 2007 to August 2008 were used to study the age structure,growth,reproduction and other biological characters of the fish. The aim of this work is to provide some basic information for successful fishery management,resource conservation and reasonable utilization in reservoirs.The main results are as follows:1.Scales were used for aging the fish efficiently.A clear feature of mixed sparseness-denseness and incision ring could be seen on the scale of X.Microlepis.A ring was formed by the connection of the density loop in the front and back area and the incision loop in side-rear areas.The annuli were laid down mainly from April to May,and the ratios of the scales with new annulus increases from34.29%to 97.70%。2.The commercial catches consisted of five age groups(age 1 to age 5) and individuals of age 1 to 3 groups were dominant(occupying more than 90%of total capture).The body length changed from 150mm to 350mm while weight changed from 200g to 500g.No significant differences in growth were detected between the females and males.Male to female ratio was about 1 to 1.3.The relationship between body length(L,cm) and the diameter of the scale(R,mm) was L=5.8+6.42R(n=337,R=0.8748).Weight(W,g)-Length relationship was W=0.0207L2.9376(R2=0.9813).The von Bertalanffy growth equations were Lt=37.0378(1-e-0.2539(t+0.8939)) and Wt=839.5033(1-e-0.2539(t+0.8939))3 for the length and weight respectively.The inflection point of body weight was about 3.35 years.The growth of X.microlepis showed two apparent phases.The growth of the before-3-aged group was increasing,while the growth of the after-3-aged group was declining.4.Secondary sexuality.During reproduction periods,some white nuptial organs were visible on cheek,orbit,opercular,head and lateral scales in males.However,for females, whose bellys were swelled and soft,and no same organs could be found.5.The fullness of female and male's of X.microlepis changed with season.The influence of the fullness was identical with feeding and propagation.The propagation seasons were from April to July.Among this period,the fullness was declining.But after propagation,the condition factor was rising with feeding.6.Spawning stocks involved four age groups,and the main individuals were two to three years old,occupying about 84.97%of the whole.The minimum mature age was 2 years old both for males and females.The minimum mature female was 14.92cm in length,146.37g in weight with a 4.28g ovary and a value of gonadosomatic index(GSI) 3.17.The corresponding values of the minimum mature male were 12.68cm,114.48g, 0.92g and 0.65,respectively.7.The absolute fecundity(F) ranged from 8247 to 157899 eggs with an average of 78629.3 eggs.The relative fecundity to weight(FW) ranged from 95 to 487 eggs with an average of 225.8 eggs,and that to length(FL) ranged from 894 to 5110 with an average of 2738.4.The results of correlation analysis indicated that fecundity of the fish could be fluctuated primarily by variations of body length,body weight,net weight,goand mass and GSI.8.The gonad development of X.microlepis could be divided into six stages.After propagation,the histology structures of female and male of X.microlepis returned to stageⅡ.The ovary maintained in stageⅢin winter,and began to develop in March, reached maturity in later April.Individuals with theⅣ-Ⅴstage ovaries could be seen till August.Value of GSI increased in March,approached a peak in May and decreased to bottom in October till the beginning of the next March.The spawning activities of the fish could last from April to July.9.In a stageⅥovary,there were oocytes both in phase 3 and phase 4,which indicated that the development of oocytes were unsynchronized.Combined with the frequency distribution of egg sizes,annually change of GSI and wild observation,it was concluded that the fish was in a successive process and female seemed to be able to spawn twice or three times in one spawning season.
|
PDF Full Text Request