Study On The Age,Growth,Reproduction And Population Dynamics Of Gymnocypris Waddelli In The Zhegu Lake,Tibet

G.waddelli is one of Gymnocypris（Cyprinidae:Schizothoracinae）species distributed in the Zhegu Lake.The lack of basic biological research makes it difficult for us to carry out resource protection and rational development.In this paper,we have studied the age structure,growth characteristics,reproductive characteristics and population dynamics of G.waddelli.The purpose is to provide basic data for the protection of this species in Tibet’s fragile ecosystem.The main results are as follows:The age structure and growth characteristics of G.waddelli were investigated by examining 432 samples collected in Zhegu Lake from 2017 to 2019.The body length（L）,body weight（W）,otolith radius（OR）and age were measured to describe the relationships between body length,body weight and age.The results showed that the body length of G.waddelli ranged 3.1～35.6 cm,and the body weight ranged from 0.4to 645.9 g.Estimated age was 1～11 years.The most individuals were 6～8 years,accounting for about 35%of total samples.The relationship between body weight and body length was described by the linear equation:W=0.0095L^3.1514（R²=0.9911,n=432）,which is consistent with uniform growth characteristics.There was no significant difference in body length,body weight and age between males and females（P>0.05）.The growth pattern of G.waddelli was described by the von Bertalanffy equation as the growth curve occurred at 8.263 years with a body length of 27.826 cm and weight of 333.811 g.The apparent growth index is 4.399.The age structure of G.waddelli in Zhegu Lake is simplified and the population is in the growing period,which may be affected by the special geographical location and ecological habitat of Zhegu Lake.The sex ratio of G.waddelli in spring and autumn is 2.85:1 and 1.63:1 respectively.The mature coefficient was 11.73%in spring and 5.17%in autumn,and the gonad development maturity in spring is relatively high.The individuals from gonad development to stage V account for 88%of the total catches.It can be preliminarily concluded that the breeding season begins in spring.The absolute fecundity was 11574eggs and the relative fecundity was 28 eggs/g.The relationship between absolute fecundity and body length and weight was linear:F=32.745L-1047.3（R²=0.6263）,F=1197.0W-23059（R²=0.6423）.The results showed that the fecundity of G.waddelli in Zhegu Lake was low,and it was easy to be affected by the environmental factors.The total mortality（Z）of G.waddelli was 0.27 per year.The natural mortality（M）was 0.22 per year.The fishing mortality（F）was 0.05 per year.The current development radio（E）of G.waddelli was 0.185 per year.Taken H.dauncus,E.oxycephaoa and G.przwalskii as reference,the life history of G.waddelli belonged to the typical k-selection.We assessed the stock status based on the spawning stock biomass per recruit model.At the current age at first capture for G.waddelli,the spawning stock biomass per recruit was 290.31,and the spawning potential ratio was 88%.The results indicated that the resources of G.waddelli were sufficient,but it also was easy to be affected by the environmental factors.In conclusion,the population of G.waddelli in Zhegu Lake was mainly limited by its harsh and changeable living environment.Weproposed to take measures to control water management in river entering the lake and limit human activities such as fishing,tourism,in order to improve the ecological environment of Zhegu Lake and protect the population of G.waddelli.