Comparative Study On The Biological Characteristics Of Ptychidio Jordani In The Water Areas Of Upstream And Downstream Of The Dam In Datengxia Gorge

A total of 662 P.jordani samples were collected in the upstream and downstream of the Datengxia Dam in 2020 and 2021 Comparative analysis of age and growth,reproduction and feeding habits were conducted to check the possible impact of the dam on the biological characteristics of P.jordani.The main results were as follows:1.A total of 454 P.jordani were collected from upstream of the dam.The standard length ranged from 73 to 283 mm,the average standard length was 182.2mm,and the dominant group of standard length was 180 to 200 mm,accounting for34.65%of the total number.The body weights ranged from 10.5 to 575.5 g,with a mean value of 161.9 g.The main body weights concentrated in 100-200 g group,accounting for 58.27%of the total number.A total of 208 P.jordani samples were collected in downstream of the dam.The standard lengths ranged from 110 to 275 mm,with an average value of 161.3 mm.The main group of standard lengths were 140 to160 mm,accounting for 33.01%of the total number.The body weights ranged from24.2 to 499.1 g,with an average value of 108.5 g.The dominant group of body weight was 0 to 100 g,with the proportion of 54.55%.The females and males in the upstream grew allometrically,while the juveniles grew uniformly.However,the overall in the downstream grew uniformly.The fitted relationships of standard length and weight in the upstream were as follows:Male:W=7.7131×10^-6SL^3.2199（R²=0.919,n=265）;Female:W=1.1318×10^-5SL^3.1478（R²=0.940,n=110）;Undetermined:W=1.8273×10^-5SL^3.0463（R²=0.937,n=49）.The fitted relationships of standard length and weight in the downstream of the dam were as follows:Overall:W=2.1876×10^-5SL^3.0145（R²=0.968,n=208）.The von Bertalanffy growth function of standard length for P.jordani were described as:Upstream:SL_t=320.9(1-e^{-0.354（t+0.9579）});Downstream:SL_t=393.6(1-e^{-0.166（t+2.2153）}).The von Bertalanffy growth function of body weight for P.jordani were described as:Upstream:W_t=899.1(1-e^{-0.354（t+0.9579）})^3.2199;Downstream:Wt=1459.3(1-e^{-0.166（t+2.2153）})^3.0145.The age inflexion point for the growth of the upstream population was 2.4 years,with the standard length and body weight were 223.2 mm and 279.12 g,respectively.Meanwhile,these values of the downstream population were 4.4 years,262.1 mm,and 429.5 g,respectively.2.The ratios of female to male in the upstream and downstream were 2.41:1 and1.39:1,respectively.The change trend graph of the Sexual Maturity Coefficient（GIS）and the percentage change graph of the sexual period inferred that the breeding period of the P.jordani is from April to July,and the peak appears in June.The standard length of the samples for fecundity in the upstream ranged from 169 to 279 mm,and the weight ranged from 120.2 to.557.2 g.The calculated absolute fecundity range was 4789 to 52921 eggs,with the mean value of 18440 eggs,The average relative fecundity ranged from 17.69 to 98.04 eggs/g,with an average of 52.04 eggs/g.The standard length of the samples for fecundity in the downstream ranged from 123 to177 mm,and the weight range was 50.5 to 142.8 g.The absolute fecundity ranged from 2369 to 17577 eggs,with an average of 9165 eggs.The relative fecundity ranged from 22.81 to 157.42 eggs/g,with an average of 87.20 eggs/g.The average absolute fecundity in the upstream was higher than that in the downstream,while the average relative fecundity was lower than that in the downstream.There was a significant index relationship between the absolute fecundity and standard length and body weight in both the upstream and downstream water areas of the dam.The best fit equation was:Upstream:F=7.084×10^-8SL^4.153（R²=0.722,n=14）,F=0.158W^1.978（R²=0.769,n=14）;Downstream:F=2.061×10^-5SL^3.989（R²=0.464,n=10）,F=0.308W^2.185（R²=0.458,n=10）.3.The standard length of the samples for dietary analysis in summer ranged from 152 to 265 mm.According to the percentage of relative importance index（IRI%）,the Chlorophyta was the most important food（22.27%）,followed by Bacillariophyta（19%）and Cryptophyta（7.61%）.In terms of dominance index,Bacillariophyta were the highest at 29.6%,followed by Cryptophyta at 11.2%and Xanthophyta at 6.57%.The most important bait in summer were Bacillariophyta and Cryptophyta.The standard length of the samples for food habit analysis in autumn ranged from 113 to215 mm.According to the percentage of relative importance index（IRI%）,Chlorophyta was the most important bait for P.jordani in autumn（32.53%）,followed by Bacillariophyta at 21.4%.The highest degree index（Ip%）was Chlorella（Chlorophyta）with 48.85%,followed by Cyclotella sp.（Bacillariophyta）with 21.85%,and Melosira granulata（Bacillariophyta）with 9.07%.The zoobenthos were also found in the autumn sampling,among which the Limnodrilus sp.were the most important component.The diversity index（H’）and evenness index（J）in summer were 2.28 and 0.65,respectively.while these two values in autumn were 2.56 and0.61,respectively.The range of food intake in summer and autumn was similar,and the diversity index in summer was lower than that in autumn.The graphic method of Amundsen（1996）showed that the dietary of P.jordani was wide.The ecological niche of the P.jordani indicated a high WPC type.Food variability among individuals was low.The main food in summer was Melosira granulata,that of which in autumn were Chlamydomonas sp.and Cyclotella sp.