| The section from Yichang to Jingzhou of the Yangtze River and the East Dongting Lake are the Significant spawning ground and feeding ground of Hypophthalmichthys molitrix and Aristichthys nobilis.Experimental samples were collected in the section from Yichang to Jingzhou of the Yangtze River and the East Dongting Lake from July 2016 to August 2017.At the secion,470 and 366 H.molitrix were collected,while 224 and 221 A.nobilis were collected at the lake.Population structure,growth,composition of bait biology and population dynamics of H.molitrix and A.nobilis have been researched to know the status of the population resources of Hypophthalmichthys molitrix and Aristichthys nobilis and to protect and utilize them better.The main results are as follows.(1)Population structuresof H.molitrix and A.nobiliswere complex,relatively stable.And the population structures in the section from Yichang to Jingzhou of the Yangtze River were better than these in the East Dongting Lake.?In the section from Yichang to Jingzhou of the Yangtze RiverThe body length of H.molitrix ranged from 27.7 to 93.8cm,according to age the fish were divided into seven groups from 1 years old to 7 years old,Then H.molitrix which ranged from 40.0 to 70.0cm accounted for 77.23%of total.individuals of 3 years old to 5 years old groups were dominant.The body length of A.nobilis ranged from 18.6 to 95.7cm,according to age the fish were divided into seven groups from 1 years old to 7 years old.A.nobilis which ranged from 40.0 to 80.0cm accounted for 81.25%of total.Then,individuals of 3 years old to 5 years old groups were dominant.?In the East Dongting LakeThe body length ranged from 11.3cm to 79.7cm,the fish were divided into four groups according to age from 1 years old to 4 years old.Samples ranged from 10.0cm to 20.0cm accounted for 91.80%and individuals of 3 years old and 4years old were dominant.The body length ranged from 10.6cm to 90.2cm,the fish were divided into four groups according to age from 1 years old to 5 years old.Samples ranged from 30.0cm to 60.0cm accounted for 56.56%,and individuals of 1 years old to 4years old were dominant.2.The growth performances of H.molitrix and A.nobilis were relatively degraded.The growth performances in the section from Yichang to Jingzhou of the Yangtze River were better than these in the East Dongting Lake?In the section from Yichang to Jingzhou of the Yangtze RiverThe relationship between body length and weight of H.molitrix was estimates as that,W= 4.0413 × 10-5L2.7546(R2 = 0.9297,n=470),by the Von Bertalanffy equations the growth curves were calculated as Lt = 104.6995[1-e-0.1603(t+0.89)],Wt=14.8141[1-e-0.1603(t+0.89)]2.7546,the inflexion point was 5.43 years old.The relationship between body length and weight of A.nobilis was estimates as that W = 2.4592 ×10-5L2.9075(R2 = 0.9675,n=224),by the Von Bertalanffy equations the growth curves were calculated as that Lt = 106.8850[1-e-0.1478(t+0.65)],Wt=19.61[1-e-0.1478(t+0.65)]2.9075,the inflexion point was 6.57 years old.?In the East Dongting LakeThe relationship between body length and weight of H.molitrix was estimates as that,W = 1.6735 × 10-5L2.9856(R2 = 0.9907,n=366),by the Von Bertalanffy equations of the growth curves were calculated as Lt = 110.3500[1-e-0.1278(t+1.46)],Wt= 21.01[1-e-0.1278(t+1.46)]2.9856,the inflexion point was 7.10 years old.The relationship between body length and weight of A.nobilis was estimates as that,W = 1.4475 × 10-5L3 0621(R2 = = 0.9817,n=221),by the Von Bertalanffy equations the growth curves were calculated as thatLt = 105.0229[1-e-0.1402(t+1.07)],Wt=22.39[1-e-0.1402(t+1.07)]3.0621,the inflexion point was 6.92 years old.3.The annual average fish fullness of A.nobilis in the East Dongting Lake was higher than that in the section from Yichang to Jingzhou of the Yangtze River.the food compositions of H.molitrix and A.nobilis are showed seasonal and spatial changes.?In the section from Yichang to Jingzhou of the Yangtze RiverThe bait biology of H.molitri was mainly respectively Bacillariophyta?Cladocera?Cladocera and Bacillariophyta in Inspring summer?autumn and winter.The bait biology of A.nobilis was mainly respectively Cladocera?Cladocera?Cladocera and Bacillariophyta in Inspring summer?autumn and winter.?In the East Dongting LakeThe bait biology of H.molitri was mainly respectively Cladocera,Cyanophyta?Bacillariophyta and Copepods in Inspring summer?autumn and winter.The bait biology of A.nobilis was mainly respectively Cladocera?Cladocera?Cladocera and Copepods in Inspring summer?autumn and winter.4.Both H.molitrix and A.nobilis were all under pressure.The fishing pressure of two fishes in the East Dongting Lake was higher than that in the section from Yichang to Jingzhou of the Yangtze River,and the resource of H.molitrix was over catched.?In the section from Yichang to Jingzhou of the Yangtze RiverThe total mortality coefficient(Z)of H.molitrix was estimated to be 0.81.The natural mortality coefficient(M)was 0.32,the fishing mortality coefficient(F)was 0.49,the exploitation ratio(E)was 0.6.The first capture age was 2.36,the first capture body length was 42.52cm.The total mortality coefficient(Z)ofA.nobilis was estimated to be 0.46.The natural mortality coefficient(M)was 0.31,the fishing mortality coefficient(F)was 0.15,the exploitation ratio(E)was 0.33.The first capture age was 3.39,the first capture body length was 48.02cm.?In the East Dongting LakeThe total mortality coefficient(Z)of H.molitrix was estimated to be 0.79.The natural mortality coefficient(M)was 0.28,the fishing mortality coefficient(F)was 0.51,the exploitation ratio(E)was 0.65.The first capture age was 1.27,the first capture body length was 32.48cm.The total mortality coefficient(Z)of H.molitrix was estimated to be 0.62.The natural mortality coefficient(M)was 0.30,the fishing mortality coefficient(F)was 0.32,the exploitation ratio(E)was 0.52.The first capture age was 1.45,the first capture body length was 31.22cm. |
PDF Full Text Request