Fish Community Structure In Jinze Reservoir And Analysis Of The Relationship Between Silver Carp Growth And Environmental Factors Based On GAM Model

Located in the west of Jinze Town,Qingpu District,Shanghai,Jinze Reservoir is on the north bank of Taipu River.Water is drawn from Taipu River.Before leading water,there were basically no fish on the bottom of the Jinze Reservoir.After leading water,fish from the Taipu River entered into the reservoir.To analyze the characteristics of fish community structure,using gillnets and cage nets to conduct a seasonal survey of fish resources in Jinze Reservoir from 2017 to 2020.A total of 29 fish species were investigated in Jinze Reservoir,belonging to 5 orders,8 families,and 22 genera.Among them,there are 26 species of freshwater fish and 3 species of migratory fish;there are 7species,3species,8species and17species of phytophagous,herbivorous,omnivorous,primary carnivorous and secondary carnivorous fishes respectively;dominant species（IRI>1000）include Aristichthys nobilis、Coilia nasus、Hypophthalmi chthysmolitri and Carassius auratus auratus.The growth analysis of dominant species in Jinze Reservoir showed that Hypophthalmi chthysmolitri in Jinze Reservoir is composed of 1-6 age,the majority are2-4 years old;Aristichthys nobilis is composed of 1-12 age,the majority are 3-6 age.The body length and weight equation of Hypophthalmi chthysmolitri and Aristichthys nobilis were W=0.0336L^2.8237and W=0.0213L^2.9953,respectively.The growth equation of body length and weight of Hypophthalmi chthysmolitri isL_t=96.44[1-e^{-0.137（t+0.775）}],W_t=12314[1-e^{-0.137（t+0.775）}]^2.7854,the growth inflection point of Hypophthalmi chthysmolitri in Jinze Reservoir is 6.68 age;the growth equation of body length and weight of Aristichthys nobilis isL_t=90.6[1-e^{-0.15（t+1.63）}],W_t=15516[1-e^{-0.15（t+1.63）]2.9953,and the growth inflection point is 5.64 age.Pearsons correlation was used to determine the fullness,visceral weight/weight,head length/body length,preanal length/body length,body height/body length and body thickness/body length of Hypophthalmi chthysmolitri in Jinze Reservoir.The relationship among 21 environmental factors such as insects,copepods,p H,and dissolved oxygen are analyzed.After the analysis of the coefficient of variation,the visceral weight/weight（CV=0.033）and body height/length（CV=0.071）,head length/body length（CV）=0.069},anterior anal length/body length（CV=0.096）is a weak variation,and its value is affected by the external environment with a relatively smaller range;plumpness（CV=0.130）and body thickness/length（CV=0.124）.It belongs to a moderate variation,and its value is affected by the external environment with a relatively large variation.It is generally believed that P<0.05 is a significant correlation.The results of pearsons correlation analysis show that the plumpness of Hypophthalmi chthysmolitri is significantly positively correlated with the number of copepods（r=0.668,p=0.049）,and the preanal length/body length is correlated with cladocerans biological density was significantly positively correlated（r=0.926,p=0.024）,body thickness/length was correlated with the number of rotifer species（r=-0.928,p=0.023）,rotifer biological density（r=-0.935,p=0.02）,rotifer biomass（r=-0.925,p=0.024）and copepod biomass（r=-0.988,p=0.012）are significantly negatively correlated,visceral weight/body weight and the number of rotifer species are significantly negative correlation（r=-.794,p=0.019）,other indicators have no significant correlation with environmental factors.According to GAM modeling analysis,the best predictor combination of body thickness/length is copepod biomass+rotifer biomass+rotifer biomass+rotifer species number,and the model contribution rate is 7.07%.This study shows that the number and biomass of copepods,the number of rotifer species,biological density and biomass,cladocerans biological density are factors that affect the growth of Hypophthalmichthys molitrix.Compared with the growth of Hypophthalmichthys molitrix,zooplankton is more capable Affects the growth of Hypophthalmichthys molitrix,mainly affecting its plumpness,body thickness/length,visceral weight/weight and preanal length/body length,but environmental factors have relatively small effects on the growth characteristics of Hypophthalmichthys molitrix in Jinze Reservoir.