| In recent years,investigations on fish resources in the Songhua River Basin have been carried out frequently in the upper reaches of the Songhua River（formerly known as the Second Songhua River）and the lower reaches of the Songhua River（Jiamusi city to Tongjiang City）,but there has been no report on fish diversity in the middle reaches of the Songhua River.This paper takes the middle reaches of Songhua River（Zhaoyuan to Yilan）as the research area,and sets up 7 samples.In 2020 and 2021,fish species composition,ecological types,species diversity and growth characteristics of dominant species of fish in this region will be systematically investigated and studied by field collection method and market research method respectively.The main research results are as follows:1.There are 80 species of fishes in the middle reaches of Songhua River（Zhaoyuan to Yilan）,belonging to 57 genera,18 families and 9 orders.The fish with the highest proportion in quantity and weight were cypriniformes and cyprinidae.In terms of ecological types,fishes are mainly omnivorous,bottom-dwelling,and sticky-producing.In addition,the fishes in this section are composed of 6 faunal taxa,and most of them are in the river plain.2.The species composition of dominant fishes in the middle reaches of Songhua River（from Zhaoyuan to Yilan）was affected by seasons,with only 5 dominant species in summer.There are eight dominant fish species in spring.The dominant species in autumn were the most abundant and varied in species composition,with a total of 10 species.Hemiculter leucisculus,Carassius auratus gibelio,Hypophthalmichthys molitrix,Acheilognathus macropterus,are the dominant species in spring,summer and autumn The dominant species in both 2020 and 2021 were 6 species,but the species composition was slightly different in different years.Among them,Hemiculter leucisculus,Carassius auratus gibelio,Cyprinus carpio haematopterus,and Pelteobagrus nitidus,are the dominant species in 2020 and 2021.3.The Shannon-Wiener index and Maralef richness index were the highest in autumn and the lowest in spring in the middle reaches of Songhua River basin.The average Pielou evenness index was the highest in spring and the lowest in autumn,and the seasonal difference was obvious.In the survey results of different seasons,the variation trend of Pielou evenness index of all points in the same season has no significant difference,and is basically the same.However,Shannon-Wiener index and Maralef richness index showed differences at different points in the same season.According to the analysis of fish species diversity in different years,the fish species diversity index in the river segment in 2020 has different degrees of change compared with that in 2021,but the mean value is relatively close with little fluctuation.It indicates that the fish community structure in this area is relatively stable.4.The dominant species of fish in the middle reaches of Songhua River（Zhaoyuan to Yilan）were calculated and the relationship between body length and body weight in different seasons and years was analyzed.The results showed that fishes in the middle reaches of Songhua River were mainly small individuals.The relationship between body length and body weight of dominant species showed a positive power function correlation,most of which showed uniform or nearly uniform growth and tended to positive allometric growth.The fattening degree of dominant species varied widely（0.42～2.97）,with the highest value being Carassius auratus gibelio and the lowest value being large Protosalanx hyalocranius.The abundance index of dominant species was highest in autumn,followed by summer and lowest in spring.The results of this study help to supplement the basic data of fish diversity in the middle reaches of Songhua River（Zhaoyuan to Yilan）,and provide scientific support for the protection of fishery resources in the basin. |
