Research On Fish Community Structure And Resource Status Of Ptychidio Jordani In The Laibin Section Of The Xijiang River

The Xijiang River is the main stream of the Pearl River basin and has rich fish resources.The original habitat environment of fish has changed and fish diversity has been threatened with the construction of cascade water conservancy projects and water pollution.Ptychidio jordani is an endemic fish in the Pearl River Basin,it is known as one of the four famous fish in the Xijiang River,it has been listed as a critically endangered species in 2016,and its biological resources are currently on a declining trend.Taking the Laibin Sanjiangkou section of the Xijiang River（Hongshuihe River,Qianjiang River and Liujiang River）as the research area.Fish samples and environmental samples were collected in October 2020 and January,April and July 2021.The main contents of the study included composition and ecological types of fish species,seasonal change characteristics of fish community structure,the relationship between fish community structure and environmental factors,and the resource status of Ptychidio jordani.The purpose of the study was to supplement the basic information of fish resources and to provide a theoretical basis for the conservation of fish diversity,the rational use of fish resources and the impact of cascade water conservancy projects on fish resources.The main results were as follows:（1）A total of 92 fish species（3611 individuals）were caught in Laibin of the Xijiang River,belonging to 3 orders,12 families,68 genera.The most species-rich families were Cyprinidae,accounted for 64.13%of the total species（59 species）,Cobitidae accounted for 13.04%（12 species）,Bagridae accounted for 5.43%（5species）,Cichlidae,Siluridae and Gobiidae respectively accounted for 3.26%（3species）,Serranidae accounted for 2.17%（2 species）,and the rest of the families accounted for 1.09%（1 species）.According to index of relative importance,there are four dominant species throughout the year:Discogobio tetrabarbatus,Squaliobarbus curriculus,Ptychidio jordani,and Cirrhinus molitorella.（2）The Margalef species richness index ranged from 3.20 to 5.60;the Shannon-Wiener species diversity index ranged from 1.82 to 2.73;the Pielou evenness index ranged from 0.62 to 0.80;and the Simpson dominance index ranged from 0.10 to 0.30.The richness and diversity of fish were highest in summer,and relatively low in spring.The seasonal differences in fish communities were not significant（P>0.05）.（3）The results of abundance and biomass curves showed that the abundance dominance curve of fish community in spring was above the biomass dominance curve,the abundance dominance curve of fish community in summer was below the biomass dominance curve,the abundance dominance curve of fish community in autumn and winter intersected with the biomass dominance curve.On the whole,the fish community in the Laibin section of the Xijiang River was in a more disturbed state due to natural and anthropogenic factors.（4）The results of biomass size spectrum showed that the percentage of fish with average individual weight less than 20 g in four seasons were spring（97.40%）>autumn（88.95%）>winter（69.20%）>summer（65.52%）,and the percentage of with average individual weight greater than 50 g were less than 15%.On the whole,the Laibin section of the Xijiang River was dominated by fish with small average individual weight,and fish tended to be smaller.（5）The results of the study on the relationship between fish community structure and environmental factors showed that water temperature,p H,dissolved oxygen,conductivity,turbidity and water level all had some effects on fish community structure.Among them,fish species abundance was mainly influenced by water level,water temperature and dissolved oxygen（P<0.05）;fish biomass was mainly influenced by water level and dissolved oxygen（P<0.05）;fish diversity was mainly influenced by water level and water temperature（P<0.05）.（6）The relationship between body length（L）and body weight（W）of Ptychidio jordani was W=0.00699×L^3.4253,with positive allometric growth,and its growth inflection age(t_tp)was 1.74 years;the age of capture（t_c）was 0.69 years;the total mortality coefficient（Z）was equal to 1.69;and the exploitation ratio（E）was equal to0.32.The resource of Ptychidio jordani in the Laibin section of the Xijiang River has not been overexploited,but has shown a trend of under-ageing and miniaturization.In summary,the fish resources in the Laibin section of the Xijiang River were rich,but with the decline in environmental quality,excessive human fishing and the construction of cascade water conservancy projects,etc.,the original habitat of fish has changed,the economic fish have degenerated,and fish individuals have shown a trend of miniaturization and under-ageing,small fish gradually evolved into the dominant species.Therefore,it is suggested to strengthen the protection of fishery resources and ecological environment in the Laibin section of the Xijiang River.