Studies On Assemblage Of Larvae And Juvenile Fish And Their Correlation With Environmental Factors In Anqing Xinzhou Section Of The Yangtze River

The Anqing river reaches Poyang lake and connects the middle and lower reaches of the Yangtze river.There are many lakes,sandbanks,twists and turns along the Anqing river which is one of famous fish producing areas and an important habitat for Neophocaena asiaeorientalis and other aquatic life in the lower reaches of the Yangtze river.The main stream of the river which is a typical branching river is divided into the north and south branch by the sandbank.Xinzhou with typical sandbank environment is in the southeast of Yingjiang district,Anqing city.It is a long from east to west and flat from south to north,with an area of about 9 km2.Studies have shown that sandbanks and other complex channel can provide habitats,foraging,breeding and shelter for many aquatic life.However,with the strengthening of human activities in recent years,overfishing,large-scale water conservancy projects construction and water pollution,leading to the fishery resources in the Yangtze river decline continuously,the fishery catches fallen sharply,the rare and endangered species and biodiversity tends to lose.The Anqing river is no exception,the species composition of fish has changed significantly,showing a trend of miniaturization and younger age,so it is urgent to study,evaluate and protect the fishery resources in the Yangtze river.Based on the above scientific questions and background,this paper selected the Anqing Xinzhou section as the daily survey area for early fish resources from April 15 to August 4,2018,there are two sections in south and the north branch respectively.The present situation of larval and juvenile fish resources in Xinzhou section was analyzed,including species composition,ecological and spawning patterns and diversity index.The temporal-spatial distribution characteristics and environmental factors on the abundance and assemblage structure of juvenile and larval fish were compared.It aims to provide basic data for early fish resources research in the lower reaches of the Yangtze river and scientific basis for the conservation and sustainable utilization of fishery resources.The main results are as follows:1、Results on present situation of larvae and juvenile fish resources in Xinzhou section showed that there were 121246 larvae and juvenile fish were identified,belonging to 6 orders,8 families and 34 species.Among them,Cypriniformes accounted for an obvious advantage both in species and quantity number(28 species,91.99%),the economic fish and four famous Chinese carps accounted for 11.74% and 0.13%.There were 5 dominant species and 6 common species,Hemiculter bleekeri was the first dominant species and other dominant species are Pseudobrama simoni、Hemiculter leucisculus and Rhinogobius giurinus.In terms of ecological patterns,Lake-sedentary species were dominated both in species and quantity number(26 species,86.04%).In terms of spawning patterns,fish with pelagic eggs had the most species(16);whereas,fish with floatability eggs had the largest quantities(76.93%).Larvae and juvenile fish diversity of time change shows: The range of Margalef index(D),Shannon-Weiner index(H),Pielou index(J)and Simpson index(C)were 2.03~2.71,0.88~1.61,0.27~0.49 and 0.29~0.62.Margalef index(D),Shannon-Weiner index(H)and Pielou index(J)had the same variation trend,which maximum value appeared in late June.While Simpson index(C)was the opposite which minimum value appeared in late June(0.29).Except the Margalef index(D),the other three diversity indexes were all at a low level,among which the Pielou index(J)and Simpson index(C)were relatively low,and the Shannon-Weiner index(H)was in the middle level.2、Results on juvenile and larval fish assemblage structure in Xinzhou section showed that the species composition from south and north branch had no significantly difference.There were 79338 larvae and juvenile fish were captured in the south branch,accounting for 65.44%;and 41908 in the north branch,accounting for 34.56%.In terms of the dominant and common species composition,there were 4 dominant species and 4 common species.The similarity between south and north branch were 66.66% and 50%.During the sampling period,the spatial variation of species number and quantity of larval and juvenile fish showed that the species number had no significantly change,while the quantity changed greatly,with the largest number in early July(31379)and south 1sampling point(51626).The density spatial and temporal characteristics of larval and juvenile fish showed that the range was 0.60~2001.38 ind/100m3,and the average was 343.87±370.28 ind/100m3.There were three significant peaks,reaching the maximum value on July 13,(2001 ind/100m3).The spatial density was the highest(99387.72 ind/100m3)in south no.1 and the lowest(7957.17 ind/100m3)in south no.3.In general,the temporal variation trend of larva and juvenile fish density in south and north branch were similar,with the highest peak occurring on July 13.The density in south branch(495.12±545.61 ind/100m3)was significantly higher than that in north branch(185.71±230.77 ind/100m3).The spatial-temporal clustering analysis of the assemblage structure shows that the similarity of species composition in all periods is higher than that in different groups(R=1,P=0.029),and there was significant difference between the sampling points(R=0.909,P=0.017).3、The monitoring of the hydrological conditions and environmental factors in the Xinzhou section showed that the trend of water level and water flow was consistent,which ranged from 15000 to 49900 m3/s,and 8.33 to 13.87 m,both reached the maximum on July 19.With the progress of sampling,the water temperature increased gradually and the dissolved oxygen decreased,while the p H,turbidity and transparency had no obvious change.Pearson correlation showed that there was a significant positive correlation between water flow,water level and turbidity(P<0.01).There was a positively correlated between the density of larva and juvenile fish and water flow,water level,water temperature,turbidity(P<0.01).The redundancy analysis between the density of main larval and juvenile fish and environmental factors showed that water flow,turbidity,water temperature and water level were correlated with the density of larval and juvenile fish.