| Gan River is one of the largest river in Jiangxi Province,it is rich in fish stocks and is the most important habitat,spawning and feeding ground of migratory fish which migration between the Ganjiang River and Yangtze River,it has great significance for the promotion and development of fishery economy,and for the protection of endemic species in Jiangxi province.With the development of society,the main stream has been planning to build six dams,three of these dams have been built.Cascade dams have long since been considered to be undesirable with destruction of habitat,fish community structure always associated with the change of habitat,such as semi-migratory fish disappear gradually because the return channel of migration being cut off.Fish resources and diversity of most rivers are decreasing after dam construction.This study analyses the effect of dams on the fish assemblages and fish stocks,and to provide scientific basises for the aquatic creatures conservation and management of fishery in Jiangxi Province.The research includes a survey of the current situation of fish resources in the middle and lower reaches of Gan River;Effect of dams on fish community structure in the river have been analysed;Population structure and growth features of main commercial fishes have been analysed;Main troubles of fishery and some feasibility suggestions have been suggested based on the following results:1.The research conducted in 7 sampling sites:Nanchang,Baqiu,Jiangsha,Shihutang,Yanxidu,Shukou and Suichuan,belong to 2 sections of trunk stream and 1tributary stream:reservoir region(Xiajiang Dam and Shihutang Dam)and channel region(Nanchang section),tributary stream(Suichuan River)from April 2015 to January 2016.Throughout the study,95 species were collected,belonging to 6 orders,17 families and 62 genera,a new record species have been found:Myxocyprinus asiaticus.In terms of abundance,the dominant species are Squalidus argentatus,Pelteobagrus fulvidraco,Carassius auratus,Hemiculter bleekeri,Pseudobrama simony,Rhinogobius giurinus,Pseudohemiculter dispar and so on.Cyprinids were the most(56.8%)classified by taxonomy;Insectivores were the most(37.89%)classified by trophic;Eurytopic were the most(50%)classified by ecotype;Demersal fish were the most(45%)classified by habitat type of water layer.Comparison with historical data,the result revealed that fish biodiversity is decreasing.2.According to the environment data,7 sampling sites can be devide as 3 kinds of habitats.The differences of fish community structure have been analysed with Bray-Curtis index base on the abundance of catches,the result indicate the fish assemblage have been devided as 3 groups:channel group,reservoir group,and tributary group,the indicator species were 48,37 and 42 species respectively.Redundancy analysis(RDA)indicated that turbidity,water depth dissolved oxygen chlorophyll content and the sediment type were significant environmental factors in the middle and lower reaches of Gan River,and the fish groups had a significant difference in trophic(P<0.05).3.Temporal spatial pattern of fish assemblages have been analysed base on the biodiversity and CPUEb(biomass of one boat),the results showed that the biological diversity is on the upward trend from the middle reaches to the lower reaches.High biodiversity were in the wet season(12.94),lower biodiversity were in the dry season(10.32),and it's not significant(P>0.1);biodiversity of tributary group is the highest(13.60)among the fish groups under the influence of dams,and reservoir group is the lowest(11.12);CPUEb of Eurytopic and Rheophilic fish shows significant difference between 3 groups;On the trophic level,piscivores,benthivores and miscellaneous consumers were rich in channel part,insectivores were rich in tributary part.According to the analysis of CV(coefficient of variation)base on the CPUEb of the wet season and dry season,the channel group and the reservoir group showed highly unstable(CV>76%),while the tributary group showed highly stable(CV<25%).4.The current situation of population structure and features of main commercial fishes have been analysed,the results showed that the changing trend of the population structure towards to smaller body and younger age,the main age range of Hypophthalmichthys molitrix is 1~+~2.years,the main length range 29~35cm;The main age range of Aristichthy nobilis is 1~+~3.years,the main length range is38~45cm;The main age range of Ctenopharyngodon idellus is 2.~3.years,the main length range is 37~49cm;The main age range of Mylopharyngodon piceus is 1~+~2~+years,the main length range is 42~49cm. |
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