| The Hejiang section of the upper maistem of the Yangtze River,where its flow condition remains as lotic and location is within the core area of the"state-level natural protection area for rare and endemic fishes in the upper Yangtze River",about 230km from Xiangjiaba Dam,is a critical habitat of reproduction and nursery to many rheophilic species.Furthermore,the confluence of the Chishui River,the last one free-flowing tributary of the upper Yangtze River,has greatly increased the importance of the Hejiang section for the conservation of fish resources.In this study,ichthyoplankton were collected in the Hejiang section in 2020 and 2021 during the peak spawning periods of fishes in the upper Yangtze River.Firstly,the temporal dynamics of ichthyoplankton and the key influencing factors were analysed;secondly,and the differences in species composition and abundance between the the Hejiang section and the Chishui River were compared.We aim to provide data to support the conservation and management of fish resources in the upper Yangtze River.The main results are as follows.1.A total of 63 species(genera)including 15 endemic fish species were identified from the collected fish eggs and larval fish in our study.Specifically,there 38 species(genera)including six endemic fish species and 55 species(genera)including 15 endemic fish species were identified in 2020 and 2021,respectively.Fish larvae were mainly dominanted by Rhinogobius spp.and Neosalanx taihuensis,while the fish eggs were mainly dominanted by Rhinogobio typus,Coreius heterodon and Gobiobotia filifer.The average densities of total fish larvae,total fish eggs,and fish larvae and eggs of endemic species in 2020 were 89.06±78.55 ind.·1000m-3,19.89±20.58ind.·1000m-3,2.22±1.65 ind.·1000m-3 and 4.25±5.53 ind.·1000m-3,respectively,and that in 2021were 9.97±14.57 ind.·1000m-3,2.76±3.54 ind.·1000m-3,1.44±1.74 ind.·1000m-3 and 0.79±0.63ind.·1000m-3,respectively.Eurytopic species accounted for 39.29%and 35.71%of the species number of the total fish larvae and the total fish eggs,respectively,and 87.89%and 34.14%of the total abundance,respectively.By comparison,rheophilic species accounted for 44.64%and 46.43%of the species number of the total fish larvae and the total fish eggs,respectively,and 6.83%and64.42%of the total abundance,respectively.Environmental factors including the disccharge,water temperature and transparency.etc.had a significant effect on the diversity and abundance of fish larvae and eggs(P<0.05).We found a significant increase in the abundance of total fish larvae and eggs during the ecological operations of the Xiangjiaba Dam in 2020,which may suggested that the ecological operations had enhanced the fish reproductive activities downstream of dam.2.A total of 32 species(genera)of larval fish,including five endemic fish species,were collected in the upper mainstem and the Chishui River by using larvae towing nets through March to June 2021.A total of 22 species(genera)from three orders and four families and 27 species(genera)from three orders and four families were collected from the upper mainstem and from the Chishui River,respectively.The average densities of larval fish in the upper mainstem and the Chishui River were 8.47±7.95 ind.·1000m-3 and 17.78±19.42 ind.·1000m-3,respectively.The average densities of endemic fish in upper mainstem and the Chishui River were 1.81±3.81ind.·1000m-3 and 3.44±5.61 ind.·1000m-3,respectively.The results revealed a significant difference in the composition and abundance of larval fish between main stem and the Chishui River(P<0.01).Water temperature and transparency had a significant effects on different ecological guilds in the upper mainstem(P<0.05),while dissolved oxygen and transparency had a significant effects on different ecological guilds in the Chishui River(P<0.05).We also noted that the majority of the substrate of the upper mainstem was rock and gravel,whereas that in the Chishui River was sand and silt.Our results revealed that the Hejing section is a key section for the spawning and nursery of fishes in the upper mainstem of the Yangtze River and is particularly important for the recruitment success of poupulations of endemic and rheophilic species.Environmental factors significantly affect the ichthyoplankton assemblages with the river discharge being the most critical factor.The significant difference in species composition of ichthyoplankton between the upper mainstem and the Chishui River could indicated that both of them play an important role in the conservation of fish biodiverty of the Yangtze River. |
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