| The Nanxi River is located in the lower Oujiang River and runs through Yongjia County, Zhejiang Province. It is an important water source, has a famous national tourist resort and provides the primary fishery for Yongjia County. However, overfishing, environmental contamination, sand excavation from river channels and hydropower projects, constructed from 2001 to 2014, seriously threaten the fishery resources in Nanxi River. To determine the status of fishery resources in Nanxi River, three field investigations were conducted: December 22, 2013 to January 10, 2014; March 27 to April 10, 2014 and July 16 to August 5, 2014. Twenty-four sampling sites were set in six river sections: four river sections on the main stem( Beixi Reservoir, Dayuanxi, Dananxi, Nanxi ) and two tributary sections(Yantanxi and Xiaonanxi). Fish samples were collected using gill nets, cages, stationary lift nets, stationary fishing gear and fishhook. Species, body length and weight of all fish collected were determined on site. The total Nanxi River catch included 65 fish species from 56 genera, 22 families and 9 orders, with the absolute dominance by Cypriniformes (35 species, 31 genera and 3 families), accounting for 53.8% of the total species. Species composition and number varied with river section; the number of species collected by section were 31, 38, 52, 29, 32 and 34, respectively for Beixi Reservoir, Dayuanxi, Dananxi, Nanxi, Yantanxi and Xiaonanxi. Zacco platypus and Acrossocheilus wenchowensis were the dominant species at all sampling sites with relative abundances of 21.45% and 10.17%, respectively. Coilia mystus, Pseudobagrus ondon, Misgurnus anguillicaudatus, Sarcocheilichys parvus and Odontobutis obscura were dominant at some sampling sites. Nonmigratory fish species were the primary target for fishing and included Cyprinus carpio, Carassius auratus, Acrossocheilus wenchowensis, Zacco platypus, Hemibarbus labeo, Liza haematocheila, Coilia mystus, Pseudobagrus ondon, Odontobutis obscura and Lateolabrax japonicus. However, the size of individuals collected was small, indicating overfishing in the Nanxi River. The fish community of the lower Nanxi River and estuary displayed low similarity (0.288-0.356) with the other sections. The fish community of Beixi Reservoir were of higher similarity (0.333-0.537) with the four riverine sections and the four riverine sections were moderately similar (0.615-0.737). For the Nanxi River fish community, the Shannon-Weiner diversity index, Wilhelm index, Simpson dominance index and Pielou evenness index were, respectively: 2.178-2.956, 2.207-3.009, 0.7813-0.9338 and 0.2848-0.6008. Fish biodiversity in the lower Nanxi River and Beixi reservoir was lower than in the four riverine sections. The fishery resource in Nanxi River is in serious decline, so conservation and ecological restoration measures should be taken to protect and restore fish populations in Nanxi River. |
