The Luoxiao Mountains (25°32'–29°28'N, 113°09'–114°26'E) are a large system of mountain ranges, located in the southeast of China’s mainland with an overall north-south trend, stretching across Hubei, Hunan, and Jiangxi provinces. It consists of Mufu Mountain, Jiuling Mountain, Wugong Mountain, Zhuguang Mountain, and others. The total length of the Luoxiao Mountains is 400 km and altitude ranges are 82–2120 m. Lingfeng Peak (2122 m) is one of the highest mountains in the southeastern Eurasia. Its average precipitation range is 1341–1943 mm and forest coverage in the watershed reaches 90% (Table 1). The tributaries of the Ganjiang River from the eastern stream of the Luoxiao Mountains flow into Poyang Lake. The tributaries of Xiangjiang River from the western stream of it flow into the Dongting Lake. The Fushui River alone flows into the Yangtze River.

Sampling sites were selected by considering habitats, variations, and anthropogenic activities in the Luoxiao Mountains. Fish samples were collected from April 2014 to 2017 in eleven streams of the Luoxiao Mountains. We selected eleven streams (42 sampling sites) (Figure 1), including the (1) Fu River (sampling code is FR; three sampling sites), Xiuhe River (sampling code is XH; six sampling sites), Jinjiang River (sampling code is JJ; three sampling sites), Yuanshui River (sampling code is YS; three sampling sites), Heshui River (sampling code is HS; three sampling sites), Shushui River (sampling code is SS; two sampling sites), Suichuan River (sampling code is SC; five sampling sites), Shangyou River (sampling code is SY; three sampling sites), Miluo River (sampling code is ML; four sampling sites), Liuyang River (sampling code is LY; four sampling sites), Mishui River (sampling code is MS; six sampling sites). We collected the fish catch from professional fishermen who captured fish using fully standardized five gillnet clusters, each consisting of six gillnets of 50–80 m in length 4–10 m in height (mesh size = 1.0–10.0 cm) in the Luoxiao Mountains rivers. In addition, we assumed similar capture efficiencies from gillnet samples at each site. At the same time, we surveyed and collected fish in the township markets along the river which enhanced the species checklists at each section. All fish specimens were identified according to Chen (1998), Chu et al. (1999), and Yue (2000), and the scientific name was corrected according to Fishbase (http://www.fishbase.org/search.php). The division of endangered categories of fish was decided according to Jiang et al. (2016) and IUCN (2017).

Figure 1. 

Map showing the sampling location of the streams of the Luoxiao Mountains.

Beta diversity is represented by the difference in species composition between different communities, which was determined by species turnover (species replacement) and nestedness (richness difference; Baselga 2010; Carvalho et al. 2012). In order to quantify the effects of two processes, Baselga (2010) systematically proposed the beta diversity decomposition method (BAS frameworks) based on the Sørensen index (β_sor), which was decomposed into species spatial turnover components (β_sim) and nestedness components (β_sne). Podani and Schmera (2011) and Carvalho et al. (2012) proposed the beta diversity decomposition method (POD frameworks) based on the Jaccard index (β_jac), which was decomposed into species replacement components (β_-3) and richness difference components (β_rich). Here, we analyzed the fish biodiversity based on both the BAS and POD frameworks.

BAS frameworks (Sørensen index):

POD frameworks (Jaccard index):

The fish specimens sampled and identified in the Luoxiao Mountains were categorized into 113 species and 17 families (Figure 2; Appendix 2). The number of Cypriniformes was the greatest, accounting for 68.1% of the total number of fish species, followed by Siluriformes and Perciformes, accounting for 14.2% each, and Beloniformes, accounting for 0.1% (Figure 2). In addition, according to the endangered categories of the Jiang et al. (2016), Least Concern fish species were the greatest, accounting for 77.9% of the catch (Appendix 3). Critically Endangered, Vulnerable, and Near Threatened fish species accounted for 7.1% (Appendix 3).

Figure 2. 

Fish composition from the streams of the Luoxiao Mountains.

The fish composition similarity in the Luoxiao Mountains had a mean value of 0.50 and 0.67, based on BAS and POD frameworks respectively (SD ± 0.06 and SD ± 0.05, respectively; Table 2). The spatial turnover and replacement components (β_sim and β_-3, 0.36 ± 0.08, and 0.39 ± 0.13) were greater than its nestedness and richness difference components (β_sne and β_Rich, 0.14 ± 0.09 and 0.28 ± 0.16). FS and SC had a high β_sor and β_jac (0.55 ± 0.07 and 0.54 ± 0.11; 0.71 ± 0.05 and 0.69 ± 0.09), a high spatial turnover and replacement components (0.39 ± 0.07 and 0.45 ± 0.12) in LY and nestedness and richness difference components (0.22 ± 0.10 and 0.41 ± 0.17) in SC (Table 2).

At the same time, fish composition similarity (β_sør and β_jac) for the entire fish fauna had a mean value of 0.66 and 0.76 (SD ± 0.24 and 0.21, Table 3). The spatial turnover and replacement components (β_sim and β_-3, 0.41 ± 0.03 and 0.32 ± 0.03) were higher than the nestedness and richness difference components (β_sne and β_rich, 0.25 ± 0.02 and 0.44 ± 0.02). The greatest β_sor and β_jac (0.93±0.16 and 0.96±0.13) and spatial turnover and replacement components (0.80 ± 0.04 and 0.49 ± 0.03) was in Hemiramphidae, followed by Amblycipitidae, and the lowest was in Syngnathidae. The greatest nestedness and richness difference components (0.53 ± 0.25 and 0.65 ± 0.26) was in Syngnathidae, followed by Siluridae, and the lowest was in Hemiramphidae (Table 3).

The PCA showed that fish composition similarity of LY, SS, SY, XH, and MS were similar based on BAS and POD frameworks; FS, JJ and SC were similar; HS and ML were similar; and YS was uniquely divided into other areas, respectively (Figure 3).

Figure 3. 

Results of the principal component analysis (PCA) on the compositional similarity of fish species in the streams of the Luoxiao Mountains. JJ: Jinjiang River; YS: Yuanshui River; HS: Heshui River; SS: Shushui River; SC: Suichuan River; SY: Shangyou River; MS: Mishui River; ML: Miluo River; FS: Fushui River; XH: Xiuhe River; LY: Liuyang River.

We found almost no significant effects of geographical drivers on overall beta diversity for the Luoxiao Mountains (Table 4). The correlation between BAS and POD frameworks and difference in length, average precipitation, mean temperature, and average gradient were not significant in the Luoxiao Mountains. The correlation between β_sne (β_rich) and differences in area and annual average runoff was significant. The correlation between β_sim (β_-3) and difference in average altitude was also significant (Table 4).

Studies on fish composition and diversity in streams is the basis for the conservation and management of stream fishes (Liu et al. 2017; Zhang et al. 2018). In this study, the fish specimens sampled and classified in the stream of the Luoxiao Mountains were categorized into 113 species. Compared with species numbers of the Shiwanda Mountains (102 species; Zhao and Zhang 2001), Wuyi Mountains (117 species; Song et al. 2017), and the Tibetan Plateau (114 species; Wu and Tan 1991), the fish abundance in the Luoxiao Mountains was also higher.

Abiotic and biotic factors and their ecological processes in different stream sizes varies substantially (Zhang et al. 2018). At least in streams, local species richness of fishes, habitat diversity and complexity often increase in large streams (Roberts and Hitt 2010; Zhang et al. 2018). Comparing alpha diversity and beta diversity at local and landscape scales is an important, yet little-understood, area of basic and applied ecological research (Kessler et al. 2009). However, most studies on fish diversity of streams have focused on alpha diversity, whereas fewer studies have investigated beta diversity (Tisseuil et al. 2013; Johnson and Angeler 2014). Knowledge of beta diversity patterns can go beyond the systematic conservation planning method that only considers the location of protected area in relation to natural physical and biological patterns (Margules and Pressey 2000; Wiersma and Urban 2005). The efficiency of protected areas not only relies on species richness, but also on how well the complementarity among sites increases biodiversity conservation (Howard et al. 1998; Bush et al. 2016; Socolar et al. 2016). In this study, as turnover brought the larger contribution to beta diversity, additional conservation efforts must target an increase in the number of protected areas, which should be spread across each one of the regions, to maximize the protection of species diversity.

The modern freshwater fish fauna of Eurasia originated in the early Tertiary (Chen et al. 1986; Liu and Quan 1996; Zhang 2012). At the same time, the primitive species of the Danioninae and Barbinae became the main component of the fish fauna with the flattened land and the warming climate (Chen et al. 1986; Tang et al. 2001). During the dramatic changes of landscape and climate of the Eurasian continent in the late Oligocene and the end of the Pliocene, the primitive species component had been reduced rapidly (Chen et al. 1986; Tang et al. 2001). After the Quaternary ice age, only some offspring fishes of the old Tertiary Period remained (Chen et al. 1986; Tang et al. 2001). Moreover, Labeoninae, Gastromyzontidae, Balitoridae and Sisoridae were dominant during the uplift of the Tibetan Plateau (Chen et al. 1986; Yang et al. 1982; Tang et al. 2001). At the same time, a large area of alluvial plains appeared in eastern China, and special habitats were created under the influence of the East Asian monsoon (Chen et al. 1986; Zhang and Chen 1997). The cold-water fishes, such as Leuciscinae and Gobioninae became the endemic fishes of the river plain in East Asia (Hypophthalmichthyinae, Culterinae, Xenocyprininae, Acheilognathinae, Gobiobotinae) and the warm-water fishes the endemic fishes of Southeast Asia (Botiinae, Clariidae, Amblycipitidae, Belontiidae, Channidae, Mastacembelidae). Since then, these taxa have become the major faunal component in southern China (Chen et al. 1986). In this study, Culterinae, Gobioninae, and Acheilognathinae had a high species composition (Appendix 2). At the same time, the spatial turnover component is the main contributor of beta diversity in Hemiramphidae, Amblycipitidae, Catostomidae, Clariidae, Balitoridae, and Percichthyidae, indicating that it would be necessary to conserve habitats in the Luoxiao Mountains.

The headwater stream is a tributary of a larger river, which is often located in a mountainous area with high altitude. Compared with large rivers, it had relatively simple habitat structure, poor nutrition, obvious hydrological change, and low species diversity (Vannote et al. 1980; Grossman et al. 1990; Zhang et al. 2018). Therefore, the ecosystem of the stream is more fragile, its resistance to external disturbance and resilience is lower, and it would be more difficult to recover once it is damaged by humans. Fish, as the apex consumers of the stream, are very important to the stability and functioning of the stream ecosystems (Nogueira et al. 2010; Yan et al., 2011; Arthington et al. 2016; Liu et al. 2017). During the long evolution process, fishes have gradually adjusted their corresponding morphological characteristics, phenological rhythms, and life history countermeasures so that they could adapt to the unique natural environment of the stream (Lytle and Poff 2004; Osorio et al. 2011; Ren et al. 2016). However, due to habitat loss, water pollution, alien-species invasions, forest overcutting, climate change, overfishing etc., the fish biodiversity of most streams in China have been seriously threatened (Dudgeon et al. 2006; Allan and Castillo 2007). For example, numerous small dams in mountain streams were established (Huang et al. 2008; Hu et al. 2009). Dam constructions modified these small fast-flowing streams, which led to the decline of fish species adapted to rapid streams (Hu et al. 2009). In addition, a large number of fishing methods such as traps, gill nets, and electro-fishing has led to overfishing which has also caused a dramatic decline in fish biodiversity (Huang and Gong 2007; Zhang et al. 2010). Heavy metal pollution has affected the aquatic ecosystem in the Luoxiao Mountains (He et al. 1998). The contents of heavy metals have greatly exceeded the recommended standards (Xu et al. 2016). In this study, critically endangered (Myxocyprinus asiaticus), vulnerable (Leptobotia elongata, Pseudobagrus pratti, Liobagrus marginatus, Siniperca roulei), and near threatened (Onychostoma barbatulum, Siniperca obscura, Siniperca undulata) fish species accounted for 7.1% of the species recovered. At the same time, the PCA results showed that the fish composition among the streams sampled in the Luoxiao Mountains were similar. As turnover brought the larger contribution to beta diversity, additional conservation efforts must target an increase in the number of protected areas, which should be spread across each of the regions, to maximize the protection of species diversity.

Freshwater fishes were thought to be the world’s most threatened group of vertebrates after amphibians (Bruton 1995; Hiddink et al. 2008; Liu et al. 2017) and, without protection, 20% of the world’s freshwater fishes may become extinct in the next 50 years (Moyle and Leidy 1992; Fu et al. 2003). Although endangered fish have raised public awareness, conservation strategies of fish biodiversity in China are concentrated on endangered species and economic fish (Fu et al. 2003; Liu et al. 2017). In addition, protected areas mainly occur in terrestrial conservation strategies, but freshwater habitats are commonly protected only incidentally as part of their inclusion within terrestrial reserves (Huang et al. 2013). For example, conservation areas of plants, animals, and wetlands in Jiangxi Province have been established, but there are very few freshwater protected areas nor are there any fish passage facilities in the rivers (Huang et al. 2013). In this study, species turnover component is the main pattern of beta diversity, implying that a larger number of protected areas would be necessary to conserve the regional biodiversity in the Luoxiao Mountains. Therefore, in order to protect fish biodiversity, the establishment of freshwater protected areas in the streams of the Luoxiao Mountains should be considered.