Leizhou Peninsula is located in the Indo-Burma biodiversity hotspot. However, information about freshwater fish species in this peninsula is very scarce. Based on surveys and a literature review, a total of 100 freshwater fish species (92 native and eight non-native) within seven orders, 21 families and 70 genera, have been recorded in the Leizhou Peninsula. Four species, Mud Carp (Cirrhinus molitorella), common carp (Cyprinus carpio), South Sharpbelly (Pseudohemiculter dispar), and Helmet Catfish (Cranoglanis bouderius) are listed as threatened species in red list of IUCN. Sand mining, aquaculture pollution, non-native aquatic species, and overfishing are the greatest threats to freshwater fish biodiversity of Leizhou Peninsula. For better sustainable development, conservation efforts should be focused on the establishment of protected areas, improvement of sustainable fishery management and control of non-native species. This study provides management recommendations that will be useful for freshwater fish biodiversity conservation and fishery management in Leizhou Peninsula.
Freshwater ecosystems cover less than 1% of the Earth’s surface, but provide habitats for about 10% of species in the world (Strayer and Dudgeon, 2010). However, the rate of biodiversity loss in fresh waters is much greater than in terrestrial ecosystems (Dudgeon et al., 2006). It is noteworthy that freshwater fishes are recognized as the second most threatened animal group, after amphibians (Sala et al., 2000; Olden et al., 2010). Freshwater biodiversity is recognized in the state of great crisis (Dudgeon et al., 2006; Vörösmarty et al., 2010). The main threats to freshwater biodiversity include: overexploitation, water pollution, flow modification, habitat degradation, and non-native species (Dudgeon et al., 2006). Therefore, many biologists focus on conservation of freshwater fishes (Abell et al., 2008; Pan et al., 2016).
China is one of the megabiodiversity countries in the world and ranks in the top five in terms of freshwater megabiodiversity (McAllister et al., 1997). Chinese freshwater ecosystems support nearly 10% of the freshwater fish species in the world (Xing et al., 2016). Most studies on freshwater fish species in China have focused on large rivers, for example, the Yangtze River (Fu et al., 2003), Yellow River (Kang et al., 2016), and Mekong River (Kang et al., 2009). However, some regions that support high freshwater fish biodiversity, such as Leizhou Peninsula, have received little attention.
Leizhou Peninsula is located in the Indo-Burma biodiversity hotspot (Myers et al., 2000). Some ichthyologists have focused on the freshwater fish biodiversity in some regions of Indo-Burma, such as Laos, Cambodia, and Vietnam (Zakaria-Ismail, 1994; Yap, 2002), however, information on freshwater fishes in some regions of Indo-Burma within Chinese territory is scarce.
The purpose of the present study is: (1) to compile an up-to-date inventory of the freshwater fish fauna of Leizhou Peninsula; (2) to review the main threats to freshwater fish biodiversity; and, (3) to provide recommendations for fish biodiversity conservation.
Materials and methods
Leizhou Peninsula is situated at the southernmost tip of Chinese mainland (109°30´−110°55´E, 20°12´−21°35´N) (Figure 1). It is 140 km from north to south and about 60–70 km from east to west, with an area of about 13,225 km2.
Leizhou Peninsula is located on gently sloped terrain. The elevation is less than 300 m, with only a few mountains over 300 m. The southern peninsula area is basalt mesa, which accounts for about 43.3% of the total peninsula area. Most of the midwestern and northern peninsula is sea terraces, which account for 26.7% of the total peninsula area. The central and eastern peninsula are alluvial and marine plain, accounting for 17.4% of the total peninsula area.
In Leizhou Peninsula, there are 50 rivers that end at the South China Sea. Most rivers in this area are short (less than 50 km) and have low slope and slow flow. The three main rivers in Leizhou Peninsula are Jianjiang ending at Zhanjiang Bay in the east, Jiuzhoujiang ending at Beibo Bay in the west, and Nandou River ending at Leizhou Bay.
Leizhou Peninsula has a northern tropical monsoon climate with mean annual temperature of 22.3 °C (28.4 °C in July and 15.5 °C in January) and the annual precipitation is 1,711 mm (about 73% in the rainy season, April–October, and 27% in the dry season). The rainfall distribution is uneven, with more rainfall in the northeast and less in the southwest. Typhoons arrive frequently during summer on the eastern coastline.
In China, wetlands are divided into four types: coastal (including to shallow sea, sea grass bed, coral reef, rocky coast, shingle foreshore, mudflat beach, mangrove, estuary, delta, and lagoon); river (including to permanent river and flood plain); lake; swamp; and constructed wetlands (reservoir, pond, canal, aquaculture pond, salt pans) (Ma, 2015). In this study, freshwater fishes including fishes that live in fresh water during part or all of their life cycles. Thus, some fishes, such as Amur Goby (Rhinogobius brunneus), Lacustrine Goby (Gobiopterus lacustris), which occur in mangroves, estuaries, and mudflat beaches, were included in this study.
Sources of fish information
Based on both field surveys and literature reviews, we compiled information about the freshwater fish species in Leizhou Peninsula. More than 10 ichthyological surveys have been conducted on Leizhou Peninsula in different seasons, 1985-2017. Fish samples were collected using gillnets (20 × 10 m, mesh size 0.5 cm), cage nets (200 × 10 × 15 cm, mesh size 0.5 cm), and electrofishing (CWB-2000P, 12V, 250HZ). For detailed sampling methods see Tang et al, (2016) and Xiong et al., (2018b). We searched for literature that contained the following combination of words: “Leizhou Peninsula” and “freshwater fish” or “freshwater ichthyo*” in the title, abstract, or keywords using the Thomson Institute for Scientific Information (ISI, http://www.isiknoledge.com) and CNKI (http://www.cnki.net). We also collected information from Chinese books, such as The Freshwater Fishes of Guangdong Province (Pearl River Fishes Research Institute 1991). The scientific names were used as found in the Catalog of Fishes (http://researcharchive.calacademy.org/research/ichthyology/catalog/fishcatmain.asp).
To identify freshwater fishes in Leizhou Peninsula at a risk of extinction, we determined if the species were assigned to each red list category (www.iucnlist.org). Fish species assessed as Critically Endangered (CR), Endangered (EN) or Vulnerable (VU) are referred as “threatened” in this study.
We identified 92 native freshwater fish species and subspecies, within five orders, 21 families and 70 genera, distributed in Leizhou Peninsula (Table 1). In total, four freshwater fishes, Mud Carp (Cirrhinus molitorella), Common Carp (Cyprinus carpio), South Sharpbelly (Pseudohemiculter dispar), and helmet catfish (Cranoglanis bouderius), of Leizhou Peninsula were classified as endangered (Table 1).
Based on our survey, there are eight non-native freshwater fish species that occur in Leizhou Peninsula, including Mrigal Carp (Cirrhinus cirrhosus), African Sharptooth Catfish (Clarias gariepinus), Mosquitofish (Gambusia affinis), Lacustrine Goby (Gobiopterus lacustris), Largemouth Bass (Micropterus salmoides), Nile Tilapia (Oreochromis niloticus), Pirapitinga (Piaractus brachypomus), and Orinoco Sailfin Catfish (Pterygoplichthys multiradiatus). Therein, Nile Tilapia, Orinoco Sailfin Catfish, and Mosquitofish, have widely established feral populations in diverse aquatic ecosystems (such as wetlands, rivers, reservoirs, ponds, mangroves).
Leizhou Peninsula, accounting for only 1.37% of Chinese area, contain 92 native freshwater fish species (about 7% of the total number of China). Thus, the freshwater fish biodiversity of Leizhou Peninsula is important in China.
The freshwater ichthyofauna of China and adjacent areas was composed of four divisions, the Palearctic, East Asia, South Asia (Oriental), and High Central Asia (He, unpublished data), corresponding to the global zoogeographic regions of terrestrial vertebrates (Palearctic, Sino-Japanese, Oriental and Saharo-Arabian) (Holt et al. 2013). The fish fauna of Leizhou Peninsula is mainly East Asian origin. 51 species of Cyprinidae belong to five subfamilies. 22 species of Xenocypridinae, 13 species of Gobioninae and six species of Acheilognathinae are endemic to East Asia. Most of the three subfamilies are only distributed in East Asia from Heilongjiang to Honghe River (Chen et al., 1986; Chen, 1998). Cranoglanididae and Percichthyidae species are also endemic to East Asia. The least abundant fishes are the South Tropical Fauna (South Asia and Southeast Asia origin), including to Danionae of Cyprinidae and Schistura, Micronemacheilus of Nemacheilidae. Anabantidae, Channidae, Osphronemidae, Mastacembelidae, Synbranchidae, Bagridae, and Gobiidae, most of them are mainly distributed in South Asia and East Asia and Africa. The third ichthyofaunal component is south montanic origin, including Labeoninae of Cyprinidae, Balitoridae, Sisoridae (Chen, 1998). Cobitis and Misgurnus of Cobitidae, Cyprininae of Cyprinidae, Silurus of Siluridae belong to Paleogene or Neogene origin, the ancestors of them were once widely distributed in China, while the most of descendants were only in the south China (Chen, 1998) (Table 1). Most of fishes in Leizhou Peninsula inhabit in running or slow-flowing streams, rivers, reservoirs and ponds. Some of species are adapted to the warm-water and torrent-adapted species (e.g. Labeoninae of Cyprindae, Gastromyzontidae of Cypriniformes, Sisoridae of Siluriformes) is also distributed on the Leizhou Peninsula (Table 1).
Threats to fish biodiversity
Many human activities have threaten Chinese freshwater fish biodiversity, including hydrological alterations, overfishing, pollution, non-native species, and habitat alteration (Xing et al., 2016). The main threats in Leizhou Peninsula including sand mining, aquaculture pollution, non-native species and overfishing. Sand mining could destroy the habitats for feeding, migration and reproduction of fishes (Chen, 2017). In past 20 years, sand mining occurred in the Leizhou Peninsula to make concrete and cement needed for rapid urbanization infrastructure (Zhang et al., 2015). Many illegal sand mining have destroyed important habitats of fishes, such as rivers and mangroves (Ye et al., 2018). Many threatened small fish species, such as Pseudohemiculter dispar, inhabit small habitats (streams, mangroves, swamps). Sand mining has destroyed habitats many of these habitats used for freshwater fish spawning, rearing, and feeding. Meanwhile, Leizhou Peninsula is the most frequent landing location by typhoons in Chinese mainland (Shang and Li, 2015). Once the habitat is destructed by sand mining, disturbances such as heavy rainfall, flooding, and high winds accompanying typhoon could deteriorate habitat quality greatly (Chen et al., 2015).
Leizhou Peninsula is one of the main aquaculture areas in China with rapidly increasing fish production. The production of Crayfishes (Penaeus vannamei, Cherax quadricarinatus, Procambarus clarkii) in Leizhou Peninsula accounts for about 1/3 of the total Crayfish production of the world (China Fisheries Statistical Yearbook 2017). The area of the shrimp pond has increased almost fivefold in the past twenty years. However, local government and fisheries farmers didn’t adopt measures for controlling aquaculture pollution. In the past three decades, there has been a rapid increase in pollution discharged into rivers, lakes and lagoons from crayfish aquaculture (Li et al., 2006). Nutrient overload has led to eutrophic and harmful algal blooms of a great number of waterbodies in Leizhou Peninsula (Liao et al., 2012). Finally, the widespread mortality of fishes occurres in Leizhou Peninsula caused by hypoxia and toxic compounds in eutrophic aquatic ecosystems (Camargo and Alonoso, 2006).
China is a hotspot for non-native aquatic species introductions. Non-native species introduced into China have caused great declines of native aquatic biodiversity (Xiong et al., 2015; 2017; Wang et al., 2016). There are eight non-native fish species recorded in Leizhou Peninsula. Six non-native fish species (Mrigal Carp, Nile Tilapia, Largemouth Bass, African Sharptooth Catfish, Orinoco Sailfin Catfish, and Pirapitinga) were introduced into Leizhou Peninsula for aquaculture. The climate of Leizhou Peninsula is similar to that of native area of these non-native fish species (Xiong et al., 2015). Therefore, many aquaculture ponds and artificial breeding sites were built in the Leizhou Peninsula. Leizhou Peninsula has become important aquaculture and breeding center of non-native fish species. Inevitably, these non-native fish species escaped and successfully established feral populations in rivers, lakes, ponds, reservoirs, and mangroves (Gu et al., 2012; Wei et al., 2017; Xiong et al., 2018a, b). Now, many non-native fish species, such as Nile Tilapia and Orinoco Sailfin Catfish, are abundant and have caused the decline of native aquatic biodiversity (Gu et al., 2015; Wei et al., 2017). Western Mosquitofish (Gambusia affinis) was introduced into China over a century ago as a biological mosquito control agent (Xiong et al., 2015). Western Mosquitofish, which occurs in all suitable waterbodies (including rivers, ponds, reservoirs, swamps, and mangroves), has become the most popular non-native freshwater fish species in Leizhou Peninsula (Pearl River Fisheries Research Institute, 1991). Some studies on western mosquitofish in other invaded regions indicate that it caused the decline and extinction of some fish species (Galat and Robertson, 1992; Cheng et al., 2018).
In China, overfishing is a substantial threat to freshwater biodiversity in every region. Fishes are an important source of food for local residents of Leizhou Peninsula. Over 100 fishing gears, including traps, gill nets, drift-gill nets, hooks, and electrofishing, are used. All details about survey and results see Chu et al. (2007), Zhou et al. (2007), Xiong et al. (2018a, b). The use of some poisons is widespread to control snails, fish, fry and crayfishes in some ponds, canals, and reservoirs, which is causing great damage to native fish biodiversity (Xing et al., 2016). Some field surveys indicated the rapid downward trend of fishery resources in Leizhou Peninsula (Lu, 1990).
Conservation of fish biodiversity
Freshwater fishes are the most important food and protein sources for local residents. However, freshwater fishes are under great threat caused by human activities (Xing et al. 2016; Xiong et al. 2018c). Thus, more attention should be paid to conservation of freshwater fishes in Leizhou Peninsula. The creation of protected areas for targeted fish species or ecosystems is an important method for conservation of fish biodiversity (Chape et al., 2005; Xiong et al., 2108c). Some protected areas have been established for conservation of mangroves, coral reef, and other ecosystems in Leizhou Peninsula (Xu et al., 2012), however, protected area for conserving freshwater biodiversity have never been established. Some protected areas should be established in streams, which are important habitats of threatened fishes, such as Yaoshan Carp (Aphyocypris arcus), Hainan Loach (Gobiobotia kolleri), Paradisefish (Macropodus opercularis) to breed and spawn (Xiong et al., 2018c).
Some studies have shown that fishing bans have been an effectively protect measure for conservation and restoration of fishery resources in South China (Li et al., 2014). Fishing bans have been established in many river basins and regions of China, such as the Yangtze River, and Pearl River. However, there are no Chinese regulations for fishing bans in Leizhou Peninsula. Thus, local departments of fishery administration should proclaim fishing bans in the breeding season for some endangered fish species. Electrofishing and some fishing gears are illegal for fishing in freshwater ecosystem, but many local residents illegally fish with destructive fishing gears (Ye et al., 2018); Therefore, fishery inspectors should inspect fishing boat and confiscated illegal fish gears.
China is the country most seriously threated by non-native aquatic species (Xiong et al., 2015; Wang et al., 2016; Xiong et al., 2017). Leizhou Peninsula is an important region for aquaculture and aquarium species in China. Thus, non-native aquatic species were introduced into this region. Prevention of introduction is cheaper than control of non-native species (Leung et al., 2002; Xiong et al., 2015). Thus, researchers should pay more attention on distribution, life-history traits, and ecological impacts of non-native species (Xiong et al., 2015). The surveillance and control the non-native species need to be strengthened. For example, local government should encouraging fishing campaigns targeting non-native species in Leizhou Peninsula.
Leizhou Peninsula, which contains high freshwater fish biodiversity and numerous endemic species, is located in global biodiversity hotspot. Many fish species support the fishery and aquaculture sector in Leizhou Peninsula. Sand mining, aquaculture pollution, non-native species, and overfishing are major threat to the fishes in the Leizhou Peninsula. Therefore, management should focus on effective protection and conservation of freshwater fishes in Leizhou Peninsula, including establishment of protected areas, control of illegal fishing, and prevention of non-native species.
The authors are very thankful to Ning Ye, Chuanhao Pan, Zhongduo Wang, and Zhongliang Wang for their assistance and useful suggestions. Special thanks to two anonymous reviewers whose comments greatly improved the manuscript.
This research was supported by CAS-SEABRI (Y4ZK111B01), the National Natural Science Foundation of China (No. 31472016).
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/uaem.