The Yellow River (39°28'N–41°05'N, 115°25'E–117°30'E) is the second longest river in China and the sixth longest river in the world with a total length of 5,464 km of mainstream and with a total drainage area of 752,773 km² (Jia et al. 2020). It originates on the east side of the Yaladazhe Mountain (Yahela Dahazhe Mountain) in Qinghai Province, and flows through a total of nine provinces (or Autonomous Regions), including Sichuan, Gansu, Ningxia, Inner Mongolia, Shaanxi, Shanxi, Henan and Shandong (Fig. 1). It eventually turns eastward into the Bohai Sea.

Figure 1. 

The location of the Yellow River Basin.

The source of the Yellow River and its upper reaches are in Hekou Town, Toketo County, Inner Mongolia Autonomous Region. This upper area of the Yellow River Basin has a length of 3,471.6 km and a watershed area of 428,000 km², accounting for 53.8% of the Basin’s total area. The middle reaches of the Yellow River extend from Hekou Town to Taohuayu in Zhengzhou City, Henan Province. The middle reaches of the river are 1206.4 km long, with a watershed area of 344,000 km², accounting for 43.3% of the total watershed area, with a drop of 890 meters and an average specific decline of 7.4‱. The downstream reach of Yellow River is from Taohuayu to the estuary of Bohai Sea. The lowermost zone of the Yellow River is 785.6 km. The watershed area of the lower most zone is 23,000 km², accounting for only 3% of the total watershed area. It has a drop of 94 m, and the specific decline in elevation is steeper at the reach’s beginning and slower near the end of the zone, with an average drop of 1.11‱.

The climate of the Yellow River Basin is mainly controlled by the continental monsoon and transforms from semiarid and arid to subhumid to humid conditions. The average rainfall of the whole basin is 476 mm. However, precipitation is dispersed unevenly over temporal and spatial scales. There are a total of 3.9 million hectares of wetlands (including rivers, lakes, marshes, artificial wetlands, and offshore and coastal areas), which account for about 6% of the total area of Chinese wetland habitats (Sun et al. 2020; Zhao et al. 2020).

Biological samples were collected between May and October between 2003 and 2024. Fish sampling was conducted in different waterbody types using several kinds of equipment including gillnets (20 × 10 m, mesh-size 5 mm), fish cages (0.5×0.5×10 m, mesh size 0.5 cm), dip nets (0.5 m in diameter with a stretched mesh size of 1 mm), and electrical fish sampling equipment (CWB-2000 P, 12V, 250 Hz). For descriptions of the sampling methodology see Xiong et al. (2015b, 2017b, 2019a). We also implemented botanical surveys beginning in 2003 and recorded non-native aquatic plant occurrences in rivers, lakes, ponds, reservoirs, and canals (for sampling methodology see Xiong et al. 2021, 2022, 2023c, 2023d, 2023e). We carried out non-native species investigations for other biological groups, including amphibians, Crustacea, Mollusca, and reptile species (Xiong et al. 2018a, 2023b, 2024a). A literature review was undertaken that contained the following combination of words: “alien OR exotic OR invas* OR non-native OR non-indigenous” and “the Yellow River” in the title, abstract, and keywords from the Web of Sciences database (WOS, https://www.webofscience.com/wos/alldb/basic-search) and Chinese National Knowledge Infrastructure database (CNKI, http://www.cnki.net). We also assembled relevant information from selected Chinese Books, such as “Alien aquatic plants and animals in China” (Li et al. 2007) and “Illustrations of Alien Invasive plants in China” (Yan et al. 2016). An updated inventory of non-native aquatic species in the Yellow River Basin based on our field surveys and literature review is provided in Suppl. material 1.

Based on our field surveys and literature review, a total of 112 non-native aquatic species belonging to 40 orders, 63 families and 88 genera occurred in the Yellow River Bain (Suppl. material 1). Fishes were the most species-rich taxonomic group (59 species), followed by plants (27 species), molluscs (21 species), reptiles (three species), and crustaceans and amphibians (one species each, respectively). The data for all taxonomic groups are presented in Fig. 2.

Figure 2. 

The number of non-native species in different biological taxonomic groups in the Yellow River Basin.

Sixty-nine non-native species (over 61.60% of the total number of non-indigenous species) were introduced for aquaculture and 30 species were imported for marketing through the aquarium and ornamental trade. Other pathways of entry include importation for use as forage (four species), unintentional introductions (four species), ecological restoration (two species), release for religious reasons (two species), and for biocontrol purposes (one species). All introduction pathways are presented in Fig. 3.

Figure 3. 

The number of non-native species introduced through different pathways of entry into the Yellow River Basin.

The primary origins for these non-indigenous groups and taxa are Asia (39 species), followed by North America (33 species), South America (16 species), Europe (10 species), Africa (nine species), and Oceania (five species). The origins of non-native species are presented in Fig. 4.

Figure 4. 

The number of non-native species by origin in the Yellow River Basin.

There are nine provincial districts (Qinghai, Sichuan, Gansu, Ningxia, Inner Mongolia, Shaanxi, Shanxi, Henan, and Shandong) of China that lie in the Yellow River Basin. Shandong Province has the greatest number of non-native species (70 species), followed by Gansu Province (40 species), Shanxi Province and Qinghai Province (38 species), Henan Province (30 species), Shaanxi Province (29 species), Ningxia Hui Autonomous Region (27 species), Sichuan Province (25 species), and Inner Mongolia Autonomous Region (23 species).

There are 77 non-native species that occur primarily in freshwater habitats, 26 species occupy marine habitats, and nine species occur in both freshwater and marine habitats.

A great number of non-native species provide significantly positive impacts on local economic development, food safety and ecological function. It is difficult to estimate the exact economic value of these non-native species used in aquaculture, the aquarium and ornamental trade, and in other applications. Many species that are native to the Yangtze River drainage, such as black carp (Mylopharyngodon piceus), grass carp (Ctenopharyngodon idella), silver carp (Hypophthalmichthys molitrix), bighead carp (Hypophthalmichthys nobilis), clearhead icefish (Protosalanx hyalocranius) and Asian swamp eel (Monopterus albus) have been widely farmed or occur in almost all natural waterbodies in the Yellow River Basin. The per capita consumption of aquatic products increased from 7.26 kg in 1981 to 14.70 kg in 2015 in China (Yue et al. 2018).

Based on field investigations and our literature review, there are at least 78 non-native species that have caused negative impacts, including 61 non-native species have initiated two or more negative impacts (Suppl. material 1). The most frequent negative impact is competition with native species (76 species), followed by predation of native species (36 species), habitat and ecosystem alteration (23 species), herbivory on native aquatic plants and rice (four species), serving as intermediate hosts of parasites, hybridization and genetic introgression (one species each, respectively).

In this study, we report that 112 non-native species have been introduced and have successfully established feral populations in the Yellow River Basin (Suppl. material 1). This is substantive when compared with invasion data for other heavily colonized sites, such as 42 non-native species in the Three Gorges Reservoir of China (Xiong et al. 2018a) and 103 non-native species in Poyang Lake of China (Xiong et al. 2023b). This may be because the area of the Yellow River Basin is 752,443 km², far greater than the areas of other invasion hotspots. A few species, such tilapia and the white freshwater prawn, were brought to China for aquaculture in the 1990s. Thus, it isn’t certain that all 112 of these non-native species successfully colonized the Yellow River Basin after 2000 (Fig. 1). It is possible that reports of non-native species were made much later than when they were actually introduced. Nevertheless, there is a significant rate of non-native species invasion that is clearly evident in the Yellow River watershed during past twenty years.

In summary, a great number of non-native aquatic species have been imported to China and seriously threaten local biodiversity (Xiong et al. 2015a, 2017a; Wang et al. 2016, 2021). Many non-native aquatic species have been introduced in some biodiversity hotspots areas and have caused large ecological and economic impacts (Xiong et al. 2015a, 2018b, 2019b, 2023b). In some large waterbodies, rapid invasion of non-indigenous species created the highest invasion rates in the world (Xiong et al. 2018a, 2023b; Wang et al. 2021). Some studies have focused upon the Yangtze River, the largest river of China, which is one of the global invasion hotspots (Xiong et al. 2018a, 2023b). Other research has shown that invasion of non-native aquatic species has occurred widely throughout China (Xiong et al. 2018b, 2019b, 2021, 2022, 2023c, 2023d, 2023e, 2023f). The Yellow River, as the second longest river in China, supports a rich freshwater biodiversity (He et al. 2020; Zhao et al. 2020) and numerous endangered fish species, such as Atrilinea macrolepis, Brachymystax lenok tsinlingensis, and Hucho taimen (Cao et al. 2020). This study is the first comprehensive summary of basic information about non-native species in the Yellow River Basin.

The aquarium and ornamental trade was the primary introduction pathway for the global spread of non-native aquatic species (Gertzen et al. 2008; Chang et al. 2009; Strecker et al. 2011; Olden et al. 2021; Olden and Carvalho 2024). As one of the largest producers and consumers for the aquarium and ornamental trade, China has imported many aquatic plants, snails, crayfish, and amphibians (Lin et al. 2006; Xiong et al. 2015a; Wang et al. 2016). For example, there are nearly 500 non-native aquatic plant species that have been introduced to China (unpublished data). To meet high market demands, many non-native aquatic plants were brought into and have been widely planted in the Yellow River Basin. Inevitably, some of these aquatic plants, such as parrot’s feather (Myriophyllum aquaticum), fanwort (Cabomba caroliniana), yellow bur-head (Limnocharis flava), yellow flag (Iris pseudacorus), and water lettuce (Pistia stratiotes), have established dense feral monospecific stands in natural waterbodies (Xiong et al. 2021, 2022, 2023c, 2023d, 2023e; Dong et al. 2023). The online trade has expanded greatly in Chinese markets during the past twenty years (Gao 2018), facilitating the spread of non-native aquatic species (Liu et al. 2021; Wang et al. 2023). For example, Physella acuta has been introduced into China as an aquarium snail. It has been discarded and unintentionally released by aquarium hobbyists, and thus, has become an invasive species in the northern regions of China (the lower reaches of the Yellow River) (Xiong et al. 2024b).

Aquaculture is one of the most important introduction gateways of non-native aquatic species (Naylor et al. 2001; Xiong et al. 2015a), and as the largest global producer of freshwater aquaculture organisms, China has introduced many non-native aquatic species to improve fishery quality and quantity (Lin et al. 2015; Wang et al. 2015). The Yellow River is one of the most important aquaculture and fishery regions in China, and it accounts for about 12.9% of the total fishery production of China in 2023 (MARA 1990–2024). Many non-native aquatic species, including fishes, crayfish, frogs, snails, and turtles have been imported into the Yellow River Basin as important aquaculture species (Suppl. material 1). During the 1960–1970s, Chinese researchers had a breakthrough in artificial breeding techniques in the “Chinese four domestic fish”, primarily distributed in the Yangtze River and Pearl River, including black carp, grass carp, silver carp, and bighead carp (Wu and Zhong 1964). Four carp species and some other Cyprinidae fish species such as common carp (Cyprinus carpio), goldfish (Carassius auratus), pond loach (Misgurnus anguillicaudatus), and large-scale loach (Paramisgurnus dabryanus), became established throughout almost all areas of the Yellow River Basin. Some fast-growing non-native species such as Nile tilapia (Oreochromis niloticus), red swamp crayfish (Procambarus clarkii), and largemouth black bass (Micropterus salmoides), were brought into the Yellow River Basin during the 1980s and 1990s. With reforms and the improvement of people’s living standards, some highly valuable farmed species, such as peled or northern whitefish (Coregonus peled), muksun (Coregonus muksun), and rainbow trout (Oncorhynchus mykiss), have been imported and farmed in the upstream regions of the Yellow River Basin. These non-native species are important species for local aquaculture. More research, regulations and management measures are needed for these non-native farmed species.

Asia was the origin of 34.82% of the non-native species introduced in the Yellow River Basin. This is because many fish species, such as grass carp, silver carp, common carp, and bighead carp, were brought from the Yangtze River to the Yellow River for aquaculture between 1960 and 1980. North America and South America were the second largest origin of non-indigenous species introduced to the Yellow River Basin (29.46%). Beginning in the 1970s, many fishes (such as channel catfish, brook trout, American eel, and largemouth black bass) and molluscs (mainly the Atlantic bay scallop and American cupped oyster) were introduced into China. South America is a large continent with a rich diversity of aquatic habitats supporting a great number of novel aquatic plants and fishes (Xiong et al. 2015a; Wang et al. 2016). Some aquatic plants and fishes were imported to the Yellow River Basin as part of the aquarium and ornamental trade and made South America (14.28%) the third greatest origin of non-native species in the Yellow River Basin.

Many non-native species contribute significantly to economic, ecological and societal values (Schlaepfer et al. 2011; Sax et al. 2022), and some are important species in aquaculture, which is the largest and fast-growing agricultural sector in China (Wang et al. 2015; Xiong et al. 2015a; Kang et al. 2023). For example, tilapia species (mainly Nile tilapia, Oreochromis niloticus) have been widely introduced into many regions (Gansu, Sichuan, Inner Mongolia, Shaanxi, Shanxi, Henan and Shandong) of the Yellow River Basin for aquaculture (Xiong et al. 2023a). The total annual production of tilapia reaches 18,138 tons, which comprised about 9.98% of the production of China in 2023 (MARA 1990–2024). Shandong has become one of the most important mariculture regions of China, and its value increased sharply from 2.66 billion dollars in 2004 to 16.53 billion dollars in 2023 (MARA 1990–2024).

In the past thirty years, many non-native freshwater fish (nearly 400 species), aquatic plant species (nearly 500 species), and molluscs (over 30 species) have been introduced in China for the aquarium and ornamental trade (Xiong et al. 2015a, 2024b; Wang et al. 2016). Many of these non-native species were farmed in the Yellow River Basin. According to our research-based studies, some non-native aquatic plants, such as yellow bur-head (Limnocharis flava), yellow flag (Iris pseudacorus), fanwort (Cabomba caroliniana) and parrots’s feather (Myriophyllum aquaticum), have been widely planted in ponds and are sold as ornamental plants (Xiong et al. 2021, 2022, 2023c, 2023d). It is difficult to accurately value these non-native species within the aquarium and ornamental trade in the Yellow River Basin, but they comprise the greatest volume sold on the largest online trade platforms (Taobao website 2024).

On the other hand, many non-native species have caused significant negative impacts on local biodiversity, human health and in some cases economic sustainable development (Xiong et al. 2015a; Wang et al. 2016). Non-native fishes are the most common group of introduced species (Fig. 2), and some of these have become serious invasive species (Xiong et al. 2015a, 2017a; Wang et al. 2021). For example, tilapia are the sixth most important aquaculture freshwater fish in China (Xiong et al. 2023a) and have had ecological impacts through competition with native species for food and habitat, predation, hybridization, the introduction of new pathogens, and alteration ecosystem traits (Xiong et al. 2015a). The tilapia species (Oreochromis mossambicus and Oreochromis niloticus) have established widely distributed feral populations which have outcompeted native endangered native fishes, such as Oryzias latipes (Xiong et al. 2015b; Cheng et al. 2018). The Yellow River Basin provides suitable habitats for over 165 freshwater fish species (24 endemic fish species, He et al. 2020) and 135 waterbirds (19 endangered species in IUCN criteria and 34 National Protected Animals, China Green Times website 2024). The invasion of these non-native fish species has potentially influenced the survival of important elements of the native aquatic flora and fauna (Xiong et al. 2015a; Kang et al. 2023).

Non-native aquatic plant species are the second largest of the introduced non-native species groups and they have caused significantly negative economic and ecological impacts (Wang et al. 2016; Macêdo et al. 2024). As de facto ecological engineers, some non-native aquatic plants have escaped and established dense monospecific stands, displacing native aquatic plants and significantly decreasing native biodiversity (fishes, crayfish, snails, amphibians and insects) by changing ecosystem structure, physical and chemical characteristics, and the relationships between plants and animals (Schultz and Dibble 2012; Hussner et al. 2021). Some ornamental aquatic plants, such as parrot’s feather, fanwort, yellow bur-head, yellow flag, and water lettuce established large feral populations and displaced some native aquatic plants (such as Trapa bispinosa, Potamogeton crispus, Nymphoides peltate, and Eleocharis dulcis) (Xiong et al. 2021, 2022, 2023c, 2023d). Another widely distributed species is smooth cordgrass (Spartina alterniflora), which forms dense monocultural stands that significantly decreased biodiversity in coastal mudflats of the Yellow River estuary (Ren et al. 2019; Jiang et al. 2022).

The estuaries of the Yellow River are important mariculture areas for shellfish farming (MARA 1990–2024). Many non-native molluscs have been introduced in the estuaries for mariculture (Xiong et al. 2024b) and have caused significant decreases and even the local extinction of certain native molluscs (Xiong et al. 2024b). For example, some native mollusc species, such as Hyriopsis cumingii have nearly disappeared because of hybridizization with the non-native mollusc Sinohyriopsis schlegelii (Li et al. 2007).