Alien fishes are regarded as one of the major causes of the decline of aquatic fauna and biodiversity. Up to now, more than 500 fish species have been introduced into China from other countries. However, nationwide documentation of the established alien fishes is still lacking and their ecological risk is unclear. We compiled a comprehensive inventory of the colonized alien fish species based on various sources, and then provided a summary of their potential ecological risk. The results indicated that 68 alien fish species (13.44%) have successfully established in the natural waters. These species belong to 12 orders and 29 families. Among them, 56 species (82.35%) were introduced for aquaculture purposes, 11 species (16.18%) were introduced for aquarium and one species (1.47%) was introduced for bio-control. Over 85% of the established fishes were introduced after the 1970s. Geographically, these species are native to 12 regions around the world. Eighteen species and two hybrid species are native to North America which is the most dominant donor. Among these species, 61 can live in freshwater, 41 species can live in brackish and 19 species can live in marine water. Although large number of species, high taxonomic diversity, intensive human activity, diverse geographical origins and high adaptability of non-native species may lead to the increase of invasion risk, previous research about invasive risk just focus on the general impact of aquaculture activities, invasiveness screening using semi-quantitative models and distribution prediction using species distribution models. Further studies will need to be conducted on comprehensive risk assessment, ecological interaction between non-native fish and new environment, on fish species, ecosystem, the impact of human activity and global change on non-native fish colonization.

Water transfer projects are effective measures to solve the uneven distribution of water resources in China. However, these projects create highways for Golden Mussels (Limnoperna fortunei), which are aquatic invasive species, to invade new habitats. This has caused a series of problems such as structure corrosion, enhanced flow resistance, pipe blocking, and water pollution. In order to design remediation strategies, it is important to understand the factors influencing the Golden Mussel invasion. This paper investigates the invasion of Golden Mussels in the East River Water Source Project and the Northern Inter-basin Water Transfer project in China. The maximum densities of Golden Mussel attachment in these projects are about 10 000 ind. m^–2. Flow velocity was found to be a significant influencing factor: the optimal flow velocity for attachment is in the range of 0.3 to 0.9 m s^–1. Water temperature was also an important factor: the water temperature in the cold season influences the density of Golden Mussels and additionally, their growth and shell size are related to food competition between different individuals and water temperature. There was no obvious relationship between the pressure and the attachment density of Golden Mussels. Because all data was obtained during an infrequent pause in the water transfer projects, the data of this study is limited and the conclusions are preliminary descriptive observations. For future management decisions, more rigorous studies should be conducted to develop quantitative models aimed at providing a confident basis for controlling Golden Mussel invasion in water transfer projects.

In the last few decades, non-native freshwater fishes have been introduced all over the world for economic purposes, including aquaculture and aquarium trade, as well as improvement for wild stocks resulting in adverse environmental and socio-economic effects. The Guangdong province of China is at a high risk of fish invasions owing to its warm and humid climate, abundance of water courses, flourishing aquaculture and ornamental fish trade, and extensive sea ports. A total of 160 non-native freshwater species were introduced in the Guangdong province and 71.9% of them were imported for aquarium purposes. Fourteen species have established self-sustaining populations and 21 species were found in the main river basin of the Guangdong province. Propagule pressure, rapid evolution and abundant resources in the environment were the factors likely to contribute to successful invasion by non-native fishes. The invasion of non-native fishes in the Guangdong province has already resulted in economic losses, decline of native species, as well as negative impacts on the functional diversity of native fish assemblages. To mitigate these effects and prevent future non-native fish invasions, scientists, policy makers and stakeholders should collaborate on the management of non-native fish introductions by developing risk assessments, statutory regulations, public education and scientific research.

We investigated the seasonal habitat selection of Mosquitofish to increase our understanding of the ecology and invasiveness of this species. Sampling was conducted during the reproductive and non-reproductive season of Mosquitofish in four habitat types: Alternanthera philoxeroides habitat, Typha angustifolia habitat, Paspalum distichum habitat, and no vegetation habitat. Mosquitofish catch per unit effort was significantly lower in Typha habitat than in the other three habitats during the reproductive season. T. angustifolia can exude allelopathic chemicals and have the potential to negatively influence western Mosquitofish abundance. In the non-reproductive season, catch per unit effort of Mosquitofish were significantly higher in Alternanthera habitat than in the other three habitats. These results suggest that mats of A. philoxeroides provided an insulating layer for Mosquitofish overwintering. Therefore, Mosquitofish could expand its range further north in China as A. philoxeroides spreads northward with climate change. We suggest that an effective way of controlling western Mosquitofish is through eradication of the invasive macrophyte (A. philoxeroides) stands while retaining and restoring more native emergent macrophyte (T. angustifolia) stands; this strategy could limit overwintering habitat for western Mosquitofish and may draw them into open water habitats where they can be more easily removed.

Despite its social and economic benefits, the trade in ornamental species (henceforth, ‘ornamental trade') has become a major source of non-native fish introductions into freshwater ecosystems. However, the ornamental trade as a vector for introductions of non-native freshwater fishes is not well defined. We developed a framework incorporating elements of the biological invasion process and a typical ornamental fish trade supply chain to fill this gap. Records of non-native ornamental fishes introduced to freshwater environments of Australia, Belgium (Flanders), Canada (British Columbia), China (Guangdong), the Philippines, Poland, Singapore, the United Kingdom (England), and the United States of America (Florida) were reviewed to explore the pervasiveness of these introduced fishes in the wild. These regional case studies confirmed the prominence of the ornamental trade as a global vector for freshwater fish introductions beyond their natural range. Additionally, we examined freshwater fishes associated with the ornamental trade to identify ‘risky' species that could establish in recipient regions based on climate match. All regions assessed were at risk of new fish introductions via the ornamental trade, with the number of ‘risky’ species ranging from seven to 256. Further, there appears to be taxonomic bias in the freshwater ornamental fish trade, with 74% of the species belonging to just 10 families (of 67). Current prevention and management approaches and associated polices, regulations and legislation on aquatic non-native species within assessed regions fit five general categories: import controls, risk assessment, whitelist, blacklist, and release ban. However, these prevention/management efforts may not be sufficient to reduce the invasion risk associated with the ornamental fish trade. Recommendations including species- and vector-based risk assessments, better recording of species import consignments, increased public education and industry engagement, and early detection and rapid response are discussed in this review.

Environmental DNA is one of the most promising new tools in the aquatic biodiversity monitoring toolkit, with particular appeal for applications requiring assessment of target taxa at very low population densities. And yet there persists considerable anxiety within the management community regarding the appropriateness of environmental DNA monitoring for certain tasks and the degree to which environmental DNA methods can deliver information relevant to management needs. This brief perspective piece is an attempt to address that anxiety by offering some advice on how end-users might best approach these new technologies. I do not here review recent developments in environmental DNA science, but rather I explore ways in which managers and decision-makers might become more comfortable adopting environmental DNA tools—or choosing not to adopt them, should circumstances so dictate. I attempt to contextualize the central challenges associated with acceptance of environmental DNA detection by contrasting them with traditional “catch-and-look” approaches to biodiversity monitoring. These considerations lead me to recommend the cultivation of four “virtues,” attitudes that can be brought into engagement with environmental DNA surveillance technologies that I hope will increase the likelihood that those engagements will be positive and that the future development and application of environmental DNA tools will further the cause of wise management.

It is more cost effective to prevent invasions than to eradicate or control invasive species once they are established. We therefore need a thorough knowledge of the pathways by which invasive species are introduced. Prayer animal release is the mainly Buddhist and Taoist tradition of releasing captive animals to gain merit. Although it is assumed to benefit the animals being released as well as the practitioners, prayer release as it is currently practiced has negative impacts that are at odds with the intended compassion. Major impacts are the introduction of invasive species and enhancement of spread and establishment. In this overview, I detail what is currently known about prayer release for aquatic invasions and provide consensus views of the best ways to address any potential impacts. Prayer release is rarely investigated as a potential pathway for introduction of invasive species and there is a marked lack of research on the subject, especially in aquatic ecosystems. Invasion researchers urgently need to 1) conduct research to establish the extent and impacts of prayer release, 2) engage with faith-based groups to encourage alteration of the practice so that it maintains its spiritual intent while promoting ecological responsibility, and 3) recognize prayer release as a major pathway for the introduction of invasive species.

The present study reports the seasonal dynamics of the fish community structure in the presence of a non-native fish (Pterygoplichthys pardalis) in tropical waterbodies of southern Mexico. The studied floodplain existed in both connected pools and disconnected pools “to the Palizada river”. Local fish fauna showed consistent assemblages across seasons, but among the 17 local fish species recorded, the non-native species P. pardalis showed the highest percentage of contribution to the fish community (ca. 20%). Conversely, the frequency of occurrence and density of the non-native species showed variation in relation to the type of waterbody and seasonality; its density was approximately four times higher in disconnected pools than in connected pools in the rainy season and its predominant size class in both pool types was 21-30 cm in standard length. Interestingly, the diversity of the native species was negatively related to the density of the non-native species, indicating that the presence of P. pardalis can be a factor involved in the decline of native fish diversity in these local communities. Currently, the possible impacts of the presence of P. pardalis on local fish diversity at the regional scale are unknown, but our results suggest that hydrological dynamics regulate the establishment of the non-native species in this region. However, future studies are needed to provide insights into the actual scenario of P. pardalis distribution in Yucatan Peninsula and the possible impacts on the native fish fauna in southern Mexico.

Growth parameters, mortality, growth performance index and exploitation ratio of Oreochromis niloticus were assessed based on the length-frequency data collected fortnightly from the Allahabad stretch of the Yamuna, India, during September 2011 to August 2013. The size of the catch ranged between 70 and 495mm total length. The data was analyzed using the Electronic Length Frequency Analysis module in FiSAT software. Asymptotic length and growth coefficient were estimated as 562mm total length and 0.58 year^–1, respectively. Total mortality, natural mortality and fishing mortality coefficients were 3.74, 1.015 and 2.725yr^–1, respectively. The growth coefficient index was calculated as 3.26. The exploitation ratio worked out as 0.667, indicated that the stock was slightly overexploited. Estimated growth at the end of I, II and III years was 247, 386 and 463mm total length, respectively. The observed multi-year survivorship based on the length frequency data from the river Yamuna in O. niloticus suggested that it has successfully established in the non-native environment and is rapidly spreading in other tributaries of the river Ganga. The recruitment pattern was observed to be continuous throughout the year, with several micro-cohorts and two overlapping peaks of unequal pulse strengths. Estimated maximum sustainable yield for this species in the Allahabad stretch of the river Yamuna was 27.13 t. This study can form an important base for future research work in the management of this invasive species in the Gangetic river system in India.

Phytoplankton is an important indicator of, and responder to, environmental changes. This study aims to reveal the response of a phytoplankton community to environmental changes, especially the level of nutrients in the Bohai Sea. The distribution pattern of net-phytoplankton communities in the central Bohai Sea and the Bohai Strait in winter and summer were studied, and the relationship between the phytoplankton communities and environment was explored. The results showed that diatoms (e.g. A. octonarius, Paralia sulcata and Detonula pumila) dominated the phytoplankton communities in winter, while diatoms (e.g. Chaetoceros sp. and Thalassiothrix frauenfeldii) and dinoflagellates (e.g. Ceratium fusus and Ceratium tripos) were both dominant in summer. By cluster analysis, the phytoplankton communities were divided into three clusters in winter and two in summer. The community that inhabited the waters around Qinhuangdao had higher abundance and distinct taxa composition in winter, related to the higher level of DIN and phosphate. Influenced by different water masses (the Yellow Sea Warm Current and the Bohai Sea Coastal Current), the phytoplankton community composition in the northern and southern parts of the Bohai Strait were also significantly different in winter. In summer, the difference in abundance and dominant species between the two phytoplankton communities was more closely linked to the N:P ratio in the environment. These results reflect that both nutrient level and hydrodynamic condition greatly influence the phytoplankton communities in the central Bohai Sea and the Bohai Strait. Our study will provide basic data for the eutrophication and environmental changes in the Bohai Sea.