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Policies and legislation for the importation and use of non-native (NN) freshwater fishes have been rapidly evolving in several countries around the world in response to heightened evidence of their adverse ecological and economic impacts. In China, the already large and growing number of NN freshwater fishes being imported from foreign countries or translocated within China has necessitated the development of management strategies supported by policies at both national and regional levels. Despite increasing awareness of the damage caused by NN fishes, such initiatives in China continue to lag behind those already implemented in other countries. This study endeavors to narrow this policy gap by: (i) providing a synoptic overview of the vectors and pathways of NN freshwater fish introductions and dispersal both into and within China; (ii) evaluating existing policies and legislation relative to those currently implemented in Europe, the USA and Canada; (iii) examining the role of decision-support tools for identifying and assessing the risks posed by NN fishes; and (iv) proposing perspectives and possible options for NN fish policies, legislation and management in China. [ABSTRACT FROM AUTHOR]

The crucian carp Carassius carassius, a cyprinid fish characteristic of small ponds, is in decline throughout most of its European range, including in England where it is currently thought to be non‐native.The present study, undertaken by the Norfolk Crucian Project, reports on reductions in pond populations of crucian carp in Norfolk, eastern England as well as the success of recent introduction/re‐introduction efforts in terms of crucian survival, recruitment and growth over the last 10 years.A 72% decline in crucian carp distribution was observed between the 1950s–1980s and the 2010s. Of 18 crucian carp introductions/re‐introductions to restored and suitable existing ponds, 17 were successful in terms of survival, increasing the number of current crucian sites in Norfolk by 37%. Recruitment of young crucian carp was demonstrated for 12 of the 18 stocked ponds, with apparent elevated juvenile growth relative to other English and European populations.Delays in, or a lack of, crucian recruitment in some ponds appeared to result from the presence of other fish species (especially threespine stickleback Gasterosteus aculeatus) with predation and interspecific competition possible contributory factors.This study shows that, through combinations of pond rehabilitation and stocking, it has been possible to achieve a substantial recovery of crucian carp populations in the study region. Although the crucian carp is currently presumed to be non‐native within England, given other scientific studies that show a lack of adverse impacts of this species on native biota, and because it is greatly threatened in its native range, the call is sounded for more crucian carp conservation projects in other parts of England as well as in Europe more generally. [ABSTRACT FROM AUTHOR]

Plasticity in life-history traits provides advantages for introduced fish in overcoming demographic bottlenecks that would otherwise inhibit establishment. Here, the influence of population density, temperature and latitude was tested on the growth increments and growth rates of invasive populations of topmouth gudgeon Pseudorasbora parva, a small Asian cyprinid fish that is invasive across Europe. Aquaria experiments tested the roles of fish number and temperature on growth increments under a fixed food supply, pond experiments tested the role of density on growth increments, and a field study completed in England and Wales tested the influence of density and latitude on growth rates. In aquaria experiments, whilst growth increments were higher at 21 and 23 °C than at 19 and 25 °C, fish number had a greater influence on growth than temperature. Higher growth increments were produced at lower densities. In experimental ponds, growth increments were significantly higher in ponds with low densities of P. parva compared with those at elevated densities. In the field study comprising 10 wild populations across a latitudinal gradient of 4.0°N, a difference in mean air temperatures of approximately 3 °C, and estimated densities between 0.5 and 65.0 m−2, population density was the only significant predictor of growth rates. Whilst populations at very low densities comprised of significantly faster growing individuals, there were no significant differences when densities were between 15 and 65 m−2. Thus, invasive P. parva populations have considerable growth plasticity, especially at low densities, with this likely to be important in their ability to colonise new environments. [ABSTRACT FROM AUTHOR]