Variations in reproductive strategies between one invasive population and two native populations of Pseudorasbora parva

Reproductive traits of one invasive population in Lake Fuxian and two native populations in Lakes Chao and Dongting for Pseudorasbora parva were investigated to determine the variations in their reproductive strategies associated with the change of environmental conditions. Compared with the two native populations,P.parva markedly experienced the protraction in their spawning time and the decrease in mortality for adult individuals in Lake Fuxian. The three populations all got their first sexual maturity at the same age,but their total lengths at maturity were quite different for those in Lake Chao were significantly lower than in Lakes Fuxian and Dongting. Additionally,in spite that no significant difference occurred in their relative fecundities for P.parva in Lakes Fuxian and Dongting,the population in Lake Chao showed the markedly higher relative fecundity than the other two populations. These results were analyzed with the variations in water temperature,nutrient status,fishing stress among the three lakes. The relative decline in fecundity for the invasive population,which conflicted with the enemy release hypothesis,was disscussed with the context of the preponderance of another invasive fish,Neosalanx taihuensis,in Lake Fuxian.     

Trophic interactions between native and introduced fish species in a littoral fish community

The trophic interactions between 15 native and two introduced fish species, silverside Odontesthes bonariensis and rainbow trout Oncorhynchus mykiss, collected in a major fishery area at Lake Titicaca were explored by integrating traditional ecological knowledge and stable‐isotope analyses (SIA). SIA suggested the existence of six trophic groups in this fish community based on δ¹³C and δ¹⁵N signatures. This was supported by ecological evidence illustrating marked spatial segregation between groups, but a similar trophic level for most of the native groups. Based on Bayesian ellipse analyses, niche overlap appeared to occur between small O. bonariensis (<90 mm) and benthopelagic native species (31·6%), and between the native pelagic killifish Orestias ispi and large O. bonariensis (39%) or O. mykiss (19·7%). In addition, Bayesian mixing models suggested that O. ispi and epipelagic species are likely to be the main prey items for the two introduced fish species. This study reveals a trophic link between native and introduced fish species, and demonstrates the utility of combining both SIA and traditional ecological knowledge to understand trophic relationships between fish species with similar feeding habits.     

Overlapping niches between two co-occurring invasive fish: the topmouth gudgeon Pseudorasbora parva and the common bleak Alburnus alburnus

Invasive fish species impact aquatic ecosystems and modify native communities, often leading to a decline in local species. These ecological impacts include the transmission of pathogens, predation, competition as well as hybridization. Two invasive fish species, the common bleak Alburnus alburnus and the topmouth gudgeon Pseudorabora parva, have both been recently found co-occurring in several regions of southern Europe, such as the Italian Arno River. Nonetheless, the trophic relationships among invasive fish species, especially cyprinids, remain poorly understood, and no studies have reported the trophic interaction between these two species. This study compared length–weight relationship and used stomach content and stable isotope analysis of two co-occurring populations in the Arno River to characterize the growth and overlap of potential trophic niches. It also found similar allometric growth in both species, a wider generalist trophic niche for P. parva and a more specialized niche for A. alburnus. A considerable niche overlap was found, suggesting that feeding competition can occur if resources were to be limited. Moreover, the niche of P. parva was more likely to overlap with that of A. alburnus than vice versa, suggesting that P. parva can be considered as a potential over competitor. Nonetheless, the authors found in the overlapping populations no evidence of realized competition, probably avoided through a combination of fine-scale mechanisms. They also highlighted that these two invasive species can co-exist and share resources, at least in an open ecosystem like a river, thus potentially doubling up their trophic impact on local communities.     

Length–weight relationships of the invasive topmouth gudgeon (Pseudorasbora parva) in ten lakes in the UK

The topmouth gudgeon (Pseudorasbora parva) is a species that is becoming invasive in UK waters. Few biological studies have been completed on the species in this extended range, resulting in sparse information in some aspects of their invasion biology. Regarding length–weight relationships, this is remedied in this study by providing data for 10 lake populations in the UK. Using fish length range 2.5–11.8 cm, values of a and b in the length–weight equation are provided. Values of b ranged between 2.76 and 3.32. Across all lakes, the relationship was W = 0.011L^3.03, with weight in grams and length (fork) in cm.     

Trophic overlap between fish and riparian spiders: potential impacts of an invasive fish on terrestrial consumers

Studies on resource sharing and partitioning generally consider species that occur in the same habitat. However, subsidies between linked habitats, such as streams and riparian zones, create potential for competition between populations which never directly interact. Evidence suggests that the abundance of riparian consumers declines after fish invasion and a subsequent increase in resource sharing of emerging insects. However, diet overlap has not been investigated. Here, we examine the trophic niche of native fish, invasive fish, and native spiders in South Africa using stable isotope analysis. We compared spider abundance and diet at upstream fishless and downstream fish sites and quantified niche overlap with invasive and native fish. Spider abundance was consistently higher at upstream fishless sites compared with paired downstream fish sites, suggesting that the fish reduced aquatic resource availability to riparian consumers. Spiders incorporated more aquatic than terrestrial insects in their diet, with aquatic insects accounting for 45–90% of spider mass. In three of four invaded trout rivers, we found that the average proportion of aquatic resources in web‐building spider diet was higher at fishless sites compared to fish sites. The probability of web‐building and ground spiders overlapping into the trophic niche of invasive brown and rainbow trout was as high as 26 and 51%, respectively. In contrast, the probability of spiders overlapping into the trophic niche of native fish was always less than 5%. Our results suggest that spiders share resources with invasive fish. In contrast, spiders had a low probability of trophic overlap with native fish indicating that the traits of invaders may be important in determining their influence on ecosystem subsidies. We have added to the growing body of evidence that invaders can have cross‐ecosystem impacts and demonstrated that this can be due to niche overlap.     

Complex interactions between native and invasive fish: the simultaneous effects of multiple negative interactions

We suggest that the ultimate outcome of interactions between native species and invasive species (extinction or coexistence) depends on the number of simultaneous negative interactions (competition and predation), which depends on relative body sizes of the species. Multiple simultaneous interactions may constrain the ability of native species to trade fitness components (i.e., reduced growth for reduced risk of predation) causing a spiral to extinction. We found evidence for five types of interactions between the adults and juveniles of introduced western mosquitofish (Gambusia affinis) and the juveniles of native least chub (Iotichthys phlegethontis). We added ten large (23–28 mm) and seven small (9–13 mm) young-of-the-year (YOY) least chub to replicate enclosures with zero, low, and high densities of mosquitofish in a desert spring ecosystem. Treatments with mosquitofish reduced the average survival of least chub by one-third. No small YOY least chub survived in enclosures with high mosquitofish densities. We also performed two laboratory experiments to determine mortality to predation, aggressiveness, and habitat selection of least chub in the presence of mosquitofish. Mean mortality of least chub due to predation by large mosquitofish was 69.7% over a 3-h trial. Least chub were less aggressive, selected protected habitats (Potamogeton spp.), and were more stationary in the presence of mosquitofish where the dominance hierarchy was large mosquitofish>>large least chubsmall mosquitofish>>small least chub. Least chub juveniles appear to be figuratively caught in a vice. Rapid growth to a size refuge could reduce the risk of predation, but the simultaneous effects of competition decreased least chub growth and prolonged the period when juveniles were vulnerable to mosquitofish predation.     

Microhabitat use and interspecific associations of introduced topmouth gudgeon Pseudorasbora parva and native fishes in a small stream

To address a lack of information on topmouth gudgeon Pseudorasbora parva introduced to watercourses, the microhabitat use of this non-native cyprinid and co-existing native species was assessed in a small stream located in southern England. Overall, microhabitat use was size-structured and significant associations were observed between topmouth gudgeon and native species, including brown trout Salmo trutta , chub Leuciscus cephalus , European bullhead Cottus gobio and stone loach Barbatula barbatula . Significant associations with environmental variables, however, were more frequent in native species than in topmouth gudgeon. Topmouth gudgeon demonstrated few habitat preferences, which were weak and limited to small specimens, emphasizing the species broad, plastic breadth of microhabitat use. This is expected to facilitate the species' successful invasion of novel aquatic systems.     

Escapees of potentially invasive fishes from an ornamental aquaculture facility: the case of topmouth gudgeon Pseudorasbora parva

Accidental escapees from aquacultural facilities are an ongoing problem facing scientists, conservationists, policy makers and naturalists throughout the world. The topmouth gudgeon Pseudorasbora parva , a small cyprinid native to Southeast Asia, was introduced to Romanian waters in 1960 via the aquaculture trade and has since spread throughout Europe. It first appeared in England in an ornamental fish farm near Romsey in Hampshire. The aim of the present study was to quantify the dispersal of this potentially highly invasive species from an ornamental fish farm into the wild. In order to measure the dispersal of escapees, intensive electrofishing surveys were carried out between June and September 2003 in the catchment downstream of the fish farm. The distribution of topmouth gudgeon in the catchment was found to be limited and patchy. The presence of small individuals suggests that the species has successfully established itself in the wild, but this remains to be confirmed. The results were examined in light of invasion theory principles of biological resistance and ecological fitness.     

Behavioral interactions under multiple stressors: temperature and salinity mediate aggression between an invasive and a native fish

Interspecific aggression is a critical determinant of the success and competitive superiority of many invasive over native species. While single abiotic stressors can alter aggression levels, the manner in which multiple stressors may alter the strength and outcome of interspecific interactions and hence the invasion potential of a species is still poorly understood, even though multiple stressors are prevalent in many ecosystems. Furthermore, multiple stressors may interact to produce synergistic or antagonistic effects on individual level behaviors, thereby modulating invasive-native species interactions in unexpected ways. Here we examined the effect of two key abiotic stressors in freshwater ecosystems-temperature and salinity-on interspecific aggression between the invasive eastern mosquito fish (Gambusia holbrooki) and juveniles of the native Australian bass (Macquaria novemaculeata). Under controlled laboratory conditions, individuals were exposed to low or high salinity levels (15 and 35‰), and low or high temperatures (21 and 28 °C), and the frequency of interspecific aggressive behaviors was scored. The effect of temperature and salinity on interspecific aggression was antagonistic for both M. novemaculeata and G. holbrooki. While elevated temperature promoted aggression, elevated salinity partially or entirely negated this effect. Moreover, regardless of temperature, M. novemaculeata was more aggressive than G. holbrooki under elevated salinity. In addition to this, the native displayed more aggression to smaller than larger heterospecifics when exposed to elevated salinity alone, while G. holbrooki showed no such preference. These results highlight the importance of considering the interplay between multiple abiotic stressors and behavioral interactions between invasive and native species, combined with the modulating effect of species-specific and size based responses to those stressors.     

Distribution of the Asiatic cyprinid Pseudorasbora parva in Serbia and Montenegro

The first record of Pseudorasbora parva in the Balkan region was in 1977 in Sasko Lake, Montenegro and in 1978 it was found in Serbia. Since then, this species has spread to almost all lowland rivers and has become a permanent member of the ichthyofauna in Serbia and Montenegro.     

Trophic interactions among native and introduced fishes in a northern Patagonian oligotrophic lake

In summer the littoral zone of Lake Rivadavia contained almost all the juveniles of the native fish species present in the lake together with juveniles of the introduced salmonid Oncorhynchus mykiss . In particular, a high degree of foraging interaction was found among juveniles of the native species Aplochiton zebra and Percichthys trucha and juveniles O. mykiss. Differences in the juvenile assemblage composition, both in the presence and in the relative proportion of the species were associated with areas with different densities of vegetation. The adults of nearly all species were generalized benthic invertebrate predators. Only adults of A. zebra were absent in the littoral. Juvenile and adult O. mykiss were the only fish that preyed on planktonic organisms. Oncorhynchus mykiss was the only species that performed an ontogenetic diet shift between juveniles and adults, changing main prey categories from benthic to planktonic species.     

Characteristics of reaction field and the reactive distance of a planktivore, Pseudorasbora parva (Cyprinidae), in various environmental conditions

The characteristics of the reaction field and the reactive distance of the Stone moroko (Pseudorasbora parva) were studied under three environmental conditions (structural complexity, light intensity and turbidity) and three prey sizes. In optimal experimental conditions, under no structural complexity, light intensity of 200 lux and turbidity less than 1 NTU (Nephelometric Turbidity Units), the cross-section of the reaction field was found to be elliptic with a bearing angle larger than the elevation angle, but both angles changed slightly depending on environmental conditions. The reactive distance was large, and the fish frequently attacked prey that was located within 15–60 degrees to each side from the frontal direction of a fish (i.e., ± 15 degrees from the axis of the fish body) horizontally. In the light intensity below 50 lux or turbidity above 10 NTU, however, the attack frequency and the reactive distance in the frontal direction of a fish did not differ from other horizontal directions in the reaction field. The average reactive distance increased proportionally with increasing strand distance, but it gradually reached a constant value for strand distances greater than about 3.6 times the fish body length. The average reactive distance increased in the light intensity range of 10–200 lux and decreased negatively with turbidity increasing. The average reactive distance increased with larger prey size, but the rate of increase of the reactive distance gradually decreased.     

Wild caught ornamental fish: a perspective from the UK ornamental aquatic industry on the sustainability of aquatic organisms and livelihoods

The ornamental aquatic industry involves the global commercial trade of live aquatic organisms such as fish, invertebrates and plants. It comprises a range of businesses including collectors, breeders, exporters, importers and retailers. Together, these form a supply chain through which aquatic organisms pass from their point of origin to the end point e.g., domestic aquaria and ponds. On a worldwide basis, the legal and legitimate ornamental aquatic trade is subject to regulation and monitoring throughout the majority of its supply chain. Approximately 90% of ornamental freshwater fish species traded are captive-bred, but, due to their complex breeding cycles, 90–95% of ornamental marine fish species are wild-caught. The ornamental aquatic industry and consumers therefore have a responsibility to ensure that wild-caught species are sourced sustainably, legally and to good welfare standards. Such good practice should be considered a necessity for the longevity, not only of the ornamental aquatic industry, but of the livelihoods which depend on it and the future of ecosystems dependent on such communities.     

Holostephanus metorchis (Digenea: Cyathocotylidae) from chicks experimentally infected with metacercariae from a fish, Pseudorasbora parva, in the Republic of Korea

Holostephanus metorchis (Digenea: Cyathocotylidae) is a parasite of birds, transmitted by freshwater fishes. H. metorchis adults were recovered from chicks experimentally infected with metacercariae collected from freshwater fishes, Pseudorasbora parva. The metacercariae were oval, surrounded with thick fibrous capsules. In adult flukes, the holdfast organ occupied the ventral concavity, and the anterior testis did not reach the level of the ventral sucker. Based on these morphological characteristics, these flukes were identified as H. metorchis.     

Competitive interactions between invasive Nile tilapia and native fish: the potential for altered trophic exchange and modification of food webs

Recent studies have highlighted both the positive and negative impacts of species invasions. Most of these studies have been conducted on either immobile invasive plants or sessile fauna found at the base of food webs. Fewer studies have examined the impacts of vagile invasive consumers on native competitors. This is an issue of some importance given the controlling influence that consumers have on lower order plants and animals. Here, we present results of laboratory experiments designed to assess the impacts of unintended aquaculture releases of the Nile tilapia (Oreochromis niloticus), in estuaries of the Gulf of Mexico, on the functionally similar redspotted sunfish (Lepomis miniatus). Laboratory choice tests showed that tilapia prefer the same structured habitat that native sunfish prefer. In subsequent interspecific competition experiments, agonistic tilapia displaced sunfish from their preferred structured habitats. When a piscivore (largemouth bass) was present in the tank with both species, the survival of sunfish decreased. Based on these findings, if left unchecked, we predict that the proliferation of tilapia (and perhaps other aggressive aquaculture fishes) will have important detrimental effects on the structure of native food webs in shallow, structured coastal habitats. While it is likely that the impacts of higher trophic level invasive competitors will vary among species, these results show that consequences of unintended releases of invasive higher order consumers can be important.     

Quantifying the recent expansion of native invasive rush species in a UK upland environment

Rushes, such as soft rush (Juncus effusus L.), hard rush (Juncus inflexus L.), and compact rush (Juncus conglomeratus L.) have become problem species within upland grasslands across the United Kingdom and the coastal grasslands of western Norway. Indeed, being largely unpalatable to livestock and having a vigorous reproductive ecology means that they can rapidly come to dominate swards. However, rush dominance results in a reduction in grassland biodiversity and farm productivity. Anecdotal evidence from the United Kingdom suggests that rush cover within marginal upland grasslands has increased considerably in recent decades. Yet, there is currently no published evidence to support this observation. Here, we use recent and historical Google Earth imagery to measure changes in rush frequency over a 13-year period within four survey years: 2005, 2009, 2015, and 2018. During each survey year, we quantified rush presence or absence using a series of quadrats located within 300 upland grassland plots in the West Pennine Moors, United Kingdom. Data were analysed in two stages, first, by calculating mean rush frequencies per sample year using all the available plot-year combinations (the full dataset), and second by examining differences in rush frequency using only the plots for which rush frequency data were available in every sample year (the continuous dataset). The full dataset indicated that rush frequency has increased by 82% between 2005 and 2018. Similarly, the continuous dataset suggested that rush frequency has increased by 174% over the same period, with the increases in frequency being statistically significant (p < .05) between 2005–2018 and 2009–2018. We discuss the potential drivers of rush expansion in the West Pennine Moors, the ecological and agronomic implications of grassland rush infestations, and priorities for future research.     

基于Maxent的两种入侵性鱼类(麦穗鱼和鲫)的全球适生区预测

受引种、贸易等人类活动的影响, 麦穗鱼(Pseudorasbora parva)和鲫(Carassius auratus)在全球范围内已经广泛分布并造成巨大的生态危害。根据野外采样和文献记录, 本文系统整理了麦穗鱼和鲫在世界各地的分布情况, 以高达2.5弧分分辨率的环境数据底图, 利用Maxent模型预测了麦穗鱼和鲫在全球的适生区, 以期为防控麦穗鱼和鲫的入侵提供早期预警。结果表明麦穗鱼和鲫在全球范围的分布区非常广泛, 除南极洲外的各个大洲均有其适生区, 因此这两种鱼还有继续扩散的潜力, 并可能在美国、巴西和阿根廷等国家出现由生物入侵导致的生态学问题。麦穗鱼的适生区主要集中在15º–55º N之间, 欧洲是麦穗鱼入侵的重灾区, 尤其是法国、荷兰周边的西欧国家和匈牙利、塞尔维亚周边的东欧国家; 而美国中部的密西西比河流域、东部及南部沿海, 以及西雅图至加拿大的温哥华之间是麦穗鱼潜在入侵风险性极高的区域。鲫自然分布于欧洲至东亚的广大地区, 目前已经在澳大利亚、加拿大、美国、马达加斯加、印度和越南等国家有分布, 未来还可能进一步扩散至大洋洲的新西兰和新喀里多尼亚, 北美洲的墨西哥至南美洲的阿根廷, 以及非洲的塞内加尔、几内亚和南非等国家; 尤其是南美洲的阿根廷和巴西, 非洲西部的几内亚、喀麦隆等国家将是鲫入侵风险极高的区域。