Reproductive parameters of invasive topmouth gudgeon Pseudorasbora parva (Temminck and Schlegel, 1846) from Slovakia

Females of an invasive population of topmouth gudgeon Pseudorasbora parva (Temmick and Schlegel, 1846) from the Šúr pond (Bratislava, Slovakia) were examined to analyze their fecundity and other life history traits. Samples were collected during both pre-spawning (n = 137) and post-spawning (n = 89) periods. Standard length of the females from the pre-spawning period ranged from 23.42 to 59.71 mm (mean 32.80 mm), body weight from 0.260 to 5.442 g (mean 0.965 g), and eviscerated body weight from 0.207 to 4.882 g (mean 0.748 g). Absolute fecundity varied between 121 and 7124 oocytes (mean 1106 oocytes). In 75.22% of the females, two or three size groups of oocytes were clearly distinguished. Overall, the life history traits observed in invasive topmouth gudgeon from the Šúr pond demonstrated a high flexibility in their reproductive strategy. This, together with previously described great morphological variability, is likely to make this species such a successful invader.     

The distribution of an invasive fish species is highly affected by the presence of native fish species: evidence based on species distribution modelling

Topmouth gudgeon (Pseudorasbora parva) is one of the most invasive aquatic fish species in Europe and causes adverse effects to ecosystem structure and functioning. Knowledge and understanding of the species’ interactions with the environment and with native fish are important to stop and prevent the further spread of the species. Creating species distribution models is a useful technique to determine which factors influence the occurrence and abundance of a species. We applied three different modelling techniques: general additive models, random forests and fuzzy habitat suitability modelling (FHSM) to assess the habitat suitability of topmouth gudgeon. The former two techniques indicated that the abundance of native fish (i.e. biotic variables) was more important than environmental variables when determining the abundance of topmouth gudgeon in Flanders (Belgium). Bitterling (Rhodeus amarus), stone loach (Barbatula barbatula), three-spined stickleback (Gasterosteus aculeatus) and predator abundance were selected as the most important biotic variables and implemented in the FHSM to investigate species interactions. Depending on the preferred food source and spawning behaviour, either coexistence or interspecific competition can occur with bitterling, stone loach and three-spined stickleback. In contrast, the presence of predators clearly had a top down effect on topmouth gudgeon abundance. These findings could be applied as a biological control measure and implemented in conservation strategies in order to reduce the abundance of earlier established populations of topmouth gudgeon.     

Environmentally induced shift in reproductive traits of a long‐term established population of topmouth gudgeon (Pseudorasbora parva)

Topmouth gudgeon (Pseudorasbora parva) is one of the most invasive organisms in recent times. It can spread very quickly due to its attributes, which predetermine its success in novel environments. One source of these attributes appears to be phenotypic plasticity. The reproductive parameters of a long‐term established population from a stable habitat exposed to a strong disturbance were the subject of the present study. The results supported the prediction that such a strong disturbance will increase the absolute number of oocytes and decrease their size significantly. Of course, changes in life‐history can be observed in any species of fish, regardless of whether the disturbance occurs in a native or an introduced habitat. However, the hypothesis of alternative ontogenies and invasive potential presumes that the wider the range between the most generalized and the most specialized phenotypes that a species can generate, the wider is its invasive potential. The observed shift in reproductive traits demonstrates the high phenotypic plasticity of topmouth gudgeon.     

Genetic variation of the mtDNA <Emphasis Type="Italic">cyt b</Emphasis> locus in topmouth gudgeon introduced into water bodies in the northern part of the Black Sea region

The up-to-date phylogeographical distribution of the topmouth gudgeon Pseudorasbora parva Temminck et Schlegel 1846 in water bodies of the Northern Black Sea region is considered. Genetic variation of mtDNA cyt b gene is analyzed. It is established that topmouth gudgeon penetrated and spread in the basins of the Dnieper and Don rivers and in water bodies of Crimea from the secondary center of its dispersion— water bodies of Central Europe. It is demonstrated that haplotypes of topmouth gudgeon in the Danube delta are the most homologous to the haplotypes in the native range of the species in China. A considerable decrease in the level of genetic variation in the populations in the Black Sea region is reported.     

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.     

Genomic footprints of a biological invasion: Introduction from Asia and dispersal in Europe of the topmouth gudgeon (Pseudorasbora parva)

Facilitated by the intensification of global trading, the introduction and dispersal of species to areas in which they are historically non‐native is nowadays common. From an evolutionary standpoint, invasions are paradoxical: not only non‐native environments could be different from native ones for which introduced individuals would be ill‐adapted, but also small founding population size should be associated with reduced adaptive potential. As such, biological invasions are considered valuable real‐time evolutionary experiments. Here, we investigated the population structure and adaptive potential of the highly invasive topmouth gudgeon (Pseudorasbora parva) across Europe and East Asia. We RAD‐sequenced 301 specimens from sixteen populations and three distinct within‐catchment invaded regions as well as two locations in the native range. With 13,785 single nucleotide polymorphisms, we provide conclusive evidence for a genome‐wide signature of two distinct invasion events, in Slovakia and Turkey, each originating from a specific area in the native range. A third invaded area, in France, appears to be the result of dispersal within the invasive range. Few loci showed signs of selection, the vast majority of which being identified in the Slovakian region. Functional annotation suggests that faster early stage development, resistance to pollution and immunocompetence contribute to the invasion success of the local habitats. By showing that populations in the invasive range have different evolutionary histories, our study reinforces the idea that populations, rather than species, are the units to consider in invasion biology.     

Native drivers of fish life history traits are lost during the invasion process

Rapid adaptation to global change can counter vulnerability of species to population declines and extinction. Theoretically, under such circumstances both genetic variation and phenotypic plasticity can maintain population fitness, but empirical support for this is currently limited. Here, we aim to characterize the role of environmental and genetic diversity, and their prior evolutionary history (via haplogroup profiles) in shaping patterns of life history traits during biological invasion. Data were derived from both genetic and life history traits including a morphological analysis of 29 native and invasive populations of topmouth gudgeon Pseudorasbora parva coupled with climatic variables from each location. General additive models were constructed to explain distribution of somatic growth rate (SGR) data across native and invasive ranges, with model selection performed using Akaike's information criteria. Genetic and environmental drivers that structured the life history of populations in their native range were less influential in their invasive populations. For some vertebrates at least, fitness‐related trait shifts do not seem to be dependent on the level of genetic diversity or haplogroup makeup of the initial introduced propagule, nor of the availability of local environmental conditions being similar to those experienced in their native range. As long as local conditions are not beyond the species physiological threshold, its local establishment and invasive potential are likely to be determined by local drivers, such as density‐dependent effects linked to resource availability or to local biotic resistance.     

Reproductive parameters of topmouth gudgeon (Pseudorasbora parva) from a heated Lake Licheńskie (Poland)

Temperature regime is known to have considerable influence on the life-histories of fish. Topmouth gudgeon is a very successful invader with high biological flexibility and phenotypic plasticity. The flexibility of topmouth gudgeon in a normal thermal regime has been well described, however there has been no information published about how it would cope with extreme conditions, e.g. permanently heated water. Several studies have demonstrated that phenotypic plasticity provides an important advantage to invasive species. To explain their invasion success, the theory of alternative ontogenies and invasive potential has been proposed. The aim of the present study was to examine if the reproductive parameters of a population living in permanently heated water differ from those living in habitats with a normal temperature regime, as well as to test a hypothesis derived from the theory of alternative ontogenies and invasive potential. Over a period of 8 years (2004–2011), a high variation in the reproductive parameters of topmouth gudgeon from Lake Licheńskie was found. With a small exception, all the observed results met the expectations predicted by the hypothesis tested. This indicates that topmouth gudgeon retains high phenotypic plasticity in life-history traits even in a habitat with extreme conditions, which is important for the species’ invasion success.     

Feeding habits and predator‐prey size relationships of mandarin fish Siniperca chuatsi (Basilewsky) in a shallow lake,central China

The diet and predator‐prey size relationships of mandarin fish Siniperca chuatsi (Basilewsky) in Lake Xiaosihai along the middle reach of the Yangtze River were studied through stomach content analysis. A total of 401 specimens (91–539 mm total length) were collected in 2007. The diet was dominated by topmouth gudgeon Pseudorasbora parva, sharpbelly Hemiculter leucisculus, redfin culter Cultrichthys erythropterus, and crucian carp Carassius auratus, with significant seasonal and ontogenetic differences. Ontogenetic variation in diet was apparent that larger prey items such as crucian carp and redfin culter became more common, while smaller prey such as topmouth gudgeon, bitterlings and shrimps gradually declined in the larger fish. Mandarin fish total length (TL) was strongly related to mouth gape width (GW) and gape height (GH). Mandarin fish TL and prey fish TL as well as mandarin fish GW and prey fish body depth (BD) were positively and linearly related for sharpbelly, redfin culter and crucian carp. Strong size selectivity for topmouth gudgeon, sharpbelly and redfin culter as prey indicated that the piscivorous mandarin fish can have potential impact on the population size structure of the three prey fish.     

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.     

Isolation and characterization of 19 polymorphic microsatellite loci from the topmouth gudgeon, Pseudorasbora parva

The Asiatic topmouth gudgeon, Pseudorasbora parva, is recognized as one of the most invasive fish species in many countries outside of Asia. We isolated and characterized 19 microsatellite loci from P. parva. The polymorphism of these 19 loci was tested on 40 individuals of P. parva sampled from a wild population located in Ezhou, Hubei province of China. The loci had 5 to 11 alleles, with a mean of 7.7 at each locus; 11 loci conformed to Hardy-Weinberg equilibrium. The expected and observed heterozygosities ranged from 0.237 to 0.973 and from 0.647 to 0.914, respectively. All microsatellite loci were in linkage equilibrium. These microsatellite markers are potentially useful for the assessment of population genetic structure during invasion and dispersal of P. parva in new habitats.     

Is topmouth gudgeon Pseudorasbora parva responsible for the decline in sunbleak Leucaspius delineatus populations?

In England, a severe decline of introduced sunbleak Leucaspius delineatus populations has been attributed to the introduction of the invasive topmouth gudgeon Pseudorasbora parva . In France, however, after 4 years of P. parva colonization in a large natural lake, no demonstrated impacts on the native L. delineatus populations have been observed. This suggests that the original impacts observed in England, such as spawning inhibition and high mortality, were the result of an emerging pathogen, the rosette-like agent, hosted by L. delineatus rather than P. parva .     

Age and growth of invasive round goby <Emphasis Type="Italic">Neogobius melanostomus</Emphasis> from middle Danube

Age and growth of the invasive population of round goby Neogobius melanostomus from the Slovak stretch of River Danube was examined. The samples (n=1130) were collected soon after the invasion was recorded (2004–2005), and later, when the population was already established (2008–2010). Invasive round goby in newly-occupied areas were found to reach smaller body size (15–153 mm standard length) compared to native populations. Age from 0+ to 4+, determined from scales, was recorded in both sexes. Annulus formed in April–May, which varied with age. Growth of freshly established gobies was negative allometric, suggesting increased allocation of their sources to reproduction, which corresponds to less specialized life-history. However, positive allometric growth found in longer established individuals suggests a shift in allocation towards somatic growth, which corresponds to more specialized life-history typical for native populations. None of the three parameters predicted by the theory of alternative ontogenies and invasive potential met the expectations, though two parameters, i.e. growth rate and age at maturation remain equivocal. This can be explained by too short of a time span that has elapsed from the beginning of invasion, or by ecological disturbances that have broken up otherwise stable environment in the habitat studied.     

Can sunbleak Leucaspius delineatus or topmouth gudgeon Pseudorasbora parva disperse through saline waters?

In order to determine the potential for the invasive fishes sunbleak Leucaspius delineatus and topmouth gudgeon Pseudorasbora parva to disperse through saline waters their behaviour and physiology were investigated during exposure to salinities of 10·0 and 12·5. Increased salinity caused an increase in whole body cortisol in both species, but sunbleak and topmouth gudgeon showed very different metabolic and behavioural responses to the salinity stress. Sunbleak displayed increased swimming activity in brackish water, which may be important for dispersal through saline waters in the wild, although there were increased metabolic costs associated with this behaviour. Conversely, topmouth gudgeon showed a reduction in both swimming activity and metabolic rate in brackish waters. A pronounced depression in food intake (70–80%) was shown by both species during the salinity exposures. Both sunbleak and topmouth gudgeon, however, showed a full recovery of food intake within 24 h following return to fresh water. Despite the fact that exposure to saline waters is stressful, and affects both physiology and behaviour, rapid recovery of appetite after return to fresh water suggests that short-term use of brackish waters is a feasible dispersal route for sunbleak and topmouth gudgeon in the wild.     

Reconciling the biogeography of an invader through recent and historic genetic patterns: the case of topmouth gudgeon <Emphasis Type="Italic">Pseudorasbora parva</Emphasis>

The genetic variability and population structure of introduced species in their native range are potentially important determinants of their invasion success, yet data on native populations are often poorly represented in relevant studies. Consequently, to determine the contribution of genetic structuring in the native range of topmouth gudgeon Pseudorasbora parva to their high invasion success in Europe, we used a dataset comprising of 19 native and 11 non-native populations. A total of 666 samples were analysed at 9 polymorphic microsatellite loci and sequenced for 597 bp of mitochondrial DNA. The analysis revealed three distinct lineages in the native range, of which two haplogroups were prevalent in China (100%), with a general split around the Qinling Mountains. Dating of both haplogroups closely matched past geological events. More recently, its distribution has been influenced by fish movements in aquaculture, resulting in gene flow between previously separated populations in Northern and Southern China. Their phylogeography in Europe indicate as few as two introductions events and two dispersal routes. Microsatellite data revealed native populations had higher genetic diversity than those in the invasive range, a contrast to previous studies on P. parva. This study confirms the importance of extensive sampling in both the native and non-native range of invasive species in evaluating the influence of genetic variability on invasion success.     

Contrasting life history traits of invasive topmouth gudgeon (Pseudorasbora parva) in adjacent ponds in England

Two topmouth gudgeon Pseudorasbora parva populations were studied in adjacent ponds in Northwest England to determine the influence of density on the expression of their life history traits. Initial introduction into one of these ponds had been in 2000, with establishment of an abundant population (density in March 2005: 6.1 ± 3.2 m^?2). Their transfer into the adjacent pond only occurred during brief periods of seasonal connection; this population was of low abundance (density in March 2005: 0.6 ± 0.5 m^?2) and was still colonising the pond at the time of sampling. In the low‐density population, individuals were significantly faster growing, maturing earlier (generally in their first year of life) and more fecund at length and age (mean batch fecundity at 50 mm: 883 compared with 473 eggs). These traits were advantageous in maximising early life reproduction, facilitating their colonisation and population establishment, a process already completed in the high‐density population.     

Life-history traits of non-native black bullhead Ameiurus melas with comments on its invasive potential

Life-history traits of non-native black bullhead Ameiurus melas from an oxbow of the River Váh (near the city of Komárno), located in the middle Danube reaches (Slovakia) were investigated during 2006 and 2007, including samples from the pre-spawning (March–May), spawning (May–June), post-spawning (late June–August) and resting (September) periods. In total, 600 specimens were examined. The sex ratio oscillated close to 1 : 1. Females were found to mature at 98.6–120 mm SL (118–145.1 mm TL, compared to 171–254 mm TL in the native North American populations). Spawning took place in May and June, although the spawning period in 2007 was more protracted. Based on the analyses of annual gonadal cycle and oocyte size distribution, the black bullhead is considered a multiple spawner with asynchronous oocyte development and indeterminate fecundity. Absolute fecundity ranged from 1238 to 4755 (mean 2610), and relative fecundity from 36.2 to 154.3 (mean 56.1) oocytes g⁻¹. The high flexibility in the life history of the black bullhead as demonstrated by its non-native populations, as well as its extreme tolerance and capability to live in systems with poor water quality, suggests that this species has a high potential to invade new areas and establish viable populations.     

Invasive cyprinid fish in Europe originate from the single introduction of an admixed source population followed by a complex pattern of spread

The Asian cyprinid fish, the topmouth gudgeon (Pseudorasbora parva), was introduced into Europe in the 1960s. A highly invasive freshwater fish, it is currently found in at least 32 countries outside its native range. Here we analyse a 700 base pair fragment of the mitochondrial cytochrome b gene to examine different models of colonisation and spread within the invasive range, and to investigate the factors that may have contributed to their invasion success. Haplotype and nucleotide diversity of the introduced populations from continental Europe was higher than that of the native populations, although two recently introduced populations from the British Isles showed low levels of variability. Based on coalescent theory, all introduced and some native populations showed a relative excess of nucleotide diversity compared to haplotype diversity. This suggests that these populations are not in mutation-drift equilibrium, but rather that the relative inflated level of nucleotide diversity is consistent with recent admixture. This study elucidates the colonisation patterns of P. parva in Europe and provides an evolutionary framework of their invasion. It supports the hypothesis that their European colonisation was initiated by their introduction to a single location or small geographic area with subsequent complex pattern of spread including both long distance and stepping-stone dispersal. Furthermore, it was preceded by, or associated with, the admixture of genetically diverse source populations that may have augmented its invasive-potential.     

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.     

Piscivorous fishes diet dominated by the Asian cyprinid invader,topmouth gudgeon (<Emphasis Type="Italic">Pseudorasbora parva</Emphasis>)

Predation on the non-native cyprinid, Pseudorasbora parva, was reported during an annual study in a small connecting canal about 40 km south of Brno, Czech Republic. Two cyprinid fish species (Pseudorasbora parva, Rutilus rutilus) were identified in the diet of 23 piscivores belonging to three native fishes (Perca fluviatilis, Sander lucioperca, Esox lucius). The relative abundance of prey fishes changed seasonally and was dominated by the topmouth gudgeon in spring. Thereafter roach incidence continuously increased. In contrast, topmouth gudgeon was found to be a more sized-available prey and was the most dominant prey species in the diet of all piscivorous fishes during the whole season. Strong piscivory towards this alien might be beneficial for its eradication or control to support ecological integrity in natural and modified seminatural habitats.