Pseudorasbora Parva Research Articles

First record of stone moroko (Pseudorasbora parva), an invasive alien fish species, in water bodies of urban green areas in Poland

Abstract Invasive alien species are currently a major ecological problem. One such species is stone moroko, Pseudorasbora parva (Gobionidae), which has only been found to date in natural or agricultural water bodies (lakes, rivers and streams, carp ponds). Therefore, the current study is the first description of stone moroko in urban green areas (Warsaw, Poland). The fish were caught with a hydrobiological net. Four catches were conducted in ponds located in Morskie Oko Park (pond 1) and the Saxon Garden (pond 2) – two in fall and two in the spring, while two spring catches were conducted in Dolinka Służewska Park (stream). The population in pond 2 apparently survived the winter, and the fish caught in June displayed visible signs of sexual dimorphism and were significantly larger (average body mass: 1648 ± 1123 mg; range: 460–6090 mg) than those caught in the pond in the two fall samplings (404 ± 122 mg; 154–729 mg). After recording substantial numbers of specimens in the fall, no fish were caught in pond 1 during either of the spring catches, while only a few moroko were caught in the stream in April (1212 ± 869 mg; 454–2901 mg) and none were caught in June. Throughout the study, 59 specimens were caught in pond 1, 74 in pond 2, and 7 in the stream.

Distribution and host range of a highly invasive parasitic copepod

AbstractThe parasitic copepod Neoergasilus japonicus (Ergasilidae), native to East Asia, has spread rapidly around the world over the past half-century and now represents a clear example of successful parasitic invader. The species is now found in western Asia, Europe, America and Africa, with aquaculture and fish introductions identified as the primary vectors of dispersal. Regional field investigations have revealed surprisingly high number of affected localities, indicating potentially wider distribution than currently recognised. Neoergasilus japonicus exhibits low host specificity, parasitising a diverse range of freshwater fishes. This study updates the global fish host species list to 132, spanning 27 families across 15 orders, with Cypriniformes identified as the most susceptible host species. Under experimental conditions in this study, however, N. japonicus avoided its natural host, topmouth gudgeon Pseudorasbora parva, suggesting a level of resistance to its native parasite. Piscivorous and demersal fish were less infected by copepods than planktivorous, benthivorous, pelagic and benthopelagic species, reflecting the ecology of both the parasite and its hosts. An ability to re-attach to another host, though limited, was confirmed under experimental conditions. Recognising the ecological impacts and potential consequences associated with the introduction of non-native parasites emphasises the need for continuous monitoring and research globally.

Isotopic niches reveal the impact of topmouth gudgeon and gibel carp on native crucian carp

Invasive species pose a major threat to natural ecosystems and directly outcompete many native species, placing them at imminent threat of extinction. The topmouth gudgeon (Pseudorasbora parva) is on the EU’s blacklist of invasive freshwater species and threatens biodiversity, especially in wetland and floodplain ecosystems, aquacultures and village ponds. The crucian carp (Carassius carassius) is native to Europe and its populations have declined in large part of its native range, with invasive gibel carp (C. gibelio) suspected as a major cause of its decline. Invasions by topmouth gudgeon have been implicated in the decline of crucian carp populations but this still needs to be verified. The aim of this study was to evaluate by the experimental approach the competitive interaction between the two species, topmouth gudgeon and crucian carp, focusing on isotopic niche sizes and their overlap in syntopy. A four-month mesocosm experiment was performed to determine the isotopic niche of crucian carp and topmouth gudgeon living alone and in syntopy. Additionally, stable isotope data were collected at the sites where the two species co-occur to compare niche sizes and overlaps. Experimental data showed that the isotopic space of topmouth gudgeon responded more flexibly (reducing niche size at syntopy) than that of the crucian carp and confirmed a high isotopic niche overlap between the species. Field studies have shown that topmouth gudgeon has invaded the isotopic niche of the crucian carp, especially when another invasive species, the gibel carp, lived in the community (25% at 40% ellipse area and 50% at 95% ellipse area). When only the topmouth gudgeon and crucian carp were present in the field, the overlap was lower (3% and 48%, respectively) and directional overlap modelling showed that the crucian carp was more likely to invade the isotopic niche of topmouth gudgeon than vice versa. The data indicated that competition between crucian carp and topmouth gudgeon is likely, especially in syntopy with other invasive species. This study shows that the feeding plasticity of topmouth gudgeon likely facilitates its establishment outside its native range and, due to high isotopic niche overlap, threatens native fish with similar feeding ecology with competitive displacement.

A good word on topmouth gudgeon Pseudorasbora parva in small impoundments in the Aral Sea watershed (Central Asia, Kazakhstan)

Biological invasions are one of the most powerful negative factors threatening the natural biological diversity and well-being of continental water bodies. In the Aral Sea (Small Aral) basin, it has now been possible to stabilize the catastrophe that arose as a result of the irrational use of water resources. However, the diversity and impact of alien fish species on water ecosystems remains little known. For 10 years, we studied the distribution of one fish species, topmouth gudgeon Pseudorasbora parva (Temminck & Schlegel, 1846) in water bodies of the Aral Basin in the Republic of Kazakhstan. Now, this species is found everywhere in the Syrdarya River itself, floodplain lakes and most tributaries, but is not numerous. Using the example of two small local impoundments, the ratio of the abundance of topmouth gudgeon and other fish species was studied. There was no significant correlation between the presence of topmouth gudgeon and the presence/absence of other fish species. There is also no any significant correlation between the total number of fish (abundance) and topmouth gudgeon abundance, diversity indices and topmouth gudgeon abundance. The findings do not suggest that topmouth gudgeon has a negative impact on other fish species. More likely, this species is able to quickly expand new habitats, but under more stable conditions of water bodies it gives way to other fish species. At high water temperatures, topmouth gudgeon remains the only fish species that feeds on the larvae of blood-sucking Culex and Anopheles mosquitoes.

Амурский чебачок Pseudorasbora parva (Cyprinidae) в водоемах и водотоках Дагестана

Information is provided on the distribution of a species alien to the ichthyofauna of Dagestan – the Amur Top-mouth gudgeon Pseudorasbora parva (Temminck et Schlegel, 1846) within the region. It was found that the species expanded its range in the region under consideration, in 2021 it was found in the rivers Manasozen (9 copies), Gamriozen (10 copies), Ulluchai (6 copies), Rubas (6 copies), Avar koisu (a tributary of the Sulak River, in the area of the Gotsatli HPP), as well as in L. Mooch. It is assumed that the widespread distribution of P. parva is associated with high ecological plasticity, migration activity of larvae and fry, their high survival rate, rapid growth and accelerated puberty. The presented morphological variability of the Amur Topmouth gudgeon population based on the study of 20 signs, including 5 meristic and 15 plastic, revealed a slight variability of morphological signs due to different habitat conditions in the region. The Amur Topmouth gudgeon is a natural focus of an infectious disease of the swim bladder, dangerous for autochthonous ichthyofauna and aquaculture facilities, and a food competitor and consumer of caviar and larvae of autochthonous fish. With high numbers and prolonged starvation, P. parva can be a serious competitor for juvenile carp and variegated carp, and exhibit a predatory reaction towards commensurate juveniles of commercially valuable fish species. To control the number of this alien in the region, it is advisable to use native predators – perch Perca fluviatilis (Linnaeus, 1758), pike Esox lucius (Linnaeus, 1758) and walleye Sander lucioperca (Linnaeus, 1758).

Supplemental description of Gyrodactylus pseudorasborae (Gyrodactylidae) parasitic on topmouth gudgeon Pseudorasbora parva (Cyprinidae) in South China

Based on morphology and ITS sequence data, we identify and supplementally describe Gyrodactylus pseudorasborae Ondračková, Seifertová & Tkachenko, 2023 on the fins of topmouth gudgeon (Pseudoraspora parva) from freshwaters of southern China. The highest similarity (99.57% and 99.47%) to G. pseudorasborae suggested they were the same species. Prevalence and mean intensity were 45% and 2.3, respectively. The gyrodactylid species morphologically resembled G. pseudorasborae recorded from the same host species P. parva in Czech Republic, Ukraine, and Central China. But there were slight morphological differences in the shape and size of the marginal hook. Comparisons of marginal hook sickles of various Gyrodactylus species suggested that G. pseudorasborae and G. parvae were members of the G. wageneri-group. A molecular phylogeny of G. pseudorasborae with related species is presented and discussed within the context of the mechanism of local evolution of these sister species.

Predicting the impact of climate change on the distribution of non-native Stone moroko fish (Pseudorasbora parva) in the rivers of the southern basin of the Caspian Sea

Predicting the impact of climate change on the distribution of non-native Stone moroko fish (Pseudorasbora parva) in the rivers of the southern basin of the Caspian Sea

Occurrence of topmouth gudgeon, Pseudorasbora parva, in relation to environmental factors in lowland streams and canals

Occurrence of topmouth gudgeon, Pseudorasbora parva, in relation to environmental factors in lowland streams and canals

Distribution of Topmouth Gudgeon Pseudorasbora parva (Cyprinidae) in Waterbodies and Watercourses of the Republic of Dagestan, Russia

Distribution of Topmouth Gudgeon Pseudorasbora parva (Cyprinidae) in Waterbodies and Watercourses of the Republic of Dagestan, Russia

Changes to fish assemblage following the selective removal of black bullhead (Ameiurus melas)

Abstract Black bullhead is among the most abundant and successful non‐native fish species in European fresh waters. A number of studies have indicated that its physical removal might be a potential solution to minimize possible adverse impacts; however, so far there have been no field studies to confirm this. This study quantified the population dynamics of both native and non‐native fishes in a small slow‐running lowland river within the Ponjavica Nature Park in Serbia before and after the black bullhead removal with fyke nets. The removal of black bullhead resulted in statistically significant changes in the abundance of two native species – an increase in rudd (Scardinius erythrophthalmus) (by 5.3 times) and a decline in bleak (Alburnus alburnus) (by 2.3 times). A significant increase was observed in three non‐native fish species – the abundances of topmouth gudgeon (Pseudorasbora parva), pumpkinseed (Lepomis gibbosus) and Prussian carp (Carassius gibelio) increased 25.5, 4.9 and 4.2 times, respectively. There were also substantial changes in the diversity of the fish assemblage after the black bullhead removal, illustrated by changes in diversity indices: Shannon's index doubled, while the Simpson's dominance index decreased threefold. The catch‐per‐unit‐effort and the biomass‐per‐unit‐effort values indicated the dominance of the black bullhead in the fish assemblage during the mass removal phase of the study. The young‐of‐the‐year/adult ratio did not vary in relation to abundance, which confirmed that black bullhead might not compensate for fishing mortality with increased recruitment. The results suggest that black bullhead plays a significant role in structuring the fish assemblage and that its removal may have both positive and negative effects on species abundance and diversity. These findings can contribute to the conservation of native fish species and improvement of future management programmes.

Distribution of Topmouth Gudgeon <i>Pseudorasbora parva</i> (Cyprinidae) in Waterbodies and Watercourses of Republic of Dagestan, Russia

The study provides information on the modern distribution of a species alien to the ichthyofauna of Republic of Dagestan, topmouth gudgeon Pseudorasbora parva (Temminck et Schlegel, 1846) (Cyprinidae). It has been established that this species is found in the rivers Manasozen, Gamriozen, Ulluchay, Rubas, Avar Koisu (a tributary of the Sulak River, in the area of the Gotsatlinskaya HPP), as well as in Lake Mochokh. The wide distribution of P. parva is associated with ecological plasticity, migratory activity, high growth rate, accelerated puberty and high level of survival of the offspring of this species of fish.

Boldness behavior and ecological adaptability of stone moroko (Pseudorasbora parva) in open-field testing

Abstract Boldness is closely related to fish species’ adaptative strategies and invasiveness and has become the focus of fish personality research. However, due to the lack of studies on behavioral stages, the ecological functions of certain behaviors remain unclear. To better understand the link between boldness and invasiveness in stone moroko (Pseudorasbora parva), an invasive Asian fish species, we exposed the fish to an open-field environment for 60 min and assessed their behavioral patterns, profiles, and stages. The results show that the boldness behavior of stone moroko was characterized by high activity, low average velocity, and diverse swimming postures. Five behavioral stages with significant differences were revealed: outbreak, inhibition, slow swimming, exploration, and adaptation. These observations suggest that stone moroko can quickly habituate to new environments. In addition, stone moroko spent more energy on exploring the living area and less on environmental risk assessment, as revealed by an analysis of their energy trade-off strategy. The behavioral strategies of stone moroko may explain their extremely high environmental adaptability and ability to invade multiple environments.

Dining amidst the decibels is not an issue when you have company: anthropogenic noise and the topmouth Gudgeon.

Journal of Fish BiologyVolume 102, Issue 6 p. 1271-1271 BETWEEN THE JFB COVERS Dining amidst the decibels is not an issue when you have company: anthropogenic noise and the topmouth Gudgeon William Bernard Perry, William Bernard Perry Assistant EditorSearch for more papers by this author William Bernard Perry, William Bernard Perry Assistant EditorSearch for more papers by this author First published: 08 June 2023 https://doi.org/10.1111/jfb.15459Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL No abstract is available for this article. References Barton, B.T., Hodge, M.E., Speights, C.J., Autrey, A.M., Lashley, M.A., Klink, V.P., 2018. Testing the AC/DC hypothesis: Rock and roll is noise pollution and weakens a trophic cascade. Ecol. Evol. 8, 7649– 7656. https://doi.org/10.1002/ECE3.4273 Britton, J.R., Davies, G.D., Brazier, M., Pinder, A.C., 2006. A Case Study of the Population Ecology of a Topmouth Gudgeon (Pseudorasbora parva) Population in the UK and the Implication for Native Fish Communities. Aquat. Conserv. Mar. Freshw. Ecosyst. 17, 749– 759. https://doi.org/10.1002/AQC.809 Candolin, U., Rahman, T., 2023. Behavioural responses of fishes to anthropogenic disturbances: Adaptive value and ecological consequences. J. Fish Biol. https://doi.org/10.1111/JFB.15322 Luo, J., Siemers, B.M., Koselj, K., 2015. How anthropogenic noise affects foraging. Glob. Chang. Biol. 21, 3278– 3289. https://doi.org/10.1111/GCB.12997 Popper, A.N., Hastings, M.C., 2009. The effects of anthropogenic sources of sound on fishes. J. Fish Biol. 75, 455– 489. https://doi.org/10.1111/J.1095-8649.2009.02319.X Popper, A.N., Hawkins, A.D., 2019. An overview of fish bioacoustics and the impacts of anthropogenic sounds on fishes. J. Fish Biol. 94, 692– 713. https://doi.org/10.1111/JFB.13948 Putland, R.L., Montgomery, J.C., Radford, C.A., 2019. Ecology of fish hearing. J. Fish Biol. 95, 39– 52. https://doi.org/10.1111/JFB.13867 Rojas, E., Prosnier, L., Pradeau, A., Boyer, N., Médoc, V., 2023. Anthropogenic noise does not strengthen multiple-predator effects in a freshwater invasive fish. J. Fish Biol. 0–2. https://doi.org/10.1111/JFB.15397 Simonis, A.E., Brownell, R.L., Thayre, B.J., Trickey, J.S., Oleson, E.M., Huntington, R., Baumann-Pickering, S., 2020. Co-occurrence of beaked whale strandings and naval sonar in the Mariana Islands, Western Pacific. Proc. R. Soc. B 287. https://doi.org/10.1098/RSPB.2020.0070 Slabbekoorn, H., Peet, M., 2003. Birds sing at a higher pitch in urban noise. Nat. 2003 4246946 424, 267–267. https://doi.org/10.1038/424267a Volume102, Issue6June 2023Pages 1271-1271 ReferencesRelatedInformation

Anthropogenic noise does not strengthen multiple-predator effects in a freshwater invasive fish.

Anthropogenic noise has the potential to alter community dynamics by modifying the strength of nested ecological interactions such as predation. Direct effects of noise on per capita predation rates have received much attention but the context in which predation occurs is often oversimplified. For instance, many animals interact with conspecifics while foraging and these nontrophic interactions can positively or negatively influence per capita predation rates. These effects are often referred to as multiple-predator effects (MPEs). The extent to which noise can modulate MPEs and thereby indirectly alter per capita predation remains unknown. To address this question, we derived the relationship between per capita predation rate and prey density, namely the functional response (FR), of single and pairs of the invasive topmouth gudgeon Pseudorasbora parva when feeding on water fleas under two noise conditions: control ambient noise estimated at 95 dB re 1 μPa and ambient noise supplemented with motorboat sounds whose relative importance over ambient noise ranged from 4.81 to 27 dB. In addition, we used video recordings to track fish movements. To detect MPEs, we compared the observed group-level FRs to predicted group-level FRs inferred from the individual FRs and based on additive effects only. Regardless of the number of fish and the noise condition, the FR was always of type II, showing predation rate in a decelerating rise to an upper asymptote. Compared to the noiseless condition, the predation rate of single fish exposed to noise did not differ at high prey densities but was significantly lower at low prey densities, resulting in an FR with the same asymptote but a less steep initial slope. Noise also reduced fish mobility, which might explain the decrease in predation rate at low prey densities. Conspecific presence suppressed the individual response to noise, the FRs of two fish (observed group-level FRs) being perfectly similar between the two noise conditions. Although observed and predicted group-level FRs did not differ significantly, observed group-level FRs tended to fall in the low range of predicted group-level FRs, suggesting antagonism and a negative effect of nontrophic interactions on individual foraging performance. Interestingly, the difference between predicted and observed group-level FRs was not greater with noise, which means that noise did not strengthen MPEs. Our results show that when considering the social context of foraging, here through the presence of a conspecific, anthropogenic noise does not compromise foraging in the invasive P. parva.

A rapid assessment of non-native fish distributions in two English river basins using environmental DNA

Environmental DNA (eDNA) surveys are increasingly used to inform management decisions for non-native species, for example, by detecting the presence and plotting distributions of species that may be in too low abundance for easy detection by conventional means. A recently-developed nested PCR protocol was used to assess the distributions of three non-native fish species in two river basins of southern England (River Test, Hampshire; River Ouse, Sussex). These river basins were known to contain three non-native fishes, either in the recent past or currently: two invasive small-bodied fish species (topmouth gudgeon Pseudorasbora parva, sunbleak Leucaspius delineatus), as well as a currently non-invasive species predicted to become invasive under future climate conditions, pumpkinseed Lepomis gibbosus. Water samples were collected at locations from headwater streams to estuary. Pumpkinseed and sunbleak were both detected downstream of an angling venue in the Sussex Ouse catchment known to contain those species, with an upstream expansion of sunbleak suggested by the detection of eDNA at a few upstream locations. Neither sunbleak nor topmouth gudgeon was detected in water samples from the River Test catchment, suggesting that neither species has persistent populations in that river catchment.

A comparative study of three fishery methods for sampling the invasive topmouth gudgeon (Pseudorasbora parva) in ponds.

Invasive fish threaten ponds' ecological status and their ecosystem services, therefore obtaining a representative sample of fish community composition is fundamental to fishery management, research and nature conservation. Estimates of the size distribution, density and biomass of the topmouth gudgeon (Pseudorasbora parva) model species of invasive fish in three ponds were compared among three sampling methods: electrofishing, fish-trapping and throw-netting. The study illustrates that the invasive fish, P. parva, can be detected by all tested fishing methods, yet our results clearly showed that there are pronounced differences among methods in population characteristic estimates. Electrofishing and throw-netting gave biased information on the size distribution of P. parva. Fish-trapping and throw-netting gave reasonable P. parva density and biomass estimates, while electrofishing clearly underestimated it. All tested methods showed a body size increment of P. parva between summer and autumn sampling sessions, yet neither throw-netting nor electrofishing recorded an increment in its density. Our study showed that fish-trapping is the most reliable and affordable method to estimate invasive P. parva population characteristics in ponds despite more time-demanding sampling. The success depends on the mesh size of sampling gear, operator skill and habitat structure. The cost-effectiveness of the selected methods and the importance of invasive fish monitoring in ponds is discussed. The sampling gear must be considered carefully according to the aim of the monitoring.

The parasites of a successful invader: monogeneans of the Asian topmouth gudgeon Pseudorasbora parva, with description of a new species of Gyrodactylus.

Monogenean parasites are often co-introduced with their fish hosts into novel areas. This study confirmed co-introduction of two dactylogyrids, Dactylogyrus squameus Gusev, 1955 and Bivaginogyrus obscurus (Gusev, 1955), and a newly described gyrodactylid species, Gyrodactylus pseudorasborae n. sp. into Europe along with their fish host, the invasive topmouth gudgeon Pseudorasbora parva (Temminck & Schlegel) from East Asia. All three species were observed in the lower Dnieper and middle Danube basin regions and had slightly larger haptoral hard parts than the same parasites in their native range. While dactylogyrids occurred sporadically, we recorded regular infection by G. pseudorasborae n. sp. at relatively high prevalence and abundance. This latter species was observed in both the native and non-native range of topmouth gudgeon, and resembles Gyrodactylus parvae You et al., 2008 recently described from P. parva in China. Both species were distinguished based on genetic analysis of their ITS rDNA sequence (6.6% difference), and morphometric differences in the marginal hooks and male copulatory organ. Phylogenetic analysis of dactylogyrid monogeneans showed that B. obscurus clustered with Dactylogyrus species parasitising Gobionidae and Xenocyprididae, including D. squameus, supporting recent suggestions of a paraphyletic origin of the Dactylogyrus genus. In addition to co-introduced parasites, topmouth gudgeon was infected with a local generalist, G. prostae Ergens, 1964, increasing the number of monogeneans acquired in Europe to three species. Nevertheless, monogenean infections were generally lower in non-native host populations, potentially giving an advantage to invading topmouth gudgeon.

Critical thermal maxima of three small-bodied fish species (Cypriniformes) of different origin and protection status

Environmental changes related to global warming are both a threat to cold-water fishes and simultaneously create favourable conditions for the spread of eurythermic or warm-water species. In both cases, it is necessary to develop conservation strategies supported by precise ecological data, including thermal requirements. In this study, we determined the upper thermal tolerance thresholds and the critical maxima for three small, non-commercial Eurasian freshwater fish species; i.e. lake minnow Eupallasella (=Rhynchocypris) percnurus, sunbleak Leucaspius delineatus and topmouth gudgeon Pseudorasbora parva using the Critical Thermal Method at different acclimation temperatures, i.e. 18, 23, 28, and 33°C (highest treatment for topmouth gudgeon only). We hypothesized that lake minnow would have the lowest thermal tolerance and the topmouth gudgeon the highest. The response to temperature rise and the upper thermal limits were species-specific and correlated with the acclimation temperature, but not with fish length. Sunbleak showed the lowest thermal tolerance, though at 28°C both E. percnurus and L. delineatus reached a similar critical thermal limit. Topmouth gudgeon showed distinctly higher upper thresholds of thermal tolerance and at the highest acclimation temperature the critical upper limit for the species was close to 42°C. The results obtained for L. delineatus were surprising as we predicted that this leuciscid fish would be more tolerant of high temperatures than E. percnurus. We discuss the results in relation to the threat of extinction and the risk of species spreading beyond their natural range in the context of a warming environment.

Contrasting population genetic responses to migration barriers in two native and an invasive freshwater fish.

Habitat fragmentation impacts the distribution of genetic diversity and population genetic structure. Therefore, protecting the evolutionary potential of species, especially in the context of the current rate of human-induced environmental change, is an important goal. In riverine ecosystems, migration barriers affect the genetic structure of native species, while also influencing the spread of invasive species. In this study, we compare genetic patterns of two native and one highly invasive riverine fish species in a Belgian river basin, namely the native three-spined stickleback (Gasterosteus aculeatus) and stone loach (Barbatula barbatula), and the non-native and invasive topmouth gudgeon (Pseudorasbora parva). We aimed to characterize both natural and anthropogenic determinants of genetic diversity and population genetic connectivity. Genetic diversity was highest in topmouth gudgeon, followed by stone loach and three-spined stickleback. The correlation between downstream distance and genetic diversity, a pattern often observed in riverine systems, was only marginally significant in stone loach and three-spined stickleback, while genetic diversity strongly declined with increasing number of barriers in topmouth gudgeon. An Isolation-By-Distance pattern characterizes the population genetic structure of each species. Population differentiation was only associated with migration barriers in the invasive topmouth gudgeon, while genetic composition of all species seemed at least partially determined by the presence of migration barriers. Among the six barrier types considered (watermills, sluices, tunnels, weirs, riverbed obstructions, and others), the presence of watermills was the strongest driver of genetic structure and composition. Our results indicate that conservation and restoration actions, focusing on conserving genetic patterns, cannot be generalized across species. Moreover, measures might target either on restoring connectivity, while risking a rapid spread of the invasive topmouth gudgeon, or not restoring connectivity, while risking native species extinction in upstream populations.

Risk of invasiveness of non-native fishes in the South Caucasus biodiversity and geopolitical hotspot

Aquatic invasions are one of the major threats for freshwater ecosystems. However, in developing countries, knowledge of biological invasions, essential for the implementation of appropriate legislation, is often limited if not entirely lacking. In this regard, the identification of potentially invasive non-native species by risk screening, followed by a full risk assessment of the species ranked as higher risk, enables decision-makers to be informed about the extent of the threats posed to the recipient (risk assessment) area. In this study, 32 non-native extant and horizon fish species were screened for their risk of invasiveness under current and predicted climate conditions for the South Caucasus – a biodiversity and geopolitical hotspot that includes the countries of Armenia, Azerbaijan and Georgia. Overall, the number of very high-risk species increased from four (12.5%) under current climate conditions to 12 (37.5%) under predicted climate conditions. The highest-risk species under both conditions included the already established gibel carp Carassius gibelio and topmouth gudgeon Pseudorasbora parva, the locally translocated pikeperch Sander lucioperca and the horizon North African catfish Clarias gariepinus. Under predicted climate conditions, a very high risk of invasiveness was predicted also for the translocated three-spined stickleback Gasterosteus aculeatus and Eurasian perch Perca fluviatilis, for the already established eastern mosquitofish Gambusia holbrooki, ruffe Gymnocephalus cernua, sharpbelly Hemiculter leucisculus and Nile tilapia Orechromis niloticus, and for the horizon pumpkinseed Lepomis gibbosus and largemouth bass Micropterus salmoides. Future research on the non-native species in the South Caucasus should be conducted both country- and region-wide and should account not only for the high biodiversity, but also for the critical geopolitical situation affecting the study area.