DOI: 10.3391/ai.2026.21.2.190069

Authors: Michaela Palmieri, Leandro E. Miranda, Melanie R. Boudreau, Corey G. Dunn, Leslie M. Burger, Dennis Riecke

Abstract: Understanding spatial distribution patterns is essential to management of invasive species. Aquatic invasive species can be notably challenging to detect due to the substantial effort required to locate them underwater. This limitation has resulted in a lack of timely distribution maps, particularly over vast regions, and hindered efforts to understand, forecast, and manage the proliferation of invasive bigheaded carps (Hypophthalmichthys spp.). Much of the Mississippi River basin, particularly the Lower Mississippi Alluvial Valley, provides access to a massive network of interconnected floodplain lakes. In the absence of lake-specific monitoring data on carp occurrence status, we used local expert knowledge, provided by fish managers interviewed virtually, in conjunction with Maximum Entropy (MaxEnt) modeling, to predict bigheaded carps distribution in relation to lake physical characteristics. We predicted widespread carp invasion in more than 60% of over one thousand floodplain lakes, with lake size, inundation, and proximity to rivers closely related to carp presence. The resultant distribution map may be imprecise given the swift proliferation of bigheaded carps and sparse monitoring data, but it offers a baseline upon which presence data and range can be compared. This assessment method is also a resource for identifying priority management and conservation areas and can serve as a first step in conservation planning.

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DOI: 10.3391/ai.2025.20.3.161320

Authors: Shoujie Tang, Ying Xing, Temesgen Tola Geletu, Jinliang Zhao

Abstract: In recent decades, the redbelly tilapia (Coptodon zillii) has become one of the most serious invasive alien fish species worldwide. The successful invasion of this fish may largely depend on the plasticity of its life-history traits. In order to explore the life-history traits of the invasive population of C. zillii, we chose Shuikou Reservoir of Minjiang River, China, as a typical invasive habitat, and 1,041 specimens were collected monthly from March 2023 to February 2024. Life-history traits were systematically investigated. The results showed that the entire population consists of individuals from age 1 to age 6, with the highest percentage (95.10%) of younger individuals at 1–2 years old. The sex ratio of males to females was 1.05:1. The equation of the length-weight relationship was W = 0.048*L2.938, and the parameters of von Bertalanffy growth equation were L∞= 32.937 cm, W∞= 1381.010 g, k = 0.131, and t0 = -2.056. The breeding season ranged from March to November, and the minimum sexually mature standard lengths of females and males were 8.7 and 9.0 cm, respectively. Mean absolute fecundity was 3854.38±254.43 eggs, while mean relative fecundity to standard length and body weight were 301.95±16.94 eggs/cm and 60.44±3.56 eggs/g, respectively. These results indicated that the population of C. zillii in Shuikou Reservoir presented characteristics such as a high proportion of young individuals, low growth rate, long spawning season, high fecundity, and smaller size at first maturity compared with the native and other invasive populations. Both opportunistic and equilibrium life-history strategies might have contributed to their successful invasion, and there is a potential risk of further population expansion.

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DOI: 10.3391/ai.2025.20.3.152950

Authors: Erin S. McCallum, Kristina M. Sefc, Tomas Brodin, Patricia Burkhardt-Holm, Karen Bussmann-Charran, Ann-Britt Florin, Juergen Geist, Michal Janáč, Pavel Jurajda, Jake M. Martin, Joachim Pander, Aneesh P. H. Bose

Abstract: River barriers such as hydropower dams and weirs can negatively affect river ecosystems by disrupting connectivity and reducing biodiversity. However, such barriers could also limit the spread of invasive species. Here, we used a spatial population genetics approach to test whether river barriers act as a hindrance to gene flow in the invasive round goby (Neogobius melanostomus Pallas, 1814). We sampled gobies from four different rivers across their invasive range in Central Europe (the Danube, Dyje, Morava, and Rhine rivers), with locations on either side of eight major river barriers. Using microsatellite genotyping, we found that round goby populations were differentiated with increasing number of river barriers and with increasing distance between sampling sites, depending on the river system in focus. We found significant population differentiation across three individual barriers, but no clear indication that this was related to barrier type as barriers were highly diverse. We also found reduced genetic diversity in populations that were more recently established. Our findings suggest that successive river barriers can sometimes slow the spread of round goby. Further research on the features of barriers that hinder round goby movement will help to design barrier passage solutions that will both limit spread of this invasive species and maintain connectivity for the native fauna.

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DOI: 10.3391/ai.2025.20.3.162564

Authors: Efim D. Pavlov, Tran Duc Dien, Ekaterina V. Ganzha

Abstract: Non-native suckermouth armoured catfish Pterygoplichthys spp. have spread extensively across many river systems in Vietnam. It is possible that their expanded distribution occurred through the brackish waters of estuaries and coastal zones, facilitating movement from one river system to another. It has been previously hypothesized that, for successful dispersal through brackish water, armoured catfish can tolerate changes in water salinity and are capable of avoiding high salinity levels that threaten their survival. In this study, we experimentally estimated the movements and the directions of juvenile and adult wild loricariids in fresh and brackish water. Our results showed that juveniles exhibit a circadian rhythm of locomotor activity similar to that of adults. However, juveniles display a more pronounced reaction to increasing water salinity ‒ at 5 PSU ‒ while adults respond at 15 PSU. This likely explains the absence of juveniles in natural brackish water environments and their reduced potential to spread through brackish waters compared to adults. Adult loricariids are likely capable of recognizing and avoiding high-salinity zones (>10 PSU) by increasing locomotor activity, predominantly directed toward the surface. Their ability to grasp air helps maintain positive buoyancy, allowing them to remain in the surface layer of freshwater over extended periods of time. Variability in salinity tolerance among adults (ranging from 2 to 16 hours in 15 PSU) may enable some individuals to be more successful in dispersing through estuaries and along coastlines.

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DOI: 10.3391/ai.2024.19.2.124660

Authors: Matthew R. Pintar, Nicole D. Strickland, Jeffrey L. Kline, Mark I. Cook, Nathan J. Dorn

Abstract: Asian swamp eels (Monopterus albus/javanensis) were first reported as introduced to Florida waterbodies in 1997 near Tampa and Miami; a third population was recorded by 1999 in Homestead. Initial assessments, published soon after swamp eels in southern Florida were first recorded in wetlands beyond canals and ponds (in 2007), concluded there was little threat to Florida’s aquatic ecosystems. Long-term data now suggest they precipitated population crashes of crayfishes and small fishes in the eastern Everglades. We used records from continuous long-term monitoring programs, sporadic monitoring studies, and online databases to reconstruct swamp eel presence across Florida. Monitoring studies provided wetland hydrologic variables to assess limits for swamp eels. From 1997–2007, populations in southern Florida remained restricted to canals; initial spread from 2007–2017 across southern Everglades National Park proceeded slowly and the two populations covered ~1500 km2 of southern Florida. From 2017–2022, the rate of spread increased as they spread west and north (~5800 km2 range). Through 2014, the Tampa population occurred only along southern/eastern Tampa Bay (~60 km2) but has since spread south along the Gulf Coast, east into central Florida, and south along the Lake Wales Ridge (~11,000 km2). We found evidence of two potentially new introductions, in Palm Beach County and Orlando. There was no clear evidence of limitation of wetland drying on swamp eel occurrence in the Everglades; they were captured in marshes that dried for 1–5 months during the previous dry season, but short-hydroperiod wetlands may have slowed spread. In the Everglades, evidence suggests swamp eels may have been inadvertently spread into marshes from canals used to deliver water for flood control and hydrologic restoration. Swamp eels are currently spreading unchecked across Florida, and there should be great concern about continued spread in this region and their establishment and spread elsewhere.

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DOI: 10.3391/ai.2024.19.1.117161

Authors: Md Shakhawate Hossain, Surya Gentha Akmal, Miloš Buřič, Jiří Patoka

Abstract: Amazon sailfin catfish are native to Latin Arica (Siluriformes: Loricariidae: Pterygoplichthys) and are popular around the world as ornamental fish. It is well-documented that these species are highly successful invaders and very prone to forming new geographical ranges. However, once established, eradicating a new population is a very challenging task. In Bangladesh, species of the genus Pterygoplichthys are expected to spread widely and have a severe detrimental impact on ecosystem health, biodiversity and economics. Here we provide new information on the future probable establishment of non-native populations of these species in the wild using a climate-matching analysis and highlight their potential area of occurrence. The potential socio-economic consequences are also discussed, as are the public perception of these species and probable economic damages caused. Control of the import of similar species, their culture and intentional or unintentional release into open water is urgently required.

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DOI: 10.3391/ai.2024.19.1.116273

Authors: Pim Lemmers, Robin Olde Wolbers, Gerard van der Velde, Rob S. E. W. Leuven

Abstract: Co-occurring and morphologically similar species have adapted to differential niches to minimize competition. An invasive alien species can occupy an ‘empty niche’ in introduced ranges. Alternatively, the invader may occupy an overlapping niche and compete with native species to a certain degree. In a Western European lowland brook with high nutrient loads, we studied a benthic community of five fish species, including two alien species: an Asian weatherfish (Misgurnus bipartitus) and the western tubenose goby (Proterorhinus semilunaris). The native species concerned stone loach (Barbatula barbatula), spined loach (Cobitis taenia), and gudgeon (Gobio gobio). Because of the unknown effects of the invaders on native benthic fish species, the trophic position, isotopic niche overlap, and potential food competition among these species were identified using nitrogen and carbon stable isotopes. The trophic levels of the five fish species indicated that they are secondary consumers. The body size of native fish species correlated significantly negatively with their δ15N (‰) signature, in contrast with the invaders indicating that the latter are generalists. Significant isotopic niche overlap was observed among all benthic species. The degree of niche overlap of M. bipartitus was the highest with G. gobio (91.8%). Proterorhinus semilunaris showed the highest degree of niche overlap with B. barbatula (91.2%). It was notable that the observed niche overlap between the native B. barbatula and C. taenia was high (99.2%). Overlap between M. bipartitus and P. semilunaris was low (8.9%), indicating little resource competition between these alien species. Native species showed wider isotopic niches than the invaders. Bayesian mixing models revealed that native and alien species slightly differ in their main diet. The results suggest that the invaders are plastic in their resource use, leading to niche differentiation and promoting the co-existence of benthic fish species.

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DOI: 10.3391/ai.2023.18.4.112766

Authors: Quenton M. Tuckett, Timothy J. Lyons, Jeffrey E. Hill

Abstract: Pet abandonment is an important introduction vector for freshwater aquarium fishes, as unwanted pets become too large for tank dimensions and are released into the environment. Concerns over pet abandonment may be particularly important for the U.S. state of Florida, which exhibits abundant access to freshwater habitats and a climate more favorable to tropical aquarium fishes than other continental U.S. states. Numerous studies have examined the factors affecting establishment for non-native species, including the importance of propagule pressure and climate suitability. For freshwater aquarium species, maximum body size can increase pet abandonment because they grow too large for the tank dimensions (i.e., “tankbusters”). Thus, large maximum body size may increase propagule pressure due to intentional release. In addition to being introduced in sufficient numbers, a match between the thermal tolerance of a species and the thermal habitat is necessary for establishment. Several large-bodied catfishes are found in the aquarium trade, including the goonch Bagarius spp., redtail catfish Phractocephalus hemioliopterus, and tiger sorubim Pseudoplatystoma tigrinum. Here, we experimentally determined the chronic lethal minimum temperature (CLmin) for the three catfishes. CLMin estimates for these three species were higher than many other ornamental species, highest for the redtail catfish (14.3 °C), lower for the tiger sorubim (11.0 °C), and lowest (9.9 °C) for the goonch. Given these lethal temperatures, the distribution of redtail catfish would be limited to South Florida while the tiger sorubim and goonch could live, provided other habitat characteristics are suitable, up to ~28°N Latitude in Florida.

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DOI: 10.3391/ai.2023.18.3.104066

Authors: Efim D. Pavlov, Tran Duc Dien, Ekaterina V. Ganzha

Abstract: In the last decade, invasive suckermouth armored catfish Pterygoplichthys spp. spread among many river systems of Vietnam. Extended distribution of armored catfish might be associated with using brackish water in estuaries for fish spread from one river system to another. The first goal of our study was to assess the occurrence of armored catfish in the estuary of the Da Rang River (Phu Yen Province, Vietnam) and their distribution depending on the horizontal salinity gradient (4–25 PSU). Fish were mainly caught by stationary bottom traps in water salinity from 4 PSU to 18 PSU. The second goal of our study was to experimentally evaluate the ability of armored catfish to move and breathe in seawater (33 PSU). Fish moved in horizontal and vertical planes after transfer into seawater during the first 15 minutes. Fish moved around less by the 13th–15th minutes in seawater. Armored catfish moved around more in seawater than in freshwater. The exposure to seawater for 6 minutes led to deterioration of fish breathing. The results of our field and experimental studies established that armored catfish are found and able to move in brackish waters but avoid high salinity water. These facts provide support for the hypothesis of armored catfish invasion through the estuaries and coastlines.

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DOI: 10.3391/ai.2023.18.1.103438

Authors: Aylin Ulman, Hasan Deniz Akbora, Ozgur Çanak, Elaine Chu, Burak Ali Çiçek, Hasan Ersönmez, Sinan Mavruk, Caner Enver Özyurt, Taner Yildiz, Amy Liu, Nazli Demirel, Daniel Pauly

Abstract: The highly toxic orange-spotted toadfish Torquigener hypselogeneion (Bleeker 1852) [conspecific Torquigener flavimaculosus Hardy & Randall, 1983] is now a very common invasive fish in the Eastern Mediterranean. Its small size, well under 20 cm, may have concealed the danger it represents, and little is known about its biology or ecology. Here, the spawning seasons, gonado- and hepato-somatic index and condition factors of T. hypselogeneion from 3 locations of the Eastern Mediterranean are presented, based on a total of 1360 individuals sampled, i.e., 216 from Finike, 817 from Fethiye (both Turkey), and 327 from Cyprus. Our results show that T. hypselogeneion is a carnivorous species that forages on sandy bottoms, with a preference for small invertebrates, especially the small invasive gastropod Cerithium scabridum, crustaceans (hermit crabs, other crabs and barnacles), and sea urchins; however, at least in some localities, they appear to forgo eating during their peak reproductive period. The parameters of the von Bertalanffy Growth Function for T. hypselogeneion in the Eastern Mediterranean were: asymptotic length = 17.4 cm (total length; TL) and K = 0.96 year-1, implying a longevity of about 4 years, while the mean length at first maturity was about 10 cm (TL) for both sexes. An average-sized adult female (13 cm TL, 45.7 g live weight) was found to contain 1,250 eggs per gram body weight. Based on its high invasiveness and negative impacts to ecology of the Eastern Mediterranean and the human health, we suggest that T. hypselogeneion should be listed as a priority invasive species and that its population closely monitored within the Mediterranean Sea.

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