Influence of invasive fish species on host-parasite interactions in river ecosystems

ABSTRACTUnderstanding the ecological differences between native and invasive species is of considerable scientific and practical interest. We examined such differences between native and invasive inland fish species from the Iberian Peninsula in order to analyse the importance of phylogenetic correction and variability (in addition to central tendency). We collected 26 quantitative and qualitative variables on the ecology, life‐history traits and human use of the 69 inland fish species of the Iberian Peninsula, including native, invasive and migratory species. The taxonomic distribution of invasive fish species deviated significantly from world freshwater richness and in contrast to native species, invasive fish belongs to only five taxonomic orders but to a wide spectrum of families not native to the Iberian Peninsula. Because the life‐history traits were highly dependent on taxonomy, the results, with or without applying phylogenetic methods, differed and after accounting for phylogeny, invasive species displayed higher and wider latitude in general and a different reproductive season mainly among salmonids and cyprinids. Human use was also significantly different between native and invasive fish species and produced more variability in life‐history traits of invasive species and uneven taxonomic distribution because of the high diversity of species introduced. We show that accounting for taxonomy and studying variability in addition to central tendency is important in the comparison of life‐history traits between native and invasive species.

Invasive species are “non-indigenous species that spread from the point of introduction and become abundant.” The invasive species cause damage to the endemic species in the ecosystem. The invasive fish species cause direct and indirect harm to the native species. The direct harm includes the predation of the native species, competing with the native species for food and other resources, causing or carrying diseases, and preventing native species from reproducing or killing the young ones. The indirect threat of invasive species includes changing the food web in an ecosystem by destroying or replacing native food sources. Invasive species can also alter the abundance or diversity of species that are important in the habitat for native wildlife. The Zoological Survey of India reported that inland wetlands alone support 1027 species of fish with more biological, nutritional, and economic value. The National Biodiversity Authority of India has recognised 14 freshwater invasive species in Indian freshwater ecosystems. The invasive fish species are Clarias gariepinus, Cyprinus carpio, Gambusia affinis, Gambusia holbrooki, Mylopharyngodon piceus, Oreochromis mossambicus, Oreochromis niloticus, Poecillia reticulata, Pterygoplichthys disjunctivus, Pterygoplichthys multiradiatus, Pterygoplichthys pardalis, Pterygoplichthys anisitsi, Pygocentrus nattereri, Aristichthys nobilis. These 14 freshwater invasive species recognised by the National Biodiversity Authority of India in Indian freshwater ecosystems are exhibiting invasiveness elsewhere, rapid multiplication and spread in different ecosystems, multiple modes of reproduction, and multiple modes of dispersion. These are leading to effects on ecosystem functions and services, biodiversity loss, economic loss, health hazards, and also range extension. Looking into the seriousness of the issues, control and remedial measures should be implemented. Regulation must be brought on unauthorised culture. Aquaculturists and aquarists should take measures so that cultivable exotic food fish cannot enter the open water body. For the same, awareness programmes to educate aquaculturists and aquarists need to be conducted to educate them about not releasing the cultivable exotic food fish into natural waterbodies. Proper quarantine is urgently needed before introducing new species for any purpose, like aquaculture, ornamental, sports, or to control mosquito populations. These control measures will surely protect the Indian freshwater fish biodiversity against the detrimental effects of invasive freshwater fish species.

Biodiversity in fluvial ecosystems is under pressure as a consequence of their degradation. Conservation strategies for endangered freshwater molluscs and for salmonid fishes have been proposed but they are typically poorly integrated. Here, we examined for the first time the genetic structure of a critically endangered obligate mollusc invertebrate parasite, the freshwater pearl mussel (Margaritifera margaritifera), and its vertebrate host fish, the brown trout (Salmo trutta m. fario), in European headwater streams. We compared genetic differentiation and diversity with productivity and ecological habitat features of both species in nine different European streams from the drainage systems of the Danube, Elbe, Weser, Tuuloma, Kemijoki and Aulne. Genetic differentiation was more pronounced in pearl mussel than in brown trout, although the drainage-specific patterns were generally similar. Genetic diversity of host and parasite was negatively correlated. The most oligotrophic, postglacially colonized areas represented genetic diversity hotspots with high conservation priority for pearl mussels, whereas their host fish displayed low diversity in these areas. This pattern can be explained by differences in the ecological niches and in the life-history strategies of both species. These results question the effectiveness of single-species approaches in the conservation of genetic aquatic resources and suggest that genetic information from species with different life-history strategies, such as invertebrates and fish, should be considered simultaneously for geographical conservation prioritization in stream ecosystems.

Effective management of invasive alien species requires location-specific strategies involving the regular update of distribution maps to identify spatial patterns, trends, and pathways of entry and the spread and hotspots of those invasions. However, a comprehensive overview of invasive alien fish species in Romania is lacking. To fill this gap, we compiled a database with occurrences of alien fish species in Romania from diverse sources, including published literature, our own field data, online databases, social media, and online questionnaires. Occurrence data covers the 1910–2022 period. From a total of 52 alien fish species reported as present in Romania’s waterways, we assigned an invasive status to 11 species, of which Pseudorasbora parva, Lepomis gibbosus, Carassius gibelio, and Ameiurus spp. are widespread. Based on the currently available occurrence records, we evaluated the presence and distribution of invasive alien fish species at the watershed level, concluding that invasive alien fish species are present in all Romanian watersheds. We identified several hotspots consistent with the main points of entry and spread of invasive alien fish species, principally located in western, central, and eastern Romania, i.e., Mures, Crisuri, and Siret watersheds.

All continents, excluding Antarctica and the Artic, have been affected by incursion from alien freshwater fish species. Australia has not been spared. Four hundred and fifty species have now been declared on the ornamental importation list, making management a real challenge. With approximately 25 non-native species documented, Papua New Guinea (PNG) has likely some problems with invasive freshwater fish. Many of these species have been intentionally introduced to increase access to food as a protein source for remote communities or have spread naturally from western parts of Java and Indonesia, and now constitute a large biomass on some floodplain areas in PNG. The Torres Strait is located between PNG and northern Queensland and was previously a land bridge, though now under higher sea levels the region exists as a series of approximately 300 islands. The threat of further range extension of freshwater fish from PNG into northern Queensland via the Torres Strait Islands is significant, with two invasive fish species already recorded on northern islands of the Torres Strait (climbing perch,Anabas testudineuswhich has been continually recorded for the past decade; and recently the GIFT tilapia,Oreochromis niloticus). Here we present a case to control further spread of invasive freshwater fish species towards Australia, using a Land and Sea Ranger program, where Rangers are trained to be confident in the identification of pest fish species and to implement strategies to protect their borders from potential future incursions. The success of this program relies on Rangers to continue partaking in surveillance monitoring of coastal waters, checking and controlling for any new invasive species moving from PNG into Australian waters. We outline the biosecurity obligation under Article 14 of the Treaty between the two nations, which identifies the importance of conservation and protection of coastal floodplains from invasive species, and the spread between both nations.

Detection of invasive freshwater fish species using environmental DNA survey

The spread of invasive species is one of the major environmental concerns which can have negative effects on biodiversity. While several life history traits have been identified as being important for increasing the invasiveness of introduced species, the physiological factors that allow certain species to become successful invaders remain poorly understood. It has been speculated that good invaders are thriving in disturbed environments. In unfavourable conditions, as during hypoxic events, invasive species might be better adapted in their physiological and behavioural responses towards this stressor. We compared physiological and behavioural traits between two freshwater fish species: the European bullhead (Cottus gobio), an invasive fish species in Scotland, and its native competitor the stone loach (Barbatula barbatula) over different dissolved oxygen concentrations (DO). Contrary to expectations, bullhead displayed a reduced hypoxia tolerance as compared to stone loach, indicated by a higher threshold (Pcrit) for the maintenance of standard metabolism. Avoidance behaviour during progressive hypoxia was similar between bullhead and stone loach. When given a choice between an open normoxic zone and a shelter located in hypoxia, both species spent most of their time hiding under the shelter in hypoxic conditions (bullhead: 100%; stone loach: 93.93%–99.73%), although stone loach showed brief excursions into normoxic conditions under 25% DO level. These results suggest that stone loach might be more resistant to hypoxia as compared to bullhead, and thus that increased hypoxia tolerance is likely not a trait by which bullhead have been able to expand their range within the United Kingdom.

Climate change can have a significant impact on the Earth’s ecosystems. Invasive species will respond to climate change, and their responses will have ecological and economic implications. Habitat suitability models (HSMs) are some of the most important tools currently available for assessing the potential impacts of climate change on species. The projections of a model of suitable conditions for three invasive fish species in Europe, Lepomis gibbosus, Perccottus glenii and Pseudorasbora parva, built using Maxent and based on the occurrence throughout the range (native and invasive), on the current climate of Europe and on the forecast climate data for the 2050s and 2070s in the SSP2 and SSP5 scenarios are presented herein. For Lepomis gibbosus and Pseudorasbora parva, climate change will lead to a significant expansion of their zones, with suitable conditions to the north and east, while the change in suitability in their existing ranges will be moderate. For Perccottus glenii, the zone with suitable conditions will shift northward, with a gradual deterioration in the southern and central parts of its current range and an improvement in the northern part. Thus, at present and until the 2070s, Lepomis gibbosus and Pseudorasbora parva can be considered potentially dangerous invasive species in most parts of Europe, while Perccottus glenii can be considered as such only in the northern part of Europe.

Identification of native and invasive fish species helps in effective management of aquatic resources, including fisheries regulation, habitat restoration, and conservation. The objective of the study is to identify the native and invasive fish species found in the waters of Aneuk Laot Lake, Kota Sabang. This research was conducted from March to May 2024 in the waters of Aneuk Laot Lake. Sampling was carried out directly (sweaping) using nets measuring 1/2 inch, 3/4 inch and 1 inch. The types of fish caught in the waters of Aneuk Laot Lake consist of 4 orders, namely Cypriniformes, Cichliformes, Anabantiformes and Cyprinodontiformes. The composition of fish species in the waters of Aneuk Laot Lake, Sabang City, was identified as 6 species, namely the presence of native fish groups (native species) and invasive species. The native lake fish caught are Barbodes sp. and Rasbora sp. while the invasive fish species are Amphilophus trimaculatus, Oreochromis niloticus, Channa striata and Gambusia affinis. The diversity of fish species is useful for the management and conservation of biological resources in Aneuk Laot Lake, which is very important for the ecosystem and community of Aneuk Laot Lake, Sabang City.

Dam‐mediated biological invasions are a serious problem all over the world. Once established in reservoirs, the invasive species have catastrophic impacts on the river ecosystems downstream, and thus, rapid monitoring of invasive species is an urgent issue for the effective removal of them and the conservation management of native ecosystems. Here, we verified the utility of environmental DNA (eDNA) analysis as a tool to effectively monitor three invasive fish species (bluegill, largemouth bass, and smallmouth bass) in reservoirs using multiplex real‐time PCR. First, to determine the optimal sampling location and season to detect eDNA from these species, we analyzed the eDNA in water samples from shore and offshore sites in three reservoirs all year around. We found that eDNA detection rates either did not differ between sampling locations or were higher for shore than offshore sites. In addition, eDNA detection rates were higher in spring (breeding season of target species) and/or summer than winter. Second, we extensively surveyed the distribution of the three species in 30 reservoirs in Japan using eDNA analysis. Consequently, a single eDNA‐based surveillance in summer allowed to match approximately 90% of the presence/absence of the invasive fish species known from 27 yr of administrative capture‐based surveillances. Given these results, we recommend collecting the replicated water samples from shore sites in summer or the breeding season for the effective detection of invasive fish eDNA in reservoirs. Our eDNA assays with multiplex real‐time PCR enable the rapid and sensitive monitoring of invasive fish distribution in reservoirs.

Keeping pets has been part of human life since the earliest civilizations. Today, exotic animals are sold online and shipped globally to enthusiasts. However, pet sellers and keepers sometimes release exotic pets into nearby natural ecosystems, leading to biological invasion. This paper examines the invasion by sailfin catfish (Pterygoplichthys spp.) of Cauvery and Vaigai river basins, and its ecological and socio-economic impacts. We assessed the ecological impacts by comparing the total abundance and biomass of the invasive fish species (IFS), Pterygoplichthys spp., with those of comparator fish species (CFS) and various physicochemical parameters. We used semi-structured interviews and case studies of IFS mechanical removal programmes to assess the socio-economic impacts. The abundance and biomass of the IFS were significantly higher than those of the CFS in most lentic and lotic ecosystems. Interviews revealed significant sociological impacts on fisherfolk, including a push from fishing (a familial profession) to non-fishing vocations. The input–cost–outcome assessment of mechanical removal programmes revealed that the expenditure incurred could not prevent further invasion of the IFS. This study advocates for increasing awareness among stakeholders to devise effective control measures and implement policy-level changes to curb the sailfin catfish invasion in India’s inland water bodies.

Invasive fish species pose major threats to fisheries, aquaculture and biological diversity. These threats are occurred by invasion of habitats and predation on local fish species, and cause rapidly to vanish of endemic species and collapse fisheries production. At present the scientists in many fields focus on the presence and distributions of invasive fish, but there are less studies about invasive species on decontamination from infested watersheds. In this paper, effectiveness of selective fishing methods on control of invasive species in infested inland waters has been reviewed. The possibilities of removing invasive species from watershed and increasing catch pressure on these species were discussed by using results both practical studies and common international applications. As a result, specially designed fishing traps and pots can be used expediently to struggle against invasive fish species in inland waters.

Invasive species have the ability to modify their life-history traits in newly colonized areas, with positive shifts in specific life history traits under favourable environmental conditions. If such positive changes in their life history result in a comparably larger population growth rate, it may give them a competitive edge over native species, support faster range expansion and contribute to their invasion success. Within the present paper we hypothesized that the demographic flexibility represents an important contribution to the invasion success of exotic species, and that demographic flexibility patterns of invasive species differ from those in unsuccessful invaders. We tested this hypothesis by the use of elasticity analysis applied on simple age-structured population models of invasive fish species in the Danube River, as well as of non-native species that failed to establish or become invasive. Findings imply that the invasive fish species could have the ability to experience a more rapid population growth under favourable environmental conditions, especially those that sustain recruitment, while at the same time being more robust to changes in survival. The highest population elasticity among the assessed alien invasive species was detected in stone moroko (Pseudorasbora parva). The described approach has the potential to be used as an additional screening tool for invasive species. When combined with other invasion risk profiling methods, it can provide additional insight into characteristics of species invasions and in invasion potential of a species.

Global change impacts are likely to compromise agricultural benefits and the ecological status of rivers. The latter would be caused by modifications in fish population dynamics as fish species react in different ways against hydrological changes, and the establishment of alien and invasive fish species. To guarantee native fish sustainability, impact assessment studies should encompass habitat evaluations and competition assessment under future scenarios (i.e., including future hydrological scenarios and land use, and changes in agricultural demands). Moreover, their interplay with economic uses should also be considered, designing adaptation measures that take advantage of synergies and minimize trade-offs between them. Dam reoperation is a promising alternative to this end, given its direct and immediate impact on downstream streamflows and its absence of building costs. However, it requires consensus between water users, including native fish; thus, it should be carefully evaluated taking into account stakeholders’ views.This contribution presents a framework to develop dam reoperation strategies that simultaneously address global change impacts on agricultural benefits, native fish habitat and competition with invasive fish species in a water resource system. The developed methodological framework has been tested in the Serpis River Basin (Spain). The global change scenarios combined CMIP6 climate change projections with three land use scenarios: current crop surface and technology (reference), drip irrigation implementation and drip irrigation with changes in crop types and areas. Hydrological discharges associated with climate change scenarios were derived using the Témez conceptual hydrological model. Future crop water needs were estimated, for each climate scenario, using the AQUACROP model. The changes in the agricultural benefits related to these scenarios were obtained with a hydroeconomic model developed with the GAMS software. The effects in the availability of suitable habitat for native fish species (Eastern Iberian chub, Squalius valentinus and European eel, Anguilla anguilla) and its competition with invasive species (Bleak, Alburnus alburnus and Pumpkinseed, Lepomis gibbosus) were assessed by combining a 2D hydraulic model with the corresponding fuzzy logic-based habitat suitability models by species. The Pareto-optimal strategies for dam reoperation were obtained with the BORG-MOEA algorithm implemented using the Platypus Python library. The goals were the maximisation of the agricultural benefits and of native fish habitat, and the minimisation of the competition between the two groups of species.Our results suggest a trade-off between economic and ecological objectives and a positive relation between native fish habitat and native-invasive competition. They also indicate that economic and ecological sustainability could not be achieved by dam reoperation in the most pessimistic scenarios. However, dam reoperation shows a significant potential to contribute to climate change adaptation, entirely reverting its impacts in the most optimistic scenarios. It also shows synergies with land use scenarios, suggesting that dam reoperation could boost the positive impacts after the implementation of drip irrigation.Acknowledgements: This study has received funding from the European Union’s Horizon 2020 research and innovation programme under the GoNEXUS project (grant agreement No 101003722); as well as from the SOS-WATER project, under the European Union’s Horizon Europe research and innovation programme (GA No. 101059264).

Oceania is a diverse region encompassing Australia, Melanesia, Micronesia, New Zealand, and Polynesia, and it contains six of the world's 39 hotspots of diversity. It has a poor record for extinctions, particularly for birds on islands and mammals. Major causes include habitat loss and degradation, invasive species, and overexploitation. We identified six major threatening processes (habitat loss and degradation, invasive species, climate change, overexploitation, pollution, and disease) based on a comprehensive review of the literature and for each developed a set of conservation policies. Many policies reflect the urgent need to deal with the effects of burgeoning human populations (expected to increase significantly in the region) on biodiversity. There is considerable difference in resources for conservation, including people and available scientific information, which are heavily biased toward more developed countries in Oceania. Most scientific publications analyzed for four threats (habitat loss, invasive species, overexploitation, and pollution) are from developed countries: 88.6% of Web of Science publications were from Australia (53.7%), New Zealand (24.3%), and Hawaiian Islands (10.5%). Many island states have limited resources or expertise. Even countries that do (e.g., Australia, New Zealand) have ongoing and emerging significant challenges, particularly with the interactive effects of climate change. Oceania will require the implementation of effective policies for conservation if the region's poor record on extinctions is not to continue.