Invasive Fish Research Articles

Effects of sample preservation techniques on dogs' (Canis familiaris) ability to detect koi carp (Cyprinus rubrofuscus)

Koi carp (Cyprinus rubrofuscus) are an invasive fish that has caused significant ecological impacts to freshwater ecosystems around the world. Current detection methods such as observation, netting, electrofishing, and environmental DNA can be time-, labour-, and cost-intensive, especially when fish densities are low. Evaluation of water samples for invasive fish by scent detection dogs could offer a more efficient method of detection. However, the odour profiles of such samples are likely unstable, and without effective preservation from the time of collection to the time of analysis by dogs, samples could degrade, making the target scent less recognisable to dogs. The aim of this study was to determine whether refrigeration (4°C), freezing (-18°C), or the addition of potassium sorbate (1.7 mM) could be used to preserve scent in water samples assessed by dogs. An ABACADA reversal design was employed. The dogs performed a baseline evaluation (A) of unpreserved water samples from aquaria containing carp (target scent; n = 7), goldfish (Carassius auratus; non-target distractor scent; n = 5), or no fish (non-target scent; n = 5) before preservation treatments were applied to the samples. The treatment phases (B = refrigeration, C = frozen, and D = dark cupboard with potassium sorbate) involved applying a preservation method to carp, goldfish, or no-fish water samples 7 or 8 days prior to assessment by the dogs. There was weak evidence that refrigeration impaired the dogs’ detection performance. In contrast, once stability criteria had been met, detection performances on frozen or potassium sorbate preserved samples were similar to or returned back to baseline levels. These findings suggest that freezing and potassium sorbate were effective in retarding scent degradation over the storage period and have the potential to be used as preservatives for water samples awaiting assessment by scent detection dogs. If laboratory-based canine scent detection becomes an invasive fish detection method, the use of dogs could prove more time- and cost-efficient than current detection methods.

Effects of predator species, composition and light environment on prey escape behaviours of invasive and native benthic fishes

AbstractThe behaviour of two benthic species, round goby (Neogobius melanostomus) and mottled sculpin (Cottus bairdii), were examined under natural relevant downwelling light during predatory attacks by Burbot (Lota lota) and Smallmouth Bass (Micropterus dolomieu). Population declines have been observed for mottled sculpin after round goby invaded the Laurentian Great Lakes, but no data exist on prey avoidance behaviours and success for either species. The activity levels of the prey species were measured in the presence and absence of predators. Predator–prey interactions were quantified for reaction, attack, capture and retention probabilities. In addition, flight initiation distance, turns per flee and a comparison between observed and optimal escape angles were used as escape metrics to examine differences in prey survival. Trials were run under downwelling irradiances calculated for Lake Superior that correlated with dark, civil twilight, and sunrise. The number of round goby movements decreased by 74% in the presence of predators while mottled sculpin movement declined by 95% compared to baselines established without predators. Round gobies were more successful at evading predation with 18.3% of mottled sculpins consumed compared to 8.5% of round gobies during a comparable number (n = 27) trials. Round gobies also fled closer to their theoretically calculated optimal angles than mottled sculpin. Greater variation in flight initiation distances at different light intensities, fleeing at optimum angles that avoid predation and a more erratic escape path led to increased escape success for round gobies. Greater success avoiding predators may be another compounding factor, combined with round goby aggression and competition, that has contributed to the success of the round goby invasion in the Laurentian Great Lakes.

A global analysis of the introduction pathways and characteristics associated with non-native fish species introduction, establishment, and impacts

BackgroundThe invasion success of introduced freshwater fishes is influenced by many factors, including ecological, species, and socioeconomic characteristics. Most studies that document the importance of these characteristics are conducted at local scales and/or focus on a single step of the invasion process. In this study, we aim to determine the species characteristics, ecological characteristics, and socioeconomic characteristics of non-native freshwater fish invasions. Our assessment was done at the global scale and considers all three steps of the invasion (i.e., introduction, establishment, and impact). For this purpose, we applied generalized linear models to 20 variables collected for 307 non-native species and modeled them as a function of ecological characteristics (i.e., environmental features), species traits (i.e., functional and morphological), and socioeconomic characteristics (i.e., human use and introduction pathways). We considered the number of countries in which each species was introduced, established, or had ecological impacts as a proxy of invasion step success. We also explored the specifics of species introduced through the aquaculture and the ornamental fish trade pathways.ResultsWe found that non-native freshwater fishes with broad diets, high parental care, and multiple introduction pathways are the most widely introduced and established worldwide. The number of countries with impacts reported was best explained by the type of introduction pathway (i.e., aquaculture or fisheries). Moreover, among non-native species introduced through aquaculture, those belonging to Cypriniformes and having broad diets were the most widely introduced and established species. In contrast, the species introduced through the ornamental fish trade pathway belonged to various taxonomic orders but were mainly native to tropical regions.ConclusionsConsidering several types of factors is important when analyzing the invasion success of freshwater fish and disentangling the different invasion steps. These findings have strong implications for anticipating the profile of species with a high potential to invade many countries.

Multiple stressors unpredictably affect primary producers and decomposition in a model freshwater ecosystem

Freshwater ecosystems are affected by various stressors, such as contamination and exotic species, making them amongst the most imperilled biological systems on the planet. In Australia and elsewhere, copper is one of the most common metal contaminants in freshwater systems and the European carp (Cyprinus carpio L.) is one of the most pervasive and widespread invasive fish species. Copper (Cu) and carp can both directly affect primary production and decomposition, which are critical and interrelated nutrient cycling processes and ecosystem services. The aim of this study was to explore the direct and indirect effects of Cu and carp individually, and together on periphyton cover, chlorophyll a concentration, growth of the macrophyte Vallisneria spiralis L., and the decomposition of leaf litter and cotton strips in a controlled, factorial experiment in outdoor experimental ponds. In isolation, Cu reduced macrophyte growth and organic matter decomposition, while chlorophyll a concentrations and periphyton cover remained unchanged, possibly due to the Low-Cu concentrations in the overlying water. Carp addition alone had a direct negative effect on the biomass of aquatic plants outside protective cages, but also increased plant biomass inside the cages, periphyton cover and chlorophyll a concentrations. Leaf litter was more decomposed in the carp only ponds compared to controls, while there was no significant effect on cotton strip decomposition. Aquatic plants were absent in the Cu + carp ponds caused by the combined effects of Cu toxicity, carp disturbance and the increase in turbidity due to carp bioturbation. Increases in periphyton cover in Low-Cu + carp, while absence in the High-Cu + carp ponds, and differences in the decomposition of surface and buried cotton strips were not as predicted, which highlights the need for such studies to understand the complex interactions among stressors for environmental risk assessment.

МИКРОБИОЛОГИЧЕСКАЯ БЕЗОПАСНОСТЬ СВЕЖЕЙ РЫБЫ, ЗАРАЖЕННОЙ ТРЕМАТОДАМИ, С УЧЕТОМ САНИТАРНОГО СОСТОЯНИЯ ВОДОЕМОВ

The purpose of research is to study the relationship between the microbiological indicators of fish infected with diplostomosis and post-diplostomosis, and the indicators of veterinary and sanitary safety of water bodies involved in its cultivation. Objectives: determination of the main parasitological indicators of infected fish (intensity of invasion (II), extensiveness of invasion (EI), species predisposition of fish to pathogens of trematodes); conducting a microbiological analysis of the obtained fresh fish and the place of its cultivation, taking into account the degree of infestation of the fish by pathogens of diplostomosis and post-diplostomosis. The study was conducted in the conditions of the North Caucasus Zonal Research Veterinary Institute in the summer and autumn seasons of the year. The study material included fish of different species: Hypophthalmichthys molitrix (silver carp), Cyprinus carpio (carp), Ctenopharyngodon idella (grass carp), Abramis brama (Bream), both infected with trematodes and clinically healthy. The water of the fish catchment site, taken from the Nizhnedonsky canal, Veselovsky, Proletarsky and Tsimlyansky re¬servoirs, was studied. The lowest AI and EI were found in fish of the species Ctenopharyngodon idella (grass carp). AI in silver carp compared to grass carp was 11.3 times higher, in carp – 9.3 times, in bream – 6.6 times; EI was 11.3 times higher in silver carp and 11.0 times higher in carp; for bream – 3.3 times. In highly invasive fish of the species Hypophthalmichthys molitrix (silver carp), Cyprinus carpio (carp), mesophilic aerobes and facultative anaerobic microorganisms were found to be 14.7 and 4.24 times more, respectively, compared to healthy fish; according to the average value of detected coliform bacteria – 2.54 and 1.86; by the number of detected Staphylococcus sp. – at 24.3 and 33.15; Escherichia sp. – at 1.5 and 0.6; Klebsiella sp. – at 110 and 85; Salmonella sp. – 45 and 0.8 times more. A correlation was established between the total microbial number of water bodies and the number of mesophilic aerobes and facultative anaerobes in caught live fish (correlation coefficient 0.99).

Live‐bait industry as a pathway for movement of nonnative and invasive species: Implications for conservation of native Texas fishes

AbstractObjectiveLive‐bait species are widely used in recreational fishing throughout the United States. However, the use of invasive fish species as live bait has been identified as a common pathway for their introduction into aquatic ecosystems. We assessed the role that the live‐bait industry has in facilitating the introduction of nonnative and invasive species into Texas rivers. We focused on two invasive cyprinodontid species, the Sheepshead Minnow Cyprinodon variegatus and Gulf Killifish Fundulus grandis, which are believed to have been introduced into inland Texas rivers via bait‐bucket releases by anglers.MethodsWe conducted telephone and in‐person surveys of live‐bait shops in Texas on a seasonal basis (summer, fall, winter, spring) for 1 year. Locally owned bait shops and regional aquaculture facilities and hatcheries were included in the surveys.ResultSurveys did not reveal the presence of these invasive cyprinodontids in inland bait shops but did reveal the sale of nonnative Goldfish Carassius auratus and their black color morph, the black salty goldfish. Surveys conducted among inland and coastal live bait shops confirmed the sale of only one nonnative bait fish and six bait items native only to certain regions of Texas. Telephone surveys with aquaculture industry experts revealed that the aquaculture industry was also facilitating the movement of nonnative game and nongame fish species throughout the state.ConclusionGiven the potential for nonnative and invasive species to negatively affect recipient aquatic ecosystems, the continued distribution of such species within the aquaculture industry represents a potential threat in Texas. Our findings highlight the need for close monitoring of the live‐bait industry in the state to prevent further introductions into inland waters and reduce potential ecological risks to native fish populations and overall ecosystem functions and services.

Concentrations of Trace Elements (Mn, Zn, Cu, Fe, Ni, Co, and Cd) in Invasive Fish Perccottus glenii in Water Bodies of Moscow

Concentrations of Trace Elements (Mn, Zn, Cu, Fe, Ni, Co, and Cd) in Invasive Fish Perccottus glenii in Water Bodies of Moscow

Effects of Flow Turbulence on the Entire Development Process of Drifting Fish Eggs

Excessive flow turbulence poses a threat to the development of drifting fish eggs, leading to mortality or developmental malformations and ultimately depleting early fish resources. Currently, there is a scarcity of quantitative studies investigating the effects of flow turbulence on the entire process of drifting fish egg development, from fertilized egg division to hatching. In this paper, the effects of different flow turbulence conditions (FTCs), including turbulent kinetic energy and shear stress, and action times on different stages of fish egg development were quantitatively explored using a transverse-oscillating-grids turbulence tank. Empirical formulas were established to predict the proportion of normal fish egg development under different FTCs within a selected range. The research findings provide a quantitative basis for protecting early fish resources, mitigating the biological invasion of specific fish, constructing fish-breeding facilities, and ensuring safe transfer and transportation.

Assessment of Piscicidal Potentials of Carica papaya (Linnaeus, 1753) Leaves, Seeds, and Peel Powder on Juveniles of Clarias gariepinus (Burchell, 1822)

In aquaculture, piscicides are used as fishing gear to combat parasitic, invasive fish species and eliminate dominant fish species in a water body. Therefore, assessment of piscicide activity is important. Hence, in this study, we have aimed to assess the piscicidal potential of Carica papaya leaves, seeds, and peel powder on juveniles of Clarias gariepinus using behavioural responses and mortality rate as the toxicity endpoints. Four hundred and fifty (450) juveniles of Clarias gariepinus were used for the 96-hour static bioassay. Five (5) different concentrations of 0 mgL-1, 25 mgL-1, 50 mgL-1, 75 mgL-1, and 100 mgL-1 containing ten (10) fish samples in triplicates were used. The physicochemical parameters of the test concentrations monitored during the exposure include Temperature, pH, Electrical Conductivity, Dissolved Oxygen, and Total Dissolved Solids. The results of the physicochemical parameters did not vary significantly compared with the control. The results of the behavioural responses showed a range of reactions, such as erratic swimming, gulping of air, loss of reflex, vertical orientation, loss of buoyancy, jumping, and discolouration. The fish mortality rate was used to determine the median lethal concentrations (LC50) of the leaves, seeds, and peel powder using the Probit method. The LC50 values estimated from Probit analysis were 147.17 mgL-1, 262.376 mgL-1, and 697.180 mgL-1, respectively. The results implied that of the three plant parts used, the leaves powder of Carica papaya showed the most promising piscicidal potential. Hence, this underscores screening whole plant parts to ascertain the most suitable for such desired activity. The substitutes of plant substances, which can act as ecologically friendly piscicides, can be encouraged against commonly used synthetic chemicals which can be detrimental to aquatic ecosystems.

Global freshwater fish invasion linked to the presence of closely related species

In the Anthropocene, non-native freshwater fish introductions and translocations have occurred extensively worldwide. However, their global distribution patterns and the factors influencing their establishment remain poorly understood. We analyze a comprehensive database of 14953 freshwater fish species across 3119 river basins and identify global hotspots for exotic and translocated non-native fishes. We show that both types of non-native fishes are more likely to occur when closely related to native fishes. This finding is consistent across measures of phylogenetic relatedness, biogeographical realms, and highly invaded countries, even after accounting for the influence of native diversity. This contradicts Darwin’s naturalization hypothesis, suggesting that the presence of close relatives more often signifies suitable habitats than intensified competition, predicting the establishment of non-native fish species. Our study provides a comprehensive assessment of global non-native freshwater fish patterns and their phylogenetic correlates, laying the groundwork for understanding and predicting future fish invasions in freshwater ecosystems.

Aggressiveness overcomes body‐size effects in contests between native and invasive cichlid fishes

AbstractIn animal fights, there are often size asymmetries between opponents. Although larger individuals typically dominate smaller ones, size is not the sole determining factor, as the competitors' motivation, aggressiveness, resource value, physiological characteristics, and strength also play crucial roles in fighting outcomes. In this study, we evaluated the influence of body size on dominance hierarchy and contest success during intra‐ and inter‐specific contests in two fish species: the native mojarra of the Balsas basin Amphilophus istlanus and the invasive convict cichlid Amatitlania nigrofasciata. We used size‐asymmetric males to carry out experimental contests. The number and type of aggressive behaviors, time to contest outcome, and dominant individual at the end of the contest were determined. In contests between two native mojarra, the smaller individual always lost. In contests between convict cichlids, the smaller contestants lost in all contests where size asymmetry was greater than 20%. In interspecific contests, the native mojarra performed more aggressive behaviors than the invasive convict cichlid and dominated convict cichlids despite a size disadvantage. This suggests that in terms of competition via interference, the native mojarra can counter the arrival of the invasive convict cichlid.

Ecological connectivity of invasive and native fishes in a historic navigation waterway

Regulated waterways, interconnected by navigation barriers (locks and dams), are uniquely difficult to manage, given interest in enabling native species connectivity while minimizing invasions. Canada's historic Rideau Canal Waterway, a 202 km navigable route located in eastern Ontario and connected by 24 lockstations, embodies this challenge. The lock(s) and water-control dam that compose each lockstation may respectively offer a connectivity pathway, though to what extent is unclear. We used acoustic telemetry (native largemouth bass ( Micropterus nigricans) and northern pike ( Esox lucius), and invasive common carp ( Cyprinus carpio); n = 224) to evaluate fish connectivity relative to lock operations and environmental data over three years (2019–2021). Thirty-five passages by 23 native fishes were recorded, with 49% of passages through locks. No common carp passages were detected; movements indicate that they favour higher flow areas downstream of dams, regions with no pathway upstream. Most passages were downstream and, of concern to obligate upstream migrators, we found that multi-flight and higher-lift locks appear impassable to upstream movements. Our results suggest that these lockstations limit, but not entirely restrict, connectivity.

Upstream experience and experimental translocation of invasive bigheaded carps results in increased upstream passage success at a navigation lock in a large river

AbstractFish movements in regulated rivers can be challenging to study because anthropogenic modifications, such as locks and dams, can influence animal behavior. Upper Mississippi River Lock and Dam 19 (LD 19), for example, is an invasive carp movement bottleneck due to an impassable dam. Upstream fish passage at LD19 is restricted to the lock chamber, making it an optimal location to test invasive fish deterrents that could limit further range expansion. Evaluating the effectiveness of experimental deterrents requires baseline knowledge of fish movements and suitable sample sizes of fish encountering the deterrents to ensure adequate statistical power. Some evidence indicates fish with prior upstream experience may return upstream or challenge potential deterrents at a higher rate than fish without such experience. To test how previous upstream experience could increase the rate at which fish moved upstream through a navigation lock chamber, we compared upstream passage through LD 19 using bigheaded carp captured below the dam (downstream‐origin) and two groups of bigheaded carp captured upstream from the dam: those that swam downstream on their own volition (upstream‐origin fish) and those that were captured upstream and translocated downstream of LD 19 (translocated upstream‐origin). Translocated upstream‐origin carp demonstrated the highest rate of upstream passage, with 59% of the fish detected downstream from LD 19 passing upstream during our study. In contrast, downstream‐origin carp made no upstream passages over 2 years. Fish origin was shown to influence upstream passage success. This may be an important consideration for fish passage studies and deterrent evaluations.

Environmental DNA for assessing impact and recovery of aquatic communities in an invaded mountain lake

Beaulieu J, Yates MC, Astorg L, Trépanier-Leroux D, Jeon H, Rudko SP, Humphries S, Fraser DJ, Cristescu ME, Derry AM. 2024. Environmental DNA for assessing impact and recovery of aquatic communities in an invaded mountain lake. Lake Reserv Manage. 40:111–131. The eradication of invasive species and associated side effects that influence the reestablishment of biological communities is a major challenge for conservation management of invaded ecosystems. We present a before-and-after-disturbance whole lake manipulation study from a high-elevation mountain lake in which we applied a 2-pronged approach to environmental DNA (eDNA) for assessing (1) impact and recovery of aquatic communities to the chemical eradication of invasive brook trout (Salvelinus fontinalis) and (2) the success of chemical eradication of the invasive fish. Using 18S and cytochrome oxidase I (COI) eDNA metabarcoding, we contribute to a paucity of literature that has comprehensively addressed nontarget effects of rotenone for invasive fish eradication on aquatic communities. We found that key trophic groups (phytoplankton, fungi, zooplankton, and macroinvertebrates) changed in community composition in response to rotenone applications. Fungi and macroinvertebrates, but not zooplankton and phytoplankton, reverted back toward pre-rotenone communities over the time scale of 2 yr. However, COI failed to detect several key species for food web reestablishment that were detected using physical specimen collection, likely due to low primer efficiency. We also found that quantitative polymerase chain reaction (qPCR), using species-specific primers, was effective for detecting brook trout presence/absence, although strong eDNA signals likely produced from carcasses in the ecosystem limited the utility of eDNA immediately following rotenone treatment. We provide specific recommendations for lake managers for the future application of eDNA approaches to monitor invasive fish eradication efforts and nontarget community effects for lake ecosystem restoration.

Interactive effects of temperature and velocity on the feeding behavior of competing native and invasive stream fishes

The integration of invasive species into native communities may result in the destabilization of food webs through predation of native prey and competition with native predators. These negative effects are likely to be exacerbated by climate change, increasing the frequency of heat waves, droughts, and high-flow events. Invasive Round Goby (Neogobius melanostomus) and native White Sucker (Catostomus commersonii) were collected from the wild and acclimated to a range of temperatures expected to capture increases in temperature under climate change. In the laboratory, we measured the effects of temperature (19, 22, 25, and 28°C) and velocity gradients (0, 0.15, 0.3, 0.6 m/s at 22 and 25°C) on the prey consumption and foraging behavior of each species. We found that the prey consumption and number of attacks (lunges at prey) of both species increased with temperature but were consistently higher in Round Goby. Velocity had an interactive effect with temperature for prey consumption and foraging behavior, where generally, velocity tolerance for both species was higher at 22°C than at 25°C. White Sucker tolerance to velocity was higher than Round Goby, suggesting that systems with higher velocities may provide a competitive advantage in high-flow environments. Our results stress the importance of interactive experiments when examining the impact of invasive species on native competitors under shifting climatic conditions.

Experimentally determined effectiveness of different electric barrier arrangements on the behavioural deterrent of silver carp (Hypophthalmichthys molitrix)

Pulsed direct current electric barrier (EB) technology has been widely used to repel invasive species, guide fish away from dangerous areas, and direct them towards favourable locations, such as bypass channels. The effectiveness of an EB is influenced by many factors, and there is no consensus concerning what are the primary and secondary effects of the factors that influence fish response to EBs. In this study, Experiment 1 was conducted to investigate primary and secondary effects. It consisted of static water tests in which four factors were varied (electrode arrangement (EA), pulse voltage (PV), pulse frequency (PF), pulse width (PW)), each taking one of three values, in three phases of electrode activation (Phase I, before activating the pulsed power supply; Phase II, during the period of electrification; Phase III, after deactivating the power supply). Since the experimental design was orthogonal, nine treatments were designed and used in each phase. Experiment 2 was to identify whether there was any difference in barrier effectiveness and fish injury at different water velocities (0 m s-1, 0.3 m s-1,and 0.5 m s-1). The result showed that times of silver carp successfully passing the barrier in Phase I were significantly greater than in Phase II or Phase III for each treatment (P < 0.05), and there were no significant differences in times of successful passage among the nine treatments in phase II (P > 0.05). The primary and secondary effects of the four factors on the blocking rate and the number of fish injuries were EA > PV > PW > PF. Barrier obstruction rate and the number of fish injuries increased as fish body length increased. There was no significant difference (P > 0.05) in blocking rate or in fish injury rate as water velocity increased. The study will provide a foundational baseline for conserving fish stocks and preventing the cross-regional spread of invasive fish species.

Status and distribution of a novel redfin lineage, Pseudobarbus sp. ‘burchelli Tradouw’ from the Cape Fold Ecoregion of South Africa

Freshwater fish are threatened globally and in addition, knowledge of their diversity is incomplete and species richness is underestimated. Within the ichthyofauna of the Cape Fold Ecoregion of South Africa, many undescribed lineages exist and for most of these, information is limited regarding their ecology, distribution and threats. The Tradouw redfin Pseudobarbus sp. ‘burchelli Tradouw’ is a novel and range-restricted lineage within the Breede River redfin Pseudobarbus burchelli. Annual monitoring conducted between 2012 and 2016 investigated spatial and temporal trends in the distribution and population dynamics of this taxon. Results indicated that it is highly fragmented within its distribution range, likely a result of the combined pressures of invasive fish and poor land use practices. Short-term monitoring results indicated that invasive fish are established in most of the catchment and that the relative abundance of redfins remained constant only in the limited section of river where alien fish were absent. Poor land use practices such as water over-abstraction and surface water pollution, are pervasive threats, but the extent to which these affect the redfins requires further investigation. The long-term survival of this taxon remains uncertain, and short-term and long-term conservation and management options are explored.

Assessing Invasive Carp in the Neosho River‐Grand Lake System of Kansas and Oklahoma

Invasive carp populations have purported a negative influence on native biota at high densities. These invasive fishes (i.e., bighead carp Hypophthalmichthys nobilis, silver carp Hypophthalmichthys molitrix, grass carp Ctenopharyngodon idella, and black carp Mylopharyngodon piceus) each exhibit similar life history characteristics. In the Neosho River‐Grand Lake system (i.e., John Redmond Reservoir, Kansas, downstream to Grand Lake O’ the Cherokees, Oklahoma), only bighead carp and grass carp have been documented to date. The distribution and status of bighead carp throughout this system were previously unknown due to limited historical data and low abundance. While few bighead carp are encountered within this system, grass carp exhibited relatively higher abundance a were used to provide insights into bighead carp. Captures of both species were used to inform management and suppression efforts. Sampling locations (n = 18) were established for environmental DNA analyses throughout the Neosho River‐Grand Lake system. We sampled 13 sites using a suite of gears for standardized targeted fish sampling. All invasive carp were measured, sexed, and otoliths removed for ageing and microchemical analysis. Grass carp were processed for ploidy testing following the U.S. Fish and Wildlife Service protocol. Environmental DNA analyses generated positive results for the eDNA presence of bighead carp and silver carp. Otolith age estimates suggest fish are long lived and supported by multiple year classes. Additionally, a sampled two‐year‐old grass carp demonstrates spawning and recruitment potential. Otolith microchemistry suggests largescale broad movement patterns. Ploidy testing confirmed the first documented evidence of diploid grass carp in the Neosho River‐Grand Lake system and revealed reproductive viability. Our results may provide future insights into locations for containment, removal, and/or eradication.

Automated identification of invasive rabbitfishes in underwater images from the Mediterranean Sea

Abstract Coastal ecosystems of the Mediterranean Sea are among the richest in non‐indigenous species, mostly due to the establishment of species coming from the Red Sea through the Suez Canal. Two herbivorous rabbitfishes, Siganus rivulatus and Siganus luridus, are already invasive in the south‐eastern part of the Mediterranean Sea where they cause ecological damage by overgrazing algae. The early detection and the counting of these non‐indigenous species in the rest of the Mediterranean Sea is thus a major challenge for scientists and ecosystem managers. However, analysing images from divers or remote cameras is a demanding task. Here, a dataset of 31,285 images of Siganus spp. and of six common native fishes to the Mediterranean Sea was built from 40 underwater videos recorded at three reef habitats. A deep learning algorithm was then trained to identify Siganus spp. on images containing the eight Mediterranean species. Finally, the algorithm and a post‐processing filtering were tested with an independent dataset of 2024 images. The model had a recall of 0.92 for the Siganus genus (i.e., two Siganus species combined). After a confidence‐based post‐processing, the recall increased to 0.98 with only 4 out of 272 images of Siganus spp. being misclassified. Accuracy reached a score of 0.61 meaning that experts would have to discard false positives. Images of five native species not present in the training dataset yielded similar false positive rates than species present in the training dataset. Overall, the automatic processing of images by the model and then the checking of putative Siganus images by experts required up to five times less effort than a full processing by experts. The algorithm can help to efficiently detect these two invasive fishes in underwater images to evaluate progress towards conservation objectives and accelerate citizen‐based monitoring of coastal ecosystems.

Mountain masses as a determinant to genetic structure of char distributed in the Chugoku region, Japan

A mountain mass from which multiple river basins originate is a possible determinant of genetic structure of freshwater fishes. In this study, subspecies composition and genetic structure were examined for Japanese white-spotted char comprising of two subspecies, Salvelinus leucomaenis imbrius (Jordan and McGregor), “Gogi,” and S. l. pluvius (Hilgendorf), “Nikkoiwana,” collected in the 19 river basins originating from 6 mountain masses in the Chugoku Region, Japan, based on mitochondrial DNA sequences. In the western mountain masses, only Gogi was collected, while in the eastern mountain mass, only Nikkoiwana was collected. A total of 27 haplotypes were detected, among which only seven were shared by two subspecies and three were detected only in Nikkoiwana whereas 17 were detected only in Gogi. As many as 11 haplotypes were distributed only in the Oyorogi Mountain mass in the middle region. In the network, one group was exclusively constructed by the samples from the Oyorogi Mountain mass. Furthermore, in a tree of river basins based on average genetic distance of char, the Gono River basin originating from the Asa Mountain mass, situated in the western region, participated in a clade constructed by the rivers originating from the westernmost Sukegatake and the adjacent Asa Mountain masses, whereas the Gono River basin originating from the Oyorogi Mountain mass participated in a different clade constructed by the rivers originating from the Oyorogi to the easternmost Hyonosen Mountain masses. These results suggest that a mountain mass is a determinative factor to subspecies composition and genetic structure of char, with an implication of invasion of fish taking advantage of some geological events or conditions.