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The manipulation of species’ attributes through selective breeding can produce domesticated traits including decreased stress responses (i.e., selecting for high stress resilience). Common carp Cyprinus carpio (“carp”) have been domesticated for centuries, with domesticated forms frequently used to enhance recreational catch-and-release fisheries around the world. In Atlantic salmon Salmo salar (“salmon”), two primary strains are evident, a wild strain and domesticated aquaculture strain. Here, we compared scale cortisol concentrations (a biomarker of fish chronic stress levels) between domesticated carp in catch-and-release pond fisheries and wild carp in waters with no angling. Carp of low scale cortisol concentration were apparent in all sampled populations, suggesting individuals of low stress sensitivity are encountered in both wild and domesticated strains, and in natural and captive environments. Carp with relatively high levels of scale cortisol were, however, only present in wild carp, suggesting high phenotypic variability in their chronic stress responses, with some individuals being highly sensitive to stress. In some wild carp, elevated scale cortisol concentrations could also have been indicative of adaptive responses to their heterogenous environments. We then compared wild versus farmed salmon scale cortisol levels, and found a similar pattern, with relatively high scale cortisol levels only detected in wild fish. These results indicate that while domesticated carp and salmon are exposed to potentially stressful environments, they appear to have some resilience against the adverse effects of chronic stress.

High phenotypic diversity should provide populations with resilience to environmental change by increasing their capacity to respond to changing conditions. The aim of this study was to identify whether there is consistency in individual behaviours on a reactive-proactive axis in European barbel Barbus barbus (\"barbel\"), a riverine and aggregatory fish that expresses individual differences in its behaviours in nature. This was tested using three sequential experiments in ex-situ conditions that required individuals to leave a shelter and then explore new habitats (‘open-field test’), respond to social stimuli (‘mirror-image stimulation test’) and forage (‘foraging behaviour test’; assessing exploratory traits). Each suite of experiments was replicated three times per individual (46 hours minimum time between replicates). There was high variability in behaviours both within and among individuals. The most repeatable behaviours were latency to exit the shelter, active time in the shelter, and the number of food items consumed. Principal component scores did, however, indicate a range of consistent behavioural phenotypes across the individuals, distributing them along a reactive-proactive axis in which most of individuals were more reactive phenotypes (shyer, less exploratory, less social). These results suggest that within controlled conditions, there is considerable phenotypic diversity among individuals in their behaviours, suggesting their populations will have some adaptive capacity to environmental change.

The ecological impacts of freshwater invasive fishes can develop through interspecific competition where they share similar resources to native species, but with this potentially mitigated by high ecological opportunity in prey resources. The trophic ecology of invasive mrigal carp Cirrhinus mrigala and native mud carp Cirrhinus molitorella were assessed in the Pearl River, southern China, through applying DNA metabarcoding on samples collected in both the wet and dry seasons between 2019 and 2021. Both fishes had diets comprising of items including algae, ciliates, arthropods, plants, rotifers, protists, and fungi. The interaction of year and season explained the most variation in the dietary composition, individual niche width and population niche width (PNW) for each species, and the interspecific niche overlap, with their niche widths being lowest but interspecific niche overlap being highest during the 2021 dry season. The ecological opportunity, influenced by river discharge and water temperature was in negative relationships with the interspecific niche overlap. The interspecific niche overlap was significantly negatively affecting the between individual component (BIC) of PNW for each species, but with the negative effects on PNW and its within individual component (WIC) being non-significant. The significant positive linear relationships between PNW and its components of WIC and BIC for each species provided a dual expansion case for the niche variation hypothesis. The dynamic nature of the trophic interactions of these fishes indicates the importance of considering temporal and seasonal variability within invasion risk screening processes and impact assessments in sub-tropical rivers.

Non-native crayfish can dominate the invertebrate biomass of invaded freshwaters, with their high ecological impacts resulting in their populations being controlled by numerous methods, especially trapping. Although baited funnel traps (BTs) are commonly used, they tend to be selective in mainly catching large-bodied males. Here, the efficacy and selectivity of BTs were tested against an alternative trapping method based on artificial refuges (ARTs) that comprised of a metal base with several tubes (refuges) attached. The target species was signal crayfish Pacifastacus leniusculus in an upland river in southwest England. Trapping was completed in April to October over two consecutive years. In total, 5897 crayfish were captured, with 87% captured in ARTs. Comparison of the catch per unit effort (CPUE) between the trapping methods in the same 24 hour periods revealed significantly higher CPUE in ARTs than of BTs. ARTs fished for 6 consecutive days had higher catches than both methods over 24 hours. Whilst catches in BTs were significantly dominated by males (1.49M:1F), the sex ratio of catches in ARTs was 0.99M:1F. The mean carapace length of crayfish was also significantly larger in BTs (43.2 ± 0.6 mm) than in ARTs (33.6 ± 0.2 mm). Thus, ARTs had higher CPUE over 24 hour and 6 day periods versus BTs and also captured a greater proportion of smaller and female individuals. These results indicate that when trapping methods are deployed for managing invasions, the use of ARTs removes substantial numbers of crayfish of both sexes and of varying body sizes. Les écrevisses non indigènes peuvent dominer la biomasse d'invertébrés des eaux douces envahies, et leur impacts écologiques élevés ont pour conséquence que leurs populations sont contrôlées par de nombreuses méthodes, en particulier le piégeage. Bien que les pièges à entonnoir appâtés (BT) soient couramment utilisés, ils ont tendance à être sélectifs surtout chez les mâles de grande taille. Ici, l'efficacité et la sélectivité des BT ont été testées par rapport à une méthode alternative de piégeage basée sur des refuges artificiels (ARTs) composés d'une base métallique avec plusieurs tubes (refuges) attachés. L'espèce cible était l'écrevisse signal Pacifastacus leniusculus dans une rivière des hautes terres du sud-ouest de l'Angleterre. Le piégeage s'est déroulé d'avril à octobre sur deux années consécutives. Au total, 5,897 écrevisses ont été capturées, dont 87% dans des ART. La comparaison des CPUE entre les méthodes de piégeage dans les mêmes périodes de 24 heures a révélé des CPUE significativement plus élevées dans les ART que dans les BT. Les ART posés pendant 6 jours consécutifs ont donné des prises plus élevées que les deux méthodes sur 24 heures. Alors que les prises dans les BT étaient significativement dominées par les mâles (1,49M: 1F), le sex-ratio des prises dans les ART était de 0,99M: 1F. La longueur moyenne de la carapace des écrevisses était également significativement plus grande chez les BT (43,2 ± 0,6 mm) que chez les ART (33,6 ± 0,2 mm). Ainsi, les ART avaient une CPUE plus élevée sur des périodes de 24 heures et de 6 jours par rapport aux BT et capturaient également une plus grande proportion d'individus plus petits et femelles. Ces résultats indiquent que lorsque des méthodes de piégeage sont utilisées pour gérer les invasions, l'utilisation des ART élimine un nombre important d'écrevisses des deux sexes et de tailles variables.

Public perception is a key factor influencing current conservation policy. Therefore, it is important to determine the influence of the public, end-users and scientists on the prioritisation of conservation issues and the direct implications for policy makers. Here, we assessed public attitudes and the perception of conservation managers to five non-native species in the UK, with these supplemented by those of an ecosystem user, freshwater anglers. We found that threat perception was not influenced by the volume of scientific research or by the actual threats posed by the specific non-native species. Media interest also reflected public perception and vice versa. Anglers were most concerned with perceived threats to their recreational activities but their concerns did not correspond to the greatest demonstrated ecological threat. The perception of conservation managers was an amalgamation of public and angler opinions but was mismatched to quantified ecological risks of the species. As this suggests that invasive species management in the UK is vulnerable to a knowledge gap, researchers must consider the intrinsic characteristics of their study species to determine whether raising public perception will be effective. The case study of the topmouth gudgeon Pseudorasbora parva reveals that media pressure and political debate has greater capacity to ignite policy changes and impact studies on non-native species than scientific evidence alone.

Many methods of controlling invasive crayfishes have limited success because they fail to target all life stages of the population, notably by capturing only large adults that can result in increased juvenile recruitment by removing intraspecific predation. An alternative approach uses the sterile male release technique that involves the mass release of sterile males into the environment, which then mate with fertile females, resulting in unfertilised eggs and, ultimately, reduced juvenile recruitment. This does, however, rely on the sterilised males exhibiting behaviours similar to non-sterilised (entire) males and remaining attractive to females during mate choice. Post-copulatory male guarding behaviour and female promiscuity might also be affected by male sterilisation. To test for the presence of normal reproductive behaviours in sterilised male American signal crayfish Pacifastacus leniusculus, a two-stage experiment examined how sterilisation affects female mate choice and promiscuity, male hierarchical status (relative dominance) and post-copulation guarding. Sterilised males showed similar reproductive behaviours to entire males and remained as attractive to females, with no differences in relative dominance. Post-copulation, guarding behaviours were also unaffected. Females did not display promiscuous behaviour and this was unaffected by whether males were entire or sterilised. The results demonstrated that sterilised males were equally as capable as entire males of achieving dominance and winning mates. In combination, these findings suggest that male sterilisation could be an effective control technique to help reduce juvenile recruitment in wild P. leniusculus populations by reducing reproductive success.

A recent threat to European fish diversity was attributed to the association between an intracellular parasite, Sphaerothecum destruens, and a healthy freshwater fish carrier, the invasive Pseudorasbora parva originating from China. The pathogen was found to be responsible for the decline and local extinction of the European endangered cyprinid Leucaspius delineatus and high mortalities in stocks of Chinook and Atlantic salmon in the USA. Here, we show that the emerging S. destruens is also a threat to a wider range of freshwater fish than originally suspected such as bream, common carp, and roach. This is a true generalist as an analysis of susceptible hosts shows that S. destruens is not limited to a phylogenetically narrow host spectrum. This disease agent is a threat to fish biodiversity as it can amplify within multiple hosts and cause high mortalities.

Background Sphaerothecum destruens is an obligate intracellular fish parasite which has been identified as a serious threat to freshwater fishes. Taxonomically, S. destruens belongs to the order Dermocystida within the class Ichthyosporea (formerly referred to as Mesomycetozoea), which sits at the animal-fungal boundary. Mitochondrial DNA (mtDNA) sequences can be valuable genetic markers for species detection and are increasingly used in environmental DNA (eDNA) based species detection. Furthermore, mtDNA sequences can be used in epidemiological studies by informing detection, strain identification and geographical spread. Methods We amplified the entire mitochondrial (mt) genome of S. destruens in two overlapping long fragments using primers designed based on the cox 1, cob and nad 5 partial sequences. The mt-genome architecture of S. destruens was then compared to close relatives to gain insights into its evolution. Results The complete mt-genome of Sphaerothecum destruens is 23,939 bp in length and consists of 47 genes including 21 protein-coding genes, 2 rRNA, 22 tRNA and two unidentified open reading frames. The mitochondrial genome of S. destruens is intronless and compact with a few intergenic regions and includes genes that are often missing from animal and fungal mt-genomes, such as, the four ribosomal proteins (small subunit rps13 and 14 ; large subunit rpl2 and 16 ), tatC (twin-arginine translocase component C), and ccmC and ccmF (cytochrome c maturation protein ccmC and heme lyase). Conclusions We present the first mt-genome of S. destruens which also represents the first mt-genome for the order Dermocystida. The availability of the mt-genome can assist the detection of S. destruens and closely related parasites in eukaryotic diversity surveys using eDNA and assist epidemiological studies by improving molecular detection and tracking the parasite’s spread. Furthermore, as the only representative of the order Dermocystida, its mt-genome can be used in the study of mitochondrial evolution of the unicellular relatives of animals.

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

Aim The distribution of the western house mouse (Mus musculus domesticus) around the world has been strongly influenced by the movement of humans. The close association between the house mouse and human phylogeography has been primarily studied in the peripheral distribution of the species. Here, we inferred the complex colonization history of Cyprus, situated close to the centre of the house mouse distribution and one of the first European islands to be colonized by the species. We investigated the resulting complexity of house mouse population genetics as well as considering the value of the house mouse as a bioproxy for studying modern human movement. Location The study was carried out on Cyprus. Methods The analysis was performed using 221 new mitochondrial D‐loop sequences and assessed the fine‐scale population genetic structure using 18 autosomal microsatellite loci from 191 modern house mice specimens. Results We found a high genetic variability in the island that is illustrated by the presence of individuals from 9 of the 11 previously identified house mouse haplogroups for the D‐loop, reflecting the hub‐like nature of the island to mice. Two main waves of mouse introductions were tentatively identified based on coalescent and mismatch analysis. The first is apparently related to the Bronze Age expansion and the second one to more recent human movements. Cyprus represents an island with high complexity due to different introductions related to human transport and activity. Main conclusions The dispersal of mice along with humans has left a complex footprint on the island with two main waves of introductions suggested. The phylogeography of the house mouse on Cyprus is in concordance with the complex human colonization history of the island and validates the use of the house mouse as a proxy to study human migration.