Human-mediated gene flow is increasingly altering the genetic composition of populations, yet conservation assessments typically focus on nuclear introgression alone. We synthesise evidence showing that mitochondrial DNA (mtDNA) introgression can have distinct consequences for performance, adaptation, and the viability of animal populations. Unlike most nuclear loci, mtDNA is uniparentally inherited, nonrecombining, and encodes core components of cellular energy metabolism that must function in tight coordination with nuclear genes. As a result, introgression of nonnative mtDNA can disrupt co-adapted mito-nuclear interactions, sometimes generating sex-specific or environment-dependent costs. Conversely, mtDNA introgression can also be neutral or beneficial in certain circumstances. We argue that ignoring mtDNA risks unintended maladaptation and that mitochondrial and nuclear genetics should be considered jointly in conservation planning.

ABSTRACT Human activity has altered nearly all ecosystems on Earth, contributing to substantial biodiversity loss across taxonomic, genetic and functional dimensions, from the intraspecific to the ecosystem scale. Yet some components of biodiversity remain hidden or underappreciated, including behavioural diversity. Behaviour is often among the earliest whole‐organism responses to environmental change, and diversity in behaviour can occur within individuals, among individuals, among populations and across communities and ecosystems. This variation may influence growth, survival, reproduction, ecological interactions and responses to anthropogenic pressures, although its effects on population stability and resilience are likely context‐, scale‐ and component‐dependent. In this review, we examine behavioural diversity in fishes, defined here as variation in behavioural traits across levels of biological organisation, from individuals to ecosystems. Our review has two complementary aims. First, we provide a conceptual overview of behavioural diversity, clarify how it differs from related constructs such as personality, plasticity, and behavioural syndromes, and summarise the evolutionary, ontogenetic, ecological, stochastic and anthropogenic processes that generate or erode it. Second, we evaluate why behavioural diversity matters for fish ecology, fisheries management, aquaculture, restoration and conservation. We conclude by identifying key research needs, including improved quantification, stronger empirical links between behavioural diversity and ecological outcomes, and the development of management approaches sensitive to behavioural diversity. More explicit consideration of behavioural diversity should improve our ability to predict fish behavioural diversity responses and to design conservation and management measures that account for variation rather than only average behavioural responses.

Freshwater ecosystems are increasingly exposed to psychoactive pharmaceuticals while also experiencing rapid warming, two stressors known to influence aquatic organism behavior. Yet, it remains unclear how temperature shapes the behavioral effects of these environmentally persistent compounds—whether occurring individually or as mixtures—particularly in aquatic invertebrates. Therefore, we experimentally tested whether and how 2-week exposure to fluoxetine (average measured concentration: 0.31 µg/L), clobazam (0.95 µg/L), or their mixture (0.33 and 1.05 µg/L, respectively), affects the locomotor and foraging behavior of northern damselfly (Coenagrion hastulatum) nymphs at two environmentally relevant temperatures (10 °C and 16 °C). Temperature strongly influenced locomotion and foraging behavior by reducing activity and feeding after 2 weeks of exposure, accounting for much of the observed variation across treatments. Pharmaceutical effects were comparatively trait-specific. Clobazam reduced active movement speed regardless of temperature, whereas fluoxetine decreased prey-capture success at 10 °C. Combined exposure did not, however, result in stronger detectable behavioral effects than single-compound exposure. Bioconcentration analyses revealed higher accumulation of fluoxetine than clobazam, suggesting that toxicokinetic differences contributed to the observed behavioral responses. Together, these results demonstrate that warming can substantially shape baseline predator behavior and should be considered when interpreting contaminant effects in freshwater ecosystems under ongoing climate change.

Sedimentary habitats such as sand and gravel are among the most widespread seafloor environments in shelf ecosystems, yet fish–habitat relationships in these substrates remain poorly understood. Although these habitats support diverse and productive benthic communities, ecological information on how fish use them is fragmented, limiting the effectiveness of conservation frameworks such as EUNIS, the EU Habitats Directive, and ecosystem‑based fisheries management. To address this gap, we conducted a systematic review of peer‑reviewed studies reporting associations between fish species and sandy and gravelly substrate types across the Northeast Atlantic shelf. The review identified 104 studies covering 77 species associated with these substrate types, divided into littoral ecozones down to 200 m depth. Study frequency strongly influenced the number of habitat types in which species were recorded, complicating assessments of habitat specialisation based on available data. Across ecozones, sand consistently supported the highest species richness, and most nursery areas were linked to sand in the littoral and infralittoral zone. Species of conservation concern (IUCN) occurred across all substrate types; however, we highlight particular concern for gravel habitats as spawning grounds and as habitat for several red‑listed species, given their more limited distribution compared to sand. Commercially important species dominated reports of spawning and nursery functions. This synthesis provides a comprehensive overview to date of fish–habitat associations in sedimentary environments of the Northeast Atlantic shelf. The resulting literature list, database and habitat‑specific species lists offer a valuable foundation for marine spatial planning and area‑based conservation, including the identification of Essential Fish Habitat.

The degradation of water quality is among the most pervasive, complex, and challenging problems that impact the world’s freshwater ecosystems and their biodiversity. Contamination pathways vary globally and involve a diverse array of pollutants that include simple (e.g., road salt) to more complex (e.g., pharmaceuticals) chemicals, as well as non-natural sources of heat, light, noise, silt, plastics, and also pathogens from wastewater or livestock. These pollutants can cause significant harm on their own, in mixtures or in combination with other stressors. Over geographically extensive areas affecting most river systems and many standing waters, pollutants have been released either legally, illegally or incidentally over inter-decadal to centennial timescales. Some pollutants and pathogens also affect people through morbidity, mortality, and economic loss, so that there is synergy in protecting freshwater biodiversity against pollution while delivering human well-being through the global Sustainable Development, ecosystem services, and climate change agenda. Existing approaches aimed at reducing water pollution are insufficient and require a previously unmatched step-change in approach to address the major impacts from both conventional and emerging pollutants, such as pharmaceuticals, pesticides and microplastics. Success stories on measures that address freshwater pollution are relatively limited such that available examples are often “works in progress” or represent partial success. Here, we review both challenges and potential solutions to freshwater pollution, focusing on case studies that range across (i) informing action through monitoring and understanding pollutant trends and ecosystem impacts; (ii) regulation and enforcement nationally and internationally to reduce pollutant loads, substitute harmful substances, and ensure that polluters pay; (iii) improving the management and remediation of pollutants at source, in situ, and across catchments, including scalable, nature-based solutions, and (iv) addressing the systemic drivers of pollution through education, incentives, and market mechanisms. Significant challenges remain, but water quality restoration in freshwater ecosystems will bring manifold benefits for freshwater biodiversity and human well-being at all scales from local to global.

Cocaine and its metabolites are increasingly being detected in aquatic environments worldwide. While previous research has demonstrated that these substances can affect brain function and behavior in wildlife, this research has exclusively been conducted under artificial laboratory conditions. How cocaine pollution affects animal behavior in the wild is, thus, unknown. Here, we combine slow-release chemical implants with acoustic telemetry tracking to reveal how environmentally realistic levels of cocaine and its main metabolite, benzoylecgonine, affect the movement of Atlantic salmon (Salmo salar) smolts in a large natural lake (Lake Vättern, Sweden). Benzoylecgonine exposure increased weekly movement rates of fish in the wild, with exposed fish swimming up to ∼1.9 times farther per week relative to controls. In addition, benzoylecgonine-exposed fish dispersed up to ∼12.3 km farther than control conspecifics. These results indicate that cocaine-derived pollutants can alter fish spatial ecology, potentially influencing habitat use, trophic interactions, and population-level dispersal patterns in natural ecosystems.

As global demand for pharmaceuticals continues to grow, pharmaceutical pollution is becoming increasingly pervasive. Research on the occurrence and distribution of pharmaceuticals in marine ecosystems remains limited, however, with coastal sewage outfalls considered to be a major source of pharmaceutical pollutants in marine environments. Here, we investigated the distribution of pharmaceuticals across a wastewater gradient in Port Phillip Bay, Melbourne, Australia, using stable nitrogen isotope ratios (δ15N) as a signal of wastewater influence. Marine invertebrates, macroalgae and marine/terrestrial plants were sampled across four sites of varying distances from Melbourne’s largest wastewater treatment plant and analyzed for δ15N and pharmaceuticals. Out of 95 target analytes, 15 were detected, with the most frequent detections being telmisartan (83%), flecainide (52%), memantine (37%), caffeine (28%) and tramadol (23%). Pharmaceutical concentration was positively associated with δ15N, supporting wastewater influence as a key driver of pharmaceutical pollution. Interestingly, concentrations were highest in primary producers, including terrestrial plants. Follow-up sampling revealed higher pharmaceutical concentrations in sea foam relative to seawater, suggesting enrichment within the air-water interface and potential transport to terrestrial environments via coastal aerosols. Overall, our findings demonstrate the role of wastewater in pharmaceutical pollution, with plants and algae emerging as potential bioindicators.

The One Health concept strongly brings into focus the important connections for human and ecosystem health. However, the incorporation of behavior method guidelines in risk assessment and regulation/policy is not equal between human and ecological disciplines. A survey was conducted on the perceptions and role of behavioral (eco)toxicology in the protection of human and ecosystem health. Those surveyed include scientists working in the field of environmental toxicology and behavioral ecology, representing industry, government, nongovernment organizations, and academia/research centers. The respondents (N = 166) agreed that contaminants "can impact" and "are impacting" wildlife (97% and 77%) and humans (84% and 62%, respectively). Overall respondents believed behavioral experiments to be repeatable (60%), reliable (61%), and relevant (84%), although those not studying behavior (43%) were more cautious in their answers. Respondents were more likely to be neutral when asked whether behavioral endpoints are more sensitive (43%), but they agreed (80%) that behavioral endpoints provide important alternative information to standard endpoints. The largest group disagreed (42%) with the statement that behavioral endpoints are currently used in risk assessment but agreed that they were essential (55%). The majority of respondents disagreed (63%) that we understood the risks of contaminants to human and ecosystem health, but they agreed (68%) that regulatory authorities should consider behavioral endpoints. When answers were compared among sectors (academia, government, or industry), industry scientists were more likely to be negative or neutral in their responses to the application of behavioral toxicology. We discuss how these data could be used to support our understanding of and confidence in the effects of contaminants on human and ecosystem health.

Rapid developments in animal-tracking technology have enabled major advances in the field of movement ecology, which seeks to understand the drivers and consequences of movement across scales, taxa, and ecosystems. The field has made ground-breaking discoveries, yet the majority of studies in movement ecology remain reliant on observational approaches. While important, observational studies are limited compared to experimental methods that can reveal causal relationships and underlying mechanisms. As such, we advocate for a renewed focus on experimental approaches in animal movement ecology. We illustrate a way forward in experimental movement ecology across two fundamental levels of biological organisation: individuals and social groups. We then explore the application of experiments in movement ecology to study anthropogenic influences on wildlife movement, and enhance our mechanistic understanding of conservation interventions. In each of these examples, we draw upon previous research that has effectively employed experimental approaches, while highlighting outstanding questions that could be answered by further experimentation. We conclude by highlighting the ways experimental manipulations in both laboratory and natural settings provide a promising way forward to generate mechanistic understandings of the drivers, consequences, and conservation of animal movement.

Chemical pollution is one of the fastest-growing agents of global change. Numerous pollutants are known to disrupt animal behavior, alter ecological interactions, and shift evolutionary trajectories. Crucially, both chemical pollutants and individual organisms are nonrandomly distributed throughout the environment. Despite this fact, the current evidence for chemical-induced impacts on wildlife largely stems from tests that restrict organism movement and force homogeneous exposures. While such approaches have provided pivotal ecotoxicological insights, they overlook the dynamic spatiotemporal interactions that shape wildlife-pollution relationships in nature. Indeed, the seemingly simple notion that pollutants and animals move nonrandomly in the environment creates a complex of dynamic interactions, many of which have never been theoretically modeled or experimentally tested. Here, we conceptualize dynamic interactions between spatiotemporal variation in pollutants and organisms and highlight their ecological and evolutionary implications. We propose a three-pronged approach-integrating in silico modeling, laboratory experiments that allow movement, and field-based tracking of free-ranging animals-to bridge the gap between controlled ecotoxicological studies and real-world wildlife exposures. Advances in telemetry, remote sensing, and computational models provide the necessary tools to quantify these interactions, paving the way for a new era of ecotoxicology that accounts for spatiotemporal complexity.

Most research comparing wild and hatchery-produced fish focuses on recently stocked individuals. As a result, these studies only investigate the behavior of naive hatchery fish, leaving a knowledge gap regarding long-term survivors. We compared the movement, space use, and survival of wild and hatchery-reared brown trout (Salmo trutta) that had survived for multiple years in a large Swedish lake (345 km2). Acoustic tracking of 38 wild and 56 naturalized, hatchery-origin trout over 4 years revealed similar weekly travel distances, sub-basin transitions, and survival rates between the groups. However, wild trout exhibited greater seasonal variability in their movement and sub-basin usage than their hatchery-reared conspecifics. These differences may reflect a reduced ability of hatchery trout to respond to environmental cues (e.g., prey availability). Our findings highlight that while hatchery-reared trout can persist in the wild, behavioral differences may influence their local ecological interactions and long-term fitness.

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.

We present a genome assembly from a specimen of Thunnus thynnus (Atlantic Bluefin Tuna; Chordata; Actinopteri; Scombriformes; Scombridae). The genome sequence has a total length of 799.05 megabases. Most of the assembly (99.17%) is scaffolded into 24 chromosomal pseudomolecules. The mitochondrial genome has also been assembled, with a length of 16.53 kilobases. Gene annotation of this assembly on Ensembl identified 23,266 protein-coding genes.

Pharmaceutical contaminants reaching natural aquatic ecosystems can affect fish behaviour, modifying activity patterns, foraging behaviour and antipredator responses. While laboratory-based studies can offer key insights, assessing the ecological relevance of these findings requires field-based approaches. Therefore, we examined the effects of oxazepam, a widely prescribed anxiolytic drug, on the behaviour of a cyprinid fish (the common roach, Rutilus rutilus) in the wild, combining slow-release exposure implants with continuous tracking via acoustic telemetry. To add ecological realism, we created a landscape of fear with an uneven distribution of resources (macrophytes) and exposure to predators (pike, Esox lucius), additionally testing the effects of the drug on roach habitat selection and predator-prey interactions. Fish exposed to the drug showed an increased swimming activity and speed, but exhibited a more constrained spatial distribution in the pond, favouring areas with higher refuge availability. Both exposed and unexposed fish modified their habitat use in the presence of predators. Exposed fish appeared to get closer to the predators when these were caged, but not when predators were free-roaming. Our findings highlight the importance of considering ecological context to understand how pharmaceuticals affect fish behaviour, which is crucial for assessing risks at population and ecosystem levels.

Despite the growing threat of pharmaceutical pollution, we lack an understanding of whether and how such pollutants influence animal behavior in the wild. Using laboratory- and field-based experiments across multiple years in Atlantic salmon (Salmo salar; n = 730), we show that the globally detected anxiolytic pollutant clobazam accumulates in the brain of exposed fish and influences river-to-sea migration success. Clobazam exposure increased the speed with which fish passed through two hydropower dams along their migration route, resulting in more clobazam-exposed fish reaching the sea compared with controls. We argue that such effects may arise from altered shoaling behavior in fish exposed to clobazam. Drug-induced behavioral changes are expected to have wide-ranging consequences for the ecology and evolution of wild populations.

This study examines the dietary composition of the recently reoccurring Atlantic bluefin tuna (ABFT, Thunnus thynnus) in the Skagerrak-Kattegat-Sound area of the North-East Atlantic. We analysed the stomach contents of 44 ABFT, with lengths between 232 and 295 cm (CFL), captured in August and September annually from 2020 to 2022 via rod-and-reel fishing. Our analysis identified 19 species of teleost fish, four types of squid, and one crab species, although the diet was dominated by pelagic schooling fish such as garfish (percentage of index of relative abundance (%IRI) = 22.5), herring (%IRI = 6.8), mackerel (%IRI = 6.8), and various demersal gadoid species (combined %IRI = 42). Regional variation in dietary composition between Skagerrak and the Sound indicates that ABFT exhibit foraging flexibility, primarily targeting locally abundant, energy-rich schooling fish, while occasionally consuming other prey. The prevalence of garfish in the diet, which is neither commercially targeted nor managed or regulated, highlights the importance of maintaining healthy stocks of this species for supporting the continuous return of ABFT to the area.

Ecosystems around the globe are under unprecedented pressure from human activities. Chemical pollution and biological invasions are two leading drivers of environmental change, each of which causes substantial harm to wildlife and the ecosystems they inhabit. However, despite their individual impacts being well-documented, the combined effects of these pervasive environmental pressures are seldom studied. Here, we address this critical gap by first examining the potential interactions between chemical pollution and biological invasions in animals. We then discuss possible impacts of chemical pollution on animals—both invasive and native—across the distinct stages of the invasion process. Further, we examine gaps in our current understanding of the potential interactions between chemical pollution and biological invasions, including the role of pollutants in mediating interactions between native and non-native species, how pollutants may influence the potential for the invasion process to act as a selective filter, and the relevance of phenotypic plasticity and behavioural syndromes in this context. By synthesizing current knowledge and identifying key research gaps, this review underscores the importance of considering chemical pollution and biological invasions in combination in ecological research. Understanding the combined impacts of these widespread and frequently co-occurring phenomena is essential for developing effective conservation and restoration measures in an increasingly human-modified world.