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For millennia humans have extracted biological and physical resources from the planet to sustain societies and enable the development of technology and infrastructure. Growth in the human population and changing consumption patterns have increased the human footprint on ecosystems and their biodiversity, including in fresh waters. Freshwater ecosystems and biodiversity face many threats and it is now widely accepted that we are in a biodiversity crisis. One means of protecting and restoring freshwater biodiversity is to better manage the exploitation of freshwater biota and aggregate resources (e.g., sand, gravel, and boulders). Here we outline the threats arising from such exploitation and identify response options to ensure that methods and levels of extraction are sustainable and allow recovery of over-exploited freshwater biodiversity and ecosystems. The guidance we provide will enable practitioners, policy-makers, and resource stewards to embrace effective, sustainable, and evidence-based approaches to resource extraction. Response options for managing species exploitation include strengthening assessment and reporting, using science-based approaches to reduce overexploitation and support recovery, embracing community engagement, and building or tightening legislation. Response options for managing exploitation of freshwater aggregate resources include reducing demand for harvest, strengthening governance, reporting, and monitoring of environmental impacts, and promoting the restoration of degraded ecosystems or compensating for losses. Diverse case studies highlight examples of where various management actions have been implemented in an effort to consider how they can be scaled up and adapted to other contexts. Managing exploitation will be a key aspect of broader initiatives needed to protect and restore freshwater biodiversity around the globe. [ABSTRACT FROM AUTHOR]

Horizon scanning is a systematic approach increasingly used to explore emerging trends, issues, opportunities, and threats in conservation. We present the results from one such exercise aimed at identifying emerging issues that could have important scientific, social, technological, and managerial implications for the conservation of inland waters in Canada in the proximate future. We recognized six opportunities and nine challenges, for which we provide research implications and policy options, such that scientists, policy makers, and the Canadian society as a whole can prepare for a potential growth in each of the topic areas we identified. The issues spanned a broad range of topics, from recognizing the opportunities and challenges of community-enabled science and the need to consider the legal rights of nature, to the likely increase of pharmaceuticals in wastewater due to an aging population. These issues represent a first baseline that could help decision makers identify and prioritize efforts while simultaneously stimulate new research avenues. We hope our horizon scan will pave the way for similar exercises related to the conservation of biodiversity in Canada. L'analyse prospective est une approche systematique de plus en plus utilisee pour explorer les nouvelles tendances, questions, occasions et menaces dans le domaine de la conservation. Nous presentons les resultats d'un de ces exercices visant a cerner les questions emergentes qui pourraient etre importantes des points de vue scientifique, social, technologique et de la gestion relativement a la conservation des eaux interieures au Canada, pour l'avenir rapproche. Nous relevons six occasions a saisir et neuf defis, dont nous abordons les repercussions sur la recherche et les possibilites d'action qu'ils presentent, afin que les scientifiques, les decideurs et l'ensemble de la societe canadienne puissent se preparer en vue d'une croissance potentielle dans chacun des domaines cernes. Ces questions couvrent un vaste eventail de sujets allant de la reconnaissance des occasions et defis de la science facilitee par la collectivite et la necessite de prendre en compte les droits de la nature en vertu de la loi, a l'augmentation probable des produits pharmaceutiques dans les eaux usees en raison du vieillissement de la population. Ces questions representent un premier etat de reference qui pourrait aider les decideurs a cerner et prioriser les efforts tout en stimulant de nouvelles avenues de recherche. Nous esperons que cette analyse prospective ouvrira la voie a des exercices semblables concernant la conservation de la biodiversite au Canada. [Traduit par la Redaction], Introduction Rivers, lakes, springs, and other inland waters (i.e., all surface waters contained within lands; FAO 2008) are often classified among the most threatened ecosystems on the planet (Dudgeon et [...]

Inland recreational fisheries provide numerous socio‐economic benefits to fishers, families and communities. Recreationally harvested fish are also frequently consumed and may provide affordable and sustainable but undervalued contributions to human nutrition. Quantifying the degree to which recreationally harvested fish contribute to food security and subsistence is impeded by lack of data on harvest and consumption and by the difficulty in differentiating among recreational and subsistence fisheries. Recreational harvest records tend to be limited to wealthy, food‐secure countries and well‐monitored fisheries with clear regulations or permitting systems. These records often neglect components of recreational harvest among food‐insecure fishers who are potentially more likely to have consumption as a motivation. Here, we highlight the 'fuzzy boundary' that can exist between inland recreational and subsistence fisheries and argue that unreported consumption is likely to be a hidden contributor to food security in some populations. We draw on local case studies from around the world to highlight specific instances where recreationally harvested fish species contribute food and subsistence benefits to participating communities. We use these examples to highlight the diversity of ways that inland recreational fisheries contribute to human nutrition, knowledge gaps in understanding recreational fishing for food, and consequences of not accounting for them as food fisheries in policy and management. The aim of this paper is to draw the attention of resource managers and policy makers, create greater social awareness of the importance of recreational fisheries and bring to light this hidden contribution of inland fisheries to nutrition and subsistence. [ABSTRACT FROM AUTHOR]

Inland fisheries support the livelihoods of millions of people in riparian communities worldwide but are influenced by increasing climate variability and change. Freshwater fishing societies are among the most vulnerable to climate change given their dependence on highly threatened aquatic resources. As climate change intensifies, building adaptive capacity within communities and understanding the efficacy of adaptive strategies for maintaining household stability is essential for coping with ongoing social and environmental change.In this study, we examined household perceptions of climate change, livelihood impacts and responses to socio‐ecological changes in fishing‐dependent households in the Lake Victoria basin in Uganda, East Africa. Through a series of household surveys and focus group discussions in five fish landing sites, we assessed social adaptive capacity (SAC) based on 207 households and identified adaptive strategies that are effective for coping with climatic change.We found that people in fishing households are aware of environmental change but that most households do not have adaptive strategies that are efficacious for securing long‐term income and food security.We also investigated household demographics that contribute to SAC, examined links between SAC and adaptive efficacy and established potential routes towards developing effective adaptive approaches in small‐scale fisheries.This work contributes to a growing foundation of documented community‐based knowledge for building adaptive capacity in inland fisheries and the communities around the world that depend on them. Read the free Plain Language Summary for this article on the Journal blog. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Recreational fisheries contribute substantially to the sociocultural and economic well‐being of coastal and riparian regions worldwide, but climate change threatens their sustainability. Fishery managers require information on how climate change will impact key recreational species; however, the absence of a global assessment hinders both directed and widespread conservation efforts. In this study, we present the first global climate change vulnerability assessment of recreationally targeted fish species from marine and freshwater environments (including diadromous fishes). We use climate change projections and data on species' physiological and ecological traits to quantify and map global climate vulnerability and analyze these patterns alongside the indices of socioeconomic value and conservation effort to determine where efforts are sufficient and where they might fall short. We found that over 20% of recreationally targeted fishes are vulnerable to climate change under a high emission scenario. Overall, marine fishes had the highest number of vulnerable species, concentrated in regions with sensitive habitat types (e.g., coral reefs). However, freshwater fishes had higher proportions of species at risk from climate change, with concentrations in northern Europe, Australia, and southern Africa. Mismatches in conservation effort and vulnerability were found within all regions and life‐history groups. A key pattern was that current conservation effort focused primarily on marine fishes of high socioeconomic value rather than on the freshwater and diadromous fishes that were predicted to be proportionately more vulnerable. While several marine regions were notably lacking in protection (e.g., Caribbean Sea, Banda Sea), only 19% of vulnerable marine species were without conservation effort. By contrast, 72% of freshwater fishes and 33% of diadromous fishes had no measures in place, despite their high vulnerability and cultural value. The spatial and taxonomic analyses presented here provide guidance for the future conservation and management of recreational fisheries as climate change progresses. [ABSTRACT FROM AUTHOR]

Freshwater biodiversity loss is one of the greatest environmental threats in our changing world. Although declines have been reported extensively in the literature, much less attention has been devoted to solving the freshwater biodiversity crisis relative to other ecosystems. The recently proposed Emergency Recovery Plan for Freshwater Biodiversity (Tickner et al., 2020, BioScience, 70(4), 330–342) outlines an ambitious but necessary set of overarching actions that can help "bend the curve" for freshwater biodiversity declines. This plan is timely given the present opportunity to adjust freshwater biodiversity targets in international biodiversity agreements and to encourage meeting targets of relevant Sustainable Development Goals. Yet, relying solely on a trickle down from such agreements to national and local scales will likely take too long, given the immediate urgency of the situation. Here, we advocate for a broader, concerted effort from all actors to ensure the Emergency Recovery Plan meaningfully influences the actions of practitioners at a local scale. We outline the roles and responsibilities of actors involved with policy, research, professional bodies and societies, advocacy, and industry, as well as practitioners themselves, in achieving this goal. It is our hope that this overview facilitates the real‐world actions needed to execute the Emergency Recovery Plan so that we can indeed "bend the curve" for freshwater biodiversity. [ABSTRACT FROM AUTHOR]

Practitioners and policymakers working in environmental arenas make decisions that can have large impacts on ecosystems. Basing such decisions on high‐quality evidence about the effectiveness of different interventions can often maximize the success of policy and management. Accordingly, it is vital to understand how environmental professionals working at the science‐policy interface view and use different types of evidence, including evidence syntheses that collate and summarize available knowledge on a specific topic to save time for decision‐makers. We interviewed 84 senior environmental professionals in Canada working at the science‐policy interface to explore their confidence in, and use of, evidence syntheses within their organizations. Interviewees value evidence syntheses because they increase confidence in decision‐making, particularly for high‐profile or risky decisions. Despite this enthusiasm, the apparent lack of available syntheses for many environmental issues means that use can be limited and tends to be opportunistic. Our research suggests that if relevant, high quality evidence syntheses exist, they are likely to be used and embraced in decision‐making spheres. Therefore, efforts to increase capacity for conducting evidence syntheses within government agencies and/or funding such activities by external bodies have the potential to enable evidence‐based decision‐making. [ABSTRACT FROM AUTHOR]

Scientific evidence is fundamental for guiding effective conservation action to curb biodiversity loss. Yet, research resources in conservation are often wasted due to biased allocation of research effort, irrelevant or low‐priority questions, flawed studies, inaccessible research outputs, and biased or poor‐quality reporting. We outline a striking example of wasted research resources, highlight a powerful case of data rescue/reuse, and discuss an exemplary model of evidence‐informed conservation. We suggest that funding agencies, research institutions, NGOs, publishers, and researchers are part of the problem and solutions, and outline recommendations to curb the waste of research resources, including knowledge co‐creation and open science practices. [ABSTRACT FROM AUTHOR]

We tested whether thermal tolerance and aerobic performance differed between two populations of Nile perch (Lates niloticus) originating from the same source population six decades after their introduction into two lakes in the Lake Victoria basin in East Africa. We used short‐term acclimation of juvenile fish to a range of temperatures from ambient to +6°C, and performed critical thermal maximum (CTmax) and respirometry tests to measure upper thermal tolerance, resting and maximum metabolic rates, and aerobic scope (AS). Across acclimation temperatures, Nile perch from the cooler lake (Lake Nabugabo, Uganda) tended to have lower thermal tolerance (i.e., CTmax) and lower aerobic performance (i.e., AS) than Nile perch from the warmer waters of Lake Victoria (Bugonga region, Uganda). Effects of temperature acclimation were more pronounced in the Lake Victoria population, with the Lake Nabugabo fish showing less thermal plasticity in most metabolic traits. Our results suggest phenotypic divergence in thermal tolerance between these two introduced populations in a direction consistent with an adaptive response to local thermal regimes. [ABSTRACT FROM AUTHOR]

Teaching can be a rewarding, yet challenging, experience for early career researchers (ECRs) in fields like ecology and evolution. Much of this challenge arises from the reality that ECRs in ecology and evolution typically receive little, if any, pedagogical training or advice on how to balance teaching, research (which can include extended field work), and other demands on their time. Here, we aim to provide accessible, pragmatic advice for ECRs in ecology and evolution who are given the opportunity to teach (as instructor of record). The advice is based on the authors' collective experiences teaching in ecology and evolution as ECRs and is meant to help ECRs address two challenges: a) balancing the demands of teaching against one's research, service, and personal life, and b) being effective in the classroom while doing so. The guidance we provide includes practical steps to take when teaching for the first time, including carefully refining the syllabus (course planning), adopting 'non-traditional' teaching methods, and taking advantage of free teaching resources. We also discuss a range of 'soft skills' to consider, including guarding against imposter syndrome (i.e., self-doubt and fear of being exposed as a fraud), managing expectations, being empathetic, compassionate, authentic, and fostering an inclusive classroom. Lastly, we emphasize the need to focus on developing students' critical thinking skills, integrating research and teaching where possible, and setting limits on class preparation time to maintain balance with your research and personal life. Collectively, we hope the examples provided here offer a useful guide to ECRs new to teaching. [ABSTRACT FROM AUTHOR]

Increasing water temperatures owing to anthropogenic climate change are predicted to negatively impact the aerobic metabolic performance of aquatic ectotherms. Specifically, it has been hypothesized that thermal increases result in reductions in aerobic scope (AS), which lead to decreases in energy available for essential fitness and performance functions. Consequences of warming are anticipated to be especially severe for warm-adapted tropical species as they are thought to have narrow thermal windows and limited plasticity for coping with elevated temperatures. In this study we test how predicted warming may affect the aerobic performance of Nile perch (Lates niloticus), a commercially harvested fish species in the Lake Victoria basin of East Africa. We measured critical thermal maxima (CTmax) and key metabolic variables such as AS and excess post-exercise oxygen consumption (EPOC) across a range of temperatures, and compared responses between acute (3-day) exposures and 3-week acclimations. CTmax increased with acclimation temperature; however, 3-week-acclimated fish had higher overall CTmax than acutely exposed individuals. Nile perch also showed the capacity to increase or maintain high AS even at temperatures well beyond their current range; however, acclimated Nile perch had lower AS compared with acutely exposed fish. These changes were accompanied by lower EPOC, suggesting that drops in AS may reflect improved energy utilization after acclimation, a finding that is supported by improvements in growth at high temperatures over the acclimation period. Overall, the results challenge predictions that tropical species have limited thermal plasticity, and that high temperatures will be detrimental because of limitations in AS. [ABSTRACT FROM AUTHOR]

Deforestation is a major threat to global aquatic biodiversity and ecosystem services. Regional studies are needed to understand and mitigate impacts of deforestation on local inland waters, yet such studies remain unavailable in many regions of the world where the risks of impact are high, for example in the tropics. Our goal was to identify such understudied regions by quantifying and mapping the global research need and effort on deforestation impacts on inland waters. We defined research need based on countries' deforestation rate, fish diversity, and vulnerability of human populations to freshwater ecosystem degradation, the latter estimated from water scarcity and consumption and trade of local freshwater fish. We quantified research effort by reviewing 1362 publications on deforestation and freshwater ecosystems, thereby providing the first quantitative literature review on this important conservation problem. We found that tropical countries exhibited strong overlap among deforestation, freshwater fish diversity, and vulnerability of human populations to freshwater ecosystem degradation, and therefore have high research need relative to temperate regions. However, we found that the best predictor of research effort on deforestation and aquatic systems was the size of a country's economy (indicated by gross domestic product), not research need. Finally, we uncovered a strong research bias against tropical Africa, the only extensive region of the world that has a high research need and a low research effort. This global analysis suggests that future research effort on deforestation impacts on inland waters should try to alleviate existing biases by increasing interregional cooperation and transfer of research resources to regions of high research need and/or low research effort, with a particular focus on the critical research zone that is tropical Africa. [ABSTRACT FROM AUTHOR]

Habitat-associated trait divergence may vary across ontogeny if there are strong size-related shifts in selection pressures. We quantified patterns of phenotypic divergence in Nile perch ( Lates niloticus) from ecologically distinct wetland edge and forest edge habitats in Lake Nabugabo, Uganda, and we compared patterns of divergence across three size classes to determine whether trends are consistent through Nile perch ontogeny. We predicted that inter-habitat variation in biotic (e.g. vegetation structure) and abiotic (e.g. dissolved oxygen concentration) variables may create divergent selective regimes. We compared body morphology using geometric morphometrics and found substantial differences between habitats, although not all trends were consistent across size classes. The most striking aspects of divergence in small Nile perch were in mouth orientation, head size, and development of the caudal region. Medium-sized Nile perch also showed differences in mouth orientation. Differences in large individuals were related to eye size and orientation, as well as caudal length. The observed patterns of divergence are consistent with functional morphological predictions for fish across divergent trophic regimes, high and low predation environments, and complex and simple habitats. Although this suggests adaptive divergence, the source of phenotypic variation is unknown and may reflect phenotypic plasticity and/or genetic differences. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110, 449-465. [ABSTRACT FROM AUTHOR]

Abstract: Nile perch (Lates niloticus) was introduced to the Lake Victoria basin in the 1950s and 1960s and eventually became one of the most valuable commercial species of East Africa''s inland fisheries. Intense fishing-induced mortality may be contributing to dramatic ecological change in this species (reductions in body size and catch rate) and reinforcing patterns of ecological divergence in some lakes in the region. We used radio telemetry to characterize Nile perch movement and home range size in Lake Nabugabo, Uganda and quantified patterns of habitat selection by Nile perch in the heavily-fished near-shore areas of this system. Nile perch exhibited high site tenacity with daily movement averaging ∼400m/day and home range size averaging 0.83km2. Body size and water temperature were both important predictors of Nile perch movement patterns. In the near-shore area of the lake, Nile perch selected regions characterized by low temperature and high oxygen conditions, and tended to prefer forest edge over wetland edge. The level of site tenacity exhibited by Nile perch suggests that ecological isolation between fish using forest and wetland ecotones may be higher than expected. These results also have important implications for development of territorial jurisdiction by Beach Management Units, the decentralized structure of fisheries management in the region. [Copyright &y& Elsevier]

Mating systems that comprise a mixture of pure males and self-fertilising hermaphrodites remain an evolutionary enigma. In particular, our understanding of the sexual selection pressures associated with such mating systems is nascent. Males can only reproduce by fertilising hermaphrodites' eggs, but hermaphrodites can also fertilise their own eggs and gain a genetic advantage by doing so. Consequently, there should be intense competition among males to access hermaphrodites. Here, we test the importance of male size, colour and heterozygosity in predicting the outcome of male-male competition using the mangrove rivulus, which has a male-hermaphrodite mixed-mating system. We pitted males against one another in dyadic laboratory trials to develop a dominance score for each male. We then correlated these scores with male length, several components of male colour, and heterozygosity. Male size was the only significant correlate of dominance: larger males dominated smaller males, implying selection for large male size. However, male mangrove rivulus are similar in size to hermaphrodites, indicating that directional selection for large body size in males is no greater than it is in hermaphrodites. Across all trials, colour was unrelated to dominance, but contests between similarly sized males were usually won by more colourful individuals. As mangrove rivulus are dichromatic, we suspect that male colour may prove to be more important in mate choice than we found it to be in intrasexual competition. Heterozygosity did not explain dominance directly, but correlated strongly with male size, implying an indirect role in intrasexual competition. [ABSTRACT FROM AUTHOR]

In reflecting on the human domination of our planet in the Anthropocene, some have argued that concrete is among the most destructive materials created by humans. Here we explore this idea, specifically in the context of what we consider "the concrete conquest of aquatic ecosystems." The ubiquitous use of concrete in transportation and building infrastructure has contributed to alterations in freshwater and coastal marine systems. Yet, in some cases, there are no appropriate alternative building materials such that concrete itself is confounded by its application. For example, as the foundation for most dams, concrete fragments rivers and channelizes streams, often creating unnatural systems, yet dams are necessary for hydropower generation and flood control with few alternative materials for construction. In riparian and coastal environments, concrete harbours and inland canal systems are often used to address erosion or reclaim areas for human development. Even when removed (e.g., dam removal, naturalization of shorelines), concrete dust is a major aquatic pollutant. Instances do exist, however, where concrete has been used to benefit aquatic ecosystems – such as the installation of fish passage facilities at barriers or the development of fish-friendly culverts – though even then, there is a movement towards nature-like fishways that avoid the use of harmful materials like concrete. There are also opportunities to achieve conservation gains in the development of seawalls that include more natural and complex features to benefit biota and allow for essential biogeochemical processes to occur in aquatic environments. There have been several innovations in recent years that increase the permeability of concrete, however these have limited application in an aquatic context (e.g., not relevant to dam construction or erosion control but may be relevant in stormwater management systems). We provide a brief overview of the history of concrete, discuss some of the direct and indirect effects of concrete on aquatic ecosystems, and encourage planners, engineers, developers, and regulators to work collaboratively to explore alternatives to concrete which benefit aquatic ecosystems and the services they offer. The status quo of concrete being the default construction material is failing aquatic ecosystems, so we recommend that efforts are made to explore alternative materials and if concrete must be used, to increase structural complexity to benefit biodiversity. • Concrete is among the most permanent human-created materials on Earth and its use appears to be increasing. • Concrete has played a major role in altering freshwater and coastal marine habitats through processes such as damming, channelization, and construction of seawalls. • Collectively, these activities have simplified habitats and reduced aquatic biodiversit.y • Concrete has, however, been used to benefit aquatic ecosystems (e.g., fishways, seawalls that have structural elements that support biodiversity.) • We encourage relevant parties to work collaboratively to explore alternatives to concrete which benefit aquatic ecosystems. [ABSTRACT FROM AUTHOR]

To address the ongoing global biodiversity crisis, conservation approaches must be underpinned by robust information. Canada is uniquely positioned to contribute to meeting global biodiversity targets, with some of the world's largest remaining intact ecosystems, and a commitment to co-application of Indigenous ways of knowing alongside scientific, socioeconomic, and other approaches. We elicited input from experts across a range of disciplines to identify the key information needed to advance policy and management actions to conserve biodiversity in Canada. Experts concluded that, in many cases, a lack of information is not the major barrier to biodiversity conservation; instead, mechanisms to translate information into action are most urgently needed. Recognizing multiple ways of knowing, especially Indigenous knowledge systems, will be critical to support the transformative change needed to conserve biodiversity at a national scale. Collaboration among natural, social and data scientists can facilitate social change and biodiversity information management. Experts identified 50 priority information needs which emphasize the importance of (i) reviewing policies and actions and disseminating lessons learned from successes and failures; (ii) better understanding mechanisms to build public support; (iii) improving, in specific instances, understanding of the status and trends of habitats, species, ecosystems, and threats for planning and management; and (iv) mobilizing biodiversity information. Through the Convention on Biological Diversity, the global community has resolved to "live in harmony with nature"; through our Canadian case-study, we conclude that the most pressing need to address this resolution is an improved understanding of how to move from conservation knowledge to conservation action. • Experts listed 50 key needs to transform biodiversity conservation in Canada. • Translating information into action is often more urgent than collecting new data. • Creating space for Indigenous knowledge systems is critical for success. • Improving policy and building public support requires a transdisciplinary approach. • Some key monitoring data are still required, where the gaps are impeding action. [ABSTRACT FROM AUTHOR]

The COVID-19 global pandemic and resulting effects on the economy and society (e.g., sheltering-in-place, alterations in transportation, changes in consumer behaviour, loss of employment) have yielded some benefits and risks to biodiversity. Here, we considered the ways the COVID-19 pandemic has influenced (or may influence) freshwater fish biodiversity (e.g., richness, abundance). In many cases, we could only consider potential impacts using documented examples (often from the media) of likely changes, because anecdotal observations are still emerging and data-driven studies are yet to be completed or even undertaken. We evaluated the potential for the pandemic to either mitigate or amplify widely acknowledged, pre-existing threats to freshwater fish biodiversity (i.e., invasive species, pollution, fragmentation, flow alteration, habitat loss and alteration, climate change, exploitation). Indeed, we identified examples spanning the extremes of positive and negative outcomes for almost all known threats. We also considered the pandemic's impact on freshwater fisheries demand, assessment, research, compliance monitoring, and management interventions (e.g., restoration), with disruptions being experienced in all domains. Importantly, we provide a forward-looking synthesis that considers the potential mechanisms and pathways by which the consequences of the pandemic may positively and negatively impact freshwater fishes over the longer term. We conclude with a candid assessment of the current management and policy responses and the extent to which they ensure freshwater fish populations and biodiversity are conserved for human and aquatic ecosystem benefits in perpetuity. • The COVID-19 pandemic has influenced (or may influence) freshwater fish populations. • We evaluated the potential for the pandemic to mitigate or amplify widely acknowledged, pre-existing threats. • We identified examples spanning the extremes of positive and negative outcomes. • We also considered the pandemic's impact on fisheries demand, assessment, research, and management interventions. [ABSTRACT FROM AUTHOR]

Fishes faced with novel thermal conditions often modify physiological functioning to compensate for elevated temperatures. This physiological plasticity (thermal acclimation) has been shown to improve metabolic performance and extend thermal limits in many species. Adjustments in cardiorespiratory function are often invoked as mechanisms underlying thermal plasticity because limitations in oxygen supply have been predicted to define thermal optima in fishes; however, few studies have explicitly linked cardiorespiratory plasticity to metabolic compensation. Here, we quantified thermal acclimation capacity in the commercially harvested Nile perch ( Lates niloticus ) of East Africa, and investigated mechanisms underlying observed changes. We reared juvenile Nile perch for 3 months under two temperature regimes, and then measured a series of metabolic traits (e.g. aerobic scope) and critical thermal maximum (CT max ) upon acute exposure to a range of experimental temperatures. We also measured morphological traits of heart ventricles, gills and brains to identify potential mechanisms for compensation. We found that long-term (3 month) exposure to elevated temperature induced compensation in upper thermal tolerance (CT max ) and metabolic performance (standard and maximum metabolic rate, and aerobic scope), and induced cardiac remodeling in Nile perch. Furthermore, variation in heart morphology influenced variations in metabolic function and thermal tolerance. These results indicate that plastic changes enacted over longer exposures lead to differences in metabolic flexibility when organisms are acutely exposed to temperature variation. Furthermore, we established functional links between cardiac plasticity, metabolic performance and thermal tolerance, providing evidence that plasticity in cardiac capacity may be one mechanism for coping with climate change., Competing Interests: Competing interestsThe authors declare no competing or financial interests., (© 2018. Published by The Company of Biologists Ltd.)