Translational participatory research for environmental management occupies a demanding space at the interface of societal needs and academic research. Projects in this space usually face the challenge of reconciling stakeholder involvement and real-world applicability with academic career requirements such as excellence in fundamental research and the attraction of substantial research funds. Here, we share our experiences from a 12-year translational participatory research initiative on the management of invasive gobies in central Europe. We describe the project, synthesize inputs, outputs, and outcomes, and summarize conditions and practices across political, administrative, societal, institutional, team, and individual levels that we found important and beneficial in our attempts to produce both academic and applied outcomes. Our impression is that an interaction of factors across these levels created windows of opportunity, and that the team constellation and setting allowed us to seize these opportunities for the sake of both scientific progress and societal impact. By reflecting from the perspective of a multidisciplinary group of natural scientists directly engaged in such a project, we aim to contribute a personal account to social science frameworks on translational, participatory, inter- and transdisciplinary research. Our retrospective potentially can inform policy makers, funders, and institutions who seek to create enabling environments for interface research, and is helpful to fellow natural scientists who want to prepare the ground for their own translational participatory research initiatives.

Ecological research towards environmental management occupies a unique and challenging realm, as it resides at the crossroads of societal needs and the realities of academic research. In this realm, research projects face fundamental challenges in meeting calls for stakeholder involvement and local applicability whilst supporting academic careers through the accumulation of academic deliverables. Here, we address such fundamental questions using a 12-year, inter- and transdisciplinary research project on the management of an invasive fish species in central Europe as a case study. After demonstrating the scope and outputs of the project, we distill the factors promoting the success of the project across the political, administrative, societal, institutional, team, and personal level. We believe our findings are broadly applicable for a variety of long-term inter- and transdisciplinary projects in the realm of environmental management. We are confident that our retrospective on the project’s challenges can help policy makers as well as research funders to develop more effective funding policies and to reassess existing evaluation criteria of similar projects. ### Competing Interest Statement The authors have declared no competing interest.

Benthic fish, such as the round goby (Neogobius melanostomus Pallas, 1814) tend to swim near the bottom, especially at increased water velocities. To test whether these fish have a hydraulic advantage from swimming near the bottom and how the substrate affects the forces experienced, we measured the hydraulic forces experienced by preserved fish in a flow channel. The fish were tested 5.0 mm above the bottom at smooth and rough surface, and in the water column (10.0 cm elevation) above smooth and rough surface at 0.95 m/s water velocity. No significant effect among the mean hydraulic forces was observed between both fish positions, whereas the mean hydraulic forces in the water column were significantly higher (P<0.05) above the rough surface (mean 0.077 N±0.025 s.d.) than above the smooth surface (mean 0.068 N±0.021 s.d.). A convolutional neural network (CNN) predicted the column smooth treatment was the most characteristic force data time series (mean F1=0.88±0.03 s.d.). We conclude that the body posture and body movements of the fish are more relevant for the hydraulic forces experienced by the fish than the vertical position in the water column. Further factors explaining the affinity to swimming near the bottom are discussed.

The round goby, Neogobius melanostomus, is a successful invasive fish species. Originating from the Caspian and Black Sea, it is now distributed widely within European fresh- and brackish waters. The River Rhine was colonized in 2008 only a few years after the opening of the Rhine-Main-Danube canal and only four years after N. melanostomus was first reported in the upper Danube River. Its invasion history of the River Rhine was unclear because the species was first detected close to the Rhine river delta which would suggest a route of invasion other than via the Rhine-Main-Danube canal. To investigate the colonization history of N. melanostomus in the Rhine, we combined abundance estimates with molecular analysis. Abundance estimates found N. melanostomus to be dominant in the Lower Rhine (> 90% of all catches). Molecular analysis was done on 286 individuals from four different sites. Using the mitochondrial control region (d-loop), we found three different haplotypes in both Rhine sites. None of the potential invasive source populations in the rivers Danube and Trave exhibited all three haplotypes. The molecular data therefore supported a scenario of two different colonization directions. Our results show that the invasion history of the River Rhine is complex and warrants further investigation.

The vertical slots of fish passes represent bottlenecks that must be passed by every fish migrating upstream. The hydraulics in fish passes are well investigated but less is known about the small scale behaviour of fish while passing the vertical slot. Understanding the species-specific swimming behaviour during the passage could allow for creation of future fish passes with hydraulics adapted to the swimming requirements of desired target species. We recorded the swimming trajectories of three fish species as point coordinates per video frame using cameras. Then, two common machine learning algorithms were used to identify species characteristic swimming patterns in the trajectories. A Random Forest model trained on 21 trajectory features revealed that water discharge, the spatial trajectory position, and the trajectory length were most distinct trajectory features among species. The model identified the species with a mean F1 score of 0.86 ± 0.08 SD for round goby [ Neogobius melanostomus (Pallas, 1814)], 0.81 ± 0.12 SD for gudgeon ( Gobio L.), and 0.58 ± 0.20 SD for bullhead ( Cottus gobio L.). A Convolutional Neural Network achieved a mean F1 score of 0.89 ± 0.03 SD for round goby, 0.76 ± 0.05 SD for gudgeon, and 0.67 ± 0.02 SD for bullhead if exclusively trained on the point coordinates of the swimming trajectories. These results demonstrate that fish species exhibit distinct swimming patterns when passing through a vertical slot, and how these patterns can be used for species identification using machine learning algorithms. Because round goby achieved the highest F1 scores, we conclude that round goby showed the most characteristic swimming trajectories among the species tested. Future fish passage research should account for the individual swimming patterns of the fish in these bottleneck flow fields and on adapting the flow to the individual swimming patterns of the target fish. Flow conditions being supportive for swimming patterns of the desired fish could have the potential to improve the river connectivity and thereby support the aquatic biodiversity.

Every fish migrating upstream through vertical slot fish passes must swim through slots, where the resistance force of flowing water could affect the passage success. We measured the hydraulic force acting on the body of preserved benthic fish in a vertical slot at different water discharge rates (80 and 130 L/s) to compare the hydraulic burden individual fish species (round goby Neogobius melanostomus Pallas, 1814, gudgeon Gobio gobio L. and bullhead Cottus gobio L.) must overcome. The forces measured in three spatial axes were then compared to acoustic Doppler velocity measurements and the passage probability of 39-45 live fish per species. Passage probability reduction of 28.26% for round goby and 39.29% for bullhead was observed at the higher water discharge. Gudgeon showed increased numbers of passages and approaches when larger hydraulic forces were experienced at 130 L/s compared to the lower water discharge. Gudgeon experienced significantly lower hydraulic forces (mean 0.27 N +/- 0.12 standard deviation) compared to round goby (mean 0.32 N +/- 0.12 SD) and bullhead (0.35 N +/- 0.14 SD). Potentially, the increased hydraulic forces at the higher water discharge contributed to the reduction in passages in round goby and bullhead. That gudgeon behaved differently from the other species illustrates how fish species deal differently with flowing water and the hydraulic forces experienced. Our approach provides a species-oriented assessment of the flow field in ecologically relevant fish passes. These findings represent an important step towards the development of purposeful fish pass designs, which is essential for ecosystem-oriented river connectivity.

Aquatic invasive species (AIS) are a major threat to freshwater and marine ecosystems worldwide. Despite management efforts, human assisted dispersal continues to distribute AIS within and across waterbodies. An understudied translocation vector for AIS, especially for invasive fish, are the cooling systems of small watercraft motors. Here, we investigate the contents of boat motor cooling systems for the presence of invasive goby larvae in a collaboration with local boat owners. Because of the exclusively nocturnal drift activity of goby larvae, we drove boats in the first hours after sunset. For an estimate of the translocation potential, we quantified drift density of goby larvae as well as boat traffic after sunset. We found a goby larva in a boat motor once in 30 drives of 1-2 hours duration each. Peak drift densities of goby larvae were 2.5 per 100 m3, which is comparable to previously reported data. Recreational boats were active after sunset throughout the reproductive season of invasive gobies and are therefore a realistic translocation vector for goby larvae. Additionally, evidence of fish and other animals inside boat motor cooling systems, gathered from online boating forums, speaks for the potential of AIS transport in small watercraft. Translocation inside motors is especially likely for in-water transport of boats, which should be a management focus in interconnected aquatic systems.

Abstract Anthropogenic structures can form novel ecosystem niches. Invasive species are often particularly successful in occupying these habitats and utilize them as beachheads for further spread. The invasive round goby (Neogobius melanostomus, Pallas 1814), an inherently bottom‐dwelling fish, uses vertical harbor walls as habitat, enabling them to reach boats (i.e., potential translocation vectors). To evaluate the relevance of vertical habitat use for population dynamics and translocation, we exemplary investigated a population of round gobies in a harbor ecosystem. Specifically, we investigated differences in trophic niche characteristics, individual trophic specialization, phenotypic traits, and breeding frequency in wall versus bottom‐dwelling round gobies. Habitat‐characteristic dietary signatures indicated habitat partitioning during the breeding season. Trophic niches overlapped but were clearly distinguishable between the habitats: Walls were inhabited by 1.4 times more trophic generalists than specialists, while the bottom was inhabited by 2.1 times more trophic specialists. Breeding frequency was 24 times higher on the walls than on the bottom. After the reproductive season, we found a higher similarity in trophic ecology of gobies inhabiting the two habitats, and differences in abundance, size, and condition. These results are in line with winter migrations to deeper habitats, which are common in round gobies in lentic and marine ecosystems. Our results suggest a high potential for microgeographic adaptation to either horizontal or vertical habitat use in invasive round gobies. We demonstrated that male gobies using the walls during the breeding season are larger and heavier, suggesting that wall climbing may select for more competitive individuals. Additionally, the overall abundance of round gobies likely increases with the additional use of vertical habitat space, which may lead to higher propagule pressure. The ability to exploit anthropogenic habitats, and a higher translocation probability of competitive individuals, can contribute to the invasion success of round gobies in anthropogenically influenced aquatic systems.

Efforts to restore river ecosystem connectivity focus predominantly on diadromous, economically important fish species, and less attention is given to nonmigratory, small‐bodied, benthic fish species. Data on benthic fish swimming performance and behaviour in comparison with ecologically similar native species are especially relevant for the study of one of the most successful invaders in the last decades: the Ponto‐Caspian gobiid species Neogobius melanostomus . To evaluate future measures against its further upstream dispersal, we conducted comparative swimming performance and behaviour experiments with round goby and two native species: the European bullhead ( Cottus gobio ) and the gudgeon ( Gobio gobio ). Experiments in a swim tunnel revealed a high variation in the swimming performance and behaviour within and among the three species. Gudgeon performed best in both U crit and U sprint experiments and displayed a rather continuous, subcarangiform swimming mode, whereas bullhead and round goby displayed a burst‐and‐hold swimming mode. Experiments in a vertical slot pass model, which contained a hydraulic barrier as a challenge to upstream movement, confirmed the high swimming performance of gudgeon. Gudgeon dispersed upstream even across the hydraulic barrier at the highest flow velocities. Round goby showed a higher capability to disperse upstream than bullhead, but failed to pass the hydraulic barrier. Our results on comparative swimming performance and behaviour can inform predictive distribution modelling and range expansion models, and also inform the design of selective barriers to prevent the round goby from dispersing farther upstream.

Migration barriers being selective for invasive species could protect pristine upstream areas. We designed and tested a prototype protective barrier in a vertical slot fish pass. Based on the individuals’ swimming responses to the barrier flow field, we assumed this barrier would block the ascension of the invasive round goby, but allow comparable native species (gudgeon and bullhead) to ascend. The barrier was tested in three steps: flow description, quantification of forces experienced by preserved fish in the flow field, and tracking the swimming trajectories of ca. 43 live fish per trial and species. The flow and the forces were homogenous over the barrier, though gudgeon experienced significantly smaller forces than round goby or bullhead. The swimming trajectories were distinct enough to predict the fish species with a random forest machine learning approach (92.16% accuracy for gudgeon and 85.24% for round goby). The trajectories revealed round goby and gudgeon exhibited increased, but varied, swimming speeds and straighter paths at higher water discharge. These results suggest that passage of round goby was prevented at 130 L/s water discharge, whereas gudgeon and bullhead could pass the barrier. Our findings open a new avenue of research on hydraulic constructions for species conservation.

Human translocations of non-native aquatic species are a global conservation challenge. Aquarists and anglers are two hobbyist groups whose practices are particularly likely to translocate non-native aquatic species, especially fish. This article aims to stipulate a change of perspective among these hobbyists, who - by acting simultaneously as anglers and aquarists - establish novel pathways for non-native fish. This study showed that: (i) 51 of 226 respondents to a questionnaire act simultaneously as anglers and aquarists; (ii) 53 of 237 non-native fish species in the European Union are used for both angling and aquarium hobbies; and (iii) hobbyists write online reports on the catch and exchange of a particularly invasive fish, the round goby (Neogobius melanostomus). This combination of knowledge on how hobbyists use non-native fish and the ecological impacts of round goby demonstrates how the impact of an invasive species can be influenced by the combined behaviours of anglers and aquarists. We suggest that future research in aquatic conservation should move beyond considering the commercial aquarium trade and angling as separate pathways for translocating non-native fish, and instead consider these hobbyist groups as interconnected.

Modern ethohydraulics is the study of the behavioral responses of swimming fish to flow fields. However, the exact drag forces experienced by fish remain poorly studied; this information is required to obtain a better understanding of the behavioral responses of fish and their current resistance strategies. We measured near-ground frontal drag forces on preserved individuals of three benthic fish species, round goby (Neogobius melanstomus), gudgeon (Gobio gobio) and bullhead (Cottus gobio), in a flow channel. The forces were compared to acoustic Doppler velocity (ADV) measurements and fish tracking data based on video observations of live fish in the flow channel. Overall, we observed drag coefficients (CD) of ∼10−3 at Reynolds numbers ∼105. The frontal drag forces acting on preserved fish with non-spread fins ranged from -1.96 mN*g-1 (force per fish wet weight, velocity 0.55 m*s-1) to 11.01 mN*g-1 (velocity 0.85 m*s-1). Spreading the fins strongly increased the drag forces for bullhead and round goby. In contrast, the drag forces were similar for gudgeon with spread fins and all fish with non-spread fins. Video tracking revealed no clear relationship between the position of the fish in the flow field and the forces experienced by the preserved fish at these positions. Collectively, these results suggest that i) the differences in frontal drag forces between species are small in homogenous flow, ii) individuals chose their position in the flow field based on factors other than the drag forces experienced, and iii) whether fins are spread or non-spread is an essential quality that modulates species-specific differences. The methodology and results of this study will enable integration of flow measurements, fish behavior and force measurements and inform ethohydraulics research. More advanced force measurements will lead to a detailed understanding of the current resistance strategies of benthic fish and improve the design of fish passes.

1.Conservation of riverine fish typically aims at improving access to spawning grounds and the restoration of longitudinal connectivity requires substantial investments. However, the removal of migration barriers also enables the upstream invasion of non-native species into spawning areas, with potential negative effects on recruitment of threatened freshwater fish through egg or fry predation. 2.Detecting egg predation is often challenging. Visual gut inspections are thought to underestimate predation on soft material such as eggs and fry, which hampers the discovery of predators preying upon these life-stages. For soft materials, molecular approaches may therefore offer a more sensitive tool for detection. 3.Here, we uncover such a macroscopically invisible conservation issue caused by predation of invasive round goby (Neogobius melanostomus) predation on eggs or fry of threatened common nase (Chondrostoma nasus) in Switzerland.4.In addition, this manuscript presents species-specific molecular assays for five more valuable native fish, including endangered salmonid and cyprinid river spawners, and confirms the applicability of the assays in a series of laboratory and field feeding experiments involving eggs and fish tissue. The manuscript also provides a guiding tool for conservation managers regarding the use and applicability of different molecular approaches in gut-content analysis.5.Our results inspire recommendations for local conservation measures such as a temporary reduction of round goby densities at the spawning site prior to the spawning period, and demonstrate how the targeted application of species-specific molecular markers can inform freshwater fish management.

This study examines the impact of boldness on foraging competition of the highly invasive round goby Neogobius melanostomus Pallas 1815. Individual risk tolerance, or boldness, was measured as the time to resume movement after a simulated predation strike. Fish that resumed movement faster were categorized as "bold," fish that took more time to resume movement were categorized as "shy" and those that fell in between these two categories were determined to have "intermediate" boldness. Competitive impacts of boldness in N. melanostomus were determined in a laboratory foraging experiment in which interspecific (juvenile Atlantic cod Gadus morhua Linnaeus 1758) and intraspecific (intermediate N. melanostomus) individuals were exposed to either bold or shy N. melanostomus competitors. G. morhua consumed fewer prey when competing with bold N. melanostomus than when competing with shy N. melanostomus, whereas intermediately bold N. melanostomus foraging was not affected by competitor boldness. Bold and shy N. melanostomus consumed similar amounts of prey, and the number of interactions between paired fish did not vary depending on the personality of N. melanostomus individuals. Therefore, intraspecific foraging competition was not found to be personality dependent. This study provides evidence that individual differences in boldness can mediate competitive interactions in N. melanostomus; nonetheless, results also show that competition is also governed by other mechanisms that require further study.

Differences between individuals in behavioral type (i.e. animal personality) are ecologically and evolutionarily important because they can have significant effects on fitness components such as growth and predation risk. In the present study we are used the invasive round goby (Neogobius melanostomus) from an established population in controlled experiments to examine the relationships among personality, metabolic performance, and growth rate (inferred as size-at-age). Boldness was measured as the time to return to normal behavior after a simulated predator attack, where fish with shorter freezing times were categorized as "bold" and fish with longer times were categorized as "shy." We show that bold fish have significantly higher standard metabolic rate (SMR) than their shy conspecifics, whereas there was no difference between personality types in their maximum metabolic rate (MMR) or aerobic scope (AS). Bold fish furthermore had a smaller size-at-age as compared to shy fish. Together this provides evidence of a metabolic underpinning of personality where the high-SMR bold fish require more resources to sustain basic life functions than their low-SMR shy conspecifics, indicating that bold round goby from established populations with high densities (and high competition for food) pay a price of reduced growth rate.

The global energy system changes towards renewables-dominated and liberalized markets. This requires making novel trade-offs between the profitable development of hydropower and its environmental effects on the natural flow regime. Here, we used a pristine river as a model for how these future changes will affect the natural flow regime and identify future changes on previously overlooked levels. We found that damming and discharging based on market prices leads to first- and second-level deviation from natural flows. Beyond these effects, we identified a third level of distance from natural flow. This third level is created by the transition towards a renewables-dominated energy system. The volatile energy input from renewables incentivizes hydropower plant operators to discharge based on more flexible trading behavior. We conclude that novel economic models be combined with tailored implementations of environmental flows. This will allow to find novel solutions for the trade-off between market liberalization and sustainable hydropower development.

The question as to how early life experiences are stored on a molecular level and affect traits later in life is highly topical in ecology, medicine, and epigenetics. In this study, we use a fish model to investigate whether DNA methylation mediates early life experiences and predetermines a territorial male reproductive phenotype. In fish, adult reproductive phenotypes frequently depend on previous life experiences and are often associated with distinct morphological traits. DNA methylation is an epigenetic mechanism which is both sensitive to environmental conditions and stably inherited across cell divisions. We therefore investigate early life predisposition in the round goby Neogobius melanostomus by growth back-calculations and then study DNA methylation by MBD-Seq in the brain region controlling vertebrate reproductive behavior, the hypothalamus. We find a link between the territorial reproductive phenotype and high growth rates in the first year of life. However, hypothalamic DNA methylation patterns reflect the current behavioral status independently of early life experiences. Together, our data suggest a non-predetermination scenario in the round goby, in which indeterminate males progress to a non-territorial status in the spawning season, and in which some males then assume a specialized territorial phenotype if current conditions are favorable.

The article addresses citizen competence for sustainable consumption in adults. It discusses whether it is possible to develop educational offerings for adults (being by nature short and isolated) that effectively promote this competence and whether it makes a difference if sustainable consumption is approached by focusing on good life (quality of life) and justice or by focusing on natural resources and environment (as is suggested by, e.g., environmental literacy approaches). Taking the case of energy policy, it presents an educational intervention (EdIn) developed, implemented, and investigated by the authors. In data-analysis, three approaches were adopted (methodological triangulation), one analysing the deliberations' cognitive structure, one analysing the participants' perception, one analysing the participants' reaction (in terms of the knowledge/concepts and values/concerns they voiced). The results show, firstly, that the didactical design of EdIn was successful with a view to supporting citizen competence in participants. Secondly, they show that in adult civic education sustainable consumption should be approached by focusing on good life and justice. Thirdly, they indicate that people do not necessarily perceive themselves to be part of societal decision-making, leading from the question of the design and content of civic educational activities to the question of their necessity.

The vast majority of global freshwater ecosystems are small lakes with less than 100m(2) surface area. These lakes are often unconnected to other water bodies but frequently host fish populations. Existing explanations for how fish colonize such remote habitats often involve birds as vectors transporting fish eggs as propagules. In this study, we aim to quantify the prevalence of these explanations among relevant societal groups as well as their scientific knowledge basis. We analyzed entries in online blogs and forums and surveyed the opinions of local stakeholders and decision makers using a questionnaire. To collect published scientific knowledge, we conducted a structured literature review. Our results reveal a discrepancy between commonly found beliefs and the empirical knowledge supporting those beliefs: Dispersal of fish eggs by water birds was overall the most frequent explanation online and in the questionnaire. In the scientific literature, however, we found hardly any empirical research on passive fish egg dispersal. We propose research directions for how to close this gap of knowledge and suggest that future empirical studies on passive fish egg dispersal may be inspired by existing work on passive dispersal in aquatic invertebrates. Mitigating the belief-evidence discrepancy on fish dispersal will be essential to better understand the patterns of fish biodiversity across landscapes, to counteract its losses, and inform management strategies for invasive fish species.

How early life experiences are stored on a molecular level and affect behavioural phenotypes later in life is not well understood. In fish, reproductive phenotypes are often easily discernible and frequently depend on previous life experiences. DNA methylation is an epigenetic mechanism which is both sensitive to environmental conditions and stable across cell divisions. In this study, we therefore investigate whether DNA methylation mediates early life experiences and predetermines the territorial male reproductive phenotype in the round goby, Neogobius melanostomus. We investigate early life predisposition by growth back-calculations and then study DNA methylation by MBD-Seq in the round goby hypothalamus as the brain region controlling vertebrate reproductive behaviour. We find that the territorial reproductive phenotype is linked to a high growth rate in the first year of life. Hypothalamic DNA methylation patterns, however, reflect the current behavioural status independently of early life experiences. Together, our data suggest a non-predetermination scenario in which indeterminate males progress to a non-territorial status in the spawning season, and in which some males then assume a specialized territorial phenotype if current conditions are favourable.