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It is reasonable to expect that hydro-morphodynamic processes in fluvial systems can affect fish habitat availability, but the impacts of morphological changes in fluvial systems on fish habitat are not well studied. Herein we investigate the impact of morphological development of a cohesive meandering stream on the quality of fish habitat available for juvenile yellow perch (Perca flavescens) and white sucker (Catostomus commersonii). A three-dimensional (3D) morphodynamic model was first developed to simulate the hydro-morphodynamics of the study creek. The results of the morphodynamic model were then incorporated into a fish habitat availability assessment. The 3D hydro-morphodynamic model was successfully calibrated using an intensive acoustic Doppler current profiler (ADCP) spatial survey of the entire 3D velocity field and total station surveys of topographic changes in a meander bend in the study creek. Two fish sampling surveys were carried out at the beginning and the end of the study period to determine presence–absence of fish as an indicator of the habitat utilization of each fish species in the study reach. It was shown that morphological development of the stream was a significant factor for the observed changes in the habitat utilization of juvenile yellow perch. It is shown that juvenile yellow perch mostly utilized habitat where deposition occurred whereas they avoided areas of erosion. The results of this study and the proposed methodology could provide some insights into the potential impact of sediment transport processes on the fish occurrence, and distribution and has implications for management of small fluvial systems.

Chemical information is one of the most important modes of communication among aquatic organisms. However, it remains unclear whether fish embryos are innately responsive to ecologically-related chemical cues from the cues of their cohort competitors, potential caring or risky cues from parents, or chemical alarm cues from damaged embryos, and whether these response patterns differ between species that model alternative parental care strategies. Here, we examined embryo responses in heart rate and incubation performance to different conspecific chemical cues (companion embryo odours, maternal odours, maternal + companion odours, embryonic alarm cues, or water controls) in zebrafish ( ; no parental care) and Nile tilapia ( ; high parental care). Zebrafish embryos did not respond to companion embryo odours but did respond similarly to maternal odours and alarm cues consistent with detecting elevated risk levels. In contrast, Nile tilapia embryos only demonstrated significant risk responses to embryonic alarm cues. These findings indicate that embryos of both species can innately recognize alarm cues but differ in their response patterns to conspecific odours. The results highlight that parental care strategies may influence intergenerational chemical communication in fish embryos.

A better understanding of the environmental and genetic contribution to migratory behavior and the evolution of traits linked to migration is crucial for fish conservation and fisheries management. Up to date, a few genes with unequivocal influence on the adoption of alternative migration strategies have been identified in salmonids. Here, we used a common garden set-up to measure individual migration distances of generally highly polymorphic brown trout Salmo trutta from two populations. Fish from the assumedly resident population showed clearly shorter migration distances than the fish from the assumed migratory population at the ages of 2 and 3 years. By using two alternative analytical pipelines with 22186 and 18264 SNPs obtained through RAD-sequencing, we searched for associations between individual migration distance, and both called genotypes and genotype probabilities. None of the SNPs showed statistically significant individual effects on migration after correction for multiple testing. By choosing a less stringent threshold, defined as an overlap of the top 0.1% SNPs identified by the analytical pipelines, GAPIT and Angsd, we identified eight candidate genes that are potentially linked to individual migration distance. While our results demonstrate large individual and population level differences in migration distances, the detected genetic associations were weak suggesting that migration traits likely have multigenic control.

Mutualistic relationships confer selective advantages to interacting species through enhanced ecological benefits but may be functionally limited to certain life history stages. However, it is not yet known whether one party can indirectly benefit from risky cues released when the other party is threatened. Larval glochidia of the Chinese pond mussel (Anodonta woodiana) attach to fishes including the rosy bitterling (Rhodeus ocellatus) for dispersal, while reproductive-phase bitterling use the gills of adult mussels as spawning substrate, and their larvae remain inside the host mussel shells until they are capable of swimming. Here, we examined heterospecific responses to risky chemical cues by rosy bitterling as an indirect indicator of species affinity consistent with mutualism at different life history stages, to test for age-dependent response patterns indicating temporal patterning of shared predation risk. Bitterling demonstrated equivocal but similar responses to water controls and mussel odor and significant antipredator responses to bitterling chemical alarm cues (CAC) independent of life stage, while only reproductive adult bitterling demonstrated significant antipredator responses to mussel CAC. These findings suggest that the mutualistic affinity to mussels present in reproductive-phase adult rosy bitterling may result in shared predation risk and therefore provide them with additional indirect antipredator benefits. Our results revealed a life history stage-dependent mutualism in this bitterling-mussel system and describe a novel application of predation risk assays for studying temporal patterning in mutualistic relationships.Significance statementInterspecific interactions, including mutualisms, are a central component of community composition. Some freshwater fishes, including the rosy bitterling, and mussels share an interesting mutualism where each species provides early life habitat to the other. However, does mutualism provide additional indirect benefits? Here, we used responses to conspecific and Chinese pond mussel chemical cues in different life stages of bitterling to identify the occurrence of mutualistic behaviors. We demonstrated that the putative occurrence of mutualistic behaviors in rosy bitterling is not consistent over time and instead varies predictably with reproductive status of different life history stages. This study provides a novel perspective for a deeper understanding of labile interspecific relationships and provides a theoretical basis for indirectly examining mutualisms through chemical communication-based behavioral assays.

Prey species possess a variety of morphological, life history and behavioural adaptations to evade predators. While specific evolutionary conditions have led to the expression of permanent, non-plastic anti-predator traits, the vast majority of prey species rely on experience to express adaptive anti-predator defences. While ecologists have identified highly sophisticated means through which naive prey can deal with predation threats, the potential for death upon the first encounter with a predator is still a remarkably important unresolved issue. Here, we used both laboratory and field studies to provide the first evidence for risk-induced neophobia in two taxa (fish and amphibians), and argue that phenotypically plastic neophobia acts as an adaptive anti-predator strategy for vulnerable prey dealing with spatial and temporal variation in predation risk. Our study also illustrates how risk-free maintenance conditions used in laboratory studies may blind researchers to adaptive anti-predator strategies that are only expressed in high-risk conditions.

The shy-bold behavioral continuum is an element of animal behavior which is often studied for its ecological relevance, particularly in the context of predation risk. How individuals respond to various predation cues is well studied at the individual level, but relatively little is known about how these responses can differ among closely related species. We exposed individual wild-caught juvenile bluegill (Lepomis macrochirus) and pumpkinseed (L. gibbosus) to kairomones of a common predator (Northern pike, Esox lucius), conspecific alarm cues, or a lake water control in a Z-maze trial commonly used to assess relative levels of bold and exploratory behaviors. Neither species exhibited any significant behavioral responses to either predation cue, but bluegill consistently displayed more bold-type behaviors than pumpkinseed. Although the lack of a behavioral response to predation cues in this study is equivocal, we identify clear differences in boldness between these two congeners and discuss the possibility of ecological niche differentiation driving these behavioral differences.Significance StatementClosely related species exposed to similar predator guilds may differ in their behavioral responses to predation risk, particularly during different life-history stages. We exposed juveniles of two co-occurring sunfish congeners (Lepomis spp.) to chemical predation cues (predator kairomones or conspecific alarm cues) in a Z-maze assay to assess relative levels of bold and exploratory behaviors. Bluegill (L. macrochirus) were consistently bolder and more proactive than pumpkinseed (L. gibbosus). Ontogenetic ecological niche differentiation between these species may be the cause of these observed differences and life-history trajectories should be considered in the design of future research questions.

Threat-sensitive behavioral trade-offs allow prey animals to balance the conflicting demands of successful predator detection and avoidance and a suite of fitness-related activities such as forag- ing, mating, and territorial defense. Here, we test the hypothesis that background predation level and reproductive status interact to determine the form and intensity of threat-sensitive behavioral decisions of wild-caught female Trinidadian guppies Poecilia reticulata. Gravid and nongravid gup- pies collected from high- and low-predation pressure populations were exposed to serial dilutions of conspecific chemical alarm cues. Our results demonstrate that there was ＇no effect of reproduct- ive status on the response of females originating from a low-predation population, with both gravid and nongravid guppies exhibiting strong anti-predator responses to the lowest concentration of alarm cues tested. Increasing cue concentrations did not result in increases in response intensity. Conversely, we found a significant effect of reproductive status among guppies from a high- predation population. Nongravid females from the high-predation population exhibited a strong graded （proportional） response to increasing concentrations of alarm cue. Gravid females from the same high-predation population, however, shifted to a nongraded response. Together, these re- sults demonstrate that accrued reproductive assets influence the threat-sensitive behavioral deci- sions of prey, but only under conditions of high-ambient predation risk.

Shoaling is an evolved behavior in fishes that has several adaptive advantages, including allowing individuals to avoid predation through risk dilution. However, factors such as size disparity and the presence of heterospecifics may influence the behavior of individual fish within shoals following exposure to elevated predation risk. Using bluegill Lepomis macrochirus as a model species, we measured changes in area use, shoaling index, and movement of a focal individual in isolation, in single-species shoals with two conspecifics, or in mixed-species shoals with two congeneric pumpkinseed L. gibbosus. The experimental shoals were exposed to one of three chemical cues selected to present graded levels of risk: lakewater controls (lowest risk), Northern pike Esox lucius predator odor (kairomones; intermediate risk), or conspecific chemical alarm cues (highest risk). Within the individual bluegill, we found that the multivariate response of area use and post-stimulus activity (line crosses) of the focal fish was significantly influenced by pre-stimulus activity, but not by cue type or fish size. As univariate responses, post-stimulus activity varied positively with pre-stimulus activity. Post-stimulus activity was greater in single-species shoals compared to mixed-species shoals, and again varied positively with pre-stimulus activity. Contrary to predictions, bluegill did not demonstrate graded antipredator responses to the chemical cues. Our findings suggest that prey fish may alter their risk-aversive behaviors in response to chemical stimuli based on shoal composition and provide further insight into the role of intra-prey guild interactions in response to predators in co-occurring prey species.

There are many syntheses on the role of animal behavior in understanding and mitigating conservation threats for wildlife. That body of work has inspired the development of a new discipline called conservation behavior. Yet, the majority of those synthetic papers focus on non-fish taxa such as birds and mammals. Many fish populations are subject to intensive exploitation and management and for decades researchers have used concepts and knowledge from animal behavior to support management and conservation actions. Dr. David L. G. Noakes is an influential ethologist who did much foundational work related to illustrating how behavior was relevant to the management and conservation of wild fish. We pay tribute to the late Dr. Noakes by summarizing the relevance of animal behavior to fisheries management and conservation. To do so, we first consider what behavior has revealed about how fish respond to key threats such as habitat alteration and loss, invasive species, climate change, pollution, and exploitation. We then consider how behavior has informed the application of common management interventions such as protected areas and spatial planning, stock enhancement, and restoration of habitat and connectivity. Our synthesis focuses on the totality of the field but includes reflections on the specific contributions of Dr. Noakes. Themes emerging from his approach include the value of fundamental research, management-scale experiments, and bridging behavior, physiology, and ecology. Animal behavior plays a key role in understanding and mitigating threats to wild fish populations and will become more important with the increasing pressures facing aquatic ecosystems. Fortunately, the toolbox for studying behavior is expanding, with technological and analytical advances revolutionizing our understanding of wild fish and generating new knowledge for fisheries managers and conservation practitioners.

Weak levels of acidity impair chemosensory risk assessment by aquatic species which may result in increased predator mortalities in the absence of compensatory avoidance mechanisms. Using replicate populations of wild juvenile Atlantic salmon (Salmo salar) in neutral and acidic streams, we conducted a series of observational studies and experiments to identify differences in behaviours that may compensate for the loss of chemosensory information on predation risk. Comparing the behavioural strategies of fish between neutral and acidic streams may elucidate the influence of environmental degradation on nonconsumptive effects (NCEs) of predation. Salmon in acidic streams are more active during the day than their counterparts in neutral streams, and are more likely to avoid occupying territories offering fewer physical refugia from predators. Captive cross-population transplant experiments indicate that at equal densities, salmon in acidic streams do not demonstrate relative decreases in growth rate as a result of their different behavioural strategies. Instead, altering diel activity patterns to maximize visual information use and occupying relatively safer territories appear sufficient to offset increased predation risk in acidic streams. Additional strategies such as elevated foraging rates during active periods or adopting riskier foraging tactics are necessary to account for the observed similarities in growth rates.