Stress and food deprivation: linking physiological state to migration success in a teleost fish

Food deprivation is a naturally occurring stressor that is thought to influence the ultimate life-history strategy of individuals. Little is known about how food deprivation interacts with other stressors to influence migration success. European populations of brown trout (Salmo trutta) exhibit partial migration, whereby a portion of the population smoltifies and migrates to the ocean, and the rest remain in their natal stream. This distinct, natural dichotomy of life-history strategies provides an excellent opportunity to explore the roles of energetic state (as affected by food deprivation) and activation of the glucocorticoid stress response in determining life-history strategy and survival of a migratory species. Using an experimental approach, the relative influences of short-term food deprivation and experimental cortisol elevation (i.e. intra-coelomic injection of cortisol suspended in cocoa butter) on migratory status, survival and growth of juvenile brown trout relative to a control were evaluated. Fewer fish migrated in both the food deprivation and cortisol treatments; however, migration of fish in cortisol and control treatments occurred at the same time while that of fish in the food deprivation treatment was delayed for approximately 1 week. A significantly greater proportion of trout in the food deprivation treatment remained in their natal stream, but unlike the cortisol treatment, there were no long-term negative effects of food deprivation on growth, relative to the control. Overall survival rates were comparable between the food deprivation and control treatments, but significantly lower for fish in the cortisol treatment. Food availability and individual energetic state appear to dictate the future life-history strategy (migrate or remain resident) of juvenile salmonids while experimental elevation of the stress hormone cortisol causes impaired growth and reduced survival of both resident and migratory individuals

Manipulating glucocorticoids in wild animals: Basic and applied perspectives

One of the most comprehensively studied responses to stressors in vertebrates is the endogenous production and regulation of glucocorticoids (GCs). Extensive laboratory research using experimental elevation of GCs in model species is instrumental in learning about stressor-induced physiological and behavioural mechanisms; however, such studies fail to inform our understanding of ecological and evolutionary processes in the wild. We reviewed emerging research that has used GC manipulations in wild vertebrates to assess GC-mediated effects on survival, physiology, behaviour, reproduction and offspring quality. Within and across taxa, exogenous manipulation of GCs increased, decreased or had no effect on traits examined in the reviewed studies. The notable diversity in r

Tracking animals in freshwater with electronic tags: past, present and future

Considerable technical developments over the past half century have enabled widespread application of electronic tags to the study of animals in the wild, including in freshwater environments. We review the constraints associated with freshwater telemetry and biologging and the technical developments relevant to their use. Technical constraints for tracking animals are often influenced by the characteristics of the animals being studied and the environment they inhabit. Collectively, they influence which and how technologies can be used and their relative effectiveness. Although radio telemetry has historically been the most commonly used technology in freshwater, passive integrated transponder (PIT) technology, acoustic telemetry and biologgers are becoming more popular. Most telemetry studies have focused on fish, although an increasing number have focused on other taxa, such as turtles, crustaceans and molluscs. Key technical developments for freshwater systems include: miniaturization of tags for tracking small-size life stages and species, fixed stations and coded tags for tracking large samples of animals over long distances and large temporal scales, inexpensive PIT systems that enable mass tagging to yield population- and community-level relevant sample sizes, incorporation of sensors into electronic tags, validation of tag attachment procedures with a focus on maintaining animal welfare, incorporation of different techniques (for example, genetics, stable isotopes) and peripheral technologies (for example, geographic information systems, hydroacoustics), development of novel analytical techniques, and extensive international collaboration. Innovations are still needed in tag miniaturization, data analysis and visualization, and in tracking animals over larger spatial scales (for example, pelagic areas of lakes) and in challenging environments (for example, large dynamic floodplain systems, under ice). There seems to be a particular need for adapting various global positioning system and satellite tagging approaches to freshwater. Electronic tagging provides a mechanism to collect detailed information from imperilled animals and species that have no direct economic value. Current and future advances will continue to improve our knowledge of the natural history of aquatic animals and ecological processes in freshwater ecosystems while facilitating evidence-based resource management and conservation

Intracoelomic Implantation of Transmitters in Longnose Gar

Fish in the family Lepisosteidae (hereafter, gars) have unique ganoid scales that pose inherent challenges to implanting electronic tags in their coeloms for telemetry studies. In this paper we outline a unique approach to conducting laparotomic surgery in gars, with a focus on the Longnose Gar Lepisosteus osseus. An electric rotary tool with a circular cutting blade was used to cut through the scales, and the same tool, with a drill bit, was used to create holes through which to run the suture material. The final incision into the body cavity was made with a scalpel, and the incision was expanded using surgical scissors. Using a passive acoustic telemetry array, the survival of 12 of 15 tagged Longnose Gars was confirmed over a 123-d period based on their detection at receivers outside of their areas of capture and release. Two individuals were recaptured 17-19 weeks postsurgery and showed complete healing of the wounds with limited evidence of scarring. This approac

On the Electroimmobilization of Fishes for Research and Practice: Opportunities, Challenges, and Research Needs

As a result of growing demand for immediate-release sedatives in fisheries research, electroimmobilization has been receiving increasing attention due to its superior induction and recovery times and practicality, particularly under field conditions. However, a review of electroimmobilization and its role in fisheries science has not been previously conducted. Here we describe and differentiate the various forms of electroimmobilization and attempt to standardize relevant terminology. We review the known efficacy of electroimmobilization of fish and summarize the current available knowledge on this topic while identifying major knowledge gaps. Although more information is needed to determine optimal forms and settings for different species, life history stages, and environmental variables, electroimmobilization is a useful tool for fish handling that equals or surpasses the capabilities of chemical sedatives without exacerbating (and sometimes reducing) the negative consequences associated with chemical sedatives and fish

Assessing occupancy of freshwater fishes in urban boat slips of Toronto Harbour

Hardening of natural shorelines in urban aquatic ecosystems can result in a loss of fish habitat and productivity. The north shore of Toronto Harbour (Lake Ontario) has been converted to hardened boat slips for commercial, industrial and recreational purposes, but its potential utility as fish habitat has not been evaluated. The objective of this study was to determine whether fish frequented and utilized four slips in the Inner Harbour of Toronto. Two western boat slips are adjacent to some natural features and have undergone some rehabilitation to increase the complexity of aquatic habitat (i.e. addition of large substrate, overhead cover, and in-water structure). In contrast, the two eastern slips are deeper and more influenced by the turbid Don River. We assessed the timing and duration of occupancy within all four slips for seven fish species using acoustic telemetry. In just under a year, tagged fishes spent

Evidence of fish spillover from freshwater protected areas in lakes of eastern Ontario

Research has identified numerous conservation benefits attributed to the use of marine protected areas (MPAs), yet comparatively less is known about the effectiveness of freshwater protected areas (FPAs). This study assessed multiple long-standing (>70 years active) intra-lake FPAs in three lakes in eastern Ontario, Canada, to evaluate their potential conservation benefits. These FPAs were intended initially to protect exploited populations of largemouth bass (Micropterus salmoides (Lacépède, 1802)), but since their establishment no empirical data have been collected to evaluate the effectiveness of FPAs for protecting bass or the broader fish community. A comparative biological census of fish species abundance, biomass and species richness was conducted using snorkelling surveys within FPAs, along the bor

Relationship of baseline and maximum glucocorticoid concentrations to migration propensity: A field test with wild subadult brown trout (salmo trutta)

There is considerable variation in glucocorticoid (GC) baseline status and stress responses of individuals, yet the cause and consequence of this variation remains ambiguous. Attempts to relate GC levels to fitness and life-history trade-offs have yielded variable results. In this study, we evaluated whether baseline and poststressor GC hormone concentrations predicted migration strategy (

Size-Dependent Consequences of Exogenous Cortisol Manipulation on Overwinter Survival and Condition of Largemouth Bass

Little is known about the size-dependent consequences of stressors on wild animals, which is particularly relevant during winter where size-specific trends in survival are common. Here, exogenous cortisol manipulation was used to investigate the effect of a physiological challenge on overwinter mortality and spring condition of largemouth bass (Micropterus salmoides) across a range of body sizes. Fish were wild-caught in the fall, assigned into either control or cortisol manipulated treatments, and held in replicated experimental ponds. For bass that survived the winter, length, mass, and health metrics (e.g., gonadosomatic index [GSI], hepatosomatic index [HSI], and water content) were determined in the spring. Winter survival was marginally lower for cortisol treated bass; however, there was no influence of initial length, mass, or condition on overwinter survival. When bass were grouped by size, survival was significantly higher for bass 300–350 mm in length compared to those <200 mm. The treatment did not strongly influence spring health metrics, suggesting that largemouth bass that survived the winter were able to recover from the effects of the cortisol elevation. Initial size and sex were linked to some spring health metrics, with large females having the highest GSI and HSI scores. Overall, results from this study do not support the notion that there are size-dependent responses to cortisol manipulation in a teleost fish. Rather, this type of physiological challenge may modulate the natural rates of winter mortality that are primarily driven by starvation and predation, independent of body size, in subadult and adult largemouth bass