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Skin darkening (luminance) of juvenile Nile tilapia reared at low (14 g l⁻¹) and high (50 g l⁻¹) density.
Source publication
Farmed fish are typically reared at densities much higher than those observed in the wild, but 1 to what extent crowding results in abnormal behaviours that can impact welfare and stress 2 coping styles is subject to debate. Neophobia (i.e. fear of the 'new') is thought to be adaptive 3 under natural conditions by limiting risks, but it is potentia...
Citations
... Animal behaviour, including behavioural responses to chemical exposure, is typically sensitive to a wide range of environmental and experiential factors (Bell, 2013). For instance, juvenile Nile tilapia (Oreochromis niloticus) reared at a high density were more neophobic and less aggressive compared to conspecifics that were reared at a low density, and these effects were more pronounced when tested in an arena without shelter compared to that with shelter (Champneys et al., 2018). It is therefore necessary that, where at all possible, all procedures and conditions (other than the experimental treatment itself) are standardised for a study to be considered reliable (see also EthoCRED reliability criterion #4, Section III.3.d). ...
Behavioural analysis has been attracting significant attention as a broad indicator of sub‐lethal toxicity and has secured a place as an important subdiscipline in ecotoxicology. Among the most notable characteristics of behavioural research, compared to other established approaches in sub‐lethal ecotoxicology (e.g. reproductive and developmental bioassays), are the wide range of study designs being used and the diversity of endpoints considered. At the same time, environmental hazard and risk assessment, which underpins regulatory decisions to protect the environment from potentially harmful chemicals, often recommends that ecotoxicological data be produced following accepted and validated test guidelines. These guidelines typically do not address behavioural changes, meaning that these, often sensitive, effects are not represented in hazard and risk assessments. Here, we propose a new tool, the EthoCRED evaluation method, for assessing the relevance and reliability of behavioural ecotoxicity data, which considers the unique requirements and challenges encountered in this field. This method and accompanying reporting recommendations are designed to serve as an extension of the “Criteria for Reporting and Evaluating Ecotoxicity Data (CRED)” project. As such, EthoCRED can both accommodate the wide array of experimental design approaches seen in behavioural ecotoxicology, and could be readily implemented into regulatory frameworks as deemed appropriate by policy makers of different jurisdictions to allow better integration of knowledge gained from behavioural testing into environmental protection. Furthermore, through our reporting recommendations, we aim to improve the reporting of behavioural studies in the peer‐reviewed literature, and thereby increase their usefulness to inform chemical regulation.
... An additional consideration to make regarding the elevated cortisol concentrations in transported fish is that soft-release fish were immediately placed into a novel environment following transport. While there is currently minimal research on the physiological effects of sudden exposure to novel environments in fish, sudden exposure to novel stimuli can result in an acute stress response and elevated corticosteroid levels in birds (Champneys et al. 2018). In addition to its novelty, the release environment could exhibit varied environmental conditions that could have contributed to the physiological stress we observed in the soft-release fish. ...
Objective
We examined whether an extended acclimatization period prior to release (soft release) can allow transported fish to recover from the physiological stress associated with transport compared with conventional release methods, which provide fish with no acclimatization period prior to release (hard release).
Methods
We monitored an Atlantic Salmon Salmo salar stocking team during a standard reintroduction operation and compared their conventional hard‐release method (i.e., immediate release after transport with no acclimatization period) to a soft‐release method (i.e., 2 and 4 days in‐river acclimatization prior to release). Following a 2.5‐h transport event, hard‐release fish were immediately blood‐sampled for their physiological stress response (cortisol, glucose, and lactate). Soft‐release fish were blood‐sampled for their physiological stress response following 2 or 4 days of in‐river acclimatization.
Result
While hard‐ and soft‐release fish demonstrated significantly higher cortisol, glucose, and lactate concentrations compared with control fish, cortisol concentrations remained elevated for both the hard‐ and soft‐release groups. However, glucose and lactate concentrations were significantly lower in soft‐release fish compared with hard‐release fish.
Conclusion
Soft‐release provides fish an extended acclimatization period that was found to impact transport‐related physiological stress in fish. Our findings will inform management agencies and practitioners focused on improving the success of salmonid stocking and reintroduction programs.
... Ultimately, adaptation to high stocking densities encourages behavioural plasticity [80,81] as part of the different habituation strategies to a challenging condition [12,82]. However, increasing experimental evidence points to complex cognitive abilities and behaviours of fish [83,84], which may differ depending on the type and intensity of stress [85,86] and, more importantly, on fish species. ...
A confinement stress test with 75% tank space reduction and behavioural monitoring through tri-axial accelerometers externally attached to the operculum was designed. This procedure was validated by demonstrating the less pronounced stress response in gilthead sea bream than in European sea bass (950–1200 g). Our study aimed to assess habituation to high stocking densities with such procedure in gilthead sea bream. Animals (420–450 g) were reared (June–August) in a flow-through system at two stocking densities (CTRL: 10–15 kg/m3; HD: 18–24 kg/m3), with natural photoperiod and temperature (21–29 °C), and oxygen levels at 5.2–4.2 (CTRL) and 4.2–3.2 ppm (HD). At the end, blood and muscle were sampled for haematology and transcriptomic analyses, and external tissue damage was assessed by image-based scoring. Four days later, fish underwent a 45 min confinement stress test over two consecutive days. HD fish showed reduced feed intake, growth rates and haematopoietic activity. Muscle transcriptome changes indicated a shift from systemic to local growth regulation and a primed muscle regeneration over protein accretion in HD animals with slight external injuries. After stress testing, HD fish exhibited a decreased recovery time in activity and respiration rates, which was shorter after a second stressor exposure, confirming habituation to high densities.
... Furthermore, studies show that high densities intensify competition between aquatic animals for key resources and lead to severe fighting [25,26]. Nile tilapia raised at high densities exhibit higher levels of chronic stress and aggression than those reared at low densities [27]. In addition, at high densities, fish that use reactive coping methods take longer to display exploring behavior [28,29]. ...
Personality is widely observed in animals and has important ecological and evolutionary implications. In addition to being heritable, personality traits are also influenced by the environment. Population density commonly affects animal behavior, but the way in which it shapes animal personality remains largely unknown. In this study, we reared juvenile crayfish at different population densities and measured their personality traits (shyness, exploration, and aggression) after reaching sexual maturity. Our results showed repeatability for each behavior in all treatments, except for the shyness of females at medium density. There was a negative correlation between shyness and exploration in each treatment, and aggression and exploration were positively correlated in medium- and high-density females. These indicate the presence of a behavior syndrome. On average, the crayfish raised at higher population densities were less shy, more exploratory, and more aggressive. We found no behavioral differences between the sexes in crayfish. These results suggested that population density may affect the average values of behavioral traits rather than the occurrence of personality traits. Our study highlights the importance of considering population density as a factor influencing personality traits in animals and, therefore, might help us to understand animal personality development.
... Group tests to characterize stress coping styles are: risk taking in new environments (Huntingford et al., 2010;Alfonso et al., 2020), food intake assessment (Pottinger, 2006;Gesto, 2019) and hypoxia (Castanheira et al., 2013a;Ferrari et al., 2015;Vindas et al., 2017). Regarding individual tests, those that have proved to be effective to characterize SCS are: feeding test (Castanheira et al., 2013b;Ferrari et al., 2015), restraining test (Castanheira et al., 2016;Höglund et al., 2020), novel object test (Champneys et al., 2018;Skov et al., 2019), new environment test (Castanheira et al., 2013a;Ibarra-Zatarain et al., 2016) and confinement test (Barreto and Volpato, 2011;Fatsini et al., 2020). ...
Identifying Stress Coping Styles (SCS) in new species of interest for aquaculture has important implications for its future domestication and adaptation to captivity. Individual variability allows to select the potential positive characteristics for fish production. The main aim of this study was to identify phenotypic individual differences and characterize proactive and reactive SCS in flathead grey mullet (Mugil cephalus) juveniles by exposing fish to different stress situations and evaluating their individual and group responses to level behavioural and physiology. Juveniles were subjected to one group test (risk-taking) and five individual tests (predator, first feeding after stress, restraining, new environment and confinement). All assays were repeated twice, with a one-month interval between tests. Blood samples were taken from each individual (before and after stress) to quantify cortisol and glucose plasma concentrations. Flathead grey mullet juveniles exhibited a high inter-individual variability with two extremes of behaviours: proactive and reactive profiles that were characterized by opposed behavioural (activity time and escape attempts) and physiological (levels of cortisol and glucose) responses to stress and were consistent over time and across contexts. The flathead grey mullet juveniles showed differences in their predisposition for risk taking. Likewise, the Principal Component Analysis showed that three individual stress tests (predator, restraining and confinement tests) were reliable to characterize SCS in this fish species. This work reported for the first time the existence of stress coping styles in M. cephalus juveniles and the selection of a set of reliable behavioural tests to identify phenotypic profiles in flathead grey mullet. These results might be of interest for the aquaculture industry to improve fish welfare and health and to adjust management protocols for rearing this fish species in captivity.
... These papers described the animals' use of hiding places in otherwise barren tanks and how the animals were affected by the hiding places. Hides were typically provided to group-housed fish in the form of tunnels [69], artificial plants [70], real plants [71], or other overhead cover [72]. Hides were provided to singly housed lobsters in the form of a dish with sides [73], a box [73], or a tunnel [74]. ...
Many wild animals perform hiding behaviours for a variety of reasons, such as evading predators or other conspecifics. Unlike their wild counterparts, farmed animals often live in relatively barren environments without the opportunity to hide. Researchers have begun to study the impact of access to hiding spaces (“hides”) in farmed animals, including possible effects on animal welfare. The aims of this scoping review were to: 1) identify the farmed species that have been most used in research investigating the provision of hides, 2) describe the context in which hides have been provided to farmed animals, and 3) describe the impact (positive, negative or neutral/inconclusive) that hides have on animals, including indicators of animal welfare. Three online databases (CAB Abstracts, Web of Science, and PubMed) were used to search for a target population of farmed animals with access to hiding spaces. From this search, 4,631 citations were screened and 151 were included in the review. Fourteen animal types were represented, most commonly chickens (48% of papers), cattle (9%), foxes (8%), and fish (7%). Relatively few papers were found on other species including deer, quail, ducks, lobsters, turkeys, and goats. Hides were used in four contexts: at parturition or oviposition (56%), for general enrichment (43%), for neonatal animals (4%), or for sick or injured animals (1%). A total of 218 outcomes relevant to our objectives were found including 7 categories: hide use, motivation, and/or preference (47% of outcomes), behavioural indicators of affective state (17%), health, injuries, and/or production (16%), agonistic behaviour (8%), abnormal repetitive behaviours (6%), physiological indicators of stress (5%), and affiliative behaviours (1%). Hiding places resulted in 162 positive (74%), 14 negative (6%), and 42 neutral/inconclusive (19%) outcomes. Hides had a generally positive impact on the animals included in this review; more research is encouraged for under-represented species.
... I previously modelled this in wild elk, showing that in a human-disturbed predation refugia, in which elk were hyper-abundant, bolder personality types were selected for at the expense of migratory shy-type elk (Found and St. Clair 2019). Density-dependent personality traits have also been observed in farmed Nile tilapia (Oreochromis niloticus), in which fish raised in high density situations exhibited less aggression and more neophobia than fish raised in low density situations (Champneys et al. 2018). ...
Context
Optimal foraging strategies can be influenced at the group level by population density, which can increase competition, hunger, and activity levels. Optimal foraging can also be influenced at the individual level by personality, which in part governs how individuals assess risk versus reward.
Aims
The purpose of this study was to quantify the influence of population density on risk-taking. I focused on captive elk that had previously been studied in tandem with wild elk in order to quantify personality trait characteristics. I hypothesised that risk-taking would be shown to be a density-dependent affect, in addition to varying individually.
Methods
Automated cameras recorded visitation to four rotating treatments sites in each of high and low density pens, and which had either: forage, a novel object, forage + novel object, or a control site. Novel objects were regularly changed to elicit a spectrum of responses ranging from neofilia to neophobia. Selection or avoidance of sites was determined by comparing elk visitation to visits to control sites. The experiment was done in summer when natural forage was most abundance, and in again in autumn when natural forage was limited.
Key results
High density elk showed year-round selection for all treatment sites. In summer low density elk showed weak selection for forage and forage + novel and no selection for novel objects, and no selection for any site in autumn. These patterns showed that elk in the high density pen, which were in poorer condition, had to increase their levels of both activity and risk taking. Neither elk pen exhibited any group-wide avoidance of novel objects, indicating a group-wide gradient of neophobia to neofilia, known personality traits in elk.
Conclusions
These results show that risk-taking behaviour can be a density dependent effect. This increase in neofilia may be driven by hunger stress, but also through increases in competition that may favour elk of certain personalities.
Implications
Increasing density may increase the prevalence of both neofilia and other personality traits correlated with neofilia, which include aggression, and so may contribute to increasing human–wildlife conflicts in areas where human disturbance has resulted in ungulate hyperabundance.
... This increase in foraging costs could lead to increased vigilance or general attention, which in turn, could protect prey while foraging in novel patches (Chapman et al., 2010;Mettke-Hofmann et al., 2013). For example, tilapia (Oreochromis niloticus) reared at high densities exhibit greater neophobia (measured as approach distance to a novel object) than do conspecifics reared at lower densities (Champneys et al., 2018). In the presence of potential competitors, neophobic common ravens, Corvus corax, select smaller, less conspicuous food items from feeders adjacent to novel objects (Kijne & Kotrschal, 2002). ...
Neophobia is defined as the avoidance of novel or unknown stimuli, including unknown predators, and can be induced by exposure to uncertain ecological conditions. In addition to uncertainty related to predation risk, uncertainty may also arise from increased foraging competition. Prey forced to spend time and energy competing for limited resources may not have enough time available to devote to predator identification and hence benefit from increased neophobia. Here, we tested the potential interaction of reduced foraging opportunities and elevated predation risk on the strength of neophobia (the antipredator response towards a novel chemical cue). In our first experiment, shoals of juvenile convict cichlids, Amatitlania nigrofasciata, were exposed to high (10% total body weight/day) or low (1% total body weight/day) relative food abundance for 7 days. During the final 3 days, we exposed the shoals to high versus low background predation risk, resulting in a 2 × 2 design. We found that while low food abundance alone and risk alone induced a weak neophobic response to a novel cue (versus water control), cichlids pre-exposed to high risk and low food abundance exhibited significantly a stronger neophobic response, in an additive pattern. In our second experiment, we exposed shoals of cichlids to a fixed amount of food distributed on a single (high competition) patch or across five (low competition) patches for 7 days, with the same risk manipulation as above for the final 3 days. As in experiment 1, we found that high competition alone and risk alone elicited a weak neophobic response to novel cues and that high risk and high competition had additive effects on the strength of induced neophobia among juvenile cichlids. Together, our results indicate that uncertainty of risk and of foraging opportunities exert additive effects on the phenotypically plastic neophobia among prey populations.
... Definitions of behaviours recorded from the videosApproachThe focal subject swims towards the stimulus until it is within less than one of its own body lengths(Frommen et al. 2009;Bevan et al. 2018) CircleThe focal subject circles around the entire circumference of the stimulus Experiment oneAggression The focal subject swims rapidly towards the stimulus until it makes contact with the stimulus chamber(Ros et al. 2006;Champneys et al. 2018;Szopa-Comley et al. 2020) ...
During the early stage of biological invasions, interactions occur between native and non-native species that do not share an evolutionary history. This can result in ecological naïveté, causing native species to exhibit maladaptive behavioural responses to novel enemies, leading to negative consequences for individual fitness and ecosystem function. The behavioural response of native to non-native species during novel encounters can determine the impact of non-native species, and restrict or facilitate their establishment. In this study we simulated novel encounters between a widespread invasive fish species, the Nile tilapia ( Oreochromis niloticus ), and a threatened native Manyara tilapia ( Oreochromis amphimelas ). In the first experiment single adult O. niloticus were presented with a stimulus chamber (a transparent plastic cylinder) which was empty during control trials and contained a pair of juvenile O. amphimelas in stimulus trials. In the second experiment, the reciprocal set up was used, with pairs of juvenile O. amphimelas as the focal species and adult O. niloticus as the stimulus. Both species approached the stimulus chamber more readily during stimulus trials, a behavioural response which would increase the prevalence of interspecific interactions in situ. This included physical aggression, observed from the competitively dominant O. niloticus towards O. amphimelas . Despite an initial lack of fear shown by O. amphimelas , close inspection of the stimulus chamber often resulted in an energetically costly dart response. Under field conditions we predict that naïve native individuals may readily approach O. niloticus , increasing the likelihood of interactions and exacerbating widely reported negative outcomes.
... 17,18 For many species, high densities increase stress, as is the case with Atlantic salmon (Salmo salar) resulting in increased disease susceptibility. 18 For territorial species, such as Nile tilapia (Oreochromis niloticus), high densities can lower stress, as social aggression is reduced 19 and consequently so too is disease susceptibility. 20 So, disease mitigation is critically dependent on the system and species. ...
Early and accurate diagnosis is key to mitigating the impact of infectious diseases, along with efficient surveillance. This however is particularly challenging in aquatic environments due to hidden biodiversity and physical constraints. Traditional diagnostics, such as visual diagnosis and histopathology, are still widely used, but increasingly technological advances such as portable next generation sequencing (NGS) and artificial intelligence (AI) are being tested for early diagnosis. The most straightforward methodologies, based on visual diagnosis, rely on specialist knowledge and experience but provide a foundation for surveillance. Future computational remote sensing methods, such as AI image diagnosis and drone surveillance, will ultimately reduce labour costs whilst not compromising on sensitivity, but they require capital and infrastructural investment. Molecular techniques have advanced rapidly in the last 30 years, from standard PCR through loop‐mediated isothermal amplification (LAMP) to NGS approaches, providing a range of technologies that support the currently popular eDNA diagnosis. There is now vast potential for transformative change driven by developments in human diagnostics. Here we compare current surveillance and diagnostic technologies with those that could be used or developed for use in the aquatic environment, against three gold standard ideals of high sensitivity, specificity, rapid diagnosis, and cost‐effectiveness.
