Using neuronal models to capture burst-and-glide motion and leadership in fish

While mathematical models, in particular self-propelled particle models, capture many properties of large fish schools, they do not always capture the interactions of smaller shoals. Nor do these models tend to account for the use of intermittent locomotion, often referred to as burst-and-glide, by many species. In this paper, we propose a model of social burst-and-glide motion by combining a well-studied model of neuronal dynamics, the FitzHugh-Nagumo model, with a model of fish motion. We first show that our model can capture the motion of a single fish swimming down a channel. Extending to a two-fish model, where visual stimulus of a neighbour affects the internal burst or glide state of the fish, we observe a rich set of dynamics found in many species. These include: leader-follower behaviour; periodic changes in leadership; apparently random (i.e. chaotic) leadership change; and tit-for-tat turn taking. Moreover, unlike previous studies where a randomness is required for leadership switching to occur, we show that this can instead be the result of deterministic interactions. We give several empirically testable predictions for how bursting fish interact and discuss our results in light of recently established correlations between fish locomotion and brain activity.

Acute noise is harmful on the anti-predator behaviour of commercially important juvenile coral reef fishes

Fish stock enhancement has been utilised in Taiwan for more than 30 years, yet the impacts of anthropogenic noise on the enhancement programs remain unknown. Anthropogenic noise can induce physiological and behavioural changes in many marine fishes. Therefore, we investigated the effects of acute boat noise (from stock enhancement release sites) and chronic noise (from aquaculture processes) on the anti-predator behaviour in three juvenile reef fishes: Epinephelus coioides, Amphiprion ocellaris and Neoglyphidodon melas. We exposed fish to aquaculture noise, boat noise and a combination of both, followed by a predator scare and documented kinematic variables (response latency, response distance, response speed and response duration). For the grouper E. coioides, their response latency decreased in the presence of acute noise, while their response duration increased in the presence of both chronic and acute noise. Among the anemonefish A. ocellaris, all variables remained unaffected by chronic noise, whereas acute noise increased the response distance and response speed. In the case of the black damselfish N. melas, chronic noise decreased the response speed, while acute noise decreased the response latency and response duration. Our results indicate that acute noise had a stronger influence on anti-predator behaviour than chronic noise. This study suggests that acute noise levels at restocking release sites can impact anti-predator behaviour in fishes, potentially altering fitness and likelihood of survival. Such negative effects and interspecific differences must be considered when restocking fish populations.

Entropy and Fractal Techniques for Monitoring Fish Behaviour and Welfare in Aquacultural Precision Fish Farming-A Review

In a non-linear system, such as a biological system, the change of the output (e.g., behaviour) is not proportional to the change of the input (e.g., exposure to stressors). In addition, biological systems also change over time, i.e., they are dynamic. Non-linear dynamical analyses of biological systems have revealed hidden structures and patterns of behaviour that are not discernible by classical methods. Entropy analyses can quantify their degree of predictability and the directionality of individual interactions, while fractal dimension (FD) analyses can expose patterns of behaviour within apparently random ones. The incorporation of these techniques into the architecture of precision fish farming (PFF) and intelligent aquaculture (IA) is becoming increasingly necessary to understand and predict the evolution of the status of farmed fish. This review summarizes recent works on the application of entropy and FD techniques to selected individual and collective fish behaviours influenced by the number of fish, tagging, pain, preying/feed search, fear/anxiety (and its modulation) and positive emotional contagion (the social contagion of positive emotions). Furthermore, it presents an investigation of collective and individual interactions in shoals, an exposure of the dynamics of inter-individual relationships and hierarchies, and the identification of individuals in groups. While most of the works have been carried out using model species, we believe that they have clear applications in PFF. The review ends by describing some of the major challenges in the field, two of which are, unsurprisingly, the acquisition of high-quality, reliable raw data and the construction of large, reliable databases of non-linear behavioural data for different species and farming conditions.

An investigation of population variation in maze exploration and its predictors in wild Trinidadian guppies (Poecilia reticulata)

Individuals often face unpredictable and harsh environments, presenting them with novel ecological problems. Behaviour can provide an adaptive response in such conditions and where these conditions vary between populations, we may predict development and evolution to shape differences in behaviour such as exploration, innovation, and learning, as well as other traits. Here, we compared in the wild the maze swimming performance of groups of female guppies from two Trinidadian populations that differ in numerous ecological characteristics, the Upper and Lower Aripo river. Compared to Upper Aripo fish, Lower Aripo fish were slower to complete the maze, our measure of propensity to innovate, and scored lower on a combined measure of activity and exploration. More active-exploratory groups were faster to complete the maze, but only in the Lower Aripo. We found no evidence for learning the maze. Our results suggest that activity-exploratory and innovative propensities can vary between populations, as can predictors of innovation. These findings are consistent with high predation risk shaping decreased activity-exploratory propensities, but further population comparisons are required to reliably determine the drivers of the observed population difference. Our results emphasize that individual and population differences in activity-exploration and innovation can be shaped by numerous factors.

Indirect predator effects influence behaviour but not morphology of juvenile coral reef Ambon damselfish Pomacentrus amboinensis

A 6-week laboratory experiment exposed juvenile Ambon damselfish Pomacentrus amboinensis to visual and chemical cues of either a predator, a herbivore or a null control (sea water) and found no effect of predator cues on prey morphology (proportion of ocellus to eye diameter, body depth, standard length and fin area). Nonetheless, behaviour was significantly affected by predator presence, with prey less active and taking half as many feeding strikes when exposed to predators compared to fish from the null control. The presence of a herbivore also affected prey behaviour similar to that of the predator, suggesting that the presence of a non-predator may have important effects on development.

Acclimation effect on fish behavioural characteristics: determination of appropriate acclimation period for different species

In the present study, the authors investigated the effect of acclimation duration (up to 4 h) on behavioural characteristics of taxonomically and functionally different fish species, i.e., the migratory rheophilic salmonids rainbow trout (Oncorhynchus mykiss) and Atlantic salmon (Salmo salar), and the non-migratory eurytopic European perch (Perca fluviatilis) and three-spined stickleback (Gasterosteus aculeatus). Specifically, the authors explored fish behavioural patterns based on specific endpoints (average, maximum and angular velocity) during the acclimation period, and determined the acclimation period suitable for the tested fish species. The performed behavioural data analysis showed that the minimum time needed to adjust fish activity to a more stable (baseline) level should be at least 2 h for O. mykiss and S. salar and 1 h for G. aculeatus. Nonetheless, P. fluviatilis behaviour did not show significant changes during the 4 h acclimation. The results of this study revealed that the effect of the acclimation duration on such rheophilic species as O. mykiss and S. salar was greater than that on the eurytopic species P. fluviatilis and G. aculeatus, indicating that acclimation period is important in managing fish stress before behavioural observations. For all species, the highest variability was found in the endpoint of maximum velocity, and the lowest in that of angular velocity. This study showed that before starting actual toxicity testing experiments, it is important to determine an appropriate, species-specific acclimation period.

Impacts of additional noise on the social interactions of a cooperatively breeding fish

Anthropogenic noise is a global pollutant known to affect the behaviour of individual animals in all taxa studied. However, there has been relatively little experimental testing of the effects of additional noise on social interactions between conspecifics, despite these forming a crucial aspect of daily life for most species. Here, we use established paradigms to investigate how white-noise playback affects both group defensive actions against an intruder and associated within-group behaviours in a model fish species, the cooperatively breeding cichlid Neolamprologus pulcher. Additional noise did not alter defensive behaviour, but did result in changes to within-group behaviour. Both dominant and subordinate females, but not the dominant male, exhibited less affiliation and showed a tendency to produce more submissive displays to groupmates when there was additional noise compared with control conditions. Thus, our experimental results indicate the potential for anthropogenic noise to affect social interactions between conspecifics and emphasize the possibility of intraspecific variation in the impacts of this global pollutant.

Leaky barriers: leaky enough for fish to pass?

Perceived as environmental-friendly hydraulic structures, leaky barriers used for natural flood management are introduced into rivers, potentially creating migration barriers for fish. Using sustainable, local materials to construct wooden barriers across river channels in upper catchments, these barriers aim to slow down the flow, reduce flood peaks and attenuate the flow reaching downstream communities. Yet little is known about their impact on hydrodynamics and fish passage. Here, we examined two model barrier designs under 100% and 80% bankfull flow conditions in an open channel flume. These barriers included a porous and a non-porous design, with the latter emulating the natural accumulation of brush, sediment and leaf material between logs over time. Flow visualization and velocity measurements recorded with acoustic Doppler velocimetry characterized the flow field upstream and downstream of the barriers. Our fish behavioural studies revealed that juvenile salmon (Salmo salar) movement between downstream and upstream sections of the flume was inhibited by barrier design rather than discharge, influencing upstream fish passage and their spatial preference, indicating the importance of barrier design criteria to facilitate fish movement.

Development of Open-Field Behaviour in the Medaka, Oryzias latipes

Simple Summary

Animal models play an important role in research on behaviour and its impairment. Fish larvae allow researchers to conduct experiments on large samples in just a few days and with small-scale experimental infrastructure, substantially increasing research output. However, several aspects of larval biology, including their behaviour, are frequently unknown. Our study has demonstrated that the most important behavioural paradigm for studying anxiety and stress in animals, the open-field test, can be used in the larvae of an important fish genetic model, the medaka. This finding will allow researchers to develop models to study anxiety and stress disorders based on medaka larvae.

Abstract

The use of juvenile and larval fish models has been growing in importance for several fields. Accordingly, the evaluation of behavioural tests that can be applied to larvae and juveniles is becoming increasingly important. We tested medaka at four different ages (1, 10, 30, and 120 dph) in the open field test, one of the most commonly used behavioural assays, to investigate its suitability for larvae and juveniles of this species. We also explored ontogenetic variation in behaviour during this test. On average, adult 120-day-old medaka showed higher locomotor activity in terms of distance moved compared with younger fish. Our analysis suggests that this effect was derived from both quantitative changes in locomotion related to the ontogenetic increase in fish size as well as qualitative changes in two aspects of locomotor behaviour. Specifically, time spent moving was similar between 1- and 10-day-old medaka, but progressively increased with development. In addition, we revealed that adult medaka showed constant levels of activity, whereas younger medaka progressively reduced their activity over the course of the entire experiment. The thigmotaxis behaviour typically used to assess anxiety in the open field test emerged at 120 days post-hatching, even though a difference in the temporal pattern of spatial preference emerged earlier, between 10 and 30 days post-hatching. In conclusion, some measures of the open field test such as total distance moved allow behavioural phenotyping in the medaka of all ages, although with some degree of quantitative and qualitative developmental variation. In contrast, immature medaka appear not to exhibit thigmotactic behaviour.

Condition-dependent responses of fish to motorboats

Anthropogenic noise is a pollutant of global concern that has been shown to have a wide range of detrimental effects on multiple taxa. However, most noise studies to-date consider only overall population means, ignoring the potential for intraspecific variation in responses. Here, we used field experiments on Australia's Great Barrier Reef to assess condition-dependent responses of blue-green damselfish (Chromis viridis) to real motorboats. Despite finding no effect of motorboats on a physiological measure (opercular beat rate; OBR), we found a condition-dependent effect on anti-predator behaviour. In ambient conditions, startle responses to a looming stimulus were equivalent for relatively poor- and good-condition fish, but when motorboats were passing, poorer-condition fish startled at significantly shorter distances to the looming stimulus than better-condition fish. This greater susceptibility to motorboats in poorer-condition fish may be the result of generally more elevated stress levels, as poorer-condition fish had a higher pre-testing OBR than those in better condition. Considering intraspecific variation in responses is important to avoid misrepresenting potential effects of anthropogenic noise and to ensure the best management and mitigation of this pervasive pollutant.

Fisheries-induced selection against schooling behaviour in marine fishes

Group living is a common strategy used by fishes to improve their fitness. While sociality is associated with many benefits in natural environments, including predator avoidance, this behaviour may be maladaptive in the Anthropocene. Humans have become the dominant predator in many marine systems, with modern fishing gear developed to specifically target groups of schooling species. Therefore, ironically, behavioural strategies which evolved to avoid non-human predators may now actually make certain fish more vulnerable to predation by humans. Here, we use an individual-based model to explore the evolution of fish schooling behaviour in a range of environments, including natural and human-dominated predation conditions. In our model, individual fish may leave or join groups depending on their group-size preferences, but their experienced group size is also a function of the preferences of others in the population. Our model predicts that industrial fishing selects against individual-level behaviours that produce large groups. However, the relationship between fishing pressure and sociality is nonlinear, and we observe discontinuities and hysteresis as fishing pressure is increased or decreased. Our results suggest that industrial fishing practices could be altering fishes' tendency to school, and that social behaviour should be added to the list of traits subject to fishery-induced evolution.

A comprehensive hypothesis on the migration of European glass eels (Anguilla anguilla)

The European eel (Anguilla anguilla) is a catadromous fish that spawns in the Sargasso Sea. As larvae, eels cross the Atlantic Ocean and reach the continental slope of Europe, where they metamorphose into post-larval glass eels. These reach the continent, where some enter fresh water, some remain in marine waters, and others move between fresh and marine waters. After 5-25 years, as adult silver eels, they migrate back from fresh water to the Sargasso Sea to spawn and die. The glass eel stage is a critical step during which the eels cross the continental shelf and recruit to estuaries, where they facultatively transition to fresh water. Extensive research has been conducted to understand the behavioural mechanisms and environmental cues that aid and guide glass eels' migration. Glass eels follow odours and salinity gradients, they avoid light, and they change orientation and depth according to the tides. Recent work revealed that European glass eels also use Earth's magnetic field and lunar cues to orient. However, while we understand many aspects of their orientation behaviour, a unifying theory describing how glass eels migrate from the continental slope to fresh water is lacking. The goal of this review is to develop a comprehensive hypothesis on the migration of European glass eels, integrating previous knowledge on their orientation behaviour with recent findings on magnetic and celestial orientation. This review follows the journey of a hypothetical glass eel, describing the nature and the role of orientation cues involved at each step. I propose that, although glass eels have the sensory capacity to use multiple cues at any given time, their migration is based on a hierarchical succession of orientation mechanisms dictated by the physical properties of the environments that they occupy: (i) lunar and magnetic cues in pelagic water; (ii) chemical and magnetic cues in coastal areas; and (iii) odours, salinity, water current and magnetic cues in estuaries.

Surgical implantation of radio tags in three eel species (Anguilla spp.) in South Africa

Studies have reported poor survival of surgically tagged freshwater fishes in warm African waters. This study aimed to assess the applicability of using radio telemetry (and surgical implantation of tags) for Anguilla spp. Nineteen yellow eels (Anguilla bengalensis, A. marmorata and A. mossambica) were surgically implanted with radio tags between October 2018 and January 2019 in the Thukela River, South Africa. Most eels were alive 6 months after tagging, and recaptured eels displayed advanced or complete healing at the incision site. Therefore, this method appears suitable for African freshwater eels.

Masking a fish's detection of environmental stimuli: application to improving downstream migration at river infrastructure

According to Signal Detection Theory, the ability to detect a stimulus (discriminability, d') is inversely related to the magnitude of internal and external noise. In this study, downstream moving brown trout Salmo trutta were used to investigate whether external hydrodynamic noise (in this case turbulence) could mask a signal that induced an unwanted response, such as rejecting accelerating velocity gradients commonly encountered at entrances to fish bypass channels. S. trutta behaviour was quantified in the absence (control) or presence of an accelerating velocity gradient created by an unconstricted or constricted channel, respectively, under two levels (low and high) of background turbulent kinetic energy (hydrodynamic noise). Experiments were conducted in an indoor recirculating flume in the dark and a range of passage metrics were quantified. Under the control condition, most (ca. 91%) S. trutta passed, usually oriented downstream (67%), with minimal delay (median 0.13 min). In comparison, fewer S. trutta (ca. 43%) passed under constricted conditions, they tended to orient facing into the flow (ca. 64%) and delay was greater (median > 20 min). When viewed from a coarse-scale perspective, discriminability of the velocity gradient was lower when turbulence was high suggesting masking of the signal occurred. However, the resulting increase in the percentage of fish that passed, decrease in time to pass and reduction in the distance at which S. trutta reacted (switched orientation) was subtle and non-significant. Despite the mixed results obtained, the use of masking to manipulate an animal's perception of environmental stimuli as a fisheries management tool is conceptually valid and the results of this experiment present a useful stepping stone for future research.

Effects of sound exposure from a seismic airgun on heart rate, acceleration and depth use in free-swimming Atlantic cod and saithe

Airguns used for offshore seismic exploration by the oil and gas industry contribute to globally increasing anthropogenic noise levels in the marine environment. There is concern that the omnidirectional, high intensity sound pulses created by airguns may alter fish physiology and behaviour. A controlled short-term field experiment was performed to investigate the effects of sound exposure from a seismic airgun on the physiology and behaviour of two socioeconomically and ecologically important marine fishes: the Atlantic cod (Gadus morhua) and saithe (Pollachius virens). Biologgers recording heart rate and body temperature and acoustic transmitters recording locomotory activity (i.e. acceleration) and depth were used to monitor free-swimming individuals during experimental sound exposures (18-60 dB above ambient). Fish were held in a large sea cage (50 m diameter; 25 m depth) and exposed to sound exposure trials over a 3-day period. Concurrently, the behaviour of untagged cod and saithe was monitored using video recording. The cod exhibited reduced heart rate (bradycardia) in response to the particle motion component of the sound from the airgun, indicative of an initial flight response. No behavioural startle response to the airgun was observed; both cod and saithe changed both swimming depth and horizontal position more frequently during sound production. The saithe became more dispersed in response to the elevated sound levels. The fish seemed to habituate both physiologically and behaviourally with repeated exposure. In conclusion, the sound exposures induced over the time frames used in this study appear unlikely to be associated with long-term alterations in physiology or behaviour. However, additional research is needed to fully understand the ecological consequences of airgun use in marine ecosystems.

The cost of infection: Argulus foliaceus and its impact on the swimming performance of the three-spined stickleback (Gasterosteus aculeatus)

For fish, there can be multiple consequences of parasitic infections, including the physical impacts on swimming and the pathological costs of infection. This study used the three-spined stickleback (Gasterosteus aculeatus) and the ectoparasitic fish louse, Argulus foliaceus, to assess both physical (including form drag and mass) and pathological effects of infection. Both sustained (prolonged swimming within an open channel flume) and burst (C-start) swimming performance were measured on individual fish before (trials 1-2) and after infection (trials 3-5). Experimental infection occurred shortly before the third trial, when the physical impacts of infection could be separated from any subsequent pathology as transmission of adult parasites causes instantaneous drag effects prior to observable pathology. Despite the relatively large size of the parasite and corresponding increase in hydrodynamic drag for the host, there were no observable physical effects of infection on either sustained or burst host swimming. By contrast, parasite-induced pathology is the most probable explanation for reduced swimming performance across both tests. All sticklebacks displayed a preference for flow refugia, swimming in low-velocity regions of the flume, and this preference increased with both flow rate and infection time. This study suggests that even with large, physically demanding parasites their induced pathology is of greater concern than direct physical impact.

Field testing a novel high residence positioning system for monitoring the fine-scale movements of aquatic organisms

Acoustic telemetry is an important tool for studying the behaviour of aquatic organisms in the wild.VEMCO high residence (HR) tags and receivers are a recent introduction in the field of acoustic telemetry and can be paired with existing algorithms (e.g. VEMCO positioning system [VPS]) to obtain high-resolution two-dimensional positioning data.Here, we present results of the first documented field test of a VPS composed of HR receivers (hereafter, HR-VPS). We performed a series of stationary and moving trials with HR tags (mean HR transmission period = 1.5 s) to evaluate the precision, accuracy and temporal capabilities of this positioning technology. In addition, we present a sample of data obtained for five European perch Perca fluviatilis implanted with HR tags (mean HR transmission period = 4 s) to illustrate how this technology can estimate the fine-scale behaviour of aquatic animals.Accuracy and precision estimates (median [5th-95th percentile]) of HR-VPS positions for all stationary trials were 5.6 m (4.2-10.8 m) and 0.1 m (0.02-0.07 m), respectively, and depended on the location of tags within the receiver array. In moving tests, tracks generated by HR-VPS closely mimicked those produced by a handheld GPS held over the tag, but these differed in location by an average of ≈9 m.We found that estimates of animal speed and distance travelled for perch declined when positional data for acoustically tagged perch were thinned to mimic longer transmission periods. These data also revealed a trade-off between capturing real nonlinear animal movements and the inclusion of positioning error.Our results suggested that HR-VPS can provide more representative estimates of movement metrics and offer an advancement for studying fine-scale movements of aquatic organisms, but high-precision survey techniques may be needed to test these systems.

The effect of hypoxia on fish schooling

Low-oxygen areas are expanding in the oceans as a result of climate change. Work carried out during the past two decades suggests that, in addition to impairing basic physiological functions, hypoxia can also affect fish behaviour. Given that many fish species are known to school, and that schooling is advantageous for their survival, the effect of hypoxia on schooling behaviour may have important ecological consequences. Here, we review the effects of hypoxia on school structure and dynamics, together with the mechanisms that cause an increase in school volume and that ultimately lead to school disruption. Furthermore, the effect of hypoxia generates a number of trade-offs in terms of schooling positions and school structure. Field observations have found that large schools of fish can exacerbate hypoxic conditions, with potential consequences for school structure and size. Therefore, previous models that predict the maximum size attainable by fish schools in relation to oxygen levels are also reviewed. Finally, we suggest that studies on the effect of hypoxia on schooling need to be integrated with those on temperature and ocean acidifications within a framework aimed at increasing our ability to predict the effect of multiple stressors of climate change on fish behaviour.This article is part of the themed issue 'Physiological determinants of social behaviour in animals'.

Sea lice infestation levels decrease with deeper 'snorkel' barriers in Atlantic salmon sea-cages

BACKGROUND

Salmon lice (Lepeophtheirus salmonis) are the most important parasites of farmed salmon. Infective larvae position themselves in the upper part of the water column to increase encounter probabilities with potential hosts. Previous studies have shown that a 'snorkel' sea-cage technology protects salmon from infection in surface waters. We tested whether deep snorkels would more effectively reduce lice infestation than shallow snorkels and still uphold adequate conditions for the fish. Five sea-cages (12 m × 12 m) each holding approximately 3000 Atlantic salmon (Salmo salar) (53 ± 10 g) were fitted with snorkels that gave protection from infection for 0, 4, 8, 12 or 16 m. We tested whether reductions in the settlement of new salmon lice copepodids were consistent among four separate infection periods.

RESULTS

Lice infestation decreased exponentially with depth in all time periods. Infection levels in shallow snorkels (0 and 4 m) were consistently 4-10 times higher than those in deep snorkels (12 and 16 m). Key welfare and production performance indices were similar across all snorkel depths.

CONCLUSION

Deeper snorkels dramatically and consistently reduced infection levels of salmon lice compared with shallow snorkels, without consequences for fish welfare and production performance. Therefore, reducing salmon sea lice encounters using a depth-based barrier is a powerful management tool for salmon farming. © 2017 Society of Chemical Industry.

Parallel and nonparallel behavioural evolution in response to parasitism and predation in Trinidadian guppies

Natural enemies such as predators and parasites are known to shape intraspecific variability of behaviour and personality in natural populations, yet several key questions remain: (i) What is the relative importance of predation vs. parasitism in shaping intraspecific variation of behaviour across generations? (ii) What are the contributions of genetic and plastic effects to this behavioural divergence? (iii) And to what extent are responses to predation and parasitism repeatable across independent evolutionary lineages? We addressed these questions using Trinidadian guppies (Poecilia reticulata) (i) varying in their exposure to dangerous fish predators and Gyrodactylus ectoparasites for (ii) both wild-caught F0 and laboratory-reared F2 individuals and coming from (iii) multiple independent evolutionary lineages (i.e. independent drainages). Several key findings emerged. First, a population's history of predation and parasitism influenced behavioural profiles, but to different extent depending on the behaviour considered (activity, shoaling or boldness). Second, we had evidence for some genetic effects of predation regime on behaviour, with differences in activity of F2 laboratory-reared individuals, but not for parasitism, which had only plastic effects on the boldness of wild-caught F0 individuals. Third, the two lineages showed a mixture of parallel and nonparallel responses to predation/parasitism, with parallel responses being stronger for predation than for parasitism and for activity and boldness than for shoaling. These findings suggest that different sets of behaviours provide different pay-offs in alternative predation/parasitism environments and that parasitism has more transient effects in shaping intraspecific variation of behaviour than does predation.

Unravelling the nocturnal appearance of bogue Boops boops shoals in the anthropogenically modified shallow littoral

In the present study the role of the nocturnal migration of bogue Boops boops shoals to anthropogenically modified shallow littoral locations was examined, evaluating four alternative hypotheses: (1) feeding, (2) reproduction, (3) attraction of B. boops to artificial light and (4) concealment in the darkness related to predation avoidance. All hypotheses apart from predation avoidance were rejected, as B. boops tended to concentrate in shaded locations of wider illuminated areas, a finding not only important concerning fish behaviour, but also with significant management implications.

Influence of depth, time and human activity on detection rate of acoustic tags: a case study on two fish farms

The detection rates of stationary acoustic transmitters deployed at three depths on two Atlantic salmon Salmo salar cage farms for c. 2 months were investigated. Deployment depth, time of day, day of the year and specific incidences at the farm substantially affected the rate of signal detection by the receiver.

Effects of acidification on olfactory-mediated behaviour in freshwater and marine ecosystems: a synthesis

For many aquatic organisms, olfactory-mediated behaviour is essential to the maintenance of numerous fitness-enhancing activities, including foraging, reproduction and predator avoidance. Studies in both freshwater and marine ecosystems have demonstrated significant impacts of anthropogenic acidification on olfactory abilities of fish and macroinvertebrates, leading to impaired behavioural responses, with potentially far-reaching consequences to population dynamics and community structure. Whereas the ecological impacts of impaired olfactory-mediated behaviour may be similar between freshwater and marine ecosystems, the underlying mechanisms are quite distinct. In acidified freshwater, molecular change to chemical cues along with reduced olfaction sensitivity appear to be the primary causes of olfactory-mediated behavioural impairment. By contrast, experiments simulating future ocean acidification suggest that interference of high CO2 with brain neurotransmitter function is the primary cause for olfactory-mediated behavioural impairment in fish. Different physico-chemical characteristics between marine and freshwater systems are probably responsible for these distinct mechanisms of impairment, which, under globally rising CO2 levels, may lead to strikingly different consequences to olfaction. While fluctuations in pH may occur in both freshwater and marine ecosystems, marine habitat will remain alkaline despite future ocean acidification caused by globally rising CO2 levels. In this synthesis, we argue that ecosystem-specific mechanisms affecting olfaction need to be considered for effective management and conservation practices.

Behavioural indicators of welfare in farmed fish

Behaviour represents a reaction to the environment as fish perceive it and is therefore a key element of fish welfare. This review summarises the main findings on how behavioural changes have been used to assess welfare in farmed fish, using both functional and feeling-based approaches. Changes in foraging behaviour, ventilatory activity, aggression, individual and group swimming behaviour, stereotypic and abnormal behaviour have been linked with acute and chronic stressors in aquaculture and can therefore be regarded as likely indicators of poor welfare. On the contrary, measurements of exploratory behaviour, feed anticipatory activity and reward-related operant behaviour are beginning to be considered as indicators of positive emotions and welfare in fish. Despite the lack of scientific agreement about the existence of sentience in fish, the possibility that they are capable of both positive and negative emotions may contribute to the development of new strategies (e.g. environmental enrichment) to promote good welfare. Numerous studies that use behavioural indicators of welfare show that behavioural changes can be interpreted as either good or poor welfare depending on the fish species. It is therefore essential to understand the species-specific biology before drawing any conclusions in relation to welfare. In addition, different individuals within the same species may exhibit divergent coping strategies towards stressors, and what is tolerated by some individuals may be detrimental to others. Therefore, the assessment of welfare in a few individuals may not represent the average welfare of a group and vice versa. This underlines the need to develop on-farm, operational behavioural welfare indicators that can be easily used to assess not only the individual welfare but also the welfare of the whole group (e.g. spatial distribution). With the ongoing development of video technology and image processing, the on-farm surveillance of behaviour may in the near future represent a low-cost, noninvasive tool to assess the welfare of farmed fish.