School of BioSciences - Research Publications
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ItemTag use to monitor fish behaviour in aquaculture: a review of benefits, problems and solutions(WILEY, 2021-06)Abstract A variety of tagging techniques are now available to monitor fish behaviour, physiology and their environmental experience. Tagging is frequently used in aquaculture research to monitor free‐swimming individuals within farmed populations. However, for information gathered from tagged fish to be representative of farmed populations, tagging must not fundamentally affect fish behaviour, physiology or survival. Here, we systematically review studies that used tags to monitor farmed fish behaviour and test factors that affect tag retrieval and tag‐related mortality. Most studies using tags assessed movement and swimming behaviour in salmonids, predominantly in Europe and North America. Mortality of tagged fish was 10 times higher in sea‐cages (mean = 25%, range = 0–61.5%, n = 22 studies) than in tanks (mean = 2.5%, range = 0–17%, n = 23 studies), while mortality of tagged fish in sea‐cages was markedly higher in longer trials (from 4% in single day trials to 36% after 100 days). Higher‐than‐usual mortality rates among tagged fish, together with largely unknown sublethal effects on behaviour, should caution against using tagging studies to make decisions related to farm management. Moreover, key metrics such as mortality rates of tagged and untagged fish or evidence of sublethal effects are often unreported. We make several recommendations to improve future tagging studies and increase transparency in reporting. A greater insight into the causes of tagged fish mortality in sea‐cages is required to secure animal welfare and data validity in studies that use tags to assess fish behaviour in aquaculture.
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ItemSentinels in Salmon Aquaculture: Heart Rates Across Seasons and During Crowding Events(FRONTIERS MEDIA SA, 2021-11-26)Advances in tag technology now make it possible to monitor the behavior of small groups of individual fish as bioindicators of population wellbeing in commercial aquaculture settings. For example, tags may detect unusual patterns in fish heart rate, which could serve as an early indicator of whether fish health or welfare is becoming compromised. Here, we investigated the use of commercially available heart rate biologgers implanted into 24 Atlantic salmon weighing 3.6 ± 0.8 kg (mean ± SD) to monitor fish over 5 months in a standard 12 m × 12 m square sea cage containing ∼6,000 conspecifics. Post tagging, fish established a diurnal heart rate rhythm within 24 h, which stabilized after 4 days. Whilst the registered tagged fish mortality over the trial period was 0%, only 75% of tagged fish were recaptured at harvest, resulting in an unexplained tag loss rate of 25%. After 5 months, tagged fish were approximately 20% lighter and 8% shorter, but of the similar condition when compared to untagged fish. Distinct diurnal heart rate patterns were observed and changed with seasonal day length of natural illumination. Fish exhibited lower heart rates at night [winter 39 ± 0.2 beats per min (bpm), spring 37 ± 0.2 bpm, summer 43 ± 0.3 bpm, mean ± SE] than during the day (winter 50 ± 0.3 bpm, spring 48 ± 0.2 bpm, summer 49 ± 0.2 bpm) with the difference between night and day heart rates near half during the summer (6 bpm) compared to winter and spring (both 11 bpm). When fish experienced moderate and severe crowding events in early summer, the highest hourly heart rates reached 60 ± 2.5 bpm and 72 ± 2.4 bpm, respectively, on the day of crowding. Here, if the negative sublethal effects on fish that carry tags (e.g., growth rate) can be substantially reduced, the ability to monitor diurnal heart rate patterns across seasons and detect changes during crowding events, and using heart rate biologgers could be a useful warning mechanism for detecting sudden changes in fish behavior in sea cages.
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ItemBehaviour in the toolbox to outsmart parasites and improve fish welfare in aquaculture(WILEY, 2019-02)Abstract Host behaviour can prevent infection and moderate the fitness of parasites. Antiparasite behaviours are prevalent in many host–parasite systems and occur over fine or broad scales. With global growth in aquaculture production and the associated proliferation of parasites in farming systems, the behaviour of the fish being farmed has seldom been investigated in relation to parasites. Epidemics and outbreaks of parasites are prevalent in most aquaculture systems, and behaviour could be harnessed in concert with current methods to prevent and control parasites and pathogens. However, this requires a systematic understanding of the behaviours of hosts, their capacity for resistance and their interaction with the environment and the parasite. Herein, we present evidence for how behaviour could be used in aquaculture, and discuss the possibility for behaviour to be used in aquaculture as (i) an indicator of welfare status, (ii) a tool in prevention or control and (iii) to maintain or improve welfare. We apply this framework to a case study of a highly problematic parasite, the salmon louse (Lepeophtheirus salmonis), on farmed Atlantic salmon (Salmo salar). We present the current state of the system, and the drawbacks of current control or prevention methods. We synergise current knowledge on host behaviours and show how behaviour could be incorporated into current and new approaches for prevention and control. Through this first evaluation of the possibilities behaviour presents in disease management, we aim to facilitate a shift in the current disease control paradigm from reactive‐based post‐infection control to pre‐infection prevention approaches.
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ItemBehaviour in Atlantic salmon confers protection against an ectoparasite(WILEY, 2018-01)Abstract Altered behaviour is believed to be the first form of defence against parasite infection, through reducing opportunity for infection or deflecting parasites to sub‐optimal sites on hosts. To determine whether the suite of behaviours fish exhibit deter or deflect infection, we tested for differences in salmon louse (Lepeophtheirus salmonis) infection level and attachment location on three groups of Atlantic salmon (Salmo salar) that were either normal, behaviourally modified via injection of ketamine hydrochloride or sham‐injected procedural controls. The frequency of behaviours differed between behaviourally modified and normal hosts, which resulted in 26–31% fewer lice in normal fish. Louse attachment locations were unaffected by behaviour. Jumping and motionless behaviours were more common and the frequency of burst swimming behaviour was reduced in non‐manipulated fish, suggesting that these behaviours restrict parasite attachment success. Our results show that the suite of fine‐scale behaviours that normal salmon display at the time of parasite encounter are associated with reduced infestation.
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ItemSusceptibility, behaviour, and retention of the parasitic salmon louse (Lepeophtheirus salmonis) differ with Atlantic salmon population origin(WILEY, 2018-03)Atlantic salmon populations across the world have diverse ecological and evolutionary histories, from wild anadromous or landlocked, to domestication and genetic modification. The natural host behaviours confer protection from infestation by ectoparasitic salmon lice Lepeophtheirus salmonis, yet whether genetic origin results in different behaviours and thus susceptibility to infestation is unknown. In common garden experiments, we tested antiparasite behaviours, susceptibility and retention of salmon lice in wild anadromous, wild landlocked, domesticated and genetically modified domesticated strains. Within domesticated strains, we tested two infestation histories (previously infested and naïve) and a new phenotype (albino colouring). Farmed stocks initially acquired 24%-44% higher levels of parasite density than the wild and landlocked strains. Burst swimming and displacement behaviours were higher in the domesticated groups, and jumping was more prevalent in the domesticated strains. At 34 days post-infestation, domesticated strains and the wild anadromous strain did not differ significantly from each other; however, landlocked salmon had increased infestation levels considerably. Domesticated strains lost ~20% (±9.9%-16.5%; 95% CI) of their initial parasite load, while parasite load increased by 5.5% (±30.1%) for wild salmon and 20.1% (±28.5%) in landlocked salmon. This study provides early evidence for diverged host-parasite interactions associated with domestication in this system.
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ItemSea lice infestation levels decrease with deeper "snorkel' barriers in Atlantic salmon sea-cages(JOHN WILEY & SONS LTD, 2017-09)
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ItemRecapturing escaped fish from marine aquaculture is largely unsuccessful: alternatives to reduce the number of escapees in the wild(Wiley, 2018-03-01)Farmed fish that escape and mix with wild fish populations can have significant ecological and genetic consequences. To reduce the number of escaped fish in the wild, recapture is often attempted. Here, we review the behaviours of escapees post‐escape, and how recapture success varies with escaped fish size, the size of the initial escape event and recapture methods. Success rates of fishing gears varied among species, with gill‐nets and coastal barrier nets most effective for recapture of salmonids. Recapture success was strongly negatively correlated with both fish size and the number of fish escaped, regardless of species. Recapture success was universally low across all studied species (8%). Numerous tracking studies of escaped fish indicate that recapture efforts should be initiated within 24 h of an escape incident for highest recapture success. However, most large escape events are due to storms, which mean recapture efforts rarely start within this timeframe. Recapture of escaped fish is broadly ineffective in marine habitats, with rare exception. High bycatch rates during ineffective recapture attempts imply that large‐scale recapture efforts should be weighed against the possibility of affecting wild fish populations negatively. We suggest three alternative approaches to reduce escapee numbers in wild habitats: (i) protect populations of predatory fish around sea‐cage farms from fishing, as they prey upon smaller escapees; (ii) construct impact offset programmes to target recapture in habitats where escapees can be efficiently caught; and (iii) ensure technical standards are legislated so that fish farmers invest in preventative technologies to minimize escapes.
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ItemEarly-stage sea lice recruits on Atlantic salmon are freshwater sensitive(WILEY, 2016-10)Sea lice are significant parasites of marine and brackish farmed fishes. Freshwater bathing is a potential control option against numerous sea lice species, although has been viewed as futile against those that are capable of tolerating freshwater for extended periods. By comparing freshwater survival times across host-attached stages of Lepeophtheirus salmonis (Krøyer), a key parasite in Atlantic salmon farming, we show the first attached (copepodid) stage undergoes 96-100% mortality after 1 h in freshwater, whereas later attached stages can tolerate up to 8 days. Thus, regular freshwater bathing methods targeting the more susceptible attached copepodid stage may successfully treat against L. salmonis and potentially other sea lice on fish cultured in marine and brackish waters.
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ItemSterilization of sea lice eggs with ultraviolet C light: towards a new preventative technique for aquaculture(JOHN WILEY & SONS LTD, 2020-03)