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Walde CS, Bang Jensen B, Stormoen M, Asche F, Misund B, Pettersen JM. The economic impact of decreased mortality and increased growth associated with preventing, replacing or improving current methods for delousing farmed Atlantic salmon in Norway. Prev Vet Med 2023; 221:106062. [PMID: 37939576 DOI: 10.1016/j.prevetmed.2023.106062] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2023] [Revised: 10/27/2023] [Accepted: 10/27/2023] [Indexed: 11/10/2023]
Abstract
Impacts of salmon lice is a major concern for a sustainable production of farmed Atlantic salmon in Norway. Most treatment methods for removal of salmon lice have associated increased mortality and decreased growth in a period after delousing, which affects the profitability of the farmer, and causes poor welfare and sustainability. In addition, the variance in mortality and growth, especially after non-medicinal treatment methods, is high, which makes it hard for a farmer to decide which control measure to apply to keep lice levels below the legal limit. In this study, we have applied a stochastic partial budget approach to assess the economic impact of reducing mortality and increasing growth of farmed Atlantic salmon by preventing, replacing and improving current delousing methods in Norway. We have simulated a production cycle of two different smolt-groups to find the outcome (harvested biomass, average end weight of the salmon, number of dead fish and feed consumption) of production cycles without or with two, three or four delousing treatments in the on-growing phase at sea. The results suggest that accounting for the biological losses associated with lice treatments is important when making choices of delousing strategies. The biological costs of increased mortality and decreased growth associated with especially non-medicinal treatments are expected to be high, but varies substantially. Therefore, the economic benefit of preventing or improving can also be high. The calculations imply that salmon producers could invest a considerable amount in measures for prevention or improvement of thermal treatments before break-even. For example could a farmer use on average 535,313 €/cage/ 1-yearling production in measure to prevent four thermal treatments before it is no longer economical beneficial. Depending on the performance of the four thermal treatments a farmer could use from 319,196-737,934 €/cage/ 1-yearling production on measures of improvement. Replacing one thermal treatment with another immediate treatment method has a minor economic benefit. The results further shows that sales value and feed consumption constitutes the largest share of the change in profit between different treatment regimes. The results from this study also show that not taking into account the risk of mortality and reduced growth associated with the different treatment methods of delousing, could lead to underestimating the benefit of improving, preventing and replacing treatments.
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Affiliation(s)
| | - Britt Bang Jensen
- Norwegian Veterinary Institute, Elizabeth Stephansens vei 1, Ås 1433, Norway; National Institute of Aquatic Resources, Technical University of Denmark, Denmark
| | - Marit Stormoen
- Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Elizabeth Stephansens vei 1, Ås 1433, Norway
| | - Frank Asche
- School of Forest, Fisheries and Geomatics Sciences and Global Food Systems Institute, University of Florida, Gainesville, FL, USA; Department of Safety, Economics and Planning, University of Stavanger, Stavanger, Norway
| | - Bård Misund
- Department of Economics and Finance, University of Stavanger Business School, Stavanger, Norway
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Bui S, Madaro A, Nilsson J, Fjelldal PG, Iversen MH, Brinchman MF, Venås B, Schrøder MB, Stien LH. Warm water treatment increased mortality risk in salmon. Vet Anim Sci 2022; 17:100265. [PMID: 35898237 PMCID: PMC9309499 DOI: 10.1016/j.vas.2022.100265] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2022] [Revised: 07/11/2022] [Accepted: 07/12/2022] [Indexed: 12/03/2022] Open
Abstract
Increased temperature gave higher mortality. The fish group that was not handled had no mortality. Eye damages were more prevalent in warm water treated groups. The salmon had clear behavioural reactions to the 27 °C water despite low Δt. The behavioural reactions were less at the second treatment compared to the first.
Thermal treatment is a controversial method to control sea lice in the Atlantic salmon farming industry. This study aimed to complement the growing evidence base to document the impact of thermal treatments on salmon welfare, behaviour, physiology and health. Here, fish were treated two times (four weeks apart) for 30 s in either 27, 30, or 33 °C warm water, and parameters were compared to a procedural control (exposed to their holding temperature of 14 °C) or a negative control (where no treatments were applied). The fish had a clear behavioural response to the warm water, despite low difference between treatment and holding temperature (Δt = 13, 16 or 19 °C). Eye damages were more prevalent in the warm water treated groups than in the controls. Little difference was recorded between treatment groups in their growth and condition factor, blood plasma values, organ health, and long-term coping ability. There was, however, a significant increase in mortality as a function of temperature after the first treatment (14 °C: 6.5%, 27 °C: 5.3%, 30 °C: 12.4% and 33 °C: 18.9% mortality). The first treatment was performed only two weeks after the fish had been tagged and moved into the experimental holding tanks, while the fish had been allowed to recover for four weeks without any handling before the second treatment. The group of fish that were not subjected to any treatments (the negative control) had no mortality throughout the entire experimental period.
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Gaffney LP, Lavery JM. Research Before Policy: Identifying Gaps in Salmonid Welfare Research That Require Further Study to Inform Evidence-Based Aquaculture Guidelines in Canada. Front Vet Sci 2022; 8:768558. [PMID: 35155641 PMCID: PMC8835349 DOI: 10.3389/fvets.2021.768558] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2021] [Accepted: 11/24/2021] [Indexed: 11/30/2022] Open
Abstract
Aquaculture is a growing industry worldwide and Canadian finfish culture is dominated by marine salmonid farming. In part due to increasing public and stakeholder concerns around fish welfare protection, the first-ever Canadian Code of Practice for the Care and Handling of Farmed Salmonids was recently completed, following the National Farm Animal Care Council's (NFACC) rigorous Code development process. During this process, both the Scientific (responsible for reviewing existing literature and producing a peer-reviewed report that informs the Code) and Code Development (a diverse group of stakeholders including aquaculture producers, fish transporters, aquaculture veterinarians, animal welfare advocates, food retailers, government, and researchers) Committees identified research gaps in tandem, as they worked through the literature on salmonid physiology, health, husbandry, and welfare. When those lists are combined with the results of a public "top-of-mind" survey conducted by NFACC, they reveal several overlapping areas of scientific, stakeholder, and public concern where scientific evidence is currently lacking: (1) biodensity; (2) health monitoring and management, with a focus on sea lice infection prevention and management; (3) feed quality and management, particularly whether feed restriction or deprivation has consequences for welfare; (4) enclosure design, especially focused on environmental enrichment provision and lighting design; and (5) slaughter and euthanasia. For each of these five research areas, we provide a brief overview of current research on the topic and outline the specific research gaps present. The final section of this review identifies future research avenues that will help address these research gaps, including using existing paradigms developed by terrestrial animal welfare researchers, developing novel methods for assessing fish welfare, and the validation of new salmonid welfare indices. We conclude that there is no dearth of relevant research to be done in the realm of farmed salmonid welfare that can support crucial evidence-based fish welfare policy development.
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Affiliation(s)
- Leigh P. Gaffney
- National Animal Welfare Representative, Code Development Committee (NFACC) for the Code of Practice for the Care and Handling of Farm Animal Care Council (NFACC), Ottawa, ON, Canada
- Department of Biology, University of Victoria, Victoria, BC, Canada
| | - J. Michelle Lavery
- Scientific Committee (NFACC) for the Code of Practice for the Care and Handling of Farmed Salmonids, National Farm Animal Care Council (NFACC), Ottawa, ON, Canada
- Department of Integrative Biology, University of Guelph, Guelph, ON, Canada
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Medaas C, Lien ME, Gismervik K, Kristiansen TS, Osmundsen T, Størkersen KV, Tørud B, Stien LH. Minding the Gaps in Fish Welfare: The Untapped Potential of Fish Farm Workers. JOURNAL OF AGRICULTURAL & ENVIRONMENTAL ETHICS 2021; 34:29. [PMID: 34602834 PMCID: PMC8475820 DOI: 10.1007/s10806-021-09869-w] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Accepted: 09/10/2021] [Indexed: 06/13/2023]
Abstract
The welfare of farmed fish is often regarded with less concern than the welfare of other husbandry animals, as fish are not universally classified as sentient beings. In Norway, farmed fish and other husbandry animals are legally protected under the same laws. Additionally, the legislature has defined a number of aquaculture-specific amendments, including mandatory welfare courses for fish farmers who have a key role in securing animal welfare, also with regards to noting welfare challenges in the production process. This article uses fish welfare courses as a site from which to inquire about the common-sense understanding of fish welfare in Norwegian fish farming. The focus is specifically on fish farm employees, their experiences of welfare-related issues and contradictions in their daily work, and the struggle to act responsibly in aquaculture settings. Through participant observation at welfare courses, as well as interviews and conversations with fish farm workers, the article details how challenges are experienced 'on the ground', and suggests how fish farm workers' own experiential knowledge might be mobilized to improve the general welfare of farmed fish.
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Affiliation(s)
- Christian Medaas
- Department of Social Anthropology, University of Oslo, Oslo, Norway
| | - Marianne E. Lien
- Department of Social Anthropology, University of Oslo, Oslo, Norway
| | | | | | | | | | - Brit Tørud
- Norwegian Veterinary Institute, Oslo, Norway
| | - Lars Helge Stien
- Research Group Animal Welfare, Institute of Marine Research, Bergen, Norway
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Oliveira VHS, Dean KR, Qviller L, Kirkeby C, Bang Jensen B. Factors associated with baseline mortality in Norwegian Atlantic salmon farming. Sci Rep 2021; 11:14702. [PMID: 34282173 PMCID: PMC8289829 DOI: 10.1038/s41598-021-93874-6] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2020] [Accepted: 06/30/2021] [Indexed: 12/12/2022] Open
Abstract
In 2019, it was estimated that more than 50 million captive Atlantic salmon in Norway died in the final stage of their production in marine cages. This mortality represents a significant economic loss for producers and a need to improve welfare for farmed salmon. Single adverse events, such as algal blooms or infectious disease outbreaks, can explain mass mortality in salmon cages. However, little is known about the production, health, or environmental factors that contribute to their baseline mortality during the sea phase. Here we conducted a retrospective study including 1627 Atlantic salmon cohorts put to sea in 2014-2019. We found that sea lice treatments were associated with Atlantic salmon mortality. In particular, the trend towards non-medicinal sea lice treatments, including thermal delousing, increases Atlantic salmon mortality in the same month the treatment is applied. There were differences in mortality among production zones. Stocking month and weight were other important factors, with the lowest mortality in smaller salmon stocked in August-October. Sea surface temperature and salinity also influenced Atlantic salmon mortality. Knowledge of what affects baseline mortality in Norwegian aquaculture can be used as part of syndromic surveillance and to inform salmon producers on farming practices that can reduce mortality.
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Affiliation(s)
| | | | - Lars Qviller
- Norwegian Veterinary Institute, 1433, Ås, Norway
| | - Carsten Kirkeby
- Department of Veterinary and Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, 1870, Frederiksberg, Denmark
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Sviland Walde C, Bang Jensen B, Pettersen JM, Stormoen M. Estimating cage-level mortality distributions following different delousing treatments of Atlantic salmon (salmo salar) in Norway. JOURNAL OF FISH DISEASES 2021; 44:899-912. [PMID: 33606885 DOI: 10.1111/jfd.13348] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/23/2020] [Revised: 01/22/2021] [Accepted: 01/24/2021] [Indexed: 06/12/2023]
Abstract
This retrospective descriptive study estimates cage-level mortality distributions after six immediate delousing methods: thermal, mechanical, hydrogen peroxide, medicinal, freshwater and combination of medicinal treatments. We investigated mortality patterns associated with 4 644 delousing treatment of 1 837 cohorts of farmed Atlantic salmon (Salmo salar) stocked in sea along the Norwegian coast between 2014 and 2017. The mortality is expressed as mortality rates. We found distributions of delta mortality rate within 1, 7 and 14 days after all six delousing treatments, using mortality rate within 7 days before treatments as baseline. The results show that we can expect increased mortality rates after all six delousing methods. The median delta mortality rates after thermal and mechanical delousing are 5.4 and 6.3 times higher than medicinal treatment, respectively, for the 2017 year-class. There is a reduction in the delta median mortality for thermal and freshwater delousing from 2015 to 2019. There is a wide variability in the mortality rates, in particular for thermal delousing. Our results suggest that the variability in delta mortality for thermal delousing has been reduced from the 2014 to 2017 year-class, indicating an improvement of the technique. However, a significant increase in the number of thermal treatments from 14 in 2015 to 738 in 2018 probably contributes to the overall increased mortality in Norwegian salmon farming.
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Affiliation(s)
| | | | | | - Marit Stormoen
- Department of Production Animal Clinical Sciences, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Oslo, Norway
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Delfosse C, Pageat P, Lafont‐Lecuelle C, Asproni P, Chabaud C, Cozzi A, Bienboire‐Frosini C. Effect of handling and crowding on the susceptibility of Atlantic salmon (Salmo salar L.) to Lepeophtheirus salmonis (Krøyer) copepodids. JOURNAL OF FISH DISEASES 2021; 44:327-336. [PMID: 33112458 PMCID: PMC7894147 DOI: 10.1111/jfd.13286] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/07/2020] [Revised: 09/26/2020] [Accepted: 09/29/2020] [Indexed: 05/08/2023]
Abstract
Lepeophtheirus salmonis is an ectoparasite causing economic concerns in Atlantic salmon farming. Salmon lice infestation management methods can be stressful and impact fish welfare. This work investigated the stress effect on the attachment of L. salmonis copepodids to Atlantic salmon through two approaches: (a) handling by netting and air exposure (acute stress), and (b) crowding with restricted surface access in a tank (chronic stress). In the first experiment, we compared the number of attached L. salmonis and cortisol levels between a group of handled salmon and a control group. In the second experiment, a group of densely packed salmon was compared to a control group based on the number of attached copepodids, cortisol levels and neutrophil:lymphocyte ratios. Handled salmon showed significantly higher plasma cortisol levels (p < .001) and more attached copepodids (p = .01) than control salmon. Conversely, the cortisol level and number of attached copepodids were not significantly different between the densely packed and control salmon (p > .05). The neutrophil:lymphocyte ratio was significantly higher (p = .0014) in the densely packed salmon than in the control salmon. Handling salmon increased their risk of infestation by L. salmonis. This has implications for reinfestation rates following delousing treatments in commercial salmon aquaculture, which often involve crowding and handling salmon.
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Affiliation(s)
- Cyril Delfosse
- Research Institute in Semiochemistry and Applied Ethology (IRSEA)AptFrance
- IRSEA‐ARCDaugstadNorway
| | - Patrick Pageat
- Research Institute in Semiochemistry and Applied Ethology (IRSEA)AptFrance
- IRSEA‐ARCDaugstadNorway
| | | | - Pietro Asproni
- Research Institute in Semiochemistry and Applied Ethology (IRSEA)AptFrance
| | - Camille Chabaud
- Research Institute in Semiochemistry and Applied Ethology (IRSEA)AptFrance
- IRSEA‐ARCDaugstadNorway
| | - Alessandro Cozzi
- Research Institute in Semiochemistry and Applied Ethology (IRSEA)AptFrance
- IRSEA‐ARCDaugstadNorway
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Myhre Jensen E, Horsberg TE, Sevatdal S, Helgesen KO. Trends in de-lousing of Norwegian farmed salmon from 2000-2019-Consumption of medicines, salmon louse resistance and non-medicinal control methods. PLoS One 2020; 15:e0240894. [PMID: 33119627 PMCID: PMC7595418 DOI: 10.1371/journal.pone.0240894] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2020] [Accepted: 10/01/2020] [Indexed: 12/02/2022] Open
Abstract
The salmon louse Lepeophtheirus salmonis has been a substantial obstacle in Norwegian farming of Atlantic salmon for decades. With a limited selection of available medicines and frequent delousing treatments, resistance has emerged among salmon lice. Surveillance of salmon louse sensitivity has been in place since 2013, and consumption of medicines has been recorded since the early 80’s. The peak year for salmon lice treatments was 2015, when 5.7 times as many tonnes of salmonids were treated compared to harvested. In recent years, non-medicinal methods of delousing farmed fish have been introduced to the industry. By utilizing data on the annual consumption of medicines, annual frequency of medicinal and non-medicinal treatments, the aim of the current study was to describe the causative factors behind salmon lice sensitivity in the years 2000–2019, measured through toxicity tests–bioassays. The sensitivity data from 2000–2012 demonstrate the early emergence of resistance in salmon lice along the Norwegian coast. Reduced sensitivity towards azamethiphos, deltamethrin and emamectin benzoate was evident from 2009, 2009 and 2007, respectively. The annual variation in medicine consumption and frequency of medicinal treatments correlated well with the evolution in salmon louse sensitivity. The patterns are similar, with a relatively small response delay from the decline in the consumption of medicines in Norway (2016 and onward) to the decline in measured resistance among salmon louse (2017 and onward). 2017 was the first year in which non-medicinal treatments outnumbered medicinal delousing treatments as well as the peak year in numbers of cleanerfish deployed. This study highlights the significance of avoiding heavy reliance on a few substance groups to combat ectoparasites, this can be a potent catalyst for resistance evolution. Further, it demonstrates the importance of transparency in the global industry, which enables the industry to learn from poor choices in the past.
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Affiliation(s)
- Elena Myhre Jensen
- Faculty of Veterinary Medicine, Sea Lice Research Center, Norwegian University of Life Sciences (NMBU), Oslo, Norway
- * E-mail:
| | - Tor Einar Horsberg
- Faculty of Veterinary Medicine, Sea Lice Research Center, Norwegian University of Life Sciences (NMBU), Oslo, Norway
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Coates A, Phillips BL, Oppedal F, Bui S, Overton K, Dempster T. Parasites under pressure: salmon lice have the capacity to adapt to depth-based preventions in aquaculture. Int J Parasitol 2020; 50:865-872. [PMID: 32652129 DOI: 10.1016/j.ijpara.2020.05.009] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2020] [Revised: 05/04/2020] [Accepted: 05/12/2020] [Indexed: 10/23/2022]
Abstract
The evolution of pesticide resistance has driven renewed interest in non-chemical pest controls in agriculture. Spatial manipulations (physical barriers and fallowing, for example) can be an effective method of prevention, but these too might impose selection and cause rapid adaptation in pests. In salmon aquaculture, various non-chemical approaches have emerged to combat parasitic salmon lice (Lepeophtheirus salmonis) - a major pest with clear signs of evolved chemical resistance. 'Depth-based' preventions, now widely implemented, reduce infestation rates by physically segregating salmon from lice in their infective copepodid stage occurring in surface waters. Copepodids distributed deeper in the water column, however, can bypass these barriers and infest farms. If swimming depth is a heritable trait, we may see rapid evolutionary shifts in response to widespread depth-based prevention. We collected lice from Norwegian salmon farms and assayed more than 11,250 of their laboratory-reared offspring across 37 families. The vertical distributions of copepodids were measured using experimental water columns pressurised to simulate conditions at 0, 5 and 10 m depths. We demonstrated that lice respond strongly to hydrostatic pressure: an increase in pressure doubled the number of lice that migrated to the top of columns. There was also a large effect of family on this response, with the percentage of lice ascending to the top of pressurised columns ranging from 17 to 79% across families. Families with a weak swimming response to pressure are expected to occur deeper in the water column and so be more likely to infest farms employing depth-based preventions. If this between-family variation reflects genetic variation, then the parasite population may have the capacity to adapt to preventative measures. Such adaptation would have important commercial and ecological implications.
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Affiliation(s)
- Andrew Coates
- Sustainable Aquaculture Laboratory - Temperate and Tropical (SALTT), School of BioSciences, University of Melbourne, Victoria 3010, Australia; Spatial Ecology and Evolution Lab (SpEEL), School of BioSciences, University of Melbourne, Victoria 3010, Australia
| | - Ben L Phillips
- Spatial Ecology and Evolution Lab (SpEEL), School of BioSciences, University of Melbourne, Victoria 3010, Australia
| | - Frode Oppedal
- Institute of Marine Research, Matre Aquaculture Research Station, 5984 Matredal, Norway
| | - Samantha Bui
- Institute of Marine Research, Matre Aquaculture Research Station, 5984 Matredal, Norway
| | - Kathy Overton
- Sustainable Aquaculture Laboratory - Temperate and Tropical (SALTT), School of BioSciences, University of Melbourne, Victoria 3010, Australia
| | - Tim Dempster
- Sustainable Aquaculture Laboratory - Temperate and Tropical (SALTT), School of BioSciences, University of Melbourne, Victoria 3010, Australia.
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Nilsson J, Moltumyr L, Madaro A, Kristiansen TS, Gåsnes SK, Mejdell CM, Gismervik K, Stien LH. Sudden exposure to warm water causes instant behavioural responses indicative of nociception or pain in Atlantic salmon. Vet Anim Sci 2019; 8:100076. [PMID: 32734093 PMCID: PMC7386744 DOI: 10.1016/j.vas.2019.100076] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2019] [Revised: 07/05/2019] [Accepted: 09/25/2019] [Indexed: 11/16/2022] Open
Abstract
Thermal treatment has become the most used delousing method in salmonid aquaculture. However, concerns have been raised about it being painful for the fish. We studied the behavioural response of Atlantic salmon acclimated to 8 °C when transferred to temperatures in the range 0-38 °C. Exposure time was 5 min or until they reached the endpoint of losing equilibrium and laying on their side, a sign of imminent death. At temperatures below 28 °C, none of the fish reached endpoint within the 5-min maximum. At 28 °C four of five fish reached endpoint, and fish reached endpoint more rapidly as temperature increased further. Fish transferred to temperatures above 28 °C had higher swimming speed immediately after transfer and maintained a high swimming speed until just before loss of equilibrium. Their behaviour was from the start characterised by collisions into tank walls and head shaking. Just before loss of equilibrium they started breaking the surface of the water, swimming in a circle pattern and in some instances displayed a side-wise bending of their body. In other words, salmon transferred to temperatures above 28 °C showed instant behavioural responses indicative of nociception or pain.
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Affiliation(s)
- Jonatan Nilsson
- Institute of Marine Research, P.O. Box 1870 Nordnes, NO-5817 Bergen, Norway
| | - Lene Moltumyr
- Institute of Marine Research, P.O. Box 1870 Nordnes, NO-5817 Bergen, Norway
| | - Angelico Madaro
- Institute of Marine Research, P.O. Box 1870 Nordnes, NO-5817 Bergen, Norway
| | | | | | | | | | - Lars Helge Stien
- Institute of Marine Research, P.O. Box 1870 Nordnes, NO-5817 Bergen, Norway
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