Thermal delousing with cold water: Effects on salmon lice removal and salmon welfare

Overton, Kathy; Oppedal, Frode; Stien, Lars Helge; Moltumyr, Lene; Wright, Daniel; Dempster, Tim

doi:10.1016/j.aquaculture.2019.02.046

Cited by 13 publications

(18 citation statements)

References 18 publications

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“… Elliott (1991) reports that for salmon parr, thermal stress due to falling temperature resulted in sudden bursts of activity followed by a coma-like state. This coma-like state was also seen in the cold-water delousing experiment by Overton et al. (2019) , but the temperature drop was here from 15 °C, and not from 8 °C as in the present study.…”

Section: Discussionsupporting

confidence: 78%

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Sudden exposure to warm water causes instant behavioural responses indicative of nociception or pain in Atlantic salmon

Nilsson

Moltumyr

Madaro

et al. 2019

Veterinary and Animal Science

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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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Section: Discussionsupporting

confidence: 78%

“…Coldwater is a new candidate method for thermal delousing ( Overton et al., 2019 ). Live chilling induces stress in salmon ( Roth, Slinde & Robb, 2006 ) and temperatures below 0 °C may be lethal ( Elliott & Elliott, 2010 ).…”

Section: Introductionmentioning

confidence: 99%

Sudden exposure to warm water causes instant behavioural responses indicative of nociception or pain in Atlantic salmon

Nilsson

Moltumyr

Madaro

et al. 2019

Veterinary and Animal Science

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“…Their impact on fish welfare have therefore been questioned. These consist of freshwater bathing, warm water dips, cold water bathing [ 13 ], use of lasers to kill individual lice on the fish, mechanical removal of parasites by soft brushes and/or high pressure pumps and deployment of cleanerfish with the farmed salmon. Overton et al [ 14 ] compared reported mortality rates associated with medicinal and non-medicinal treatments and found that thermal operations caused greatest mortality increase, followed by mechanical treatments, hydrogen peroxide treatments and then treatments with azamethiphos, deltamethrin and cypermethrin.…”

Section: Introductionmentioning

confidence: 99%

“…Preventive strategies such as synchronized fallow periods within production zones, synchronization of treatments, use of snorkel cages, functional feed, deep water feeding and plankton nets will not be addressed further in this study. In later years, concerns have been raised not only about fish wellbeing during some of these practices [ 13 – 16 ], but also that the lice may in fact adapt to these challenges as well [ 12 , 17 ] as there may be genetic variation in susceptibility, and hence survival and onward input into the gene pool [ 18 ].…”

Section: Introductionmentioning

confidence: 99%

Trends in de-lousing of Norwegian farmed salmon from 2000–2019—Consumption of medicines, salmon louse resistance and non-medicinal control methods

et al. 2020

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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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“…Those include delousing treatments such as freshwater bathing, mechanical removal, thermal treatments and laser delousing (Overton et al., 2018). Mechanical and thermal delousing (using cold or warm water) typically involves some pumping and crowding prior to the treatments, which can themselves damage the skin and the mucus layer, leading to significant physical stress (Espmark et al., 2016; Gismervik et al., 2019; Overton et al., 2019).…”

Section: Introductionmentioning

confidence: 99%

Effect of handling and crowding on the susceptibility of Atlantic salmon (Salmo salar L.) to Lepeophtheirus salmonis (Krøyer) copepodids

Delfosse

Pageat

Lafont-Lecuelle

et al. 2020

Journal of Fish Diseases

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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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Thermal delousing with cold water: Effects on salmon lice removal and salmon welfare

Cited by 13 publications

References 18 publications

Sudden exposure to warm water causes instant behavioural responses indicative of nociception or pain in Atlantic salmon

Sudden exposure to warm water causes instant behavioural responses indicative of nociception or pain in Atlantic salmon

Trends in de-lousing of Norwegian farmed salmon from 2000–2019—Consumption of medicines, salmon louse resistance and non-medicinal control methods

Effect of handling and crowding on the susceptibility of Atlantic salmon (Salmo salar L.) to Lepeophtheirus salmonis (Krøyer) copepodids

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