Salmon lice-induced mortality of Atlantic salmon during post-smolt migration in Norway

Abstract With different ecological characteristics amongst salmonid species, their response to parasitic infestation is likely to vary according to their spatial and temporal overlap with the parasite. This study investigated the host–parasite interactions amongst three species of salmonids and the ectoparasitic salmon louse, Lepeophtheirus salmonis. To determine any variation in infestation parameters amongst salmonids, single population groups of Atlantic salmon (Salmo salar), chinook salmon (Onchorhynchus tshawytscha), and previously-infested and naïve sea trout (Salmo trutta) were exposed to a controlled infestation challenge. We found that chinook salmon and both sea trout groups were more susceptible to acquiring lice than Atlantic salmon. Behavioural responses during infestation were more pronounced in Atlantic and chinook salmon. Parasite development was similar in lice attached to Atlantic salmon and sea trout, but hindered on chinook salmon. At 16 days post-infestation, chinook salmon had reduced lice loads to the same level as Atlantic salmon, whilst sea trout retained their lice. These results demonstrate differences in interactions with L. salmonis amongst these species, and highlight the vulnerability of sea trout to infestation.

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Estimating the temporal overlap between post-smolt migration of Atlantic salmon and salmon lice infestation pressure from fish farms

Aquaculture Environment Interactions ◽

10.3354/aei00195 ◽

2016 ◽

Vol 8 ◽

pp. 511-525 ◽

Cited By ~ 15

Author(s):

KW Vollset ◽

BT Barlaup ◽

S Mahlum ◽

PA Bjørn ◽

OT Skilbrei

Keyword(s):

Atlantic Salmon ◽

Fish Farms ◽

Salmon Lice ◽

Temporal Overlap

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Risk assessment of the environmental impact of Norwegian Atlantic salmon farming

ICES Journal of Marine Science ◽

10.1093/icesjms/fsu132 ◽

2014 ◽

Vol 72 (3) ◽

pp. 997-1021 ◽

Cited By ~ 175

Author(s):

Geir Lasse Taranger ◽

Ørjan Karlsen ◽

Raymond John Bannister ◽

Kevin Alan Glover ◽

Vivian Husa ◽

...

Keyword(s):

Risk Assessment ◽

Atlantic Salmon ◽

Viral Disease ◽

Organic Load ◽

Genetic Introgression ◽

Wild Populations ◽

Fish Farms ◽

Marine Research ◽

Salmon Farming ◽

Salmon Lice

Abstract Norwegian aquaculture has grown from its pioneering days in the 1970s to be a major industry. It is primarily based on culturing Atlantic salmon and rainbow trout and has the potential to influence the surrounding environment and wild populations. To evaluate these potential hazards, the Institute of Marine Research initiated a risk assessment of Norwegian salmon farming in 2011. This assessment has been repeated annually since. Here, we describe the background, methods and limitations of the risk assessment for the following hazards: genetic introgression of farmed salmon in wild populations, regulatory effects of salmon lice and viral diseases on wild salmonid populations, local and regional impact of nutrients and organic load. The main findings are as follows: (i) 21 of the 34 wild salmon populations investigated indicated moderate-to-high risk for genetic introgression from farmed escaped salmon. (ii) of 109 stations investigated along the Norwegian coast for salmon lice infection, 27 indicated moderate-to-high likelihood of mortality for salmon smolts while 67 stations indicated moderate-to-high mortality of wild sea trout. (iii) Viral disease outbreaks (pancreas disease, infectious pancreatic necrosis, heart and skeletal muscle inflammation, and cardiomyopathy syndrome) in Norwegian salmon farming suggest extensive release of viruses in many areas. However, screening of wild salmonids revealed low to very low prevalence of the causal viruses. (iv) From ∼500 yearly investigations of local organic loading under fish farms, only 2% of them displayed unacceptable conditions in 2013. The risk of eutrophication and organic load beyond the production area of the farm is considered low. Despite several limitations, especially limited monitoring data, this work represents one of the world’s first risk assessment of aquaculture. This has provided the Norwegian government with the basis upon which to take decisions for further development of the Norwegian aquaculture industry.

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Thermal delousing in anaesthetised small Atlantic salmon (Salmo salar) post-smolts: A case study showing the viability of anaesthesia prior to delousing for improved welfare during treatment for salmon lice

Animal Welfare ◽

10.7120/09627286.30.2.117 ◽

2021 ◽

Vol 30 (2) ◽

pp. 117-120

Author(s):

O Folkedal ◽

SO Utskot ◽

J Nilsson

Keyword(s):

Atlantic Salmon ◽

Salmo Salar ◽

Experimental Research ◽

Acute Stress ◽

Small Scale ◽

Lepeophtheirus Salmonis ◽

Salmon Lice ◽

Sequence Of Events ◽

Present Case Study

Delousing treatment for salmon sea lice (Lepeophtheirus salmonis) is considered a significant welfare concern in farming of Atlantic salmon ( Salmo salar), where both industry and legislative bodies prompt for better methods. Currently, the most common method is thermal delousing, where fish are crowded, pumped into a vessel and exposed to ∼28–34°C for ∼30 s. Physical collisions occurring as a result of a loss of behavioural control lead to acute stress. Crowding triggers vigorous escape behaviour as salmon respond not only to treatment but also to being channeled to and from the treatment zone. A sequence of events considered to cause mortality and poor welfare. The present case study was motivated by an urgent need for delousing in groups of small salmon post-smolts in experimental research. For this purpose, a simple, small-scale system for thermal delousing was constructed, including anaesthesia to alleviate behavioural responses. The anaesthetised fish showed little behavioural response to thermal treatment, strong appetite within hours, and negligible mortality. The described method is regarded as a welfare-friendly alternative to industrial delousing in smaller fish groups, for example, in experimental research. We would encourage detailed research aimed towards gaining a deeper under-standing of the welfare effects of anaesthesia prior to treatment for delousing.

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Survival and growth of sea-ranched Atlantic salmon, Salmo salar L., treated against sea lice before release

ICES Journal of Marine Science ◽

10.1016/j.icesjms.2006.04.012 ◽

2006 ◽

Vol 63 (7) ◽

pp. 1317-1325 ◽

Cited By ~ 33

Author(s):

Ove T. Skilbrei ◽

Vidar Wennevik

Keyword(s):

Atlantic Salmon ◽

Treated Group ◽

Sea Lice ◽

Control Fish ◽

Release Date ◽

The Third ◽

Salmon Lice ◽

Survival And Growth ◽

The Difference ◽

Adipose Fin

Abstract Cultured Atlantic salmon smolts were treated with Slice®, orally administered emamectin benzoate, before release in the Dale River, western Norway, to study the potential effects of sea lice during the early stages of their marine phase. In all, 10 470 treated and untreated (control) fish from ten family groups were adipose fin-clipped, coded-wire tagged, and released on three different dates in 2002 (11 May, 25 May, and 7 June), which coincided with the natural smolt run. The percentage of released smolts recaptured as one-sea-winter salmon in 2003 did not differ between the treated and untreated groups released on the two dates in May 2002, but the recapture rate of fish from the treated group released on 7 June 2002 was almost twice that of the controls. The weights of the recaptured one-sea-winter salmon tended to decline from the first to the third release date, and one-sea-winter salmon from the treated groups were approximately 15% heavier than the controls. The difference in recapture rate between the treated and untreated groups increased after inclusion of the two-sea-winter and three-sea-winter salmon recaptured in 2004 and 2005, respectively. We conclude that the infestation level of salmon lice changed from non-lethal to lethal levels during the period of the smolt migration in 2002 and that non-lethal infestation levels may adversely affect Atlantic salmon populations by reducing the growth rate of fish and, consequently, their size at spawning.

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