Egg production in the salmon louse [<i>Lepeophtheirus salmonis</i>
 (Krøyer)] in relation to origin and water temperature

Heuch, Peter Andreas; Nordhagen, Jonas; Schram, Thomas A.

doi:10.1046/j.1365-2109.2000.00512.x

Cited by 96 publications

(99 citation statements)

References 19 publications

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“…In Ireland, salmon lice from wild hosts had ca 1000 eggs brood -1 , and lice from farmed fish had ca 500 eggs brood -1 . Heuch et al (2000) found that egg strings collected from farm sites and wild salmon in different parts of Norway did not have this clear pattern, though the longest egg strings came from lice on wild fish. Following our cautionary approach, we have included the former numbers ) in the present model.…”

Section: Assumptionsmentioning

confidence: 97%

A model of salmon louse production in Norway: effects of increasing salmon production and public management measures

Heuch¹,

Mo²

2001

Dis. Aquat. Org.

127

109

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Salmon lice Lepeophtheirus salmonis Krøyer have caused disease problems in farmed Atlantic salmon Salmo salar L. since the mid-1970s in Norway. High infection intensities and premature return of wild sea trout Salmo trutta L. were first reported in 1992. Later emaciated wild Atlantic salmon smolts carrying large amounts of lice have been observed both in fjords and offshore. The Norwegian Animal Health Authority regulations to control the problem, which came into operation in 1998, included compulsory louse level monitoring in farms and maximum legal numbers of lice per fish. Here, we present a model of salmon louse egg production in Norway and show that the effect of the current public management strategy is critically dependent on the yearly increase in salmon production. This is because the infection pressure is the product of the number of fish in the system, and the number of lice per fish. Due to the much larger number of farmed than wild salmonids, it is highly likely that lice originating from farmed salmon infect wild stock. Estimated tolerance limits for wild salmonids vary widely, and the level of louse egg production in farms which would be neaded to decimate wild populations is not known. Two possible thresholds for total lice egg production are investigated: (1) 1986 to 1987 level (i.e. before adverse effects on sea trout were recorded), and (2) a level corresponding to a doubling of the estimated natural infection pressure. The farm lice per fish limits that would have to be observed to keep louse production within the 2 thresholds are calculated for the period 1986 to 2005. A steady decrease in the permitted number of lice per fish may keep the total louse production stable, but the number of salmon required for verification of lice numbers will increase as the prevalence to be verified is decreased. At threshold (2), the model estimated that lice limits should have been 0.05 louse per fish in 1999. This would require 60 fish from each pen to be collected, anaesthetised and examined for a good estimate at a confidence level of 95%. Such sample numbers are likely to be opposed by farmers. The use of national delousing programs to solve the problem is discussed.

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Section: Assumptionsmentioning

confidence: 97%

A model of salmon louse production in Norway: effects of increasing salmon production and public management measures

Heuch¹,

Mo²

2001

Dis. Aquat. Org.

127

109

View full text Add to dashboard Cite

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“…Once attached to a host, copepodids eventually develop into adults, and adult females potentially release 26 to 68 nauplii through the protruding egg sacs daily, which then are free to develop to the copepodid stage and to infect other hosts (Heuch et al 2000, á Norði et al 2016. The growth of a sea lice population has an exponential nature (Frazer et al 2012) and is generally modelled as such (Costello 2006, Krkošek et al 2010, Frazer et al 2012.…”

Section: Introductionmentioning

confidence: 99%

“…Several dispersion models have been developed which assume that the planktonic stages of the sea lice drift freely with prevailing currents close to the surface (Amundrud & Murray 2009, Adams et al 2012, Salama et al 2013, with recent works including vertical positioning as a response to environmental cues (Johnsen et al , 2016. Sea temperature is widely accepted as a basic factor influencing the growth rate of sea lice populations, as the generation time decreases with increasing temperature (Tully 1992, Heuch et al 2000. However, the relationship between temperature and the sea lice abundance is not a simple relationship, and annual peaks and troughs in the abundance of mobile L. salmonis may appear delayed compared with maximum and minimum annual temperature (Jansen et al 2012).…”

Section: Introductionmentioning

confidence: 99%

Effect of exposure on salmon lice Lepeophtheirus salmonis population dynamics in Faroese salmon farms

Patursson¹,

Simonsen²,

Visser³

et al. 2017

Aquacult. Environ. Interact.

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We assessed variations in salmon lice Lepeophtheirus salmonis population dynamics in Faroese salmon farms in relationship to their physical exposure to local circulation patterns and flushing with adjacent waters. Factors used in this study to quantify physical exposure are estimates of the freshwater exchange rate, the tidal exchange rate and dispersion by tidal currents. Salmon farms were ranked according to the rate of increase in the average numbers of salmon lice per fish. In a multiple linear regression, physical exposure together with temperature were shown to have a significant effect on the rate of lice infection. The sites with low exposure revealed higher rates of self-infection and internally driven outbreak dynamics, while high-exposure sites showed lower rates of self-infection, tending towards externally driven outbreak dynamics. The lowexposure sites also appeared to have a lower threshold of salmon stocking numbers for outbreaks of infection. The study presents a simple method of characterizing salmon farming fjords in terms of their different exposure levels and how they relate to potential self-infection at these sites.

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“…It belongs to the subclass Copepoda and has 8 developmental stages: 2 naupliar stages which disperse by drift, an infective free-swimming copepodite stage, 2 attached chalimus stages, 2 preadult stages, and the mature and reproductive stage (Heuch et al 2000, Boxaspen 2006, Hamre et al 2013). The louse is motile on the host in the preadult and mature stages.…”

Section: Introductionmentioning

confidence: 99%

Effects of salmon lice infection on the behaviour of sea trout in the marine phase

Gjelland¹,

Serra‐Llinares²,

Hedger³

et al. 2014

Aquacult. Environ. Interact.

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Salmon lice Lepeophtheirus salmonis Krøyer may affect survival and growth of anadromous salmonids through physiological stress and/or behavioural changes. Using acoustic telemetry tracking, we investigated the behaviour of 30 infected sea trout Salmo trutta throughout the summer in a fjord with very high salmon lice infection pressure. Most of the tracked sea trout adopted a movement pattern expected to suppress salmon lice infestation, as they showed a strong preference for fresh or brackish water, spending most of the time close to a river outlet or even migrating into the river. Highly infested sea trout preferred shallower depths, associated with lower salinity. The fish lost to predation stayed further away from the river outlet than nonpredated fish, and were likely subjected to a stronger infection pressure. Half of the tracked group were treated with a salmon lice prophylaxis, emamectin benzoate. The effect of treatment on infestation was monitored in a separate group held in a sea cage and found to be moderate; the mortality in this group was associated with infestation by motile lice stages. In contrast, treatment was not found to have an effect on tracked fish behaviour. It is likely that some physiological and behavioural responses to high salmon lice infection pressure may be present even after a prophylaxis treatment, in particular when the treatment is given after exposure to salmon lice infection. We conclude that increased salmon lice infection pressure associated with altered salmon farming practice may have the potential to influence the marine behaviour and growth of sea trout.

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Egg production in the salmon louse [Lepeophtheirus salmonis (Krøyer)] in relation to origin and water temperature

Cited by 96 publications

References 19 publications

A model of salmon louse production in Norway: effects of increasing salmon production and public management measures

A model of salmon louse production in Norway: effects of increasing salmon production and public management measures

Effect of exposure on salmon lice Lepeophtheirus salmonis population dynamics in Faroese salmon farms

Effects of salmon lice infection on the behaviour of sea trout in the marine phase

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