Sea Lice

The productus-group within the sea lice genus Caligus Müller, 1785 is characterised by the loss of two and the reduction or loss of the third of the three plumose setae normally carried on the posterior margin of the distal exopodal segment of the first swimming leg. We describe a new species, Caligus lethrinicola n.sp., from a lethrinid host collected in New Caledonia. We review the group and recognize 15 species as valid, including the new species. The type material of the three varieties of Caligus mauritanicus Brian, 1924 is re-examined and the var. temnodontis is here recognized as a distinct species, Caligus temnodontis Brian, 1924. The typical and miniscula varieties are recognised as synonyms of Caligus dakari van Beneden, 1892 and C. haemulonis Krøyer, 1863 respectively. Additional synonymies are proposed within the group. Supplementary observations are presented on the morphology of C. dakari, C. haemulonis and C. temnodontis. A brief differential diagnosis is presented for each of the 14 previously described valid species and a key to species has been constructed.

The ecology of infectious diseases in wild and managed salmon populations is reviewed. Few pathogens have caused significant disease epidemics in the wild, and although parasites of returning adults are best documented, diseases among parr (e.g., Gyrodactylus salaris) are probably most important. The greatest diversity of parasites is known from the marine phase but few are likely to be significant pathogens, although conclusive evidence is lacking because diseased salmon cannot be tracked. The importance of stress as an immunosuppressant of fishes in degraded habitats is discussed. In addition, releases and restocking have probably also reduced the genetic disease resistance of wild fishes. We note that myxozoans, furunculosis, G. salaris, and sea lice are the pathogens most likely to threaten wild and managed salmon stocks in future. Despite abundant research on pathogens of farmed salmon, little is known of their impact on wild or managed stocks and an adequate theoretical framew...

 The seasonal presence of Amoebic Gill Disease (AGD) in farmed Salmo salar was detected in preliminary samplings to characterize AGD in relation to other coinfections on the east coast of Chiloé Island. Histopathological and PCR analyses of gills revealed AGD and its etiological agent, Neoparamoeba perurans, in the Hueihue farm in March and April 2013. Therefore, to determine the spread of AGD in the Chilean salmon industry, data from the Passive Surveillance Program by SERNAPESCA were analyzed from 2013 to 2022. The reports of five farms with amebiasis in 2013 increased to 496 in 2022, but particularly, there was an explosive increase in the number of fish with other pathogens in their gills, due to Complex Gill Disease (CGD) sometimes concurrently occurring with AGD. The annual incidence of AGD ranged from 1 week to 37 weeks per farm as discontinuous outbreaks. Infected fish were almost all adults, with S. salar being the most affected species, with the largest production, but showing low correlations between production and the number of affected farms. Positive farms and production were reduced for Oncorhynchus kisutch, and it was almost zero in Oncorhynchus mykiss. More infected farms were identified in autumn and summer for both S. salar and O. kisutch. The impact of AGD is probably low in Chile, due to the focus on S. salar production and the continuous harvesting model. More AGD-infected farms were in insular locations compared to continental areas, more in Los Lagos rather than Aysén Region, but almost zero farms were in Magallanes. Risk factors and oceanographic characteristics that explain the occurrence of disease outbreaks are discussed, as well as gill surveillance in live fish and management methods.

Sea lice threaten the welfare of farmed Atlantic salmon and the sustainability of fish farming across the world. Chemical treatments are the major method of control but drug resistance means that alternatives are urgently needed. Selective breeding can be a cheap and effective alternative. Here, we combine experimental trials and diagnostics to provide a practical protocol for quantifying resistance to sea lice. We then combined quantitative genetics with epidemiological modelling to make the first prediction of the response to selection, quantified in terms of reduced need for chemical treatments. We infected over 1400 young fish with Lepeophtheirus salmonis , the most important species in the Northern Hemisphere. Mechanisms of resistance were expressed early in infection. Consequently, the number of lice per fish and the ranking of families were very similar at 7 and 17 days post infection, providing a stable window for assessing susceptibility to infection. The heritability of li...

Sea lice (Copepoda, Caligidae) are the most widely distributed marine pathogens in the salmon industry in the last 30 years. Caligus rogercresseyi is the most important species affecting Chile's salmon industry. Vaccines against caligid copepods have the potential to be a cost-effective means of controlling the infestation and avoid many of the disadvantages of medicine treatments. However, research in the development of such vaccines has begun only recently and approaches used thus far have met with little or no success. In the present study, we characterized a novel gene (denoted as my32) from C. rogercresseyi which has the highest identity with the Lepeophtheirus salmonis gene akirin-2. To assess the function of the gene an RNA interference experiment was developed and a reduction in the number of ectoparasites on fish in the my32-dsRNA treated group was observed. The recombinant my32 protein was used in a vaccinationchallenge trial to evaluate its ability to protect against sea lice infestations. A significant reduction in the number of parasites per fish was observed at 24 days post-challenge. These results, together with the delay observed in the development of parasites from the vaccinated group suggest that the major effect of immunization was on the second parasite generation. The results of these experiments suggest that the my32 protein may be a promising target for vaccine development to control sea lice infestations in fish.

A survey was carried out between March 2006 and February 2007 on the fecundity of Caligus rogercresseyi in four areas of Region X (Lat 42°S) in Chile. An average length of 4.83 AE 0.4 mm for gravid females and 4.78 AE 0.56 mm for males was recorded from the four areas, with no significant differences in length between sexes. Although females were largest in spring and summer, egg strings were longer and there were higher number of eggs per string in winter. The lowest salinity values were recorded in the Hornopire ´n area, which had the largest gravid females and the highest number of eggs per string during the study. The number of lice treatments showed no influence on the fecundity rate in the four areas. Prevalence and abundance of C. rogercresseyi were influenced by salinity and temperature.

Salmon aquaculture is the fastest growing industry in Norway, contributing to food security and nutrition. The industry ensures social, economic and environmentally sustainable development by utilizing natural resources efficiently. However, this industry consistently encounters challenges; idle capacity, pollution, diseases, parasites and fish escaping, to name a few. The considerably longer production cycle is largely responsible for brewing these challenges. Moreover, these limitations have elevated the concern about the significant economic losses and ecological impacts. With the current technologies, under current regulatory and ecological conditions, despite increasing salmon demand in the global market, room for industrial growth is constrained. This has led to an increase of a significant attention in the area of new technology development and new ways for sustainable expansion. A number of variables determine profitability in aquaculture, including capacity utilization, bio...

Parasitic sea lice are serious problems in aquaculture. The true cost of these parasites is unknown. We demonstrate the economic burden imposed by sea lice, so that researchers, aquatic specialists, and policy makers can approximate the economic cost of this problem and work towards developing alternative control methods.

Sea lice (Copepoda, Caligidae) are the most widely distributed marine pathogens in the salmon industry in the last 30 years. Caligus rogercresseyi is the most important species affecting Chile's salmon industry. Vaccines against caligid copepods have the potential to be a cost-effective means of controlling the infestation and avoid many of the disadvantages of medicine treatments. However, research in the development of such vaccines has begun only recently and approaches used thus far have met with little or no success. In the present study, we characterized a novel gene (denoted as my32) from C. rogercresseyi which has the highest identity with the Lepeophtheirus salmonis gene akirin-2. To assess the function of the gene an RNA interference experiment was developed and a reduction in the number of ectoparasites on fish in the my32-dsRNA treated group was observed. The recombinant my32 protein was used in a vaccinationchallenge trial to evaluate its ability to protect against sea lice infestations. A significant reduction in the number of parasites per fish was observed at 24 days post-challenge. These results, together with the delay observed in the development of parasites from the vaccinated group suggest that the major effect of immunization was on the second parasite generation. The results of these experiments suggest that the my32 protein may be a promising target for vaccine development to control sea lice infestations in fish.

prepared by Glenn paGe, andrew StaroScik JHU@ eaStern| 1101 e 33rd Street c310 | baltimore md 21218 D R A F T ACKNOWLEDGMENTS We acknowledge the many contributions of all those who participated in the process of this external assessment which featured five site visits, multiple phone calls, emails and assorted connections across a wide range of colleagues in Maine. The kindness, hospitality, honesty and warmth displayed by all serves as the foundation for this document and hopefully builds collaborative energy to help further develop the Aquaculture Research Institute at the University of Maine. Specifically, and in alphabetical order, we acknowledge the involvement of

Acetylcholinesterase (AChE) is the target of a major pesticide family, the organophosphates, which were extensively used as control agents of sea lice on farmed salmonids in the early 1990s. From the mid‐1990s the organophosphates dichlorvos and azamethiphos were seriously compromised by the development of resistance. AChE insensitive to organophosphate chemotherapeutants has been identified as a major resistance mechanism in numerous arthropod species, and in this study, target‐site resistance was confirmed in the crustacean Lepeophtheirus salmonis Krøyer isolated from several fish‐farming areas in Norway and Canada. A bimolecular rate assay demonstrated the presence of two AChE enzymes with different sensitivities towards azamethiphos, one that was rapidly inactivated and one that was very slowly inactivated. To our knowledge this is the first report of target‐site resistance towards organophosphates in a third class of arthropods, the Crustacea. Copyright © 2004 Society of Chemic...

This review surveys the available literature on the effieaey and eeotoxieology of chemotherapeutic agents for the control of sea lice (Copepoda: Caligidae) infestations in marine aquaculture. To date, treatment for the disease has relied almost exclusively on the use of the organophosphorus pesticides, trichlorfon and dichlorvos. While use of dichlorvos and trichlorfon appears to have little, if any, environmental impact, protracted use in some areas has led to reduced efficacy. Compounds proposed for sea lice control currently under field evaluation include azamethiphos (organophosphate), ivermectin (avermectin), pyrethrum (pyrethrin) and hydrogen peroxide. Although all of these eompounds are effi cacious, at present published information on marine environmental toxicology is scarce and is limited to in vitro toxieity testing. Other compounds that have been considered for sea lice control include formalin, malathion (organophosphate), earbaryl (earbamate), diflubenzuron (insect growth regulator) and natural remedies (i.e. onions and garlic). In general, formaldehyde (aldehyde), malathion and natural compounds show either poor efficacy or unsuitable therapeutic margins. Although earbaryl and diflubenzuron are both efficacious and exhibit suitable therapeutic margins, available data suggests that the compounds, due to undesirable environmental toxieologieal characteristics, would be unsuitable for sea lice control. tf I. Geographic ;iiul laxonomic dislribution of parasitic copcpods and branchiurians recorded in marine fish larming (with iclcrcncc to the genera Argulus, Caligus, Ergasilus, Lepeophtheirus and Pseudocaligus

Offshore aquaculture has gained momentum in recent years, and the production of an increasing number of marine fish species is being relocated offshore. Initially, predictions of the advantages that offshore aquaculture would present over nearshore farming were made without enough science‐based evidence. Now, with more scientific knowledge, this review revisits past predictions and expectations of offshore aquaculture. We analysed and explained the oceanographic features that define offshore and nearshore sites. Using Atlantic salmon (Salmo salar) as a case study, we focussed on sea lice, amoebic gill disease, and the risk of harmful algal blooms, as well as the direct effects of the oceanography on the health and physiology of fish. The operational and licencing challenges and advantages of offshore aquaculture are also considered. The lack of space in increasingly saturated sheltered areas will push new farms out to offshore locations and, if appropriate steps are followed, offsho...

Review of the Environmental Impacts of Salmon Farming in Scotland 02468_0001, Issue 01, 24\01\2018 P a g e | iii ii. Antimicrobial compounds; iii. Metals. d. Escapes from fish farms and potential effects on wild populations; e. Sustainability of feed suppliesincluding research on plant meal substitution; f. Emerging environmental impacts, including: i. Impact on wild wrasse; ii. Impact on marine mammals. This report was prepared for the Scottish Parliament by a group of subject experts from throughout Scotland. The review focuses on Atlantic salmon, Salmo salar. Reference to 'salmonid' is to any fish of the genera Salmo and Oncorhynchus, i.e. including species of trout and Pacific salmon. The review may be seen as an update of the "Review and Synthesis of the Environmental Impacts of Aquaculture" published in 2002, but which focuses on salmon farming only. Two main sources of evidence were consulted: -Scientific papers published after peer review; -Reports that are in the public domain and that the authors have assessed as reliable. By preference, those studies that were carried out in Scottish waters were used as evidence. However, where these were scarce, evidence has been taken from investigations of salmonid-farming in Norway, Canada, Australia, New Zealand and Chile, and in some cases, from research into the farming of other species of fin-fish in other waters. Review of the Environmental Impacts of Salmon Farming in Scotland 02468_0001, Issue 01, 24\01\2018 P a g e | x Chemicals used in bath treatments for sea lice include hydrogen peroxide, synthetic pyrethroids, and organophosphates (the latter including the widely used azamethipos). Systemic (in feed) treatments tend to be more efficient; of these, only emamectin benzoate (EMB) is currently used in Scotland. Excepting hydrogen peroxide, both bath and in-feed treatment chemicals can persist in the environment. Lice are becoming resistant to existing medicines treatments. Review of the Environmental Impacts of Salmon

This paper reports Pseudocycnus appendiculatus Heller,
1865, a previously known parasitic copepod belonging to the family
Pseudocycnidae Wilson C.B., 1922, found on the gill filaments of E.
alletteratus (Rafinesque, 1810) for the first time from the Turkish
Seas. Unlike its previous descriptions that used conventional
description techniques, in this study, we used confocal laser scanning
microscope (CLSM) for the first time to examine the morphology of
the key diagnostic characters of P. appendiculatus.

This report entails a critical review of the factual basis concerning interactions between farmed and wild salmonids as it applies to salmon lice. The report is roughly divided into three main areas/chapters. The current knowledge is summarised below along with separate conclusions for each area. Population dynamics; various factors that affect stocks of wild (anadromous) salmonids: The development on both sides of the North Atlantic Ocean show the same population trends from a geographical perspective: In recent decades the stocks of wild salmon are described as stable in northern areas and decreasing towards the south in both Europe and North America (on both sides of the North Atlantic Ocean). In large parts of the southern area of distribution, the salmon population in river systems is regarded as threatened and/or extinct. This relatively clear north-south gradient and correlation in the size of the populations of wild salmonids on such a large geographic scale suggests a common response by populations to large, global or sectorial environmental conditions (changes or variations that have an effect on population regulation of wild fish which are common and/or function the same over a large geographical area). There is increasing documentary evidence that the environmental conditions necessary for survival of anadromous salmonids during their marine life stage could explain such a correlation: Plausible explanations for population regulatory effects on such a large scale include climate changes and natural fluctuations in sea temperature that may cause fluctuations in the food availability and, consequently, of the marine survival for salmon.

Salmon production, at $17.1 billion in 2018, is the second largest component of global aquaculture by value (FAO, 2020). Although production is increasing, several issues act to limit the sustainability of this growth (Taranger et al., 2015). Sea lice are considered to have serious impacts on sustainable marine salmon aquaculture in almost all areas where salmon are farmed (Pike and Wadsworth, 1999; Jones and Beamish, 2011), and are the most focused on pathogen of salmon for scientifc research (Murray et al., 2016). Tese ectoparasitic copepods are a dominant factor in limiting the maximum sustainable biomass of farmed salmon (Taranger et al., 2015). Lice are consequently the main limiting factor for growth in the salmonid farming industry under the Norwegian 'trafc light' management system and are key considerations for salmon aquaculture planning, not only in Norway, but also in most countries with marine salmonid aquaculture. In Europe, a particular concern is the salmonid specialist Lepeophtheirus salmonis (Krøyer, 1837), but the more generalist Caligus lice species such as Caligus elongatus (von Nordmann, 1832) in the North Atlantic, C. clemensi (Parker & Margolis 1964) in Pacifc Canada and especially C. rogercresseyi (Boxshall & Bravo 2000) in Chile cause signifcant infestations on marine salmon farms (Hemmingsen et al., 2020).

prepared by Glenn paGe, andrew StaroScik JHU@ eaStern| 1101 e 33rd Street c310 | baltimore md 21218 D R A F T ACKNOWLEDGMENTS We acknowledge the many contributions of all those who participated in the process of this external assessment which featured five site visits, multiple phone calls, emails and assorted connections across a wide range of colleagues in Maine. The kindness, hospitality, honesty and warmth displayed by all serves as the foundation for this document and hopefully builds collaborative energy to help further develop the Aquaculture Research Institute at the University of Maine. Specifically, and in alphabetical order, we acknowledge the involvement of

The immune response of Atlantic salmon to sea lice has been extensively studied, but we still do not know the mechanisms by which some fish become resistant and others do not. In this study, we estimated the heritabilities of three key proteins associated with the innate immunity and resistance of Salmo salar against the sea louse Caligus rogercresseyi. In particular, we quantified the abundance of 2 pro-inflammatory cytokines, Tnfα and Il-8, and an antioxidant enzyme, Nkef, in Atlantic salmon skin and gill tissue from 21 families and 268 individuals by indirect ELISA. This covers a wide parasite load range from low or resistant (mean sea lice ± SE = 8.7 ± 0.9) to high or susceptible (mean sea lice ± SE = 43.3 ± 2.0). Our results showed that susceptible fish had higher levels of Nkef and Tnfα than resistant fish in their gills and skin, although gill Il-8 was higher in resistant fish, while no significant differences were found in the skin. Furthermore, moderate to very high heritab...

This study investigated effects of sea lice pharmaceuticals on egg-bearing deep-water shrimp (Pandalus borealis). Both mortality and sub-lethal effects (behavior, embryo development, and reproductive output) were studied for each of three pharmaceuticals alone and in different sequential combinations. The most severe effect was observed for deltamethrin where 2 h exposure to 330 times diluted treatment dose (alone and in sequential application with hydrogen peroxide and azamethiphos) induced almost 100% mortality within a few days after exposure. Similar effects were not observed for hydrogen peroxide or azamethiphos. However, sequential treatment of hydrogen peroxide and azamethiphos (2 h exposure to each pharmaceutical; 500 times dilution) resulted in >40% mortality during the first week following treatment. No sub-lethal effects or loss of eggs in female shrimp could be related to exposure to the bath treatments. Future studies should investigate potential sub-lethal effects at exposure concentrations close to the no-effect concentration.

Some polyunsaturated aldehydes (PUAs) such as 2-trans, 4-trans decadenial (A3) have a detrimental effect on the development of copepod sharmful to the salmon industrysuch as Caligus rogercresseyi (sea lice). The purpose of this study was to evaluate the potential use of A3 as a salmon feed ingredient in order to reduce reproduction of Caligus rogercresseyi in infested Atlantic salmon (Salmo salar). The toxicity of A3 was assessed histopathologically for 7 days, using intra-peritoneal injections of different doses (0, 0.24, 0.47, 2.37, 11.86, and 23.71 mg kg-1) in brain, intestine, skin, liver, and muscletissues of Salmosalar at the end of each treatment. The effect of A3 on sea lice was evaluated using 250 Atlantic salmon in an open-flow system of seawater (~13°C). The effect of the dosage in the fish diet was evaluated at two levels (9 mg kg-1 , 18 mg kg-1) and considering a control (without A3) for 4, 8, and 12 days, once the sea lice had reached maturity. As a complement, the persistent effect of diluted A3 in sea water (0.5 g L-1) was evaluated at 10, 12, and 14°C for 0, 1, 3, 6, 10, and 15 days; and the maximum persistence was found at 10 days at 10°C. The results showed that the dosages over 0.47 mg kg-1 had no toxic effect on Atlantic salmon, but induced a detrimental effect on Caligus rogercresseyi (reduction of 15% of mature females with a dose of 18 mg kg-1), which could be attributed to alterations in the embryonic development of the sea lice. A3 is a potential supplement in the diet of salmon. However, studies ofits mechanism of action should be undertaken prior to its use.

Growth in salmon aquaculture over the past two decades has raised concerns regarding the potential impacts of the industry on neighboring ecosystems and wild fish productivity. Despite limited evidence, sea lice have been identified as a major cause for the decline in some wild Pacific salmon populations on the west coast of Canada. We used sea lice count and management data from farmed and wild salmon, collected over 10 years (2007-2016) in the Muchalat Inlet region of Canada, to evaluate the association between sea lice recorded on salmon farms with the infestation levels on wild out-migrating Chum salmon. Our analyses indicated a significant positive association between the sea lice abundance on farms and the likelihood that wild fish would be infested. However, increased abundance of lice on farms was not significantly associated with the levels of infestation observed on the wild salmon. Our results suggest that Atlantic salmon farms may be an important source for the introduct...

Some polyunsaturated aldehydes (PUAs) such as 2-trans, 4-trans decadenial (A3) have a detrimental effect on the development of copepod sharmful to the salmon industrysuch as Caligus rogercresseyi (sea lice). The purpose of this study was to evaluate the potential use of A3 as a salmon feed ingredient in order to reduce reproduction of Caligus rogercresseyi in infested Atlantic salmon (Salmo salar). The toxicity of A3 was assessed histopathologically for 7 days, using intra-peritoneal injections of different doses (0, 0.24, 0.47, 2.37, 11.86, and 23.71 mg kg-1) in brain, intestine, skin, liver, and muscletissues of Salmosalar at the end of each treatment. The effect of A3 on sea lice was evaluated using 250 Atlantic salmon in an open-flow system of seawater (~13°C). The effect of the dosage in the fish diet was evaluated at two levels (9 mg kg-1 , 18 mg kg-1) and considering a control (without A3) for 4, 8, and 12 days, once the sea lice had reached maturity. As a complement, the persistent effect of diluted A3 in sea water (0.5 g L-1) was evaluated at 10, 12, and 14°C for 0, 1, 3, 6, 10, and 15 days; and the maximum persistence was found at 10 days at 10°C. The results showed that the dosages over 0.47 mg kg-1 had no toxic effect on Atlantic salmon, but induced a detrimental effect on Caligus rogercresseyi (reduction of 15% of mature females with a dose of 18 mg kg-1), which could be attributed to alterations in the embryonic development of the sea lice. A3 is a potential supplement in the diet of salmon. However, studies ofits mechanism of action should be undertaken prior to its use.

Recent recurring infestations of Sea Lice, Lepeophtheirus salmonis, on juvenile Pacific salmon (Oncorhynchus spp.) and subsequent annual declines of these stocks have made it imperative to identify the source of Sea Lice. While several studies now identify farm salmon populations as sources of Sea Louse larvae, it is unclear to what extent wild salmonid hosts also contribute Sea Lice. We measured Sea Louse numbers on adult Pink Salmon (Oncorhynchus gorbuscha) migrating inshore. We also measured Sea Louse numbers on wild juvenile Pink and Chum salmon (Oncorhynchus keta) migrating to sea before the adults returned, and as the two age cohorts mingled. Adult Pink Salmon carried an average of 9.89 (SE 0.90) gravid lice per fish, and thus were capable of infecting the adjacent juveniles. Salinity and temperature remained favourable to Sea Louse reproduction throughout the study. However, all accepted measures of Sea Louse infestation failed to show significant increase on the juvenile sal...

Thanks to Mark Lewis and the University of Alberta for contributing a research vessel, a seine net, and station fees for students. Special thanks to the Musgamagw Dzawada'enuxw Tribal Council for their continued support in funding a Musgamagw Dzawada'enuxw field technician position. Special thanks also to the Kwikwasut'inuxw Haxwa'mis Nation for allowing their dock to be used for a sea lice training session.

The association between Polysiphonia spp and ovigerous females of Caligus rogercresseyi is analysed. Females carrying egg sacs exhibited individuals of Polysiphonia spp externally attached to the cuticle of both dorsal cephalothorax and abdomen by a mounting disk without penetrating the tissues.

Sentinel Atlantic salmon, held in cages, were used to estimate the monthly infestation pressure of sea lice at 3 locations along a salmonid migration route in Loch Shieldaig, a Scottish west coast sea loch. The study lasted 30 mo, covering an entire production cycle and fallow period at nearby fish farms. A total of 5007 sea lice were sampled from 3097 sentinel fish, with over 99% of these being Lepeophtheirus salmonis. Infestation pressure was higher in cages nearer the head of the loch and the River Shieldaig estuary. Copepodids were the main infective life cycle stage, but a few (0.5% of total lice sampled) mobile pre-adult and adult stages were also found on the sentinel fish. Infestation pressure on the sentinel fish was correlated with gravid L. salmonis counts from nearby farms. However, there was no evidence that particular events, such as treatments, at the farms led directly to changes in infestation pressure. These findings suggest that, although aquaculture is a contributor of sea lice larvae into the Torridon system, further work is required to determine factors influencing the relationship between farm sea lice levels and infestation pressure in the wider environment.

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Salmon lice are a serious threat to the Norwegian salmon aquaculture industry. Salmon have been found to develop higher infestation of salmon lice at the upper parts of the water column. The use of tarpaulin skirts for shielding the upper part of a salmon cage has therefore been used as a measure for reducing the salmon lice infestation. A tarpaulin skirt will however increase the effective solidity of the net, and it is necessary to study the cage mooring loads, the net deformation and the water flow through and around the cage to prevent damage to the structures and the fish. Experiments were conducted at the North Sea Centre Flume Tank in Hirtshals, Denmark, with a model salmon cage and skirt in scale 1:17. The experiments showed that the skirt sheet on the upstream side gets increasingly pulled back and up toward the surface as currents increase, and lice are likely to pass underneath and into the cage. The mooring load on the cage was also increasing with the current speed, and approximately 40% higher than that of a cage without skirt. Due to the increase in mooring loads applied by a shielding skirt it is important to include the effects of a skirt when calculating mooring loads on a farm system.

Salmon louse Lepeophtheirus salmonis Krøyer infection levels in both wild sea trout Salmo trutta L. and sentinel Atlantic salmon Salmo salar L. smolts were investigated inside and outside a temporary protected zone with limits on fish farming in the intensively farmed Romsdalsfjord system. Wild sea trout outside the protected zone had higher prevalence and significantly higher abundances than those inside the zone. Furthermore, sentinel caged Atlantic salmon smolts confirmed significant differences in infection pressure: Eresfjord (non-farmed inner part of the protected zone) had the lowest infection risk, a moderate risk was found in Langfjord (intermediately farmed middle part of the protected zone), while Karlsøyfjord (intensively farmed area outside the protected zone) had the highest infection risk. No clear bias between the near-shore and pelagic areas of the fjord were found, although significant differences between pelagic and near-shore cages were occasionally observed. Results show that small sentinel cages can be used as an alternative method to monitor the infection pressure in a fjord system. Overall, our results indicate that wild salmonids may benefit from the protection zone. However, the infection level on wild sea trout inside the temporary protected zone was higher compared to completely farm-free fjords in Norway, and infection levels likely to have a negative physiological impact on wild sea trout were found. This may indicate that the zone is too small to have the necessary protective effect against salmon lice.

Salmon louse Lepeophtheirus salmonis Krøyer infection levels in both wild sea trout Salmo trutta L. and sentinel Atlantic salmon Salmo salar L. smolts were investigated inside and outside a temporary protected zone with limits on fish farming in the intensively farmed Romsdalsfjord system. Wild sea trout outside the protected zone had higher prevalence and significantly higher abundances than those inside the zone. Furthermore, sentinel caged Atlantic salmon smolts confirmed significant differences in infection pressure: Eresfjord (non-farmed inner part of the protected zone) had the lowest infection risk, a moderate risk was found in Langfjord (intermediately farmed middle part of the protected zone), while Karlsøyfjord (intensively farmed area outside the protected zone) had the highest infection risk. No clear bias between the near-shore and pelagic areas of the fjord were found, although significant differences between pelagic and near-shore cages were occasionally observed. Results show that small sentinel cages can be used as an alternative method to monitor the infection pressure in a fjord system. Overall, our results indicate that wild salmonids may benefit from the protection zone. However, the infection level on wild sea trout inside the temporary protected zone was higher compared to completely farm-free fjords in Norway, and infection levels likely to have a negative physiological impact on wild sea trout were found. This may indicate that the zone is too small to have the necessary protective effect against salmon lice.

The intensity and timing of infestation events of caligid copepods in wild or cultured fish populations may be predicted from previous local production of nauplius I of the parasite. However, this relationship is not well established, the spatial scales over which it operates are unclear, and the role of host reactions to the inv-ding copepodid is unknown. Rate of development (and population structure), generation time and rate and actual reproductive output are temperature-dependent. In Ireland between five and seven generations of Lepeophfheirus salmonis (Krqer) can develop annually and generation time varies from over 120 days in winter to 23 days in summer. Host reactions may affect the rate of development of the parasite but are less important than temperature. Host reactions may also cause parasite mortality, but this effect is specific for individual host parasite associations. The distribution of L. salmonis in cultured host populations is typically normal but is very over-dispersed in wild populations with heavy infestations. Parasiteinduced morphological damage to the host is correlated with physiological impacts. Physiological effects are present even when morphological damage is slight and so intermittent chemotherapeutic control of infestations cannot prevent some parasite impact from occurring. Lepeophtheirus salmonis Salmo salar X X Tully (1989); White (1940) Salmo truna X Tully et al. (1993a, 1993b) Oncorhynchus nerka X Johnson (personal comm.) Galigus elongatus Salmo salar X Tully (1989), author unpub. Melanogrammus X Neilson et al. (1987) aeglefinus X Gadus morhua Neilson et al. (1987) Sciaenops ocellatus X Landsberg et al. (199 1) Clupea harengus X MacKenzie and Morrisson (1989) Galigus epidemicus Oreochromis X Lin and Ho (in press) mossambica Caligus curtus Salmo salar X Hogans and Trudeau (1989) Caligus minimus Dicentrarchus labrax X Paperna (1 980) Galigus spinosus Senola quinqueradiata X Izawa (1969) Galigus orientalis Oncorhynchus mykiss X Urawa and Kato (199 1)

Measuring baseline cortisol in wild salmonids is problematic because of the stress induced by most capture methods. The cortisol response to different periods of con®nement stress was modelled in a laboratory population of rainbow trout [Oncorhynchus mykiss (Walbaum)]. A quadratic model was used to predict baseline (precapture) cortisol levels in these ®sh. A similar quadratic response pattern of cortisol was observed in wild sea trout (Salmo trutta L.). These were captured in timed sequences on four dates by seine netting in Clew Bay, west coast of Ireland. The estimated precapture cortisol for these ®sh indicated higher levels soon after migration to sea and a positive correlation with the level of infestation by Lepeophtheirus salmonis (Krùyer). Curvilinearity of the quadratic model was correlated with levels of lice infestation, indicating an enhanced cortisol response to con-®nement stress during capture when parasitic abundance was high. Estimated precapture cortisol for individual sea trout was positively correlated with numbers of lice although the linear regression had low predictive power. The method provides, for the ®rst time, a means to estimate baseline cortisol levels in wild salmonids, and addresses one of the most dif®cult problems in working with wild ®sh.

Variation in sensitivity of Lepeophtheirus salmonis (Krùyer) to dichlorvos in static toxicity tests was recorded on salmon farms in Ireland. Five hour LC50s ranged from 60 to 202 mg l ±1 at 15°C for ®ve farms in Autumn 1991 and 76±151 mg l ±1 at 10°C for four farms in Spring of 1992. Resistance ratios, calculated using the most sensitive sites as baseline, were low and ranged from 1.32 to 3.27 in 1991 and 1.28±1.98 in 1992. Repeat sampling on three farms in 1991 and 1992 also indicated short-term changes in sensitivity to dichlorvos within farms.

Please cite this article as: D. Price, E. Laurin, F.O. Mardones, et al., Effect of sampling time and surveillance strategy on the time to onset and magnitude of piscirickettsiosis (Piscirikettsia salmonis) outbreaks in Chilean farmed Atlantic salmon, Aquaculture (2020),

Sea lice are ectoparasites associated with wild and cultured salmonid species. In Chile, the dominant species affecting aquaculture is Caligus rogercresseyi (Boxshall & Bravo 2000), which is present in 99% of the established cultured cages, and is distributed on both salmonid and native hosts. The objective of this study was to test the hypothesis that the intra-and interspecific relationships of sea louse, C. rogercresseyi are mediated by semiochemicals, and to test the hypothesis that these chemical cues are responsible for differences in the susceptibility of the host. Our results show that an attractant effect was observed when conditioned water from Atlantic salmon, Salmo salar was used as the stimulus, indicating that adult males of C. rogercresseyi showed a preference for the host conditioned water. A repellent effect was elicited by conditioned water of the non-host, Hypsoblennius sordidus on adult males of C. rogercresseyi. Moreover, both young and adult females of C. rogercresseyi elicited an attractant response from conspecific adult males. A difference in the susceptibility of the host was observed when first generation (F1) of adult male C. rogercresseyi reared on Rainbow trout, Oncorhynchus mykiss were used in bioassays. F1 males were attracted to conditioned water of O. mykiss, but an avoidance behaviour was observed when they were stimulated by conditioned water of S. salar. In summary, our results provide evidence for the hypothesis that semiochemicals mediate the parasite-host interaction between C. rogercresseyi and S. salar similar to the relationship between Lepeophtheirus salmonis with conspecific females and host fish. Furthermore, these results support the hypothesis that semiochemicals could be involved in the difference in the susceptibility of the host.

The arthropod salmon louse (Lepeophtheirus salmonis) is a major threat to Atlantic salmon aquaculture and wild salmonids. Essentially like in monoculture, very high concentrations of susceptible hosts may result in high reproduction and severe production of waves of pests. Pest management is crucial both for fish health and protection of wild fish populations from aquaculture influence. Various methods have been utilized to control salmon lice infestations, such as pesticide use, physical treatments, construction modifications, fallowing, breeding, vaccination, and biological control. Most of the methods are partially successful, but none completely fulfills the necessary pest control strategy. Like in agriculture, lice/pest management is an arms race, but the marine environment makes it even more difficult to precisely hit the target pest and avoid unintended negative effects on general wildlife. In this study, we provide an overview of the methods and principles of salmon lice man...

Caligus rogercresseyi is a sea louse that affects salmon farming industry throughout the Southern hemisphere. In Chile, oral delivery of emamectin benzoate (EMB) to salmon was the main treatment used; however, C. rogercresseyi became resistant to EMB. The aims of this study were determine the effect of EMB on proteins involved in metabolism and drug resistance in rainbow trout (Oncorhynchus mykiss) and C. rogercresseyi. Since no commercial antibodies are available for these salmon's proteins, the expression of trout cytochrome P450 CYP2K1, CYP2M1, CYP3A and CYP3A27, and the multidrug transporters Pgp and MRP1 were investigated by semi-quantitative duplex RT-PCR. Trout specimens infested with C. rogercresseyi were medicated with EMB by a standard seven-day oral treatment in salmon farms from southern Chile, and collected between 10 and 25 days after the completion of medication. The samples examined were liver, muscle, gill, middle kidney and intestine from control and EMB treated rainbow trout, and C. rogercresseyi's total homogenates. In trout tissues most CYP and MDR gene expressions were up-regulated by EMB treatment, being MRP1 mRNA in all tissues, but particularly in the kidney and intestine, and CYP2M1 mRNA from muscle and gill, the most augmented. CYP3A, CYP3A27, CYP2K1 and Pgp mRNAs were slightly affected in the most tissues analyzed. In C. rogercresseyi minimal up-regulation of the expression for most of mRNA analyzed was observed, except for CYP2M1 mRNA, decreasing its expression by half, and CYP3A27 doubling its expression levels. Nonetheless, CYP3A mRNA expression was not detected in this parasite. These results suggest that treatment with EMB in salmon regulates the transcriptional expression of proteins involved in metabolism, distribution and elimination of endobiotics and xenobiotics, such as hormones and drugs, and even could affect the pharmacokinetics of EMB in the same treatment.

Adult Pacific salmon were captured individually during their coastal migration and examined for sea lice in two marine areas in the central coast area of British Columbia. Virtually all salmon had sea lice. Pink, chum, and sockeye salmon had average intensities ranging from 41.5 to 52.0 sea lice. Chinook and coho salmon had average intensities ranging from 16.1 to 18.5 sea lice. Chinook salmon had the lowest intensities of sea lice and the smallest number of chalimus stages. The prevalence and intensities of sea lice were similar in each study area, one of which had salmon farms and one that had no salmon farms. Lepeoptheirus salmonis were about twice as numerous as Caligus clemensi. Most C. clemensi were in the chalimus stage and most L. salmonis were in the mobile stage. Gravid female L. salmonis represented 33.3% of all mobile stages. Gravid female C. clemensi were rare. In general, two species of sea lice were observed to be a common parasite on five species of Pacific salmon in the area that contained salmon farms and the reference area that had no farms.

Current sea louse models attempt to estimate louse burdens on wild and cultured salmon by predicting the production and distribution of lice larvae and estimating the risk of transmission. While physical characteristics of water bodies and weather can be accurately modelled, many aspects of sea lice biology require further parameterization. The aims of this review are (i) to describe current knowledge regarding the production, mortality, and infectivity of planktonic sea lice larvae and (ii) to identify gaps in knowledge and suggest research approaches to filling them. Several major gaps are identified, and those likely to have the greatest impact on infection levels are (i) egg production, viability and hatching success, (ii) predation in plankton and (iii) copepodid infectivity profiles. A key problem identified in current parameter estimates is that they originate from a number of sources and have been determined using a variety of experimental approaches. This is a barrier to the provision of "best" or consensus estimates for use in modelling. Additional and more consistent data collection and experimentation will help to fill these gaps. Furthermore, coordinated international efforts are required to generate a more complete picture of sea louse infections across all regions experiencing problems with sea lice.

There is tremendous variation in life-history strategies among anadromous salmonids. Species that enter the ocean environment at small sizes (< 20 g) are likely under more physiological pressure from pathogens; however, little data is available on responses at these early stages. With this in mind, we performed salmon louse challenges with Coho salmon either immediately after seawater entry (SW; ca. 10 g) or after 30 days in SW (ca. 20 g). Irrespective of size or time in SW, parasites were rapidly rejected by the host, with > 90% of all parasites lost by 16 days post-infection (dpi). Rejection was concomitant with host epithelial granulomatous infiltrations that initially targeted the embedded frontal filament (4 dpi) and the entire parasite by 10 dpi. Illumina sequencing, followed by functional enrichment analysis, revealed a concerted defense response in the fin within 1 dpi that included multiple innate and adaptive immunity components. Strikingly, early indications of an allergictype inflammatory response were associated with chitin sensing pathways orchestrated by early overexpression of the IgE-receptor, fcer1g. Additionally, there was profound overexpression of several classes of c-type lectin receptors, including dectin-2, mincle, and dc-sign at 1 dpi onward. These profiles and upregulation of cellular effector markers were corroborated by histopathological evaluation, revealing the simultaneous presence of mast cell/eosinophilic granular cells, sacciform cells, macrophages/histiocytes, and granulocytes in fin. At 10 dpi and concurrent with parasite expulsion, there was evidence of immunoregulation in addition to tissue remodelling pathways. At 16 dpi, the response was effectively abrogated. Simultaneous profiling of the parasite transcriptome revealed early induction of chitin metabolism and immunomodulation, toxin production and ECM degradation; however, after 7 dpi, these were replaced with overexpression of stress and immune defense genes. These data present the first evidence for Coho salmon demonstrating chitin-and sugar moiety-sensing as key drivers of salmon louse rejection. Anadromous salmonids emerge as yolk-sac fry in fresh water streams and lakes but soon migrate to the marine environment to feed and grow before returning to their natal streams to spawn, and most often, die 1. This evolutionary life-history adaptation has been associated with differences in resource availability. The benefit of increased productivity in the marine environment and greater fecundity due to larger body size significantly outweigh the costs of increased mortality due to smoltification and predation 2. In the Pacific Ocean, there has been a considerable evolutionary divergence of the salmonids from a common ancestor ca. 15-20 Mya, resulting in five species of salmon. Each species has a distinct life history, physiology, and behavior 3,4. For example, despite similar biogeographic ranges, Pacific salmonids are spatially segregated within the same watershed 3,4. These differences are observed in general behavior throughout development, including the size of seawater entry 2,4. During the shift from freshwater (i.e., parr) to marine habitat (i.e., smolts), there is tremendous physiological stress on