Salmon Aquaculture Industry Research Articles

Price Dynamics in Biological Production Processes Exposed to Environmental Shocks

AbstractThis paper demonstrates a mechanism by which environmental shocks in biological production processes can lead to extreme price movements and thus be a contributing factor to short‐term food price volatility. In biological production processes, environmental shocks can lead to a stock‐out when the harvest transitions to a new stock (year class) with a different marginal value. The result in the market is a temporary price spike, or bubble, bounded by the marginal value of the new stock. We highlight this phenomenon in a cohort, or year class, biological production setting. Each year class in the model is a finite “non‐renewable” capital stock, and capital theory is used to solve for the stochastic dynamic competitive equilibrium. The model is parameterized to be representative of the Norwegian salmon aquaculture industry. Results suggest that the model can replicate much of the observed patterns in price, harvest, and capital stock dynamics, including the infrequent occurrence of extremely high prices in the market.

Overview of infectious salmon anaemia virus (ISAV) in Atlantic Canada and first report of an ISAV North American-HPR0 subtype.

The infectious salmon anaemia virus (ISAV) is an important viral disease of farmed Atlantic salmon that has caused considerable financial losses for salmon farmers around the world, including Atlantic Canada. It is listed as a notifiable disease by the World Organization for Animal Health, and to this day, culling of infected cages or farms remains the current practice in many countries to mitigate the spread of the virus. In Atlantic Canada, ISAV was first detected in 1996 and continues to be detected. While some outbreaks seemed to have arisen from isolated infections of unknown source, others were local clusters resulting from horizontal spread of infection. This study provides a description of the detected ISAV isolates in Atlantic Canada between 2012 and 2016, and explores the phylogenetic relatedness between these ISAV isolates. A key finding is the detection for the first time of a North American-HPR0 ISAV subtype, which was predicted to exist for many years. Through phylogenetic analysis, a scenario emerges with at least three separate incursions of ISAV in Atlantic Canada. An initial ISAV introduction follows a genotypic separation between North America and Europe which resulted in the NA and EU genotypes known today; this separation predates the salmon aquaculture industry. The second incursion of ISAV from Europe to North America led to a sublineage in Atlantic Canada consisting of EU-HPR∆ isolates detected in Nova Scotia and New Brunswick, and the predominant form of ISAV-HPR0 (EU). Finally, we observed what could be the third and most recent incursion of ISAV in Newfoundland, in the form of an isolate highly similar to ISAV EU-HPR0 isolates found in the Faroe Islands and the one isolate from Norway.

Genotyping of Tenacibaculum maritimum isolates from farmed Atlantic salmon in Western Canada.

Mouthrot infections (bacterial stomatitis) have a significant impact on the Atlantic salmon aquaculture industry in Western Canada due to economic losses and fish welfare. Bacteria isolated from lesions in the field have been identified as Tenacibaculum maritimum. Mouthrot is different to classical tenacibaculosis, which is most commonly associated with ulcerative lesions, frayed fins and tail rot. The marine fish pathogen T.maritimum is found worldwide; however, in Western Canada, the knowledge of the genetic profile of T.maritimum is limited. This study looked at increasing this knowledge by genotyping T.maritimum isolates collected from Atlantic salmon from farms in Western Canada. These genotypes were compared to other species of the genus Tenacibaculum, as well as other known sequence types within the species. The Western Canadian isolates belong to two new sequence types within the T.maritimum species. Phylogenetic analysis shows that the isolates form a distinct branch together with T.maritimum NCIMB 2154T separate from other Tenacibaculum type strains, and they are most closely related to strains from Norway and Chile.

Ploidy elicits a whole-genome dosage effect: growth of triploid Atlantic salmon is linked to the genetic origin of the second maternal chromosome set

BackgroundThe Atlantic salmon aquaculture industry is investigating the feasibility of using sterile triploids to mitigate genetic interactions with wild conspecifics, however, studies investigating diploid and triploid performance often show contrasting results. Studies have identified dosage and dosage-compensation effects for gene expression between triploid and diploid salmonids, but no study has investigated how ploidy and parent-origin effects interact on a polygenic trait in divergent lines of Atlantic salmon (i.e. slow growing wild versus fast growing domesticated phenotype). This study utilised two experiments relating to the freshwater growth of diploid and triploid groups of pure wild (0% domesticated genome), pure domesticated (100% domesticated genome), and F1 reciprocal hybrid (33%, 50% or 66% domesticated genome) salmon where triploidy was either artificially induced (experiment 1) or naturally developed/spontaneous (experiment 2).ResultsIn both experiments, reciprocal hybrid growth was influenced by the dosage effect of the second maternal chromosome, with growth increasing as ploidy level increased in individuals with a domesticated dam (from 50% to 66% domesticated genome), and the inverse in individuals with a wild dam (from 50% to 33% domesticated genome).ConclusionsWe demonstrate that the combined effect of ploidy and parent-origin on growth, a polygenic trait, is regulated in an additive pattern. Therefore, in order to maximise growth potential, the aquaculture industry should consider placing more emphasis on the breeding value of the dam than the sire when producing triploid families for commercial production.

Accountability as a Governance Paradox in the Norwegian Salmon Aquaculture Industry

The aquaculture industry in Norway currently represents 60% (US$ 5.4 billion) of Norwegian seafood exports. Of these, farmed Atlantic Salmon (Salmo salar) represents over 80% (850,000 tonnes). These production levels are driven by a strong and growing demand for farmed fish, and has a stated political goal of increased growth by a factor of 5 by 2050 in Norway alone. However, growth is potentially more challenging without the public support and trust in the governance regime that regulates the industry. The theoretical framework of this paper rests on accountability theory, whereby the research team highlighted and tested the paradox between the ideal and the actual practices on a group of stakeholders representing the aquaculture industry and municipal, regional and sector management in northern Norway relative to their interactions and need thereof – versus the expectations of the public. The findings of a workshop were used to develop a conceptual model and test our theory on stakeholder driven future scenarios using a combination of systems thinking and fuzzy cognitive mapping. We found that stakeholders and management alike in a workshop setting valued flexibility of legislation and expert opinions highly, whereby regulatory standardization is not prioritized – in line with soft accountability. The industry acknowledged, though, that the public perception and negative media attention of the industry, in turn depended on hard accountability.

Factors influencing the long-term dynamics of larval sea lice density at east and west coast locations in Scotland

Sea lice (Copepoda: Caligidae) are marine copepods that parasitize finfish, and in cases of high infestation can result in severe epithelial damage and mortality. In Scotland, 2 species of sea louse, Lepeophtheirus salmonis and Caligus elongatus, pose a significant economic burden to the marine Atlantic salmon aquaculture industry and potentially impact wild salmonids. The purpose of this study was to determine how the density of pelagic sea lice is affected by external variables, in order to improve our understanding of sea lice dynamics. Long-term data from 2 sampling sites on the east and west coasts of Scotland were modelled independently in conjunction with environmental and anthropogenic variables. Statistical analysis identified that at the east coast site, the most influential factor affecting lice density was salinity. On the west coast, salinity, rainfall and farmed salmon production year were most influential. Molecular and morphological techniques also showed that the individuals recorded on the east coast were C. elongatus, a generalist copepod parasite, whereas only the salmonid-specific L. salmonis were found on the west. These results reiterate the role of environmental factors in influencing sea lice dynamics, and that salmonids are the primary hosts of sea lice on the west coast, but there could be non-salmonid host species as well as salmonid species influencing east coast sea lice densities.

Assessing swimming capacity and schooling behaviour in farmed Atlantic salmon Salmo salar with experimental push-cages

The Atlantic salmon aquaculture industry is expanding to more exposed locations that often are characterized by occasional very strong currents. This necessitates new guidelines concerning acceptable animal welfare and a need for fundamental ethological knowledge in these high energy environments. To assess the critical current velocity in growing Atlantic salmon during commercially relevant conditions, a push-cage setup was constructed, which allowed for the exposure of an entire stocked sea cage to controlled current velocities generated by a fixated ship. Three replicates of a critical swim speed trial were made each containing approximately 1500 novel adult Atlantic salmon (3.4kg). At 125cms−1 (1.97BLs−1) fish would start to become fatigued meaning that short durations of currents at or above this magnitude in an exposed setting would be detrimental to animal welfare. Furthermore, the normal circular schooling pattern started to become disrupted at current velocities of 30–35cms−1, and above 45–65cms−1 all fish would stand on current evenly spread out in the entire sea cage. This change from a voluntary cruising speed at low currents to a swimming speed solely dictated by the environment at intermediate to high currents could become a significant stress factor if chronically exposed. Regarding welfare guidelines in exposed aquaculture, it is therefore important to both consider the magnitude and duration of current velocities when moving to new locations. Technological solutions in current damping through sea cages could potentially mitigate these challenges.

The rise of fish oil: From feed to human nutritional supplement

ABSTRACTThis article tells the story of how fish oil has gone from an inferior to a premium oil product. With the growth of aquaculture, fish oil became a valuable feed component. Its value increased further as the belief in the health benefit of Omega-3 opened the market for direct human consumption through nutritional supplements. Strong demand, limited supply growth and weaker substitution between Omega-3 and Omega-6 has led to diverging trends between fish oil and vegetable oil prices, with fish oil now a premium oil product. We also investigated how the salmon aquaculture industry has responded to the challenge of rising fish oil prices. Concerted effort in nutrition and feed research is shown to have allowed a reduction in the share of fish oil in feed from around 25% in the early 2000s to around 12% today. This substitution effort has allowed salmon production to grow without using substantially more fish oil.

Potential environmental risks associated with biofouling management in salmon aquaculture

The accumulation of biofouling organisms on farm infrastructure is an on-going problem for the global salmon aquaculture industry. Most salmon farmers in production regions worldwide undertake regular in situ net cleaning using specialised high-pressure washing rigs. Generally, the material removed from the net during cleaning is discharged into the surrounding environment. This 'cleaning waste' consists predominantly of biofouling organisms (intact and fragmented), but may also contain fish pathogens and antifouling coating particles containing bio- cides. The suspension, dispersal and deposition of this material are associated with a range of potential risks that can be grouped into 4 main categories: (1) health or disease risks (e.g. direct damage to sensitive tissues upon contact with cleaning waste, and facilitation of infection by patho gens); (2) deposition and pollution risks (impact on benthic communities around farms through deposition of organic material and antifouling biocides); (3) invasive species risks (localised dispersal of non-indigenous propagules and fragments); and (4) biofouling exacerbation (e.g. 'self-seeding' of downstream production cages). Here, we describe and discuss these 4 potential risks associated with in situ cleaning and present an agenda and research priorities to better understand and manage these risks.

Sex-biased gene expression and sequence conservation in Atlantic and Pacific salmon lice (Lepeophtheirus salmonis).

BackgroundSalmon lice, Lepeophtheirus salmonis (Copepoda: Caligidae), are highly important ectoparasites of farmed and wild salmonids, and cause multi-million dollar losses to the salmon aquaculture industry annually. Salmon lice display extensive sexual dimorphism in ontogeny, morphology, physiology, behavior, and more. Therefore, the identification of transcripts with differential expression between males and females (sex-biased transcripts) may help elucidate the relationship between sexual selection and sexually dimorphic characteristics.ResultsSex-biased transcripts were identified from transcriptome analyses of three L. salmonis populations, including both Atlantic and Pacific subspecies. A total of 35-43 % of all quality-filtered transcripts were sex-biased in L. salmonis, with male-biased transcripts exhibiting higher fold change than female-biased transcripts. For Gene Ontology and functional analyses, a consensus-based approach was used to identify concordantly differentially expressed sex-biased transcripts across the three populations. A total of 127 male-specific transcripts (i.e. those without detectable expression in any female) were identified, and were enriched with reproductive functions (e.g. seminal fluid and male accessory gland proteins). Other sex-biased transcripts involved in morphogenesis, feeding, energy generation, and sensory and immune system development and function were also identified. Interestingly, as observed in model systems, male-biased L. salmonis transcripts were more frequently without annotation compared to female-biased or unbiased transcripts, suggesting higher rates of sequence divergence in male-biased transcripts.ConclusionsTranscriptome differences between male and female L. salmonis described here provide key insights into the molecular mechanisms controlling sexual dimorphism in L. salmonis. This analysis offers targets for parasite control and provides a foundation for further analyses exploring critical topics such as the interaction between sex and drug resistance, sex-specific factors in host-parasite relationships, and reproductive roles within L. salmonis.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2835-7) contains supplementary material, which is available to authorized users.

Domestication compromises athleticism and respiratory plasticity in response to aerobic exercise training in Atlantic salmon (Salmo salar)

Commercially selective breeding of Atlantic salmon (Salmo salar) primarily for rapid growth may compromise cardiorespiratory robustness and its related phenotypes. Therefore, a suite of respiratory indices was used to evaluate aerobic capacity and hypoxia tolerance to test the hypothesis that exercise training can improve the athletic robustness in both domesticated and wild strains of Atlantic salmon, but with the domesticated strain having a less cardiorespiratory plasticity and a lower athletic robustness than the wild strain. We also tested a second hypothesis that a constant acceleration screening protocol should segregate fish according to athletic robustness based on their swimming ability. These hypotheses were tested with parr from Bolaks (domesticated) and Lærdal (wild) strains of Atlantic salmon that were reared under identical hatchery conditions. After screening into either inferior (bottom 20%) or superior (top 20%) swimmers, the four groups of fish (two strains and two swimming performance levels) either were given an 18-day exercise-training regime (an incremental water current of 2.0–2.8forklengthss−1), or were maintained at the control water current (0.5forklengthss−1) for 18days. Subsequently, fish were sampled for metabolic enzyme analysis in red and white swimming muscles (citrate synthase, CS, and lactate dehydrogenase, LDH; n=15 from each group) and their individual respiratory capacities were comprehensively assessed by measuring the standard metabolic rate (SMR), maximum rate of oxygen uptake (ṀO2max), absolute aerobic scope (AAS), factorial aerobic scope (FAS), excess post-exercise oxygen consumption (EPOC), critical oxygen level (O2crit) and incipient lethal oxygen saturation (ILOS). Contrary to our expectations, the inferior and superior swimmers were indistinguishable in either strain and these data were pooled. While exercise training produced several tangible benefits for the wild fish, it produced very few for the domesticated fish. For example, the wild strain, but not the domesticated strain, had a significantly higher ṀO2max, AAS and EPOC as a result of training. Also, CS activity in red muscle increased after training to a larger extent in the wild strain than in the domesticated strain. When compared with the wild strain, the domesticated strain had a significantly lower ṀO2max, AAS, FAS and CS activity in white muscle. Thus, the domesticated strain appeared to be athletically less robust than the wild strain. These results imply that approximately ten generations of selective breeding for rapid growth in commercial aquaculture have reduced the overall athletic robustness of domesticated salmon as compared to their wild conspecifics, and given the success in improving athletic robustness of the wild strain, it still remains to be seen whether an exercise training protocol can be developed that will provide benefits to the salmon aquaculture industry. Statement of relevanceThis manuscript fits perfectly with the scope of aquaculture. We address the possibility that the Norwegian Atlantic salmon (Salmo salar) breeding program that extensively focuses on commercial benefits traits may be compromising the cardiorespiratory system, which may contribute to the mortality of smolts after seawater transfer. We hypothesized that a combination of exercise-screening and exercise-training protocols could select for superior cardiorespiratory performance. This hypothesis was tested by comparing domesticated and wild Norwegian Atlantic salmon strains, and using comprehensive measurements of athletic and hypoxia performance in individual fish.We believe this paper will be of specific interest to aquaculture professionals who are seeking the enhanced husbandry approaches for achieving higher survival rate over seawater transfer as well as general physiologists. To our knowledge our study is the first to comprehensively illustrate athleticism of domesticated Atlantic salmon from biochemical and cardiorespiratory system levels. Furthermore, we believe this is the first study to show the promising results of enhancing cardiorespiratory system of domesticated Atlantic salmon strain in a hatchery setting.We used a suite of respiratory indices to evaluate athletic robustness and hypoxia performance in individual fish. We discovered that a domesticated strain of Atlantic salmon demonstrated a reduced athleticism and less plasticity in response to a short exercise-training regime compared with a wild strain of Atlantic salmon. We conclude that commercial aquaculture practices may trade off the robustness of the cardiorespiratory system, but not to an extent of completely losing the potential of benefiting from exercise training.

Viral co-infections in farmed Atlantic salmon, Salmo salar L., displaying myocarditis.

Several different viruses have been associated with myocarditis-related diseases in the Atlantic salmon aquaculture industry. In this study, we investigated the presence of PMCV, SAV, PRV and the recently identified Atlantic salmon calicivirus (ASCV), alone and as co-infections in farmed Atlantic salmon displaying myocarditis. The analyses were performed at the individual level and comprised qPCR and histopathological examination of 397 salmon from 25 farms along the Norwegian coast. The samples were collected in 2009 and 2010, 5-22months post-sea transfer. The study documented multiple causes of myocarditis and revealed co-infections including individual fish infected with all four viruses. There was an overall correlation between lesions characteristic of CMS and PD and the presence of PMCV and SAV, respectively. Although PRV was ubiquitously present, high viral loads were with a few exceptions, correlated with lesions characteristic of HSMI. ASCV did not seem to have any impact on myocardial infection by PMCV, SAV or PRV. qPCR indicated a negative correlation between PMCV and SAV viral loads. Co-infections result in mixed and atypical pathological changes which pose a challenge for disease diagnostic work.

Diversity and occurrence of siphonophores in Irish coastal waters

Siphonophores are at times amongst the most abundant invertebrate zooplankton predators in the oceans. Historically, siphonophores have been under-sampled and of the studies conducted there has been a bias towards oceanic oligotrophic waters where they are considered to be more important. In temperate coastal regions, comparatively less is known about the diversity and abundance of siphonophores, where periodic blooms can restructure the plankton communities and have been correlated with high mortalities in the salmon aquaculture industry. To address this lack of knowledge, plankton samples were collected during two periods (March 2009-March 2011 and April 2014-November 2015) from a coastal embayment in the southwest of Ireland. In total, three siphonophore species were found, the calycophoran Muggiaea atlantica, and the physonects, Nanomia bijuga and Agalma elegans. Muggiaea atlantica was the most abundant species (250 colonies m−3), with densities an order of magnitude higher than either physonect. Muggiaea atlantica displayed a distinct seasonality, whereas the physonect species were sporadic in occurrence. Comparing siphonophores in Bantry Bay and the Western English Channel (Plymouth Marine Laboratory's L4 station) indicates both regions share a similar pattern of inter-annual occurrence and provides novel information on the seasonality and occurrence of siphonophores in Irish coastal waters.

Transcriptome immunomodulation of in-feed additives in Atlantic salmon Salmo salar infested with sea lice Caligus rogercresseyi.

One of the most significant threats to the Chilean salmon aquaculture industry is the ectoparasitic sea louse Caligus rogercresseyi. To cope with sea lice infestations, functional diets have become an important component in strengthening the host immune response. The aim of this study was to evaluate molecular mechanisms activated through immunostimulation by in-feed plant-derived additives in Atlantic salmon infected with sea lice. Herein, a transcriptome-wide sequencing analysis was performed from skin and head kidney tissues, evidencing that the immune response genes were the most variable after the challenge, especially in the head kidney, while other genes involved in metabolism were highly expressed individuals fed with the immunostimulants. Interestingly, defensive enzymes such as Cytochrome p450 and serpins were down-regulated in infested individuals, especially in skin tissue. Additionally, MHC-I and MHC-II genes were differentially expressed after the incorporation of the in-feed additives, giving some cues about the protection mechanisms of plant-derived compound as immunostimulants for infested salmons. This is the first published study that evaluates the transcriptomic response of sea lice-infested Atlantic salmon fed with in-feed additives.

The Atlantic Salmon Salmo salar in Australia

The multimillion dollar Tasmanian Atlantic Salmon aquaculture industry grew from a shaky beginning with just 36 ripe females in the 1970's. The early unsuccessful attempts to introduce Atlantic Salmon (Salmo salar) to Australia which started in 1841 are summarised. By 1960 no known populations of Atlantic Salmon existed in Australia so Dr D.D. Francois arranged the import of Atlantic Salmon ova in 1963, 1964 and 1965. By 1972 when I took over management of Atlantic Salmon in N. S.W., the remaining stocks had become very low, only 36 ripe females remaining, and the importation of new stocks were prohibited. By 1979 1,000,000 ova were laid down for that year although mortalities were high. In the 1980's several shipments of these Atlantic Salmon ova were supplied to Tasmania, and from these, the multimillion dollar Tasmanian Salmon aquaculture industry has developed. Lake Jindabyne is still stocked annually with Atlantic Salmon and reasonable angler returns result, but no breeding in the wild has been reported.

Next-Generation Transcriptome Profiling of the Salmon Louse Caligus rogercresseyi Exposed to Deltamethrin (AlphaMax™): Discovery of Relevant Genes and Sex-Related Differences.

Sea lice are one of the main parasites affecting the salmon aquaculture industry, causing significant economic losses worldwide. Increased resistance to traditional chemical treatments has created the need to find alternative control methods. Therefore, the objective of this study was to identify the transcriptome response of the salmon louse Caligus rogercresseyi to the delousing drug deltamethrin (AlphaMax™). Through bioassays with different concentrations of deltamethrin, adult salmon lice transcriptomes were sequenced from cDNA libraries in the MiSeq Illumina platform. A total of 78 million reads for females and males were assembled in 30,212 and 38,536 contigs, respectively. De novo assembly yielded 86,878 high-quality contigs and, based on published data, it was possible to annotate and identify relevant genes involved in several biological processes. RNA-seq analysis in conjunction with heatmap hierarchical clustering evidenced that pyrethroids modify the ectoparasitic transcriptome in adults, affecting molecular processes associated with the nervous system, cuticle formation, oxidative stress, reproduction, and metabolism, among others. Furthermore, sex-related transcriptome differences were evidenced. Specifically, 534 and 1033 exclusive transcripts were identified for males and females, respectively, and 154 were shared between sexes. For males, estradiol 17-beta-dehydrogenase, sphingolipid delta4-desaturase DES1, ketosamine-3-kinase, and arylsulfatase A, among others, were discovered, while for females, vitellogenin 1, glycoprotein G, transaldolase, and nitric oxide synthase were among those identified. The shared transcripts included annotations for tropomyosin, γ-crystallin A, glutamate receptor-metabotropic, glutathione S-transferase, and carboxipeptidase B. The present study reveals that deltamethrin generates a complex transcriptome response in C. rogercresseyi, thus providing valuable genomic information for developing new delousing drugs.

Frequent haplotypes of caged Caligus rogercresseyi in the austral south of Chile: The result of a long term serial passage experiment?

Caligus rogercresseyi is an ectoparasite that causes enormous economic losses to the Chilean salmon aquaculture industry. It has been proposed that native fish are a reservoir of this parasite and that pesticide treatments to control it have led to pharmacological resistance to the chemotherapeutic substances that are broadly used in the austral south of Chile. During 2012–2013, 686bp in the 18s rRNA gene of C. rogercresseyi were sequenced, collected from Salmo salar cultured in five areas between 41°30′S and 45°30′S in Chile. The results show a total of 24 haplotypes, two of which were highly frequent and present in all studied areas (A=36.7% and B=16.3%), as well as in larvae raised under laboratory conditions (A=44% and B=25%). A and B haplotypes were also present in stored sequences of this parasite in the GenBank database from 2003. Seven less frequent haplotypes were found dispersed in four of the areas studied, and the remaining fifteen haplotypes were only present in low frequencies and only in one area. Analysis of the population structure of C. rogercresseyi indicated that the samples collected are part of a panmictic population but with low genetic flow inside the study area, as following a bottleneck event. Hypothetically, after over a decade of this population parasitizing a caged host with low genetic diversity (S. salar), and after repeated exposure to neurotoxic pesticides, the most frequent haplotypes A and B could be the result of drug selective pressure acting inside the cages in a kind of long term serial passage experiment. Finally, the characterization of the molecular footprints of these most frequent haplotypes makes them good candidates for use in experiments to test their resistance to drug treatments. Statement of relevanceThe use of haplotypes described in this study, especially A and B, in experiments of drug resistance in this parasite is relevant compared to the use of unknown haplotypes. This could be important for determining the kind of drugs used against this parasite as well as in the study of resistance mechanisms to the chemotherapeutic substances used in Chilean aquaculture.

In silico transcriptome analysis of cuticle-related genes associated with delousing drug responses in the sea louse Caligus rogercresseyi

The present report examined changes in cuticle protein expression in sea lice strains resistant or susceptible to delousing drugs. Specifically, the transcriptome profiles of genes related to cuticle biosynthesis were evaluated in the sea louse Caligus rogercresseyi in response to the antiparasitics azamethiphos (Bayer®) and deltamethrin (AlphaMax®). For bioassays, putative cuticle-related genes from sea lice exposed to deltamethrin or azamethiphos were evaluated using high-throughput transcriptome sequencing and RT-qPCR analysis. From the previously reported C. rogercresseyi transcriptome, a total of 479 transcripts were annotated as proteins linked to cuticle formation. RNA-Seq analysis evidenced high transcription levels of cuticle precursors during the larval stage, while in adults cuticle proteins were highly regulated. Furthermore, 234 transcripts were highly regulated in response to delousing drugs, such as cuticle proteins, P4H, PDI, and chitinase. Principle components analysis revealed a high correlation between exposure to azamethiphos and cuticle precursors, suggesting a putative modulation of organophosphates against cuticle-related proteins in sea lice. Moreover, transcript expression of collagen and cuticle genes revealed significant differences between sexes. These results suggest a modulation by C. rogercresseyi of cuticle biogenesis in response to delousing drugs.Statement of relevanceThe present report examined changes in cuticle protein expression in sea lice exposed to delousing drugs. The study gathers high-throughput sequencing features to suggest novel aspects of the drug response to organophosphates and pyrethroids used by the salmon aquaculture industry.

Profiting from Agglomeration? Evidence from the Salmon Aquaculture Industry

Asche F., Roll K. H. and Tveteras R. Profiting from agglomeration? Evidence from the salmon aquaculture industry, Regional Studies. Even though most celebrated clusters seem to be in high-cost areas, many econometric studies represent agglomeration externalities as increased primal productivity or reduced cost. While this certainly can be consistent with some observed agglomeration effects, it may be insufficient for the growth of a cluster. The key condition for this is that profitability is higher. The paper tests for agglomeration effects using a profit function approach. This may be particularly important for firms in high-cost clusters, where revenue effects can be as important as productivity and cost effects. The paper tests for both intra- and inter-industry agglomeration externalities using firm-level data.

Towards a consensus: Multiple experiments provide evidence for constitutive expression differences among sexes and populations of sea lice (Lepeophtheirus salmonis) related to emamectin benzoate resistance

Sea lice (Lepeophtheirus salmonis) are ectoparasitic copepods that impose a heavy financial burden on the salmon aquaculture industry. A parasiticide, emamectin benzoate (EMB; trade name SLICE®), was widely used to control sea lice before EMB resistant strains of lice emerged. Several genetic mechanisms are likely responsible for EMB resistance however these are not yet fully understood. Resistance is further complicated by sex differences in EMB tolerance with males often showing better survival upon EMB exposure compared to females. Here, candidate EMB-resistance genes were used to explore differences between sex, population, and exposure to EMB using two in vitro bioassays and an in vivo experiment. Two acetylcholine receptor subunits (nAChRα3 and nAChRα7) showed opposite expression profiles across the assays, with male and EMB-resistant lice showing significant overexpression of nAChRα7 and downregulation of nAChRα3 compared to females and EMB-sensitive lice, respectively. Furthermore, a novel gene candidate LR9 showed induced expression upon EMB exposure with the highest expressing group being EMB-resistant males. An ABC transporter, pgp, also showed highest expression in EMB-resistant males but this finding was not consistent across all experiments. Other gene candidates like CYP18A and peroxinectin did not show similar expression profiles to work completed on other populations or species of sea lice. These data have provided a consensus with other transcriptomic studies showing that neuronal acetylcholine receptor subunits are differentially regulated between sexes and populations of sea lice. This unique expression profile, alongside analysis of other EMB resistance genes, provides a detailed snapshot of mechanisms responsible for resistance in sea lice. Statement of relevanceSea lice are a major threat to salmon aquaculture and its' sustainability. With the advent of drug resistance, this problem has only become more troubling. The mechanisms of resistance are largely unknown, with a requirement on consensus findings across meta-populations of lice due to varying levels of resistance within them. This project shows consensus findings across multiple experiments for both previously explored targets as well as new, potential resistance markers.