Wild Salmon Populations Research Articles

Climate change-driven disease in sympatric hosts: Temporal dynamics of parasite burden and proliferative kidney disease in wild brown trout and Atlantic salmon.

Global climate change is altering the abundance and spread of various parasites, which has important consequences not only for host-parasite interactions but also for the relationships between different host species. Here, we focus on the myxozoan endoparasite Tetracapsuloides bryosalmonae that causes temperature-dependent proliferative kidney disease (PKD) in salmonids. We characterized the temporal changes in the parasite load and the severity of PKD signs (renal hyperplasia, haematocrit) in two sympatric populations of wild brown trout (Salmo trutta) and Atlantic salmon (Salmo salar). We found that both the parasite load and disease signs vary considerably between individuals, species, rivers and sampling periods. We showed that Atlantic salmon was able to slow down the initial parasite proliferation rate and subsequently tolerate high parasite burden without obvious disease signs. In contrast, the initial parasite proliferation rate was much higher in brown trout, which was followed by the development of severe PKD signs. Thus, the speed of parasite proliferation, rather than the absolute number of the parasites in the host kidney, may play an important role in interspecific variation in PKD susceptibility. To conclude, this study illustrates the usefulness of temporal perspective for understanding host defence mechanisms and climate change-mediated impacts in the wild.

Early-life fitness trait variation among divergent European and North American farmed and Newfoundland wild Atlantic salmon populations

It has long been clear that interbreeding between domesticated and wild Atlantic salmon can lead to negative fitness consequences for native populations. Few studies, however, have examined these consequences at critical early life stages, particularly in the context of distinct geographical and ancestral relationships among populations as well domestication selection. In Newfoundland (NF), Canada, while the majority of aquaculture sites use the North American (NA) Saint John River strain, site-specific permission has been granted to farm a strain of European origin (EO). We designed a common-garden experiment to compare fitness-related traits (e.g. development time, survival, size and growth) at different early-life stages (eye development, hatch and yolk absorption) among EO and NA farmed, 2 NF wild and F1hybrid groups. Significant differences (p < 0.001) were observed in development time, survival, growth and energy conversion among farmed, F1hybrid and wild populations. While pure populations (farmed and wild) differed amongst one another, we found few differences in fitness-related traits between F1hybrids and their maternal wild/farmed strains. This suggests that the early-life fitness consequences of F1hybridization will be largely manifested through the action of maternal effects. Additionally, significant associations between the maternal effects of egg size and alevin development time, size, survival, growth, condition and energy conversion efficiency were found. These findings suggest that early-life fitness-related trait differences among farmed, wild and their related F1hybrids are generated by the geographic and ancestral relationship and maternal effects of egg size and less so by domestication selection.

Genetic evidence of farmed straying and introgression in Swedish wild salmon populations

Escaped farmed Atlantic salmon represent a well-documented and ongoing threat to wild conspecific populations. In Norway, the world-leading producer of farmed salmon, annual monitoring of straying and genetic introgression by farmed escapees in wild salmon rivers has been carried out since the late 1980s. In this study, we applied molecular and statistical methods routinely used in the Norwegian monitoring programme to investigate the magnitude of escaped farmed salmon and genetic introgression in salmon rivers on the west coast of Sweden, where suspected escapees have been observed. Our results confirm that escaped farmed salmon stray, successfully spawn, and produce offspring at levels similar to those observed in neighbouring Norway. These findings raise concerns over population productivity and long-term viability and highlight the need for more permanent monitoring of the presence and consequences of escaped farmed salmon in Swedish salmon rivers. Our results further illustrate that farmed gene flow may constitute a transboundary problem with potential international implications.

Evaluation of genetic effects on wild salmon populations from stock enhancement

Abstract Many salmonid populations are of conservation concern, and the release of hatchery-produced juveniles is a frequently used measure to alleviate declines and increase harvest opportunities. While such releases may be of conservation value for some populations, stocking may also decrease the effective population size and subsequently impose additional strain on already threatened populations. In this study, we assessed how the cohort-wise effective number of breeders in five populations of Atlantic salmon (Salmo salar) were affected by supplementation. Altogether, 19 cohorts were studied (2–7 cohorts per population) by estimating the proportion hatchery-released individuals and the effective number of wild and captive breeders in each cohort of the respective populations. We show that the effect of releasing captive-bred individuals varies both between populations and between years within the same population. A Ryman–Laikre effect—where the effective number of breeders has decreased as a consequence of supplementation—was observed for 11 cohorts. We discuss how supplementation can be adapted to optimize the effective population size, demonstrate that evaluation of supplementation can be reliably achieved, and show that supplementation programmes that lead to high proportions of hatchery-origin fish on spawning grounds are more likely to induce a Ryman–Laikre effect.

Salmon on the lam: Drivers of escaped farmed fish abundance in rivers

Abstract The production of Atlantic salmon in aquaculture has grown substantially over the last 40 years. The unintentional release of domesticated salmon poses a significant risk to the long‐term persistence of wild Atlantic salmon populations through ecological interactions and genetic introgression. Our ability to link aquaculture production to farmed escaped salmon in rivers is still limited and hinders identifying the appropriate production capacity of salmon aquaculture to reduce unwanted interactions between wild and escaped Atlantic salmon. Here we use a 14‐year dataset of farmed escapee abundance in rivers to model how the a priori selected covariables of wild salmon abundance, aquaculture intensity, river discharge, hydropower and fjord placement of the river affects escapee abundance across 54 rivers in western Norway. Then, we evaluate the predictive strength of the model to provide context for its use to minimize escapees. We found that the abundance of escaped farmed Atlantic salmon in rivers is correlated to aquaculture intensity. Furthermore, the abundance of wild Atlantic salmon, mean yearly discharge, and the interaction between fjord placement and wild salmon abundance were important predictors of escapee abundance in rivers. The model was 40% accurate when predicting the abundance of farmed escaped salmon in rivers. However, the accuracy improved to 75% when using risk categories derived from modelled intrusion rates that induced long‐term genetic changes to the wild population (low < 4%, medium 4%–10%, and high > 10% escaped farmed salmon). Synthesis and applications. This study links aquaculture production, at relevant spatiotemporal scales (75 km from rivers), to the abundance of escaped farmed Atlantic salmon in rivers, and provides governmental agencies with a tool to help regulate domesticated salmon production based on the carrying capacity of the system to buffer against introgression between conspecifics. Furthermore, understanding this relationship will be beneficial when establishing new aquaculture sites in pristine ecosystems where they would overlap with wild Atlantic salmon. Finally, future mitigation efforts should continue to focus on new technologies (e.g. triploid females) that can eliminate the risk of introgression without limiting aquaculture production.

Soil erosion and sediment dynamics in the Anthropocene: a review of human impacts during a period of rapid global environmental change

PurposeHumanity has been modifying the planet in a measurable way for thousands of years. Recently, this influence has been such that some feel we are in a new geological epoch, the Anthropocene. This review will describe how soil erosion and sediment dynamics have (i) been used to assess the impact of humans on the planet and (ii) affected the global climate and influenced water security. Emphasis is placed on changes since the middle of the twentieth century, as this coincides with what many suggest is the start of the Anthropocene Epoch.Results and discussionThe use of sediment archives has been instrumental in our understanding of how environmental systems have developed over time, both naturally and in response to anthropogenic activities. Additional information has come from measurement and monitoring programs, and tracing and fingerprinting studies. In turn, models have been developed that enable forecasting. Some of the main global impacts of enhanced soil erosion and changes in sediment dynamics and sediment composition include: changes in radiative energy balances and impacts on the cryosphere; the global carbon cycle; and greenhouse gas emissions. Impacts on water security include: effects on freshwater biota, including wild salmon populations; fluxes of contaminants, including microplastics; and reservoir and river channel sedimentation, including flooding. Sediment archives and monitoring programs have also been used to document the effect of mitigation measures and environmental policies.ConclusionSediment archives enable us to assemble information over a variety of timescales (i.e., 100 to 105 years and longer) and a range of spatial scales (from sub-watershed to continental), in addition to environments ranging from arid to tropical to polar. Often the temporal resolution is better than other paleoenvironmental reconstruction approaches. As such, sedimentary records, when combined with measurement and monitoring approaches and other sources of information, have enabled us to determine changes in atmospheric, terrestrial, and aquatic systems, especially over the last 100 years. While soil erosion and sediment dynamics have provided a wealth of information and greatly enhanced our understanding of the role of humanity in modifying the planet, suggestions are given for further research.

Increasing temperatures accentuate negative fitness consequences of a marine parasite

Infectious diseases are key drivers of wildlife populations and agriculture production, but whether and how climate change will influence disease impacts remains controversial. One of the critical knowledge gaps that prevents resolution of this controversy is a lack of high-quality experimental data, especially in marine systems of significant ecological and economic consequence. Here, we performed a manipulative experiment in which we tested the temperature-dependent effects on Atlantic salmon (Salmo salar) of sea lice (Lepeophtheirus salmonis)—a parasite that can depress the productivity of wild-salmon populations and the profits of the salmon-farming industry. We explored sea-louse impacts on their hosts across a range of temperatures (10, 13, 16, 19, and 22 °C) and infestation levels (zero, ‘low’ (mean abundance ± SE = 1.6 ± 0.1 lice per fish), and ‘high’ infestation (6.8 ± 0.4 lice per fish)). We found that the effects of sea lice on the growth rate, condition, and survival of juvenile Atlantic salmon all worsen with increasing temperature. Our results provide a rare empirical example of how climate change may influence the impacts of marine disease in a key social-ecological system. These findings underscore the importance of considering climate-driven changes to disease impacts in wildlife conservation and agriculture.

Wild salmonids are running the gauntlet of pathogens and climate as fish farms expand northwards

Abstract Salmon farming has multiplied from a side business of coastal farmers to one of the world's major aquaculture species. This has dramatically altered the disease dynamics between farmed and wild salmonids. As salmon fish farming has increased, new restrictions have been enforced to combat emerging density-dependent impacts of pathogen spillover. In most northern and arctic regions, the effects of pathogens from fish farms on wild salmonids have been minimal for two key reasons: (i) relative low density of fish farms in the north and (ii) cold water temperatures. However, both factors are set to change dramatically. On one side, there is an increasing interest in utilizing northern areas for fish farming due to limited capacity for expansion in mid-latitude regions. On the other side, climate change is rapidly changing these northern ecosystems. High-latitude regions inhabit some of the largest remaining wild Atlantic salmon populations in the world along with sea trout and Arctic charr. Wild salmonids in the north have most likely seldom been exposed to high infection pressure, and we question how these populations will cope with changes that are coming. We identify 12 research questions emerging from these imminent changes and discuss methodologies for addressing them. We conclude that policies related to fish farming must consider uncertainties with respect to pathogen dynamics in the north until these research questions are fully addressed.

Density‐dependent effects of eastern Kamchatka pink salmon (Oncorhynchus gorbuscha) and Japanese chum salmon (O. keta) on age‐specific growth of western Alaska chum salmon

AbstractHatcheries release >4.5 billion juvenile Pacific salmon (Oncorhynchus spp.) into the North Pacific Ocean annually, raising concerns about competition with wild salmon populations. We used retrospective scale analysis to investigate how the growth of chum salmon (O. keta) from western Alaska is affected by the abundance of chum salmon from Japanese hatcheries and wild pink salmon (O. gorbuscha) from the Russian Far East. Over nearly five decades, the growth of Kuskokwim River chum salmon was negatively correlated with the abundance of Japanese hatchery chum salmon after accounting for the effects of sex and spring/summer sea‐surface temperature in the Bering Sea. An effect of wild eastern Kamchatka pink salmon abundance on the growth of Kuskokwim River salmon was detectable but modest compared to the intraspecific competitive effect. A decrease in Japanese hatchery chum salmon releases in 2011–2013 was not associated with increased growth of Bering Sea chum salmon. However, the abundance of wild chum salmon from the Russian Far East increased during that time, possibly obscuring reduced competition with hatchery chum salmon. Our results support previous evidence that chum salmon are affected by intraspecific competition, and to a lesser extent interspecific competition, in the North Pacific, underscoring that the effects of salmon hatchery production transcend national boundaries.

Emergence and Spread of Piscine orthoreovirus Genotype 3.

Piscine orthoreovirus (PRV) is a relevant pathogen for salmonid aquaculture worldwide. In 2015, a new genotype of PRV (genotype 3, PRV-3) was discovered in Norway, and in 2017 PRV-3 was detected for first time in Denmark in association with complex disease cases in rainbow trout in recirculating aquaculture systems (RAS). To explore the epidemiology of PRV-3 in Denmark, a surveillance study was conducted in 2017 to 2019. Fifty-three farms, including both flow through and RAS, were screened for PRV-3. Of the farms examined, PRV-3 was detected in thirty-eight (71.7%), with the highest prevalence in grow-out farms. Notably, in Denmark disease outbreaks were only observed in RAS. Additionally, wild Atlantic salmon and brown trout populations were included in the screening, and PRV-3 was not detected in the three years where samples were obtained (2016, 2018, and 2019). Historical samples in the form of archived material at the Danish National Reference Laboratory for Fish Diseases were also tested for the presence of PRV-3, allowing us to establish that the virus has been present in Denmark at least since 1995. Sequence analyses of segment S1 and M2, as well as full genome analyses of selected isolates, did not reveal clear association between genetic makeup in these two segments and virulence in the form of disease outbreaks in the field.

Ionic aluminium concentrations exceed thresholds for aquatic health in Nova Scotian rivers, even during conditions of high dissolved organic carbon and low flow

Abstract. Acid deposition released large amounts of aluminium into streams and lakes during the last century in northern Europe and eastern North America. Elevated aluminium concentrations caused major environmental concern due to aluminium's toxicity to terrestrial and aquatic organisms and led to the extirpation of wild Atlantic salmon populations. Air pollution reduction legislation that began in the 1990s in North America and Europe successfully reduced acid deposition, and the aluminium problem was widely considered solved. However, accumulating evidence indicates that freshwater systems still show delays in recovery from acidification, with poorly understood implications for aluminium concentrations. Here, we investigate spatial and temporal patterns of labile cationic forms of aluminium (Ali) from 2015 to 2018 in 10 catchments in Nova Scotia, Canada; this region was one of the hardest hit by acid deposition, although it was not considered to have an aluminium problem due to its high dissolved organic carbon (DOC) concentrations that were expected to reduce Ali concentrations. Surprisingly, our results show the widespread and frequent occurrences of Ali concentrations that exceed toxic thresholds in all sampled rivers despite high DOC concentrations. Generalized linear mixed model results reveal that DOC, instead of being inversely related to Ali, is the strongest predictor (positive) of Ali concentrations, suggesting that the recruitment properties of DOC in soils outweigh its protective properties in streams. Lastly, we find that, contrary to the common conceptualization that high Ali levels are associated with storm flow, high Ali concentrations are found during base flow. Our results demonstrate that elevated Ali concentrations in Nova Scotia continue to pose a threat to aquatic organisms, such as the biologically, economically, and culturally significant Atlantic salmon (Salmo salar).

The environmental effectiveness of sea lice regulation: Compliance and consequences for farmed and wild salmon

Wild Atlantic salmon populations are declining. Since the 1970s, the proportion returning to Norwegian rivers has been almost halved, while Norwegian sea farming has undergone massive industrialization and expansion. As the proliferation of sea lice is an important part of the explanation for the decline in wild salmon, Norway has enacted increasingly stricter regulatory thresholds for the average number of lice per farmed fish at production sites. This study shows that setting stricter thresholds has led to declining lice-levels within sea farms, but that more frequent de-lousing measures to ensure compliance leads to farmed-salmon welfare problems and higher mortality rates. Compliance with stricter thresholds has not lessened the sea-lice infestation pressure on surrounding, wild salmonid populations. The environmental effectiveness of such regulation is thus limited. This raises the important question of whether a regulatory regime focused on minimizing the average number of sea lice per farmed fish may do more harm than good, unless accompanied by a broader set of regulatory instruments targeting other variables that affect sea-lice infestations in the wild salmon habitat.

Migratory hosts can maintain the high-dose/refuge effect in a structured host-parasite system: The case of sea lice and salmon.

Migration can reduce parasite burdens in migratory hosts, but it connects populations and can drive disease dynamics in domestic species. Farmed salmon are infested by sea louse parasites, often carried by migratory wild salmonids, resulting in a costly problem for industry and risk to wild populations when farms amplify louse numbers. Chemical treatment can control lice, but resistance has evolved in many salmon‐farming regions. Resistance has, however, been slow to evolve in the north‐east Pacific Ocean, where large wild‐salmon populations harbour large sea louse populations. Using a mathematical model of host–macroparasite dynamics, we explored the roles of domestic, wild oceanic and connective migratory host populations in maintaining treatment susceptibility in associated sea lice. Our results show that a large wild salmon population, unexposed to direct infestation by lice from farms; high levels of on‐farm treatment; and a healthy migratory host population are all critical to slowing or stopping the evolution of treatment resistance. Our results reproduce the “high‐dose/refuge effect,” from the agricultural literature, with the added requirement of a migratory host population to maintain treatment susceptibility. This work highlights the role that migratory hosts may play in shared wildlife/livestock disease, where evolution can occur in ecological time.

Escape history and proportion of farmed Atlantic salmon Salmo salar on the coast and in an adjacent salmon fjord in Norway

To gain more knowledge about escaped farmed salmon Salmo salar in the wild, we investigated the proportion of escapees, body length at escape, proportion escaped as smolts/post-smolts (≤300 mm) and number of winters in the wild (winter zones in the growth pattern in the scale samples) in catches on the Norwegian coast and in an adjacent fjord from 2013 to 2017. The mean proportion of escapees was higher on the coast (26%) than in the fjord (4%), and escapees caught on the coast had a slightly larger mean body length at escape (607 mm) than in the fjord (557 mm). However, the mean proportion escaped as smolts/post-smolts did not differ significantly between the coast (8%) and the fjord (11%). There was also no significant difference in the mean proportion of farmed salmon with 1 or more winter zones after escape (50% on the coast and 56% in the fjord). The proportions of escapees with 1, 2, 3 or 4 winter zones after escape were 28, 20, 2 and 0.4% in catches on the coast and 30, 21 and 4% in catches in the fjord, respectively. This study found that the proportion of escapees was considerably higher in coastal waters than in the fjord. Escapees consisted of farmed salmon from several escape events over several years, and approximately 50% of the escapees had one or more winter zones after escape. Thus, escaped farmed salmon may pose a threat to wild salmon populations for several years after the escape event.

Behavioural variation among divergent European and North American farmed and wild Atlantic salmon (Salmo salar) populations

Animals often display consistent differences in behaviours across situations and contexts. However, little is known about how behavioural traits might vary in a context-dependent manner, with selection favouring correlated sets of behaviours in particular types of environments. Comparative studies of behavioural trait differences and associations among different populations can provide valuable insights into how this might operate. For example, farmed Atlantic salmon (Salmo salar) often escape into the wild and may produce hybrid and feral offspring that interact with wild conspecifics. Interactions between these offspring types may be mediated by differences in behaviour reflective of their different selective histories, which may in turn affect their relative fitness. In Newfoundland, Canada, site-specific permission has been granted to farm a strain of European origin (EO) salmon in addition to the current North American (NA) Saint John River strain. However, because these two farmed strains are genetically divergent, there is concern that behavioural trait differences will exist that affect interactions with native wild populations. We thus designed a common-garden experiment to compare the behaviour of individual fish from NA and EO farm strains in four different contexts (exploration, response to a novel object, boldness under predation risk and aggression) relative to that of wild fish and hybrid conspecifics. NA and EO farm fish did not differ in their behaviour (P > 0.05), but both were more explorative (P < 0.001 in 2016; P < 0.05 in 2017), responsive to a novel object (P < 0.05, both years), bold (P < 0.05, both years), and aggressive (P < 0.001, both years) than wild fish and related hybrids. We found the presence of behavioural correlations in some circumstances suggesting that behavioural syndromes covary consistently with aspects of the selective environment. Overall, these results suggest that the variation in the behavioural traits studied among divergent EO and NA farmed and NA wild populations largely reflect domestication selection, and less so the geographic and ancestral relationships.

Sustainable Aquaculture in the Baltic Sea Region of Russia: Ecotoxicological Issues of Restocking Wild Salmon and Whitefish Populations

It is widely recognized that aquaculture plays an important role in rural development, contributing significantly to food availability, household food security, and income generation in particular. In developing sustainable aquaculture in the Baltic Sea region of Russia, it is essential to strike a balance between the need for aquaculture development and the need for natural resource conservation, especially in the case of Atlantic Salmon and Whitefish—the most valuable object of fishery, which almost lost their native spawning areas due to negative anthropogenic impacts. Without sufficient information about the accumulation of dangerous pollutants in fish tissues it is hard to develop a sustainable strategy for restocking populations of wild Salmonids and Whitefish in their natural habitats. In this paper, the accumulation of heavy metals in the tissues of wild Salmonids and Whitefish caught for artificial reproduction and their fry from the state hatcheries of northwest Russia was studied with the use of voltammetry, X-ray fluorescence analysis, and capillary electrophoresis. Analysis of the obtained data showed that significant bioaccumulation of heavy metals happens during growth and feeding after Salmon fry are released into the wild. This study demonstrates the necessity of improving state hatcheries with automatic control systems for ecological parameters.

Beyond large-effect loci: large-scale GWAS reveals a mixed large-effect and polygenic architecture for age at maturity of Atlantic salmon

BackgroundUnderstanding genetic architecture is essential for determining how traits will change in response to evolutionary processes such as selection, genetic drift and/or gene flow. In Atlantic salmon, age at maturity is an important life history trait that affects factors such as survival, reproductive success, and growth. Furthermore, age at maturity can seriously impact aquaculture production. Therefore, characterizing the genetic architecture that underlies variation in age at maturity is of key interest.ResultsHere, we refine our understanding of the genetic architecture for age at maturity of male Atlantic salmon using a genome-wide association study of 11,166 males from a single aquaculture strain, using imputed genotypes at 512,397 single nucleotide polymorphisms (SNPs). All individuals were genotyped with a 50K SNP array and imputed to higher density using parents genotyped with a 930K SNP array and pedigree information. We found significant association signals on 28 of 29 chromosomes (P-values: 8.7 × 10−133–9.8 × 10−8), including two very strong signals spanning the six6 and vgll3 gene regions on chromosomes 9 and 25, respectively. Furthermore, we identified 116 independent signals that tagged 120 candidate genes with varying effect sizes. Five of the candidate genes found here were previously associated with age at maturity in other vertebrates, including humans.DiscussionThese results reveal a mixed architecture of large-effect loci and a polygenic component that consists of multiple smaller-effect loci, suggesting a more complex genetic architecture of Atlantic salmon age at maturity than previously thought. This more complex architecture will have implications for selection on this key trait in aquaculture and for management of wild salmon populations.

Outmigration survival of wild Chinook salmon smolts through the Sacramento River during historic drought and high water conditions

Populations of wild spring-run Chinook salmon in California’s Central Valley, once numbering in the millions, have dramatically declined to record low numbers. Dam construction, habitat degradation, and altered flow regimes have all contributed to depress populations, which currently persist in only a few tributaries to the Sacramento River. Mill Creek (Tehama County) continues to support these threatened fish, and contains some of the most pristine spawning and rearing habitat available in the Central Valley. Despite this pristine habitat, the number of Chinook salmon returning to spawn has declined to record low numbers, likely due to poor outmigration survival rates. From 2013 to 2017, 334 smolts were captured and acoustic tagged while out-migrating from Mill Creek, allowing for movement and survival rates to be tracked over 250 km through the Sacramento River. During this study California experienced both a historic drought and record rainfall, resulting in dramatic fluctuations in year-to-year river flow and water temperature. Cumulative survival of tagged smolts from Mill Creek through the Sacramento River was 9.5% (±1.6) during the study, with relatively low survival during historic drought conditions in 2015 (4.9% ± 1.6) followed by increased survival during high flows in 2017 (42.3% ± 9.1). Survival in Mill Creek and the Sacramento River was modeled over a range of flow values, which indicated that higher flows in each region result in increased survival rates. Survival estimates gathered in this study can help focus management and restoration actions over a relatively long migration corridor to specific regions of low survival, and provide guidance for management actions in the Sacramento River aimed at restoring populations of threatened Central Valley spring-run Chinook salmon.

Vaccination with Ectoparasite Proteins Involved in Midgut Function and Blood Digestion Reduces Salmon Louse Infestations.

Infestation with the salmon louse Lepeophtheirus salmonis (Copepoda, Caligidae) affects Atlantic salmon (Salmo salar L.) production in European aquaculture. Furthermore, high levels of salmon lice in farms significantly increase challenge pressure against wild salmon populations. Currently, available control methods for salmon louse have limitations, and vaccination appears as an attractive, environmentally sound strategy. In this study, we addressed one of the main limitations for vaccine development, the identification of candidate protective antigens. Based on recent advances in tick vaccine research, herein, we targeted the salmon louse midgut function and blood digestion for the identification of candidate target proteins for the control of ectoparasite infestations. The results of this translational approach resulted in the identification and subsequent evaluation of the new candidate protective antigens, putative Toll-like receptor 6 (P30), and potassium chloride, and amino acid transporter (P33). Vaccination with these antigens provided protection in Atlantic salmon by reducing adult female (P33) or chalimus II (P30) sea lice infestations. These results support the development of vaccines for the control of sea lice infestations.

Effects of laboratory salmon louse infection on osmoregulation, growth and survival in Atlantic salmon.

Anadromous Atlantic salmon (Salmo salar) rely on long ocean migrations to build energy stores for maturation and spawning. In seawater, wild Atlantic salmon are threatened by high salmon lice (Lepeophtheirus salmonis) infestation levels resulting from intensive salmonid sea-cage aquaculture. Salmon lice infection can cause a stress response and an osmotic imbalance in the host. The lice infection intensity threshold values for these responses, however, remain to be identified in Atlantic salmon. In order to define this under laboratory conditions, individually tagged F1 wild origin Atlantic post-smolts (40 g) were infected with salmon lice copepodids or left as uninfected controls. Twenty-eight days post infection, infected post-smolts had a mean of 0.38 (range of 0.07–0.9) mobile lice g−1 fish weight. During this period, specific growth rates (SGRs) were lower in infected than control fish (0.4 vs 1.0% day−1). Higher plasma Na+, Cl− and osmolality in infected fish also indicate osmoregulatory impairment. SGR correlated negatively with plasma Na+, Cl−, osmolality and cortisol in the infected, but not in the control group. Infection intensity (lice g−1 fish) correlated positively with mortality rate and plasma Na+, Cl−, osmolality and cortisol and correlated negatively with SGR and condition factor. Calculated lice intensity threshold values for changes in plasma ions were 0.18 lice g−1 for plasma Cl−, and 0.22 lice g−1 for plasma Na+. Moribund infected fish occurred at infection intensities above 0.2 lice g−1, and these fish had extreme plasma Cl−, Na+, osmolality and cortisol levels. There was a positive correlation between plasma cortisol and plasma Na+, Cl− and osmolality in infected fish. This study provides vital information that can be used to define thresholds in the monitoring and conservation of wild Atlantic salmon populations affected by aquaculture-driven salmon lice infestations.