Search Results (42)

Background/Objetives: Sea lice (Caligus rogercresseyi) pose a major threat to Atlantic salmon (Salmo salar) aquaculture by compromising fish health and reducing production efficiency. While genetic variation in parasite load has been reported, the molecular mechanisms underlying this variation remain unclear. Methods: two sea lice challenge trials were conducted, achieving high infestation rates (47.5% and 43.5%). A total of 85 fish, selected based on extreme phenotypes for lice burden (42 low, 43 high), were subjected to transcriptomic analysis. Differential gene expression was integrated with allele-specific expression (ASE) analysis to uncover cis-regulatory variation influencing host response. Results: Sixty genes showed significant ASE (p < 0.05), including 33 overexpressed and 27 underexpressed. Overexpressed ASE genes included Keratin 15, Collagen IV/V, TRIM16, and Angiopoietin-1-like, which are associated with epithelial integrity, immune response, and tissue remodeling. Underexpressed ASE genes such as SOCS3, CSF3R, and Neutrophil cytosolic factor suggest individual variation in cytokine signaling and oxidative stress pathways. Conclusions: several ASE genes co-localized with previously identified QTLs for sea lice resistance, indicating that cis-regulatory variants contribute to phenotypic differences in parasite susceptibility. These results highlight ASE analysis as a powerful tool to identify functional regulatory elements and provide valuable candidates for selective breeding and genomic improvement strategies in aquaculture. Full article

Sea lice have been a persistent pest of the salmon farming industry for more than 50 years. In this study, we aimed to identify if different strains of Atlantic salmon with discrete long-term lice exposure histories had variable resistance to copepodid attachment and/or different attachment-specific transcriptome patterns. We additionally sought to characterize lice distributions on fins, head, and skin and identify if attachment location influenced transcriptomic profiles of lice. Lice counts were correlated with body size and highest on St. John River (SJR; open ocean-run) relative to Grand Lakes Stream (GLS; 200-year restricted ocean-run) or Sebago Lake (CAS; ~11,000 years landlocked) Atlantic salmon. However, lice density was similar between strains. Skin and fins had expectedly different transcriptomic profiles; however, notable differences were not observed between salmon strains. Variance in lice transcriptomes was minimally affected by attachment location even though lice strongly preferred fins relative to head or body. Attached lice did have different transcriptomic profiles on GLS relative to CAS or SJR. This study cumulatively identified a minimal host evolutionary component for sea lice attachment resistance, although lice behavior post-attachment appeared somewhat affected by strain. Non-uniform settlement distributions and tank-specific variability in lice attachment were observed across populations. Full article

Aquaculture is currently the fastest-growing sector in animal production, with an average annual growth rate of 7.5% since 1970. In Chile, the industry is largely driven by salmonid farming, with Salmo salar (Atlantic salmon) accounting for over 65% of national production. This species has shown the most significant growth within the sector. This growth is achieved by having high-density farming, which results in high levels of stress due to overcrowding and the appearance of pathogens such as the Infectious Salmon Anemia (ISA) virus, Bacterial Kidney Disease (BKD), Caligus sea lice (Caligus rogercresseyi), and Piscirickettsiosis (SRS) caused by Piscirickettsia salmonis, among others. This study evaluated the toxicity of the two most commonly used antibiotics in the salmon industry—oxytetracycline and florfenicol—at four concentrations each, using primary liver cell cultures of Atlantic salmon (Salmo salar). Oxidative stress was assessed through enzymatic activity and gene expression of oxidative markers, including cytochrome P450, catalase (CAT), superoxide dismutase (SOD), glutathione reductase (GR), and glutathione peroxidase (GPx). Samples were analyzed at 1, 3, 6, 12, and 48 h post-exposure. These findings reveal time- and dose-dependent oxidative responses in salmon liver cells to OTC and FLO, providing critical insights into the sublethal cellular effects of antibiotics commonly used in aquaculture, which indicates the presence of a high amount of free radicals in the liver cells, indicating toxicity of both antibiotics. Full article

Acoustic lice treatment (AcuLice) is a newly developed system which uses a composite acoustic sound image with low-frequency sound to remove salmon lice (Lepeophtheirus salmonis) from Atlantic salmon (Salmo salar). The effect of AcuLice treatment on salmon lice dynamics was measured by weekly salmon lice counting at a full-scale production facility from mid-summer 2019 to late-spring 2024. We monitored four production cycles, with AcuLice applied for two of the production cycles and with no AcuLice treatment applied during the other two production cycles as control. This is a follow-up study to our previous work. The numbers of salmon lice treatments and of weeks until the first salmon lice treatment were also compared in the two experimental groups. For the small (sessile and mobile stages) salmon lice, a significantly lower number (mean ± SEM) was shown for the AcuLice group (0.73 ± 0.03) compared with the control group (1.18 ± 0.05). For the mature female salmon lice, a significantly lower number (mean ± SEM) was found for the AcuLice group (0.12 ± 0.01) compared with the control group (0.22 ± 0.03). In addition, the mean (±SEM) number of C. elongatus varied between the two experimental groups and was higher in the control group (0.12 ± 0.01) compared with the AcuLice group (0.03 ± 0.01). In addition, a lower number (mean ± SEM) of salmon lice treatments (1.4 ± 0.17 vs. 4.22 ± 0.20) and a longer production period before the first salmon lice treatment occurred was observed for the AcuLice group (11.2 ± 0.1 weeks) compared with the control group (24.1 ± 2.3 weeks). These data suggest that the use of the AcuLice system significantly reduces the number of salmon lice (by 40–60%) and C. elongatus (by 70%) on farmed Atlantic salmon and reduces the need for traditional salmon lice treatments (by 65%). Full article

Coastal aquaculture and local fisheries interact in shared marine environments, influencing each other synergistically and/or antagonistically. Salmon farming, notably with open-net sea cages along the Norwegian coast, attracts wild fish due to increased food availability from uneaten feed, but it also exposes wild fish to farm emissions like waste and toxic chemicals (de-lice treatments, antifouling and medical agents). The attraction behaviour of wild fish can impact fatty acid composition in fish tissues, influenced by the high terrestrial fat content in salmon aquafeed. We study how the Atlantic cod, aggregating around salmon farms in a subarctic fjord in Northern Norway, can be affected, potentially altering their natural diet and fatty acid profiles. Our study compares the muscle-tissue fatty acid compositions of cod caught near aquaculture facilities (impact) versus fish caught in neighbouring fjords (control), and we hypothesise decreased omega-3 fatty acids near farms. The analysis revealed no significant differences in the fatty acid concentrations or categories between the impacted and control fish, challenging our initial expectations. However, differences were found for C18:1(n9)t (elaidic acid), with a higher value in the impacted fish. These findings suggest that salmon farming’s influence on cod’s fatty acid profiles in the flesh (i.e., relevant for the nutritional quality of the fillets that consumers eat) may be limited or minimal despite their aggregative behaviours around farms. The threshold levels of salmon feed consumed by wild cod before it affects the quality and survival of, e.g., sperm or other life stages, are not known and require new investigations. This study underscores the complexity of interactions between aquaculture and wild fisheries, impacting both ecological dynamics and consumer perspectives on seafood quality and health benefits. Full article

The salmon industry’s challenges with skin health and sea lice emphasize the necessity for fish-sensitive measures like functional nutrition to boost skin health and fish welfare. The present study investigated the efficacy of krill meal (KM) for skin mucosal health and sea lice in Atlantic salmon (170 g). Following an 8-week feeding period, in duplicate tanks, on test diets (8% KM, 12% KM, and the control group), fish underwent a 2-week sea lice challenge, reaching 350 g. The 8% KM diet group had thicker skin epithelium (72.3 µ) compared to the 12% KM (51.3 µ) and the control groups (43.8 µ) after 8 weeks. Additionally, skin mucosal health parameters—cell size (208 µ²), cell density (25.2%), and defense activity (1.19)—were significantly enhanced with 8% KM compared to the 12% KM (cell size: 162.3 µ², cell density: 17%, defense activity: 1.04) and the control group (cell size: 173.5 µ², cell density: 16.4%, defense activity: 0.93). Furthermore, fish fed with 8% KM significantly showed the lowest sea lice, along with reduced cell size while maintaining a high abundance of skin mucous cells, suggesting efficient turnover of the skin mucosal layer to remove sea lice effectively. This study highlights the potential of KM as part of a functional nutrition strategy to enhance skin mucosal health and mitigate sea lice challenges. Full article

Lumpfish (Cyclopterus lumpus) are used as cleaner fish in Atlantic salmon (Salmo salar) aquaculture as one of multiple control measures against salmon lice (Lepeophtheirus salmonis). Numerous studies have documented weight as an important factor for characterising the cleaning efficacy of individual lumpfish. Hence, the efficacy of lumpfish in fish farms depends on the size at stocking and the weight development over time. Here, we aimed to quantify how weight developed over time for lumpfish deployed in salmon farming sea cages in Norway through modelling the daily growth rate. We found that the coefficient of variation for lumpfish weight increased over time, implying that the standard deviation increased more than the expected weight. The data thus showed heterogeneous growth for lumpfish in salmon farming cages, where some individuals exhibited no apparent growth, and others significant proliferation. We found that the daily growth rate was best described as bell-shaped functions of weight and temperature, consistent with a sigmoid-shaped growth curve and an optimal temperature around 10 °C. These results allow for more realistic modelling of the efficacy of lumpfish in controlling salmon lice in fish farms, as one can combine estimates of weight-dependent cleaning efficacy with weight development over time. Full article

Lumpfish are broadly used as biological sea lice removers in Norwegian salmon farming and are mostly produced in hatcheries. To date, there is little systematic documentation on the mortality causes of lumpfish in hatcheries. In the current study, data from 12 selected fish groups from four hatcheries in Norway were collected to understand the challenges and opportunities related to the categorization of mortality causes of lumpfish in hatcheries. This study indicated that a high proportion of lumpfish mortality was categorized by the hatcheries as unspecified. When specified, mortality was primarily assessed as due to fin damage. Our analyses showed that mortality categorized as fin damage correlated with the detection of infectious agents in dead fish, suggesting that mortality was due to infections rather than fin damage. It was not possible to conclude whether infection with pathogens present in the environment caused fin damage or if injuries from aggression were a gateway for pathogens. Furthermore, due to the lack of information regarding production conditions, it was not possible to assess risk factors causing eventual aggression or the presence of pathogens. This study revealed that mortality causality—the chain of events leading to death—is mainly unclear in lumpfish hatcheries because (1) mortality categorization does not focus on underlying causes and (2) there is little documentation of production conditions, making it very difficult to relate mortality rates to external factors. The present findings highlight that there are gaps in the registrations made by hatcheries and that there is an urgent need to implement standardized monitoring protocols for lumpfish hatcheries. This will help identify the causes of mortality and, therefore, allow for the implementation of proper measures that will ensure better survival. Full article

Azamethiphos is used in the salmon industry to treat sea lice and is subsequently discharged into the sea, which may affect non-target species (NTS). A rise in seawater temperature could enhance the sensitivity of NTS. Thus, in the present investigation, the combined effects of azamethiphos (0 µg L⁻¹, 15 µg L⁻¹ and 100 µg L⁻¹) and temperature (12 °C and 15 °C) was assessed over time (7 days) in the gonads and gills of the oyster Ostrea chilensis, assessing its oxidative damage (lipid peroxidation and protein carbonyls) and total antioxidant capacity. Our results indicated that in gonads and gills, lipid peroxidation levels increased over time during exposure to both pesticide concentrations. Protein carbonyl levels in gills increased significantly in all experimental treatments; however, in gonads, only pesticide concentration and exposure time effected a significant increase in protein damage. In both, gill and gonad temperature did not influence oxidative damage levels. Total antioxidant capacity in gonads was influenced only by temperature treatment, whereas in the gills, neither temperature nor azamethiphos concentration influenced defensive responses. In conclusion, our results indicated the time of pesticide exposure (both concentrations) had a greater influence than temperature on the cellular damage in this oyster. Full article

Proteins present in blood samples from Atlantic salmon (Salmo salar) infected with salmon lice (Lepeophtheirus salmonis) were analyzed using liquid chromatography–high-resolution mass spectrometry. Bioinformatic analyses revealed 1820 proteins, of which 58 were assigned to lice. Among these, peroxiredoxin-2, an antioxidant protein, was found relevant with respect to blood feeding of the parasite. The three-dimensional structure analysis of the protein revealed a surface amino acid sequence of interest. A 13-amino-acid peptide was selected as a potential antigen due to its predicted solubility, antigenicity, probable non-allergenic, and non-toxic nature. This peroxiredoxin-2-derived peptide was synthesized, combined with a commercially available adjuvant, and used for vaccination. The test vaccine demonstrated a 60–70% protection rate against early-stage Lepeophtheirus salmonis infection in a challenge trial in Norway. Additionally, the vaccine was tested against salmon lice (Caligus rogercresseyi) in Chile, where a remarkable 92% reduction in the number of adult lice was observed. Thus, in combination with the selected adjuvant, the peptide showed antigenic potential, making it a suitable candidate for future vaccine development. The approach described holds promise for the development of peptide vaccines against various ectoparasites feeding on blood or skin secretions of their hosts. Full article

Salmon lice (Lepeophtheirus salmonis) constitute a major challenge during the production of farmed Atlantic salmon in Norway. Preventive measures are considered to have a higher impact on sustainable control than lice treatment. Therefore, the studies presented here aimed to document the preventive effects of probiotic Aliivibrio spp. on lice infestation in experimental challenges. A reduction in salmon lice attachment success (58–65%) was observed in two separate aquarium trials, where Atlantic salmon were exposed to different compositions of Aliivibrio species 91 and 155 days prior to lice challenge. In a third trial, no difference in attachment was observed in groups exposed to probiotics 58 days prior to lice challenge compared to controls. However, a relative reduction in lice counts was seen on movable stages later in the trial. High levels of probiotic bacteria had no impact on lice viability in an in vitro bioassay on the preadult life stage; thus, the mechanism behind the preventative effect remains unknown. In conclusion, probiotic Aliivibrio bacteria can likely be used as a preventive tool to reduce salmon louse infestations in the salmon industry. The mechanism is still unknown, and this novel approach to lice control warrants further investigation to understand its optimal use and potential. Full article

Aquaculture of the lumpfish (Cyclopterus lumpus L.) has become a large, lucrative industry owing to the escalating demand for “cleaner fish” to minimise sea lice infestations in Atlantic salmon mariculture farms. We used over 10K genome-wide single nucleotide polymorphisms (SNPs) to investigate the spatial patterns of genomic variation in the lumpfish along the coast of Norway and across the North Atlantic. Moreover, we applied three genome scans for outliers and two genotype–environment association tests to assess the signatures and patterns of local adaptation under extensive gene flow. With our ‘global’ sampling regime, we found two major genetic groups of lumpfish, i.e., the western and eastern Atlantic. Regionally in Norway, we found marginal evidence of population structure, where the population genomic analysis revealed a small portion of individuals with a different genetic ancestry. Nevertheless, we found strong support for local adaption under high gene flow in the Norwegian lumpfish and identified over 380 high-confidence environment-associated loci linked to gene sets with a key role in biological processes associated with environmental pressures and embryonic development. Our results bridge population genetic/genomics studies with seascape genomics studies and will facilitate genome-enabled monitoring of the genetic impacts of escapees and allow for genetic-informed broodstock selection and management in Norway. Full article

Salmon lice are one of the biggest challenges to sustainable salmonid aquaculture. The species display high evolutionary potential, which is evident by its development of resistance to numerous chemical compounds used for delousing. In response to this, salmon farms now use non-chemical delousing methods to minimize the damage done by salmon lice, including heavy reliance on cleaner fish. Anecdotal reports from farmers and fish health personnel in areas where cleaner fish are used have suggested that salmon lice are becoming less pigmented, potentially making them harder for cleaner fish to visually detect. This experiment investigated changes in the pigmentation of salmon lice in relation to the use of cleaner fish, louse stage and sex, temperature, preferred salmon swimming depth, daylength, and salinity. Salmon lice were sampled from snorkel cages on a commercial salmon farm where three cages were stocked with farmed lumpfish and ballan wrasse, and three cages were without cleaner fish. Water temperature, salinity, and depth were recorded using a conductivity, temperature, and depth recorder. Pigmentation was measured via photographic analysis of individual lice. Although louse pigmentation varied considerably throughout the experiment, using cleaner fish throughout a single production cycle did not reduce average louse pigmentation compared to control cages. On average, male lice were significantly darker pigmented than females, but otherwise there were no patterns in louse pigmentation in relation to life stage, salinity, temperature, or daylength. Salmon lice exhibit a high degree of evolvability and have become resistant to every chemical removal treatment developed thus far. The present data suggest that, with the densities and species of cleaner fish commonly used in commercial salmon production, there is not strong directional selection on louse pigmentation. Lice, at least with regard to visual appearance, are not likely to adapt in a way which reduces cleaner fish efficacy anytime soon. Full article

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 heritable genetic variation was estimated for Nkef (h² skin: 0.96 ± 0.14 and gills: 0.97 ± 0.11) and Tnfα (h² skin: 0.53 ± 0.17 and gills: 0.32 ± 0.14), but not for Il-8 (h² skin: 0.22 ± 0.12 ns and gills: 0.09 ± 0.08 ns). This work provides evidence that Nkef and Tnfα protein expressions are highly heritable and related to resistance against sea lice in Atlantic salmon. Full article

Salmon aquaculture is constantly threatened by pathogens that impact fish health, welfare, and productivity, including the sea louse Caligus rogercresseyi. This marine ectoparasite is mainly controlled through delousing drug treatments that have lost efficacy. Therein, strategies such as salmon breeding selection represent a sustainable alternative to produce fish with resistance to sea lice. This study explored the whole-transcriptome changes in Atlantic salmon families with contrasting resistance phenotypes against lice infestation. In total, 121 Atlantic salmon families were challenged with 35 copepodites per fish and ranked after 14 infestation days. Skin and head kidney tissue from the top two lowest (R) and highest (S) infested families were sequenced by the Illumina platform. Genome-scale transcriptome analysis showed different expression profiles between the phenotypes. Significant differences in chromosome modulation between the R and S families were observed in skin tissue. Notably, the upregulation of genes associated with tissue repairs, such as collagen and myosin, was found in R families. Furthermore, skin tissue of resistant families showed the highest number of genes associated with molecular functions such as ion binding, transferase, and cytokine activity, compared with the susceptible. Interestingly, lncRNAs differentially modulated in the R/S families are located near genes associated with immune response, which are upregulated in the R family. Finally, SNPs variations were identified in both salmon families, where the resistant ones showed the highest number of SNPs variations. Remarkably, among the genes with SPNs, genes associated with the tissue repair process were identified. This study reported Atlantic salmon chromosome regions exclusively expressed in R or S Atlantic salmon families’ phenotypes. Furthermore, due to the presence of SNPs and high expression of tissue repair genes in the resistant families, it is possible to suggest mucosal immune activation associated with the Atlantic salmon resistance to sea louse infestation. Full article