Search Results (196)

The infectious pancreatic necrosis virus (IPNV) used to be one of the largest loss factors in Atlantic salmon farming. Since 2009, marker-assisted selection for resistance to IPN, targeting a single major quantitative trait locus (QTL), has led to a ten-fold decrease in the number of IPN outbreaks in Norway. However, some IPN-related problems remain, due to isolates of the virus which seem to bypass the resistance mechanism of the QTL. We comparatively characterized a classical isolate affected by the IPN-QTL (cIPNV) and an isolate that circumvents the QTL-based protection (rIPNV). Using both in vivo and in vitro challenges, the viral infection dynamics and host responses were evaluated by RT-qPCR and by gene ontology (GO) enrichment analysis from the RNA sequencing data of infected hepatocytes and the whole liver. Overall, cIPNV showed rapid replication with pronounced lytic cytopathology and enrichment for DNA damage, apoptosis and cell cycle disruption GO terms, while rIPNV exhibited slower accumulation of viral RNA and a transcriptional footprint consistent with pro-survival states in hepatocytes. While further research is needed to resolve the causality of QTL evasion, this work provides a first characterization of the pathogenicity of emerging QTL-insensitive IPNV isolates. Full article

A prolonged dietary phosphorus (P) deficiency can result in reduced growth and vertebral deformities in farmed Atlantic salmon (Salmo salar). Severe deformities can impair swimming and lead to chronic stress associated with muscular fibrotic scarring. Conversely, excess dietary P contributes to farm effluents and environmental pollution. Vertebral centra ash content and mechanical strength both respond rapidly to suboptimal dietary P supply, but measuring all of salmon’s 59 vertebrae is time consuming. As such, this study assessed whether vertebrae from two commonly assessed regions (transitional and caudal) vary in their response to different dietary P levels. Atlantic salmon with an initial average weight of 1.8 kg (December 2022) were fed one of four experimental diets containing an increasing level of inorganic P (6.1–10.7 g/kg total P, 2.3–5.8 g/kg available P). Animals were distributed across 16 sea cages in a quadruplicated design. The regional differences in vertebral centra were assessed at two sampling points: in April 2023 following a slow growth period, and in July 2023 following a fast growth period. The growth of the caudal vertebrae in length surpassed the extension of the transitional vertebrae during the fast growth period. The bone mineralisation measured through vertebral centra ash and mechanical strength was however comparable between the regions, indicating that the rate of mineralisation was adjusted to the growth of the vertebrae. Only two parameters, yield point, which specifies the amount of energy that vertebra can absorb before it is permanently compressed, and toughness, a measure of stress per unit volume required to cause a fracture, showed regional differences. Considering transitional vertebrae, the estimated requirements were 4.1 g/kg available P in April and 4.4 g/kg in July, while the requirements based on caudal vertebrae were 3.7 g/kg in April and 4.6 g/kg in July. As such, both the transitional and caudal regions are equally suitable for a prompt recognition of suboptimal dietary P levels. Full article

The rapid expansion of the salmon industry has generated increasing amounts of waste sludge with negative environmental impacts. Sustainable alternatives, such as using stabilized sludge in agriculture, are needed to mitigate these effects. At the same time, fruit production has grown globally, with hazelnut (Corylus avellana L.) emerging as a crop of high economic importance. However, the effect of salmon sludge application on hazelnut orchards is poorly understood. This study evaluated the application of thermally stabilized fish farming sludge (DS) compared with a slow-release mineral fertilizer (MF) intwo hazelnut varieties, ‘Barcelona’ (B) and ‘Tonda di Giffoni’ (TDG). Growth parameters including trunk cross-sectional area (TCSA), cumulative growth, shoot growth rate, leaf mass area (LMA) and chlorophyll index (SPAD), as well as soil physicochemical properties and enzymatic activities (fluorescein diacetate, β-glucosidase, acid phosphatase) were assessed. No significant differences (p > 0.05) in physiological parameters were found between DS and MF. However, the DS application increased soil pH by up 18%, electrical conductivity by ~48% at peak values, and enzymatic activities by 44% (acid phosphatase in B variety), 38% (β-glucosidase in TDG) and 169% (FDA in TGD), suggesting a great organic matter contribution and enhanced soil metabolic activity. Additionally, the B variety showed superior physiological performance, while TDG exhibited higher enzymatic activity. Overall, these findings provide a preliminary assessment of DS as a sustainable supplement to mineral nitrogen fertilization in hazelnut orchards, supporting both soil quality improvement and circular economy strategies in agriculture and aquaculture. Full article

Background: Chilean salmon aquaculture, a sector crucial for global food security, faces persistent challenges from bacterial pathogens, particularly Piscirickettsia salmonis, resulting in substantial antimicrobial use (351.1 tons in 2024). Objective and methods: To address this issue, the “Sustainable Management of Aquaculture Bacterial Diseases” workshop convened 27 experts to develop a roadmap for prudent antimicrobial stewardship, with the goal of informing public policies and industry best practices. Discussions focused on four critical areas. Results: Antimicrobial Resistance Prevention recognized aquaculture’s dual role in antimicrobial resistance development, underscoring its ecological dimension, the need for international collaboration, proactive policy design, and the establishment of comprehensive “One Health” surveillance systems guided by expert committees. Communication and Education identified critical gaps in specialized veterinary aquaculture training and public outreach, advocating for interdisciplinary teams and clear communication strategies, with a projected timeline of a decade for effective implementation. Therapeutic Alternatives acknowledged current limitations of vaccines against P. salmonis but underscored promising Chilean innovations, including the use of plant extracts, gut-microbiota modulation, and passive immunotherapy, as well as the importance of early intervention. Finally, environmental impact discussions revealed data deficiencies in aquatic ecosystems, emphasizing the need for advanced molecular tools, adaptive regulatory frameworks, and harmonized requirements for environmental risk-assessment procedures. Conclusions: The workshop’s findings provide a vital framework for advancing sustainable antimicrobial use within the Chilean salmon industry as a case study. The insights and lessons derived from this sector can significantly contribute to global aquaculture’s transition toward sustainability, providing a solid foundation for developing a comprehensive roadmap and universally applicable recommendations for stakeholders across aquaculture and other animal-farming industries worldwide. This roadmap, with its essential components, is designed to enhance the understanding of AMU in farmed salmon through a One Health approach, incorporating global guidance for all aquaculture stakeholders. Full article

Salmon farming has been affected by various bacterial diseases, and the use of antibiotics (such as oxytetracycline “OTC”) to control these diseases has become necessary and thus routine. This study aimed to determine how the gill cells are affected by OTC in Salmo salar. Gill tissue culture was performed in periods of 0.5, 1, 3, 6, 12, and 24 h, assessing the enzymatic activity and mRNA expression of catalase (CAT), cytochrome p450, glutathione peroxidase (GPx), glutathione reductase (Gr), and superoxide dismutase (SOD), HSP70 and HSP90, in response to two doses of OTC: 0.25 (low), and 3 µL/mL (high). The results indicated that the enzymatic activity of SOD and CAT showed low enzyme activity at both doses. At the same time, GR presented varied response patterns depending on the time and dose of OTC used, contrary to GPx, which just increased the enzyme activity at early times. Although the mRNA expression presented the most precise pattern of expression, they were not in line with the enzymatic activities. The HSP70 and HSP90 mRNA expression response (as a cellular damage marker) increased mRNA levels at low and high doses, respectively, but at different times, alluding to a differentiated response given by the size of the chaperone. These results suggest an oxidative response of the gills to OTC exposure and constitute significant information on the amount of OTC used in aquaculture and on methods for improving the optimal dose of drugs, fish health, and, consequently, environmental health. Full article

Infectious hematopoietic necrosis virus (IHNV), a salmonid rhabdovirus, causes severe mortality exceeding 90% in both wild and farmed salmon and trout. Frequent outbreaks of IHNV highlight the urgent need for rapid detection methods to support effective prevention and control. This study developed a double-antibody sandwich ELISA (DAS-ELISA) targeting the nucleocapsid (N) protein of IHNV. Two peptides derived from the N protein—selected for their strong antigenicity, high level of conservation, and surface accessibility—were used as immunogens to generate two specific monoclonal antibodies. Following optimization, the DAS-ELISA was established using monoclonal antibody N-15 as the capture antibody and horseradish peroxidase (HRP)-conjugated antibody N-106 as the detection antibody. The results of this study demonstrated that DAS-ELISA exhibited high specificity for multiple IHNV strains and showed no cross-reactivity with IPNV, SVCV, or VHSV. The detection sensitivity of DAS-ELISA for IHNV was determined to be 10³ TCID₅₀/mL. Parallel analysis of 293 clinical samples using DAS-ELISA and WOAH reference method demonstrated a concordance rate of 92.83% (κ = 0.856). These results confirm that the established DAS-ELISA exhibits high sensitivity, specificity, broad-spectrum applicability, and repeatability. In conclusion, this DAS-ELISA provides a reliable and efficient tool for high-throughput early detection of IHNV infection in clinical settings. Full article

Background/Objectives: Metagenomic analyses are an important tool for understanding ecological effects, particularly in sites exposed to antimicrobial treatments. Marine sediments host diverse microbial communities and may serve as reservoirs for microbial resistance. Although it is known that antimicrobials can alter microbial composition, specific impacts on sediments surrounding salmon farms remain poorly understood. This study analyzed bacterial community structure in marine sediments subjected to florfenicol treatment from salmon farms in the Los Lagos Region of southern Chile. Methods: Sediment samples were collected and examined through DNA extraction and PCR amplification of the 16S rRNA gene (V3-V4 region). Sequences were analyzed using a bioinformatics pipeline, and amplicon sequence variants (ASVs) were taxonomically classified with a Naïve Bayesian classifier. The resulting ASV abundance were then used to predict metabolic functions and pathways via PICRUSt2, referencing the MetaCyc database. Results: Significant differences in bacterial phyla were observed between the control farm and two farms treated with florfenicol (17 mg kg⁻¹ body weight per day) for 33 and 20 days, respectively. Farm 1 showed notable differences in phyla such as Bacteroidota, Bdellovibrionota, Crenarchaeota, Deferrisomatota, Desulfobacterota, Fibrobacterota, Firmicutes, and Fusobacteriota, while Farm 2 exhibited differences in the phyla Bdellovibrionota, Calditrichota, Crenarchaeota, Deferrisomatota, Desulfobacterota, Fusobacteriota, Nanoarchaeota, and Nitrospirota. Shannon Index analysis revealed a reduction in alpha diversity in the treated farms. Comparative analysis between the control and the treated farms showed pronounced shifts in the relative abundance of several bacterial phyla, including statistically significant differences in Chloroflexi and Firmicutes. Predicted functional pathways revealed a notable enrichment of L-methionine biosynthesis III in Farm 2, suggesting a shift in sulfur metabolism potentially driven by antimicrobial treatment. Additionally, increased activity in fatty acid oxidation pathways indicates a higher microbial potential for lipid degradation at this site. Conclusions: These findings highlight the considerable influence of florfenicol on sediment microbial communities and reinforce the need for sustainable management strategies to minimize ecological disruption and the spread of antimicrobial resistance. Full article

The large environmental and economic impact of sea lice infestation in the salmon industry has encouraged the development of non-medical methods and preventive strategies to combat sea lice infestation. Sea lice (Lepeophtheirus salmonis and Caligus elongatus) are sensitive to low salinities, and using fresh water as protection against infection may thus significantly reduce sea lice infestation of salmon while reducing the costs and impacts of traditional delousing methods. A new concept presented here is based on the manipulation of salinity within cages by adding fresh water to create an unfavourable environment for sea lice infestation. A full-scale set-up was tested in a salmon farm in northern Norway: two commercial-size cages with Atlantic salmon (Salmo salar) were enclosed with a 2 m deep tarpaulin skirt and supplied with fresh water at the centre to establish a surface layer with reduced salinity. Two reference cages had no skirt or fresh water supply. Time series of CTD-data showed that the fresh water supply caused a shallow and unstable salinity gradient, with salinities lower than 10 ppt measured for short periods in the upper 0.5 m. Despite these instabilities, significantly lower sea lice infestation in cages supplied with fresh water was observed, as infestation rates for pre-adult and adult stages of L. salmonis were reduced by 48% and 57%, respectively, in the treatment cages compared to controls. This preventive strategy is therefore very promising and deserves further development under more stable and controlled conditions. Future studies should focus on improving freshwater regulation, ensuring higher spatial resolution of salinity data in surface layers and documenting the effect on the more salinity-sensitive planktonic stages of L. salmonis. In addition, there is a need to examine the effectiveness of the technique at multiple sites and under a wide range of site conditions, especially various current rates through the site. Full article

A global debate is underway about how to achieve economic growth, which has led to a push for even greater ‘better regulation’ than already exists in the US and UK, including Scotland. ‘Better regulation’ can include softer regulation, less regulation, or even deregulation. Another regulatory model involves the precautionary principle and there is tension between the two. The ‘better regulation agenda’ has influenced the environmental quality standards adopted for emamectin benzoate in Scottish sea lice treatment. To explore how these complex regulatory models have been used or advocated for and why over 25 years, a process tracing analysis focusing on Scottish Government and Parliament web entries was conducted. Such an analysis has both strengths, providing new perspectives, and weaknesses, regarding the possible quality and extent of information available. The results reveal the ‘better regulation’ model in practice was initially adopted in the 2000s, supported by Scottish Government advisors and implemented by its regulators. Gradually, however, the model was challenged, at times, by researchers, regulators, Members of the Scottish Parliament, environmental non-governmental organizations, and by investigative journalists. This resulted in new environmental quality standards on emamectin benzoate being proposed, then sometimes tightened or blocked. Hence, ‘better regulation’ remains highly influential in the sector, with the fish farming industry able to weaken precautionary policies and enforcement in practice, directly and indirectly. Full article

The emergence and spread of pathogens pose significant challenges to the sustainability and productivity of aquaculture globally. For the Chilean salmon farming industry, salmonid rickettsial septicemia (SRS), caused by the facultative intracellular bacterium Piscirickettsia salmonis, constitutes one of the main disease challenges. In this study, the efficacy of various oral doses of florfenicol (FFC) (5, 7.5, and 10 mg/kg BW/day) against SRS was assessed in Atlantic salmon, when treatment was initiated at an early stage of infection. Since salmonids infected with P. salmonis typically lose appetite as the disease progresses, and the therapeutic FFC dose is dependent on a normal specific feeding rate (SFR), the treatments were administered 5 days post-challenge (DPC5). On the day of challenge, experimental fish were intraperitoneally (IP) injected with 0.2 mL of P. salmonis genogroup LF-89 inoculum (9.07 × 10⁷ CFU mL⁻¹). Fish mortality, behavior, clinical signs of disease, feed intake and SFR were monitored throughout the study. Conclusions: An important finding in this study was that all tested antibiotic doses halted disease progression and prevented mortality in fish challenged with P. salmonis when administered DPC5. In the control group, mortality reached 32.2% with fish displaying clinical signs of SRS. Full article

A new polypeptide vaccine towards salmon lice (Lepeophtheirus salmonis) was given to experimental groups of 2 × 8000 Atlantic salmon parr (Salmo salar L.), following the vaccination of a total of 4 × 8000 parr with a common set of vaccines used in Norwegian aquaculture to prevent infestation in salmon growing at sea. The remaining 2 × 8000 salmon served as control. The trial was conducted at a sea farm research facility at Knappen-Solheim in Masfjorden, Norway. Natural infestation with sea lice were staged and counted once a week from January–December 2023. The infestation was never above two mature female lice per salmon, the maximum limit set specifically for the present trial by the Norwegian Food Safety Authorities, thus delousing with chemicals or other methods was avoided. Mortality, growth, feed consumption, sexual maturation, slaughter quality, and welfare quality parameters were not significantly different between vaccinated and control salmon. The effect size showed a moderate positive difference of 0.07 mature female salmon lice per salmon in favor of the vaccinated groups from a fish size above 600 g in May until November. All fish were slaughtered and marketed at a size of 5.8 kg (>83% superior quality). Full article

Chile is the second-largest producer of Atlantic salmon (Salmo salar), a key industry facing challenges such as infestations by Caligus rogercresseyi, which cause significant economic losses. However, there are no studies exploring how environmental variables in marine culture centers affect salmon’s immune response, considering their poikilothermic characteristics. This study analyzed the effect of the seasonal temperature on the skin transcriptome of Atlantic salmon infested with C. rogercresseyi in fjord-based farms in the Aysén Region during autumn and spring. Two different centers were analyzed (autumn: Farm-A; spring: Farm-S) to ensure the same age of the fish sampled in each season. RNA sequencing (RNA-seq) and functional network analysis revealed notable seasonal transcriptomic differences. In autumn, 253 differentially expressed genes (DEGs) were found, primarily associated with stress response and negative regulation of T-cell proliferation, suggesting an impaired response against the ectoparasite. In spring, 103 DEGs were detected, associated with protein synthesis and the activation of immune mechanisms, including complement activation, granulocyte chemotaxis, and antigen presentation. This is the first study to evaluate the transcriptomic response of healthy skin in C. rogercresseyi-infested salmon under farming conditions, highlighting the importance of considering seasonal variations for the development of more effective management strategies in the aquaculture industry. Full article

Global marine coastal aquaculture increased by 6.7 million tons in 2024, with whiteleg shrimp (Penaeus vannamei) dominating crustacean production. However, reliance on a single species raises sustainability concerns, particularly in the face of climate change. Diversifying shrimp farming by cultivating native species, such as the European brown shrimp (Crangon crangon), presents an opportunity to develop a sustainable blue bioeconomy in Europe. C. crangon holds significant commercial value, yet overexploitation has led to population declines. Integrated Multi-Trophic Aquaculture (IMTA) offers a viable solution by utilizing fish farm wastewater as a nutrient source, reducing both costs and environmental impact. Research efforts in Germany and other European nations are exploring IMTA’s potential by co-culturing shrimp with species like sea bream, sea bass, and salmon. The physiological adaptability and omnivorous diet of C. crangon further support its viability in aquaculture. However, critical knowledge gaps remain regarding its lipid metabolism, early ontogeny, and reproductive biology—factors essential for optimizing captive breeding. Future interdisciplinary research should refine larval culture techniques and develop sustainable co-culture models. Expanding C. crangon aquaculture aligns with the UN’s Sustainable Development Goals by enhancing food security, ecosystem resilience, and economic stability while reducing Europe’s reliance on seafood imports. 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

Standard blood agar medium with 2% NaCl (BAS) and Marine Agar (MA) are commonly used in bacteriological investigations of winter ulcers in farmed Atlantic salmon (Salmo salar Linnaeus) in Norway and allow easy recovery of Moritella viscosa based on its characteristic viscous colonies and β-hemolytic activity. However, the recent increase in cases of winter ulcers involving Tenacibaculum spp. and the potential emergence of T. maritimum due to rising temperatures highlight the need for improved methods of isolation and identification. Indeed, the recovery of Tenacibaculum spp. from outbreaks of winter ulcers or tenacibaculosis can be challenging. Despite the development of several agar media over the years to overcome this issue, such as Flexibacter maritimus medium (FMM), it remains difficult to differentiate Tenacibaculum species. We evaluated the growth dynamics and phenotypic characteristics of 13 bacterial isolates commonly associated with ulcer outbreaks on five different agar media, including two new formulations: kanamycin-supplemented marine blood agar for the selective isolation of Tenacibaculum spp. (KABAMA) and general blood agar for marine bacteria (BAMA). These new media facilitate the identification of Tenacibaculum spp., including T. maritimum, by distinguishing colonies based on their specific color, shape, and hemolytic activity. Full article