Search Results (383)

Pancreas disease (PD), caused by Salmonid alphavirus (SAV), is a notifiable disease in Atlantic salmon (Salmo salar L.) in Norway. Conventional inactivated virus vaccines have shown variable effects in mitigating the disease, and a DNA vaccine has been used over the last 7–8 years, which may have resulted in the reduction in the number of reported PD cases. This manuscript provides a comprehensive overview of DNA vaccination in farmed fish, with a focus on the licensed DNA vaccine, Clynav^®, against SAV3 infection. It explores the biological underpinnings of SAV infection, immune mechanisms activated by DNA vaccines, and the benefits and limitations of this approach. Although antigen processing and presentation mechanisms following DNA vaccination in fish remain incomplete, studies document robust innate responses and measurable adaptive immunity, including neutralizing antibodies, as seen in Clynav, and transcriptomic studies indicate that cell-mediated immunity is evoked under experimental conditions. Comparative trials demonstrate that DNA vaccination reduces viral load, tissue pathology, and, potentially, viral transmission, outperforming traditional oil-adjuvanted vaccines. Additionally, DNA-vaccinated fish show improved growth performance under field conditions. These findings support DNA vaccination as a promising strategy for controlling PD in salmon aquaculture, with implications for fish health, welfare, and sustainable production. Full article

Salmonid fish only reproduce in habitats that meet specific environmental requirements, including appropriate gravel–cobble substrate, suitable flow velocity, and adequate oxygenation. Long-term drainage practices and river channel regulation have led to substantial alterations of river systems, particularly affecting bed structure. The aim of this study was to assess habitat conditions in the Ina river catchment and to restore spawning grounds for salmon and sea trout through the construction of artificial redds, as well as to evaluate the effectiveness of these measures over subsequent years. The number of fish nests recorded prior to the implementation of the restoration project in 2011 was significantly lower (3 ± 1, mean ± SD) compared to post-restoration periods in 2013 (23 ± 11) and 2015 (21 ± 14). Spawning nests were predominantly located in areas characterized by high flow velocity and elevated water conductivity, hardness, and alkalinity. During the spawning migrations in 2013–2015, a total of 4593 individuals were recorded using a fish scanner. Despite a gradual decline in water levels from pre-restoration to post-restoration periods, the number of nests remained consistently high. The results indicate that ongoing environmental and climatic changes necessitate continued efforts to improve spawning conditions for anadromous salmonids. Currently (2024–2025), the potential for natural reproduction in the Ina River catchment remains comparable to the study period (89 redds), largely determined by the availability of gravel habitats and river discharge enabling upstream migration. Full article

Smolt production in freshwater is an essential component of the salmonid aquaculture production chain. But it generates sludge (feed waste and fish feces) that must be managed to meet environmental regulations. While sludge can be reused as a resource, there are limited empirical results about cost structures, market conditions, and energy implications in industrial aquaculture. This study analyzes sludge collection, processing, and utilization based on a single-case study of a Norwegian smolt producer (Sisomar AS). The analysis combines company-level production data, accounting information, and process descriptions. In 2023, the company produced approximately 9.2 million smolt (1184 tons of biomass), generating 140 tons of dried sludge. Sisomar’s value creation from production of bio-based fertilizer from sludge is relatively close to that of comparable mineral fertilizers, but a direct comparison here is difficult because of large variations in the prices of mineral fertilizers. The energy consumption is significantly lower for organic fertilizer from Sisomar compared to standard technology for mineral fertilizer production. Bio-based fertilizers are looked at as an important contribution to dealing with environmental challenges, and this study discusses the characteristics of how market structures have importance for this. Full article

Intensive salmon farming is associated with high mortality rates, highlighting the need for new welfare indicators that can detect adverse conditions earlier and less invasively than many current approaches. Existing animal-based indicators used in the industry typically depend on subjective scoring and provide information mostly after welfare problems have already developed, thereby raising questions about their efficacy. Examples include emaciation, wounds, or scale loss, etc. Preliminary data and ongoing investigation suggest that melanin-based skin pigmentation may change dynamically with stress and condition in salmonid fishes. In this study, we present a semi-automated methodology for assessing changes in the grayscale intensity of melanin-based skin spots within the operculum region of adult Atlantic salmon (Salmo salar) kept in seawater. The pipeline combines computer vision models to detect the operculum, segment individual spots, and extract grayscale-based features for spot-level analysis over time. The method was applied to out-of-water images collected before and after exposure to a confinement episode. The results showed an overall shift in grayscale intensity from black to pigmentation fading after the challenge, although responses varied among individuals. These findings indicate that the proposed methodology can detect temporal changes in opercular melanin-based spots under applied experimental conditions. We therefore present this work as proof of principle for using computer vision to quantify changes in melanin-based skin spots as a potentially useful, non-invasive indicator of stress and welfare in Atlantic Salmon. Full article

Background: Sulfated chitosan (ChS) is a chemically modified polysaccharide derived from chitin that mimics heparan sulfate (HS) structures and has emerged as a promising antimicrobial biomaterial. Piscirickettsia salmonis, the etiological agent of Salmonid Rickettsial Septicemia (SRS), represents the main driver of antibiotic use in Chilean aquaculture. Objective: In this study, the in vitro antibacterial activity of ChS against P. salmonis was evaluated. Methods: Elemental characterization by SEM-EDS and FTIR analysis confirmed successful sulfation of the polymer, with a degree of sulfation ranging from 0.92 to 0.95. Additionally, X-ray diffraction (XRD) analysis revealed a reduction in polymer crystallinity, indicating a transition toward a more amorphous structure associated with increased molecular flexibility and functional group accessibility. Results: Antibacterial assays revealed a minimum inhibitory concentration (MIC) of 1500 µg/mL and a minimum bactericidal concentration (MBC ≥ 1500 µg/mL). LIVE/DEAD™ fluorescence imaging showed the formation of bacterial aggregates with increasing size, frequency, and red fluorescence compared to controls over the exposure to ChS, indicating progressive membrane damage. This was supported by a reduction (p < 0.05) in the Green/Red fluorescence ratio of 37–46% between 5 h and 96 h of exposure, corresponding to alteration of the cell membrane. Scanning electron microscopy revealed pronounced morphological alterations by ChS, including surface disruption and loss of cellular integrity. This was more severe compared to commercial chitosan (ChC). Also, ChS reduced (p < 0.05) biofilm formation (>50% at day 6 and 34.8% at day 8). Conclusions: These results demonstrated that ChS disrupts the cell membrane and reduces biofilm formation in P. salmonis, thereby affecting viability. This is the first report of the antibacterial effect of ChS, an HS analogue, against P. salmonis. Full article

Background/Objectives: It is challenging to develop efficient vaccines against intracellular pathogens such as viruses, and since viral infections are one of the main challenges for farmed salmon, a novel vaccine strategy is needed. mRNA vaccines are optimized and approved for humans, but for fish, the mRNA technology is new, and optimization is required to ensure efficient protein expression. We made an mRNA tailored to salmon and studied the effect of modified nucleosides and the length of the poly(A) tail on protein expression from in vitro-transcribed mRNA in CHSE-214 cells, using enhanced green fluorescent protein (EGFP) as a reporter. Methods: Different lengths of the poly(A) tail were tested, and various modified nucleotides were incorporated in the mRNA during in vitro transcription, including pseudouridine (Ψ), N1-methylpseudouridine (m1Ψ), N6-methyladenosine (m6A), 5-methyluridine (m5U), and 5-methylcytidine (m5C). Protein expression was observed in fluorescence microscopy and quantified using flow cytometry. Results: mRNA containing Ψ resulted in the strongest EGFP expression 1–3 days post-transfection (dpt), while EGFP expression from m5C mRNA was high throughout the experiment (<10 dpt). m5U-containing mRNA had low EGFP expression until 6 dpt, but reached the level of m5C mRNA at 10 dpt. The m5U mRNA, however, expressed EGFP at much higher intensity than all the other mRNAs at all time points. Poly(A) tails with lengths of 40, 100, and >100 were tested, and the one with >100 adenines showed the highest expression. The effects of phosphatase treatment and purification of the mRNA were also investigated. Furthermore, EGFP expression was observed in yolk-sac salmon larvae following micro-injection. Conclusions: Our study provides an important basis for the development of efficient mRNA-based vaccines in the future. Full article

The decline of salmonid stocks in the Baltic Sea region is a matter of serious concern, prompting many countries to implement widespread stocking of artificially reared individuals to restore or enhance populations. While such interventions are intended to be beneficial, their efficacy remains a subject of ongoing debate. Artificially reared fish often face challenges in adapting to natural environments and may struggle to compete with wild counterparts, potentially leading to reduced growth rates and diminished overall fitness. This study evaluated the growth and physiological condition of naturally hatched versus artificially reared Salmo trutta juveniles during their first two years of life, prior to smoltification and seaward migration. The results demonstrated that stocked juveniles exhibited significantly slower growth, a higher incidence of fin damage, and a greater abundance of cultivable gut bacteria compared to wild individuals. Conversely, no significant differences were observed in blood parameters. Such growth retardation suggests potential difficulties in adaptation and recruitment. Consequently, while the release of artificially reared S. trutta fry facilitates the restoration of extinct populations, its capacity to enhance existing stocks within Baltic Sea riverine ecosystems may be limited. Full article

Understanding salmonid spawning dynamics is critical for conserving cold-water river ecosystems amid increasing human and climate pressures. This study developed and validated a species-specific eDNA (Salmo cf. trutta and Thymallus thymallus) and evaluated its performance for seasonal spawning activity monitoring using droplet digital PCR (ddPCR). Species-specific primers and probes targeting mitochondrial nd5 (S. trutta) and cytb (T. thymallus) genes were designed and optimized as a duplex assay. Performance assessments included in vitro validation, cross-amplification testing, and determining the LOB, LOD, and LOQ. Field validation over a year at two spawning sites in the Gradac River, Serbia, involved seasonal eDNA sampling, filtration, extraction, and ddPCR analysis. Fish community composition was also assessed with electrofishing and metabarcoding. The assay showed high specificity and sensitivity, with LODs of 0.14 cp/µL and LOQs of 0.99 and 1.25 cpµL for S. trutta and T. thymallus. S. trutta eDNA peaked in late autumn during spawning, while T. thymallus remained at or below detection limits, reflecting its lower abundance and different spawning season. Filter type affected filtration efficiency but not eDNA yield. These findings confirm ddPCR-based eDNA as a powerful, non-invasive tool for monitoring salmonid spawning and seasonal changes, supporting adaptive fisheries management and conservation amid environmental changes. Full article

Infectious pancreatic necrosis virus (IPNV), a member of the family Birnaviridae, is a major pathogen of farmed salmonids and an important model in fish virology. Despite its small genome, which encodes only five viral proteins, IPNV exhibits complex molecular processes that govern genome expression, replication, and particle assembly. Comprehensive descriptions of the molecular biology and replication cycle of IPNV were largely established in reviews published in the mid-1990s, whereas more recent reviews have primarily focused on virulence determinants, epidemiology, or host–virus interactions. This review provides an updated synthesis of available experimental knowledge on the molecular biology of IPNV by integrating classical and recent studies addressing virion architecture, genome organization, and the functions of viral proteins. Particular attention is given to the molecular events involved in the viral replication cycle, including virus entry, genome transcription, translation and replication in the cytoplasm, polyprotein processing by the viral protease, and the coordination between genome replication and virion assembly. When appropriate, experimental observations from the related Avibirnavirus infectious bursal disease virus are considered to provide additional context for molecular mechanisms conserved within the family Birnaviridae. Together, these studies outline the current understanding of the molecular processes governing IPNV replication and morphogenesis. Full article

The brown trout (Salmo trutta) is a commercially and ecologically significant salmonid fish, yet its hepatic cellular and functional dynamics throughout the reproductive cycle remain poorly characterised, particularly in males. This study investigated seasonal and sex-specific liver plasticity across four reproductive stages: spawning capable (December), regressing (March), regenerating (July), and developing (November). We quantified mRNA and protein abundance of key oestrogen-responsive targets—vitellogenin (VtgA) and zona pellucida (ZP) proteins—alongside cell turnover markers, caspase 3 (Casp3) and proliferating cell nuclear antigen (PCNA). These molecular endpoints were integrated with stereological analyses to estimate hepatocyte, nuclear, and cytoplasmic volumes. Results revealed stage-dependent mobilisation and transient hepatic retention of reproductive proteins; females exhibited stronger vitellogenic signatures and more pronounced seasonal shifts than males. Although VtgA and ZP mRNA levels peaked during the developing and spawning-capable stages, males maintained low but consistent levels throughout the cycle, indicating constitutive hepatic oestrogen sensitivity. Regarding cell turnover, PCNA protein data indicated heightened proliferative activity during the spawning-capable and regressing stages. In contrast, while Casp3 mRNA levels remained stable across all stages, protein detection suggested a post-transcriptional increase in apoptotic signalling during the developing phase, consistent with controlled tissue remodelling rather than extensive cell loss. Stereological data confirmed enlarged hepatocyte and nuclear volumes during periods of high secretory and proliferative demand. Overall, these findings demonstrate significant stage-dependent and sex-specific plasticity in brown trout liver, providing a robust reference framework for ecological monitoring, endocrine disruption assessments, and studies of teleost reproductive physiology. Full article

Background: Infectious hematopoietic necrosis virus (IHNV), a rhabdovirus classified within the genus Novirhabdovirus, continues to be one of the most detrimental pathogens impacting salmonid aquaculture on a global scale. Notable for inducing high mortality rates among fry and fingerlings, IHNV represents a substantial threat to the economic stability of the aquaculture industry. This review offers an in-depth analysis of the contemporary advancements in IHNV vaccine development. Methods: We assess the efficacy and immunological mechanisms of traditional vaccine platforms, including inactivated and live-attenuated vaccines, while emphasizing the groundbreaking success of DNA vaccines, particularly those encoding the viral glycoprotein (G). Although nucleic acid-based therapies provide high levels of protection, they face logistical challenges related to delivery and regulatory obstacles associated with Genetically Modified Organisms (GMOs). Additionally, we examine emerging “next-generation” platforms, such as viral vector vaccines, subunit proteins produced in yeast or plant systems, and RNA-based technologies. We critically analyze technical bottlenecks, including the lack of efficient mucosal delivery systems and the limited understanding of long-term cellular memory in teleosts. Results: We propose future research directions that emphasize the development of multivalent formulations and the incorporation of molecular adjuvants to augment mucosal immunity. Conclusions: This synthesis seeks to integrate fundamental viral pathogenesis with applied immunology to develop a strategic framework for the sustainable, long-term management of IHNV in global salmonid populations. Full article

Research designed to reduce or eliminate fishmeal (FM) in trout feeds, for reasons that have changed over time, has been conducted for over a century. Reducing the dependency on FM remains one of the most urgent issues facing the industry. Feed represents the most expensive operational cost of fed aquaculture, and is responsible for ecosystem disturbance following nutrient discharges. Rainbow trout, the second most farmed salmonid globally, can be raised completely without FM or fish oil (FO), with its growth and efficiency not differing from trout fed FM-based feeds. However, ingredient choice and nutrient supplementation strongly influence physiological responses, efficiency, and long-term outcomes. As land animal proteins are increasingly used in place of FM, both with and void of dietary FO, their distinct biological effects warrant focused evaluation. Although numerous studies have synthesized findings across various alternative protein categories including those with insect proteins and animal by-products, this literature is widely disseminated and sometimes difficult to access. The present contribution focuses on terrestrial/aerial animal proteins that have been used to totally replace FM in rainbow trout feeds. Attention is given to their effects on physiological control processes that may influence production efficiency. Areas worthy of future study are identified and include long-term performance and health dynamics, the refinement of nutritional and formulation strategies, and the broader evaluation of biological interactions and system-level outcomes. Full article

The Anastasia River (southern Sakhalin Island) is a key salmon spawning ground, where summer storm floods can drastically alter benthic communities that form the diet of fish. This study assessed the impact of heavy rainfall on the benthic macroinvertebrates in the lower reaches of the river by analyzing taxonomic composition, biomass, and fatty acid (FA) profiles of dominant taxa before and after a flood event. A catastrophic decline in biomass was observed (from 35.7 ± 4.4 g m⁻² to 1.74 ± 0.68 g m⁻²), alongside a significant shift in community structure. Crustaceans (dominated by Eogammarus kygi), with a unique FA profile rich in long-chain n-3 and n-6 polyunsaturated fatty acids (PUFAs), were the primary bearers of high nutritional value. All crustaceans exhibited omnivorous diets, with river crabs (Eriocheir japonica) having a broader spectrum than conspecifics inhabiting the marine littoral zone. Amphipods were key processors of allochthonous matter. The flood caused not only a quantitative but also a severe qualitative reduction in community nutritional value, with the content of physiologically crucial n-3 and n-6 PUFAs dropping by a factor of 25 and 15 on average, respectively. The disproportionately high loss of n-3 PUFAs indicates that the qualitative degradation of food resources by extreme floods may be an underestimated factor limiting the post-flood recovery of fish populations. Full article

Floodplain disconnection caused by channel incision and/or levee construction has led to widespread loss of riparian habitats and ecosystem functions globally. Restoring full stream–floodplain connectivity is increasingly promoted, yet evidence of ecological outcomes remains limited. This study evaluates the initial performance of two Stage 0 restoration projects on Whychus Creek, Oregon, which reconnected incised channels to their historical floodplains in 2012 and 2016. We combined pre- and post-restoration vegetation surveys along fixed transects with hydrogeomorphic-based riparian and wetland function assessments and applied quantitative analyses, including Kruskal–Wallis tests, Jaccard correlations, Sorensen similarity indices, and factor analysis, to compare changes in plant assemblages and ecosystem functions across restored, transitional, and unrestored reaches. Our research results indicate that two years post-restoration, the active riparian area expanded 2.5-fold, species richness and structural diversity increased significantly, and riparian and wetland functions such as water storage, sediment retention, and habitat support for fish and amphibians improved markedly. Numbers of anadromous salmonids also increased markedly. This is important as salmon recovery is a regional stream restoration goal. Comparisons with a reach restored six years earlier suggest a positive trajectory toward mature, resilient ecosystems. These findings demonstrate that Stage 0 restoration can rapidly reestablish complex habitat mosaics and enhance ecosystem services critical for biodiversity, water quality, and flood resilience. Practically, this evidence supports process-based restoration strategies that prioritize full floodplain reconnection as a cost-effective approach to reversing long-term ecological degradation. Continued monitoring is essential to guide adaptive management and strengthen the evidence base for the wide-scale implementation of valley-floor wide stream restoration. Full article

Light is a critical factor influencing fish behavior, yet the low-light conditions in deep-sea cages may impair feeding in visual species like rainbow trout Oncorhynchus mykiss (Walbaum, 1792). This study investigated the effects of light intensity and photoperiod on the feeding behavior of rainbow trout. Using green light, a factorial design tested three light intensities (10, 100, and 1000 lx) and three photoperiods (8L:16D, 16L:8D, and 24L:0D), alongside a complete darkness control (0 lx and 0L:24D). Key behavioral parameters during feeding were quantified via video analysis. The results showed significant main and interactive effects of light intensity and photoperiod on feeding behaviors. Feeding activity was substantially suppressed under continuous darkness. On the initial experimental day, exploratory movement was greatest under 10 lx and 8L:16D. Following 50 days of exposure, fish in light groups exhibited more focused swimming trajectories near the feeding point, indicating behavioral adaptation and spatial learning. Correlation analyses suggested a strategic shift from broad exploration to precise, efficient localization over time. In conclusion, specific lighting conditions, notably low intensity under a regular photoperiod, promote efficient feeding behavior in rainbow trout, whereas darkness or extreme light regimens are inhibitory. These findings reveal adaptive behavioral plasticity in this species and provide a scientific basis for optimizing light management in offshore salmonid aquaculture. Full article