Salmon Farming Research Articles

Efficient Hydroxyapatite Extraction from Salmon Bone Waste: An Improved Lab-Scaled Physico-Chemico-Biological Process.

The demand for novel tissue grafting and regenerative wound care biomaterials is growing as traditional options often fall short in biocompatibility, functional integration with human tissue, associated cost(s), and sustainability. Salmon aquaculture generates significant volumes of waste, offering a sustainable opportunity for biomaterial production, particularly in osteo-conduction/-induction, and de novo clinical/surgical bone regeneration. Henceforth, this study explores re-purposing salmon waste through a standardized pre-treatment process that minimizes the biological waste content, followed by a treatment stage to remove proteins, lipids, and other compounds, resulting in a mineral-rich substrate. Herein, we examined various methods-alkaline hydrolysis, calcination, and NaOH hydrolysis-to better identify and determine the most efficient and effective process for producing bio-functional nano-sized hydroxyapatite. Through comprehensive chemical, physical, and biological assessments, including Raman spectroscopy and X-ray diffraction, we also optimized the extraction process. Our modified and innovative alkaline hydrolysis-calcination method yielded salmon-derived hydroxyapatite with a highly crystalline structure, an optimal Ca/P ratio, and excellent biocompatibility. The attractive nano-scale cellular/tissular properties and favorable molecular characteristics, particularly well-suited for bone repair, are comparable to or even surpass those of synthetic, human, bovine, and porcine hydroxyapatite, positioning it as a promising candidate for use in tissue engineering, wound healing, and regenerative medicine indications.

Wild salmon migration routes influence sea lice infestations: An agent-based model predicting farm-related infestations on juvenile salmon.

This study presents an Agent-Based Model (ABM) simulation to assess the impact of varying migration routes on sea lice (Caligus clemensi) infestation levels in juvenile wild sockeye salmon (Oncorhynchus nerka) in the Discovery Islands, British Columbia, Canada. This research highlights the importance of migratory routes in determining the extent of exposure to sea lice originating from nearby salmon farms. Three northward out-migration routes were modelled, each exposing the fish to different levels of infestation pressure based on proximity to salmon farms. The ABM incorporates spatially explicit migration patterns of juvenile sockeye salmon using a detailed raster map of the Discovery Islands. Key variables such as swimming speed, progression rate, and infestation levels were integrated into the model, offering a comprehensive analysis of migration and infestation dynamics. The study revealed that infestation rate is highly variable, depending on migration routes. Specifically, salmon traveling longer migration routes with lower infestation pressure may experience higher sea lice loads compared to those on shorter routes with higher infestation pressure. This underscores the role of low infestation pressures and the critical influence of swimming speed, which affects exposure time, and thus infestation rates. Additionally, the study conducted a sensitivity analysis to understand the influence of various parameters on infestation rates. This analysis highlighted the importance of swimming speed and progression rate, particularly in routes closer to the farms. The findings suggest that slower swimming speeds and meandering routes increase exposure to lice, thereby elevating infestation levels. The research contributes to understanding the dynamics of sea lice transmission and its relationship with salmon migration patterns. It underscores the necessity of considering migratory routes and farm proximity in managing and mitigating the impact of sea lice infestation on wild salmon populations. This study's insights are crucial for developing strategies to balance aquaculture practices with the conservation of wild salmon.

Intermittent Detections of ISAV-HPR0 in a Salmon Recirculating Aquaculture System, and Implications for Sampling

Infectious salmon anemia virus (ISAV) is an important pathogen in global Atlantic salmon (Salmo salar L.) aquaculture. The existence of both non-pathogenic (ISAV-HPR0) and pathogenic (HPR-deleted ISAV) forms of the virus impacts hatchery management. In November 2016, fish tested positive for ISAV-HPR0 at the National Cold Water Marine Aquaculture Center in Maine. A cohort exposed to the fish testing positive for ISAV were lethally sampled over a 7-month period (February–August 2017). No positive samples were detected during this time. Additional testing aimed to determine the extent of the ISAV infections in the facility’s fish and to investigate the water sources as potential virus entry points. Fish testing was designed to detect 2% pathogen prevalence with 95% confidence (assuming diagnostic sensitivity of 85%). Over a three-year period, ISAV-HPR0 was detected in spawning fish annually and once in smolts. Repeat testing of smolts from the affected tank three weeks later failed to detect ISAV-HPR0. Over a one-year period of weekly or biweekly evaluation of the incoming water sources, ISAV was never detected. These findings suggest that ISAV-HPR0 infections in monitored hatchery populations can evade detection and that episodes of high prevalence of ISAV-HPR0 associated with spawning can be highly transient. In both cases, conventional surveillance based on recurrent testing of healthy populations may provide only a very limited indication of the HPR0 status. Instead, targeting surveillance to periods of physiological stress, such as spawning and smoltification, and adjusting the sample sizes to account for a related surge in prevalence, should enhance the detection capacity in hatchery settings while also reducing testing costs.

Characterization of the impact of dietary immunostimulant CpG on the expression of mRNA biomarkers involved in the immune responses in Atlantic salmon (Salmo salar)

Infectious diseases have significantly impacted Atlantic salmon aquaculture worldwide. Modulating fish immunity with immunostimulant-containing functional feeds could be an effective strategy in mitigating disease problems. Previously, we characterized the impact of polyriboinosinic polyribocytidylic acid (pIC) and formalin-killed typical Aeromonas salmonicida bacterin on miRNA expression in Atlantic salmon fed a commercial diet with and without immunostimulant CpG. A set of miRNA biomarkers of Atlantic salmon head kidney responding to pIC and/or bacterin immune stimulations was identified (Xue et al., 2019) [1]. Herein, we report a complementary qPCR study that investigated the impact of the pIC, bacterin and dietary CpG on the expression of immune-relevant mRNAs (n = 31) using the same samples as in the previous study (Xue et al., 2019) [1]. Twenty-six of these genes were predicted target transcripts of the pIC- and/or bacterin-responsive miRNAs identified in the earlier study. The current data showed that pIC and/or bacterin stimulations significantly modulated the majority of the qPCR-analyzed genes involved in various immune pathways. Some genes responded to both stimulations (e.g. tnfa, il10rb, ifng, irf9, cxcr3, campb) while others appeared to be stimulation specific [e.g. irf3, irf7a, il1r1, mxa, mapk3 (pIC only); clra (bacterin only)]. A. salmonicida bacterin stimulation produced a strong inflammatory response (e.g. higher expression of il1b, il8a and tnfa), while salmon stimulated with pIC showed robust interferon responses (both type I and II). Furthermore, the current data indicated significant down-regulation of immune-relevant transcripts (e.g. tlr9, irf5, il1r1, hsp90ab1, itgb2) by dietary immunostimulant CpG, especially among pre-injection and PBS-injected fish. Together with our prior miRNA study, the present research provided complementary information on Atlantic salmon anti-viral and anti-bacterial immune responses and on how dietary CpG may modulate these responses.

Dynamics of Gill Responses to a Natural Infection with Neoparamoeba perurans in Farmed Tasmanian Atlantic Salmon.

Gill health has become a significant global challenge for Atlantic salmon (Salmo salar) aquaculture, particularly during the marine phase of farming. The increasing prevalence of gill pathologies has been linked to rising seawater temperatures, underscoring the need to evaluate existing tools for monitoring gill health and to develop novel approaches for early detection. In this study, we investigated the gill responses of commercially farmed Atlantic salmon to natural infection with Neoparamoeba perurans during an outbreak of amoebic gill disease (AGD) in Tasmania. Our focus spanned the low AGD prevalence, high AGD prevalence, and post-freshwater treatment stages of the outbreak. Evaluations of gill tissue included assessments of the gross AGD score, histopathological score, abundance of N. perurans (measured by 18S rRNA gene expression), and expression levels of inflammation-related transcripts. We demonstrated a strong correlation between different measures of AGD-related gill pathology and significant differences between distinct stages of the N. perurans outbreak. Post-treatment, fish exhibited considerable variability in their responses to the freshwater bath, highlighting the necessity for personalized management strategies that consider genetic, environmental, and health status factors. The expression patterns of angiogenin-1 (ANG1) and complement C1q tumour necrosis factor-related protein 3-like (C1QTNF3) emphasize their potential as biomarkers for early detection of gill damage in salmon aquaculture worldwide.

Improvement of the immunological and antioxidant capacity of rainbow trout (Oncorhynchus mykiss) by using the paraprobiotic Bacillus subtilis subsp. spizizenii

The aim of this study was to produce Bacillus subtilis subsp. spizizenii as a paraprobiotic for the nutrition of rainbow trout (Oncorhynchus mykiss). Fifty-four trout (74.51 ± 3.15 g) were transferred to nine 300-liter tanks and fed PRO (live freeze-dried form), PAR (irradiated freeze-dried form) and control feed (n=3) for 8 weeks. Growth, hematological, immunological and enzymatic liver functions, as well as antioxidant capacity were then analyzed. Kidney, liver, and intestinal tissue as well as the expression of cytokines (TNF-1, TNF-2, IL-1β1, and IL-1β2) in spleen, and kidney were analyzed. The growth indices, white, and red blood cells, neutrophils, monocytes and granulocytes, total protein and globulin improved in the PAR and PRO groups compared to the control group (p<0.05). The results showed that the PAR and PRO groups resulted in modulation of ALT, AST and ALP compared to the control group (p<0.05). Antioxidant indices were highest in the PAR group compared to the PRO and control groups (p<0.05). Intestinal histology results showed that the height of intestinal folds and goblet cells increased in fish fed PRO and PAR compared to the control group (p<0.05). Although melatonin increased in the PAR and PRO groups, it decreased in the liver of PAR compared to PRO (p<0.05). Immunological indices improved in the PAR and PRO groups compared to the control group (p<0.05), with no differences between PAR and PRO (p<0.05). The results of this study show that the paraprobiotic produced in this study is effective under culture conditions and can therefore be used as a supplement in trout farming.

Post-smolt Atlantic salmon can regulate buoyancy in submerged sea-cages by gulping air bubbles

Salmon lice (Lepeophtheirus salmonis) are the most severe health challenge facing Atlantic salmon (Salmo salar) aquaculture. Infestations threaten farmed and wild salmonids, drive up production costs, and limit industry growth. Submersible sea-cages can reduce infestation pressure by holding salmon below the surface layers where lice larvae are most abundant. However, submergence leads to loss of buoyancy over time, as salmonids must periodically refill their swim bladders by gulping air. Pockets of air held at depth within ‘air domes’ enable salmon to gulp air, but air domes are large and unwieldy structures. A more intuitive solution may be to deliver a stream of air bubbles at depth, as bubbling is commonly used in sea-cages to promote vertical mixing, and salmon interact with these bubbles. Here, we conducted a pilot study to test whether newly sea-transferred salmon would use bubbles for buoyancy regulation. We conducted 3 trials in sequence, each involving 15–19 days of continuous submergence, and recorded buoyancy-related behaviors in 1 cage with full surface access, 1 cage submerged without air, and 2 cages submerged with air bubbling. Bubbling was provided continuously in the first two trials, before being reduced to 90 min day−1 in the third trial. Salmon submerged with bubbling maintained their swim bladder volume and swimming speed at similar levels to the cage with full surface access throughout all trials, indicating that they successfully refilled using bubbles. The same parameters deteriorated in salmon in the cage submerged without air. Acclimation to bubbles took ∼3 days whether at the surface or after submergence, indicating that several days of bubbling before submergence may be beneficial. Some fish accumulated fluid in the swim bladder during submergence (more severe in fish submerged without bubbling). Together, the results suggest that bubbling can improve outcomes for salmon undergoing prolonged submergence. Moreover, bubbling offers an alternative to air domes that is less technically demanding, provides a greater spatial distribution of air, and supports welfare through behavioral enrichment.

Progress and challenges for the establishment of a sustainable blue economy in Chiloe (Chile): Exploring the connections of a socio-ecological system

The use of coastal-marine resources is currently based on an unsustainable development model that leads to deterioration of the environment and consequent reductions in economic activities and the well-being of coastal societies. According to the conceptual framework provided by the sustainable blue economy model, this paper evaluates the effects of anthropogenic activities on the ecosystem services (ESs) of the coastal areas of the island and the sea of Chiloe, an archipelago located in Chilean Patagonia. It also analyzes how the degradation of the environment ultimately affects the economy itself and human well-being. The methodology employed is based on the construction of three matrices that connect 12 economic activities identified in the study area, with three ESs groupings (provisioning, regulating, and cultural) and four components of human well-being (security, material assets, health, and social relations). The impacts are assessed using four categories: high impact (3), moderate impact (2), low impact (1), and positive impact (0). The results reflect the domination of economic sectors that negatively affect the environment, among which salmon farming, the main activity in Chiloe, stands out. In contrast, small-scale fishing has been the highest evaluated sector, largely because of the new management instruments that have been developed in Chile. The establishment of a sustainable blue economy in Chiloe requires the application of sustainability standards –such as those proposed for small-scale fisheries– in the sectors that generate the most socio-ecological impacts.

Association of microbial community structure with gill disease in marine-stage farmed Atlantic salmon (Salmo salar); a yearlong study

BackgroundUnderstanding the relationship between resident microbiota and disease in cultured fish represents an important and emerging area of study. Marine gill disorders in particular are considered an important challenge to Atlantic salmon (Salmo salar) aquaculture, however relatively little is known regarding the role resident gill microbiota might play in providing protection from or potentiating different gill diseases. Here, 16S rRNA sequencing was used to examine the gill microbiome alongside fish health screening in farmed Atlantic salmon. Results were used to explore the relationship between microbial communities and gill disease.ResultsMicrobial community restructuring was observed throughout the sampling period and linked to varied drivers of change, including environmental conditions and severity of gill pathology. Taxa with significantly greater relative abundance on healthier gills included isolates within genus Shewanella, and taxa within family Procabacteriaceae. In contrast, altered abundance of Candidatus Branchiomonas and Rubritalea spp. were associated with damaged gills. Interestingly, more general changes in community richness and diversity were not associated with altered gill health, and thus not apparently deleterious to fish. Gross and histological gill scoring demonstrated seasonal shifts in gill pathology, with increased severity of gill damage in autumn. Specific infectious causes that contributed to observed pathology within the population included the gill disorder amoebic gill disease (AGD), however due to the uncontrolled nature of this study and likely mixed contribution of various causes of gill disease to observed pathology results do not strongly support an association between the microbial community and specific infectious or non-infectious drivers of gill pathology.ConclusionsResults suggest that the microbial community of farmed Atlantic salmon gills undergo continual restructuring in the marine environment, with mixed influences upon this change including environmental, host, and pathogenic factors. A significant association of specific taxa with different gill health states suggests these taxa might make meaningful indicators of gill health. Further research with more frequent sampling and deliberate manipulation of gills would provide important advancement of knowledge in this area. Overall, although much is still to be learnt regarding what constitutes a healthy or maladapted gill microbial community, the results of this study provide clear advancement of the field, providing new insight into the microbial community structure of gills during an annual production cycle of marine-stage farmed Atlantic salmon.

Novel insights on microbiome dynamics during a gill disease outbreak in farmed rainbow trout (Oncorhynchus mykiss)

The generic term “Gill disease” refers to a wide range of disorders that affect the gills and severely impact salmonid aquaculture systems worldwide. In rainbow trout freshwater aquaculture, various etiological agents causing gill diseases have been described, particularly Flavobacterium and Amoeba species, but research studies suggest a more complex and multifactorial aetiology. Here, a cohort of rainbow trout affected by gill disease is monitored both through standard laboratory techniques and 16S rRNA Next-Generation Sequencing (NGS) analysis during a natural disease outbreak and subsequent antibiotic treatment with Oxytetracycline. NGS results show a clear clustering of the samples between pre- and post-treatment based on the microbial community of the gills. Interestingly, the three main pathogenic bacteria species in rainbow trout (Yersinia ruckeri, Flavobacterium psychrophilum, and Flavobacterium branchiophilum) appear to be weak descriptors of the diversity between pre-treatment and post-treatment groups. In this study, the dynamics of the gill microbiome during the outbreak and subsequent treatment are far more complex than previously reported in the literature, and environmental factors seem of the utmost importance in determining gill disease. These findings present a potential novel perspective on the diagnosis and management of gill diseases, showing the limitations of conventional laboratory methodologies in elucidating the complexity of this disease in rainbow trout. To the authors’ knowledge, this work is the first to describe the microbiome of rainbow trout gills during a natural outbreak and subsequent antibiotic treatment. The results of this study suggest that NGS can play a critical role in the analysis and comprehension of gill pathology. Using NGS in future research is highly recommended to gain deeper insights into such diseases correlating gill’s microbiome with other possible cofactors and establish strong prevention guidelines.

Salmon lice biology, environmental factors, and smolt behaviour with implications for the Norwegian salmon farming management system: A critical review

AbstractIn 2017, a new regulatory management system, the traffic light system (TLS), was implemented to estimate the effects of salmon lice from Norwegian salmon aquaculture on marine survival of wild Atlantic salmon and forms the basis of aquaculture capacity regulation. The TLS relies on observational data and a set of models to estimate the risk for negative impact on wild salmon populations. This review of the literature that forms the basis for the TLS as well as other relevant studies is presented in the context of the currently practiced TLS and suggestions are made for immediate and long‐term improvements. The main findings of this review are that: (1) assumed timing and duration of smolt migration contribute to unreliable observational and modelled data and overestimates of infection pressure; (2) production of lice larvae from farmed salmon is overestimated; (3) TLS model systems rely on or are calibrated by the same potentially flawed data; (4) lice‐associated mortality in wild salmon smolts may be overestimated; and (5) lice infection levels on farms are not associated with measurable effects on wild salmon. Recommendations to improve the accuracy and reliability of the TLS, and hence its environmental efficiency include the more complete use of available biological and physical environmental variables, adjusting the time period that observational data are registered and modelled data are integrated, adjusting the interpretation of data including recognition of uncertainty in model outcomes, and use of more realistic assumptions concerning lice‐induced mortality thresholds.

Keratinocytes drive the epithelial hyperplasia key to sea lice resistance in coho salmon

BackgroundSalmonid species have followed markedly divergent evolutionary trajectories in their interactions with sea lice. While sea lice parasitism poses significant economic, environmental, and animal welfare challenges for Atlantic salmon (Salmo salar) aquaculture, coho salmon (Oncorhynchus kisutch) exhibit near-complete resistance to sea lice, achieved through a potent epithelial hyperplasia response leading to rapid louse detachment. The molecular mechanisms underlying these divergent responses to sea lice are unknown.ResultsWe characterized the cellular and molecular responses of Atlantic salmon and coho salmon to sea lice using single-nuclei RNA sequencing. Juvenile fish were exposed to copepodid sea lice (Lepeophtheirus salmonis), and lice-attached pelvic fin and skin samples were collected 12 h, 24 h, 36 h, 48 h, and 60 h after exposure, along with control samples. Comparative analysis of control and treatment samples revealed an immune and wound-healing response that was common to both species, but attenuated in Atlantic salmon, potentially reflecting greater sea louse immunomodulation. Our results revealed unique but complementary roles of three layers of keratinocytes in the epithelial hyperplasia response leading to rapid sea lice rejection in coho salmon. Our results suggest that basal keratinocytes direct the expansion and mobility of intermediate and, especially, superficial keratinocytes, which eventually encapsulate the parasite.ConclusionsOur results highlight the key role of keratinocytes in coho salmon’s sea lice resistance and the diverged biological response of the two salmonid host species when interacting with this parasite. This study has identified key pathways and candidate genes that could be manipulated using various biotechnological solutions to improve Atlantic salmon sea lice resistance.

Diagnosis of The State and Changes in The Ecosystem of Lake Onego and Watershed Based on The Information-Analytical System

The results of the diagnosis of the state and changes in the ecosystem of Onegskoe Lake (Lake Onego) and the watershed are presented using the developed information and analytical system “Lake Onego-watershed” (IAS), consisting of a comprehensive database (DB), a combined database of Roshydromet and Northern water problems institute/Karelian Research Center of the Russian Academy of Sciences on the nutrient load for the modern period 1995–2022, the ILLM mathematical model for assessing the removal of nutrients from the watershed and the formation of the nutrient load on the lake and the 3D-mathematical model SPLEM, developed for Lake Onego. Information was collected on the main sources of nutrient load in the Lake Onego catchment area, as well as available field observation data on the flow of nitrogen and phosphorus into the lake. The contribution of different nutrient sources coming from river runoff, diffuse sources, urban discharges and from trout farms was calculated for the lake and the main limnic areas. Based on data from field observations over the past 30 years and the results of numerical experiments using the SPLEM model with a grid resolution of 1 km it is shown that the ecosystem of the lake not only did not restored after the reduction in anthropogenic load after 1991, but eutrophication of waters in the lips and bays continues due to the influence of industrial and agricultural enterprises, trout farms and noticeable climate warming. Functional for the IAS “Lake Onego-catchment” to visualize the main modeling results on a 1 km grid was developed, and a web application interface has been created.

Exposure of female lobsters to sediments spiked with emamectin benzoate: Effects on eggs and larvae early development

The salmon aquaculture industry is an important economic activity established on both the west and east coast of Canada. To control sea lice infestations, in-feed products like emamectin benzoate (EMB) are widely used. Due to its low solubility and persistence EMB can accumulate in marine sediments and be potentially bioavailable to non-target organisms from months to years. The American lobster (Homarus americanus) is a key species in the Northwest Atlantic with high economic and ecological value. It may be exposed to therapeutants considering lobster habitats overlap with aquaculture locations requiring a better understanding of the potential impact of these therapeutants through varied pathways of exposure. In this study, we investigated the exposure of gravid female lobsters to EMB spiked sediment to mimic the likely presence of these females at aquaculture sites for a 10-day period. We completed testing by assessing EMB effects on adult molting and quality, embryo hatching rates, and larval offspring quality and larval molting. Our results show that a single, 10-day exposure of ovigerous females to EMB concentrations higher than environmentally relevant values did not affect females or their offspring.

A flexible policy instrument to encourage externality abatement technologies in salmon aquaculture

Aquaculture has been identified as a food sector with potential to provide protein and essential micronutrients to a growing global population, with salmon aquaculture often viewed as a leader in innovation and adoption of new technologies. Despite a broad range of negative externalities in salmon aquaculture, sea lice infestations remain the most harmful of environmental issues within the industry. In response to these challenges and driven by the need for a higher degree of control over the production conditions, salmon producers in Norway have been investing in new technologies that are often perceived as the last resort for sea lice abatement. The challenge is to design a regulatory regime that encourages innovation toward a sustainable mix of production technologies in the future. In this paper, we propose to use feed-in tariffs (FITs), a dynamic Pigouvian subsidy, as a regulatory instrument that can promote investments in abatement technologies by the salmon farming industry. We ground our discussion of FITs for aquaculture in experiences from the renewable energy sector in Spain and Germany.

Detachment and re-attachment of Salmon lice during full-scale delousing operations on Salmon farms

This study examined salmon lice (Lepeophtheirus salmonis) numbers during different full-scale lice treatments of salmon, with focus on detachment during crowding and re-attachment post-treatment. Data was collected from 259 non-medicinal treatments (NMM) during 2018 and 2019. The dataset included data from thermal (Optilicer), mechanical (Flatsetsund Engineering, SkaMik, Hydrolicer) and freshwater treatments. Salmon lice were counted by the staff at the aquaculture sites, and registered in the following categories: sessile, preadult/adult male (PA/AM) and adult female. A counting protocol was established in collaboration with staff from the aquaculture companies taking part, where the time for counting the parasitic salmon lice was: Sample 0: before crowding; Sample 1: at the end of the first crowding; Sample 2: during unloading of the salmon after treatment; and Sample 3: after delousing of the salmon, in the net pen. In addition to the treatments registered directly according to the protocol, we retrieved data for additional treatments directly from the aquaculture companies' own registration system. The objectives of this observational study was (1) investigate whether salmon lice detach during crowding before an NMM; (2) investigate the effect of NMM; and (3) investigate possible re-attachment after delousing. We observed an overall trend of a reduction of salmon lice numbers, with a median percentage decrease of 22% for PA/AM and 29% for adult female lice during crowding. A likely explanation for these observations is that lice detach from the salmon due to mechanical action associated with the increased density of crowding. One-sided Wilcoxon tests corroborated the hypothesis of a reduction in lice counts during crowding for PA/AM and adult female lice (p < 0.05). As expected, we also observed a substantial reduction in lice numbers from Sample 1 to Sample 2, which is most likely due to the effect of the delousing treatment with the NMM. We observed an increase in sessile and PA/AM salmon lice when studying possible re-attachment after delousing. For sessile lice, the increase in lice numbers was most likely due to new infestation. For PA/AM, the increase can primarily be explained by re-infestation with lice that detached during crowding. The increase for PA/AM was greater when the salmon were placed in the same cage (a doubling of lice numbers), compared to placing them in a new cage (p < 0.05), indicating that the salmon lice could re-infest to a greater extent when the salmon were moved a shorter distance. The results presented in this article shed light on the possible dispersal of parasitic salmon lice, which is largely an unexplored topic.

Epidemiological cutoff values and genetic antimicrobial resistance of Lactococcus garvieae and L. petauri

Lactococcus garvieae and L. petauri are etiological agents of lactococcosis, which cause significant losses in trout aquaculture at elevated water temperatures. Optimizing antimicrobial dosage regimens and identifying the minimum inhibitory concentration (MIC) are important prerequisites for determining clinical breakpoints and effective antimicrobial use. In the present study, epidemiological cutoff values (ECV) were established for 14 antimicrobials using L. garvieae (n = 32) and L. petauri (n = 78), isolated from rainbow trout farms in Türkiye, Spain, Italy, and Greece. The provisional ECVs were calculated using the ECOFFinder and normalized resistance interpretation (NRI) approaches. Furthermore, gene cassettes, capsule gene clusters, and the presence of fourteen antibiotic resistance genes (ARGs) that encode resistance against seven antimicrobial agents, were evaluated. The calculated ECVs of antimicrobials ranged from 1.25 μg mL−1 for amoxicillin to 80.25 μg mL−1 for streptomycin. The percentages of wild type (WT) and non-wild type (NWT) isolates differed based on the approach, and ECVs calculated based on ECOFFinder approach were generally higher. Among the ARGs, those encoding resistance against tetracycline (tetA), β-lactamase (blaSHV, blaTEM, and blaOXA), amphenicol (floR), and macrolide (ermA) were detected in <10% of the isolates. The genes encoding resistance against quinolones (gyrA and qnrA) and aminoglycosides (strB) were the most detected genes. While 40.9% of the isolates contained Class 1 integron cassette regions, 33.6% of the isolates contained Class 2 integron cassette regions, and 9.1% of the isolates contained both cassette regions. None of the screened isolates were positive for the capsule gene cluster. Significant but weak correlations were found among and between ARGs and MIC distribution of antibiotics. The results of this study could be useful for identifying WT and non-WT isolates, as well as for susceptibility surveillance.

Forecasting ocean hypoxia in salmonid fish farms

IntroductionHypoxia is defined as a critically low-oxygen condition of water, which, if prolonged, can be harmful to fish and many other aquatic species. In the context of ocean salmon fish farming, early detection of hypoxia events is critical for farm managers to mitigate these events to reduce fish stress, however in complex natural systems accurate forecasting tools are limited. The goal of this research is to use a machine learning approach to forecast oxygen concentration and predict hypoxia events in marine net-pen salmon farms.MethodsThe developed model is based on gradient boosting and works in two stages. First, we apply auto-regression to build a forecasting model that predicts oxygen concentration levels within a cage. We take a global forecasting approach by building a model using the historical data provided by sensors at several marine fish farms located in eastern Canada. Then, the forecasts are transformed into binary probabilities that indicate the likelihood of a low-oxygen event. We leverage the cumulative distribution function to compute these probabilities.Results and discussionWe tested our model in a case study that included several cages across 14 fish farms. The experiments suggest that the model can detect future hypoxic events with a commercially acceptable false alarm rate. The resulting probabilistic predictions and oxygen concentration forecasts can help salmon farmers to prioritize resources, and reduce harm to crops.

Vgll3 regulates the timing of puberty in farmed Atlantic salmon, but it does not explain family discordance in male maturation following different smolt production regimes

Atlantic salmon (Salmo salar) farming is moving towards extended periods of land-based production to minimise the time at sea, but this increases the risk of unwanted male sexual maturation. As the timing of puberty is driven by genetics (e.g. vgll3) and the environment, optimising rearing strategies and broodstock management may help alleviate the problem. Subsequently, we used a domesticated strain of vgll3 heterozygous broodstock to produce three all-male half-sibling families using three different production regimes to assess the timing of first puberty. Firstly, “large smolts” were produced in a flow-through system on 13 °C freshwater and constant light from first feeding (day 0) up to 1 kg (day 354). The mean incidence of pubertal males increased from 2% at 30 g, up to 78% at 1 kg. Genetics explained a significant (p < 0.05) amount of the variation, with 93, 71, and 34% of the expected early, intermediate, and late maturing vgll3 genotypes being pubertal on day 354, respectively. In addition, pubertal males in the early vgll3 genotype were found at the first sampling at ≈30 g, while it was not observed in the heterozygous and late genotypes until the fish were ≈90 g and ≈280 g, respectively. Secondly, “post-smolts” were produced by switching half the large smolts to 13 °C seawater at 420 g (day 272) and growing them in tanks to 0.95 kg (day 354). This led to a significant 14% reduction in the total incidence of puberty by day 354 compared to the large smolts. However, the regulation of pubertal timing by vgll3 did not interact with salinity. Thirdly, traditional “under-yearling” smolts were produced using periods of natural or manipulated temperature and photoperiod, followed by transfer to a sea-cage at 150 g in December (day 290) where they stayed for one year until harvest at 4.75 kg (day 648). None of these fish were mature at sea transfer, but 9% were at harvest, with 22, 7, and 2% of the early, intermediate, and late vgll3 genotypes being mature, respectively. When comparing the regimes, family effects outside of vgll3 on the prevalence of sexual maturation were significant for the land-based regimes (family means from 46 to 93% on day 354), but not in sea-cages (family means from 7 to 11% on day 648) and evidence for either vgll3 allele being dominant was mixed. Vgll3 also had minimal effects on body size/growth in any regime/family. In conclusion, i) selecting for the late vgll3 allele is an effective method to delay puberty over a range of production regimes, ii) family effects outside of vgll3 were not consistent across regimes, and iii) using seawater reduced the incidence of precocious puberty during land-based production.

Changes in blood serum parameters in farmed rainbow trout (Oncorhynchus mykiss) during a piscine lactococcosis outbreak.

The aquaculture sector plays a vital role in global food security, yet it grapples with significant challenges posed by infectious diseases. Piscine lactococcosis is one of the significant threats in rainbow trout aquaculture due to its potential to cause severe economic losses through mortalities, reduced growth rates, and increased susceptibility to other pathogens. It poses challenges in disease management strategies, impacting the sustainability and profitability of rainbow trout farming. The current study focuses on the variations in serum blood parameters of farmed rainbow trout Oncorhynchus mykiss during a lactococcosis outbreak caused by Lactococcus garvieae. Blood samples were collected for biochemical analysis, fish were examined for parasites and bacteria, and DNA from bacterial colonies was PCR-amplified and sequenced for identification. Overall, 13 biochemical parameters, including proteins, enzymes, lipids, chemicals, and minerals, were measured in serum blood samples from both diseased and healthy fish. The results indicate significant alterations in the levels of these parameters during the outbreak, highlighting the impact of infections on the blood profile of farmed rainbow trout. Urea levels were significantly higher in diseased fish compared to controls, and creatinine, phosphorus, and magnesium also showed similar trends. Alanine aminotransferase and total protein levels were higher in control fish. Chloride levels differed significantly between groups. Iron levels were higher in controls and lower in diseased fish. No significant differences were found in other parameters. This study reveals significant changes in serum blood parameters of rainbow trout during a lactococcosis outbreak caused by L. garvieae. These changes highlight the potential of these parameters as tools for monitoring health status, stress, and aquaculture management. Continuous monitoring can provide valuable insights into disease severity and overall fish health, aiding in the development of improved management practices. The presented data contribute to understanding the pathophysiology of piscine lactococcosis and developing effective mitigation strategies for farmed rainbow trout.