Atlantic Salmon Post-smolts Research Articles

Operculum PIT tagging: a viable alternative to avoid human consumption in processed salmon

BackgroundPassive integrated transponder (PIT) tags are commonly used to identify individual fish. However, use of PIT tags in commercial aquaculture research is limited by consumer safety concerns. For farmed fish, it is critical that tags do not end up in the final product. One possibility to enable the use of PIT tags in commercial research is to insert tags into a part of the body that will be separated from the trunk during processing. We compare tag loss, mortality rate and welfare scores between Atlantic salmon post-smolts (n = 798) marked with PIT tags either in the operculum musculature or the abdominal cavity (standard practice) before and after mechanical delousing.ResultsWe found that neither condition factor (K) (range 0.60–1.99) nor tagging location significantly affected tag loss (operculum = 6%, intraperitoneal = 8%, z = 1.46, p = 0.14) or mortality (operculum = 2%, intraperitoneal = 2%, z = 0.55, p = 0.58). However, on average, the fish which died weighed 20% less at the time of handling (271 ± 13 g, K = 1.12 ± 0.02) than those which survived (340 ± 3 g, K = 1.14 ± 0.004), and those which lost tags (291 ± 7 g, K = 1.11 ± 0.02) weighed 15% less than those which retained them (340 ± 3 g, K = 1.14 ± 0.004), irrespective of tagging location or handling treatment.ConclusionsFish tagged in the operculum musculature had comparable rates of mortality and tag loss to the current “best practice” standard of intraperitoneal tagging. We show that placement of PIT tags in operculum musculature is a viable alternative to placement in the peritoneal cavity.

Infectious Salmon Anemia Virus Shedding from Infected Atlantic Salmon (Salmo salar L.)—Application of a Droplet Digital PCR Assay for Virus Quantification in Seawater

Infectious salmon anemia virus (ISAV) infection is currently detected by fish sampling for PCR and immunohistochemistry analysis. As an alternative to sampling fish, we evaluated two different membrane filters in combination with four buffers for elution, concentration, and detection of ISAV in seawater, during a bath challenge of Atlantic salmon (Salmo salar L.) post-smolts with high and low concentrations of ISAV. Transmission of ISAV in the bath challenge was confirmed by a high mortality, clinical signs associated with ISA disease, and detection of ISAV RNA in organ tissues and seawater samples. The electronegatively charged filter, combined with lysis buffer, gave significantly higher ISAV RNA detection by droplet digital PCR from seawater (5.6 × 104 ISAV RNA copies/L; p < 0.001). Viral shedding in seawater was first detected at two days post-challenge and peaked on day 11 post-challenge, one day before mortalities started in fish challenged with high dose ISAV, demonstrating that a large viral shedding event occurs before death. These data provide important information for ISAV shedding that is relevant for the development of improved surveillance tools based on water samples, transmission models, and management of ISA.

Consequences of continuous ozonation on the health and welfare of Atlantic salmon post-smolts in a brackish water recirculating aquaculture system.

This study investigated the biological consequences of 45-day continuous ozonation on Atlantic salmon (Salmo salar) post-smolts in a brackish water recirculating aquaculture system (RAS). There was no significant difference in survival, operational welfare indicators, and average weight at termination between the ozone-treated and control groups. Plasma biochemical analyses revealed that the creatinine level was significantly higher in the ozone-treated group than in the control at termination. Histological evaluation of skin health showed no significant difference between the two groups. On the other hand, quantitative histopathology disclosed that the ozone group exhibited a better gill health status than did the control group, particularly at the end of the trial. Mucosal transcriptomics revealed a distinct response profile between the gills and skin. At day 45, there were no differentially expressed genes (DEG) identified in the skin, in contrast to 242 ozone-induced DEGs in the gills. Assessment of the transcriptomic profiles over time revealed that temporal effects were of greater impact in skin compared to gills, regardless of the treatment. The treatment did not result in metabolomic dysregulation and the overall profile lent support to the transcriptomics data that temporal effects had a greater influence on the changes observed. Exposure to handling-confinement stress revealed that ozone treatment did not alter the ability of post-smolts to respond to a secondary stressor. In summary, the suite of health and welfare indicators collectively indicated that continuous ozonation resulted in minimal physiological perturbations in salmon post-smolts. The results are expected to contribute to optimising the rearing conditions for post-smolts in RAS.

The stress response in Atlantic salmon (Salmo salar L.): identification and functional characterization of the corticotropin-releasing factor (crf) paralogs

Corticotropin-Releasing Factor (CRF) is one of the main mediators of the Hypothalamic-Pituitary–Interrenal (HPI) axis to stress response. In Atlantic salmon, a comparative understanding of the crf1 paralogs role in the stress response is still incomplete. Our database searches have identified four crf1 genes in Atlantic salmon, named crf1a1, crf1a2, crf1b1 and crf1b2. Brain distribution analysis revealed that the four crf1 paralogs were widely distributed, and particularly abundant in the telencephalon, midbrain, and hypothalamus of Atlantic salmon post-smolts. To increase the knowledge on crf1-mediated response to stress, Atlantic salmon post-smolts were exposed to either repeated chasing, hypoxia or a combination of chasing and hypoxia for eight days, followed by a novel-acute stressor, confinement. Cortisol, glucose, lactate, and creatinine levels were used as markers for the stress response.The crf1 paralogs mRNA abundance showed to be dependent on the stress exposure regime. Both crf1 mRNA levels in the telencephalon and crf1a1 mRNA levels in the hypothalamus showed similar response profiles to the serum cortisol levels, i.e., increasing levels during the first 24 h after stress exposure followed by a decline during the eight-day exposure. The similar trend between crf1 and cortisol disappeared once exposed to the novel-acute stressor. There was a minor response to stress for both crf1b1 and crf1b2 in the hypothalamus, while no changes at mRNA level were observed in the hypothalamic crf1a2 under the different stress conditions. No or weak relationship was found between the crf1 paralogs mRNA expression and the other serum stress-indicators analysed. In summary, our data provide novel insights on the dynamic of the HPI axis activation in Atlantic salmon, and thus underline the involvement of the crf1 paralogs as additional factors in the regulation of the stress response in this species. Likewise, the data highlight the importance of analysing all crf1 paralogues response to a stress-condition, in particular in this premature knowledge stage of their functionality. Further analysis and a more detailed time-point series will help to elucidate the response of the HPI axis and the link of crf1 paralogs in the stress response mechanism.

Full compensatory growth before harvest and no impact on fish welfare in Atlantic salmon after an 8-week fasting period

Individually tagged Atlantic salmon postsmolts (≈1200 g, 46 cm) reared in triplicate indoor holding tanks were fasted for 8 weeks at 12 °C and subsequently refed for 5 weeks, whereafter they were transferred to triplicate sea cages in a common garden setup together with a continuously fed control group until harvest size of ≈6100 g and 73 cm. At the end of the fasting period fish had lost 7.3% mass and the condition factor had decreased from 1.23 to 1.06. Furthermore, fasted fish were 544 g lighter and 3.8 cm shorter than fed controls, corresponding to a size difference of 50%. Following refeeding, feed intake gradually increased and surpassed the feed intake of controls. As such, fasted fish eventually showed compensatory growth and at harvest weight and length were similar to controls. At harvest, males were larger than females, and immature fish were larger than maturing fish in both treatment groups. The proportion of maturing fish was 25% higher in the fed control group. During the fasting period fish behaviours were video monitored, but no aggressions were observed. After the 8-week fasting period, fish welfare was scored based on the salmon welfare index model. Only minor deviations were found and at similar regularities between fasted and control fish. To assess potential long-term impacts on welfare status, vertebral deformities were quantified with radiology at harvest. Occurrence of vertebral deformities were low and similar between treatments. In conclusion, this study shows that Atlantic salmon are highly flexible with regards to growth patterns in response to food availability, and that a prolonged fasting period neither cause signs of reduced welfare in the short or in the long term.

Growth, feed conversion, sexual maturation, and cataract formation in coho (Oncorhynchus kisutch) and Atlantic (Salmo salar) salmon post-smolts reared at different salinities in recirculating aquaculture systems for over one year

There is increasing interest in defining optimal conditions for rearing salmon to market size in recirculating aquaculture systems (RAS). Salinity, however, as a parameter that can be potentially manipulated, has been poorly studied. To address this knowledge gap, we reared coho (Oncorhynchus kisutch (Walbaum, 1792)) and Atlantic (Salmo salar Linnaeus, 1758) salmon from smolt to market size over ∼460 days at five different salinities (0, 5, 10, 20, and 30 ppt) and examined their growth performance. We found that both species reared at intermediate salinities (5–10 ppt) started to show significantly larger body mass than fish reared either in freshwater or full-strength seawater at around days 250–300. These growth-enhancing effects were maintained until day 460. The higher growth in Atlantic salmon at intermediate salinities was associated with a reduced economic feed conversion ratio, but this was not observed in coho salmon. The all-female coho salmon showed no incidence of sexual maturation and negligible cataract formation, while the mixed-sex Atlantic salmon showed high levels of sexual maturation (up to 50%) and presence of cataracts (up to 60%). Our results indicate that all-female coho salmon may be better suited to RAS than Atlantic salmon in some aspects. However, in both species, long-term rearing at intermediate salinities improved growth in RAS.

A Novel Miniaturized Biosensor for Monitoring Atlantic Salmon Swimming Activity and Respiratory Frequency.

Simple SummaryGood fish welfare is one of the prerequisites for sustainable aquaculture. Knowing how fish respond to the production conditions would allow us to better understand their biology and to further optimize production. The new miniaturized biosensor AEFishBIT was successfully used to monitor individual physical activity and respiratory frequency of two Mediterranean farmed fish species (gilthead sea bream and European sea bass). In this study, we aimed to test the use of AEFishBIT to monitor the performance of Atlantic salmon under experimental conditions. An adapted tagging procedure for salmon was developed and used to record salmon responses to handling and changing light conditions. AEFishBIT data showed a stabilization of swimming activity 8 h after handling and tagging with changes in activity or activity and respiratory quotient after changes in light intensity regimes. The results of this study supported the use of AEFishBIT to generate new behavior insights in Atlantic salmon culture.The advanced development of sensor technologies has led to the emergence of fish biosensors that are currently used for research and commercial purposes. AEFishBIT is a miniaturized biosensor attached to fish operculum that measures physical activity and respiration frequencies. In this study, we determined the effect of the tagging method and evaluated the use of this biosensor to monitor post-smolt Atlantic salmon in a tank-based system. The use of piercing fish tag had a negative impact on the gills and operculum, unlike the identical protocols used in gilthead sea bream and European sea bass. In contrast, a surgical thread did not show any apparent tissue damage. Two data recording schedules were considered to monitor immediate early reaction to fish handling and light regime changes (records every 15 min over 2 days) or adaptation to new light conditions (records every 30 min over 4 days). Data showed stabilization of physical activity 8 h post-tagging, with different steady states for the activity/respiratory ratio after changes in light intensity that reflected a different time course adaptation to new light conditions. High correlations were observed between AEFishBIT and video recording data. These findings supported the use of AEFishBIT as a promising tool for smart sensing of Atlantic salmon.

Molecular Mechanism Involved in Carotenoid Metabolism in Post-Smolt Atlantic Salmon: Astaxanthin Metabolism During Flesh Pigmentation and Its Antioxidant Properties

A better understanding of carotenoid dynamics (transport, absorption, metabolism, and deposition) is essential to develop a better strategy to improve astaxanthin (Ax) retention in muscle of Atlantic salmon. To achieve that, a comparison of post-smolt salmon with (+ Ax) or without (- Ax) dietary Ax supplementation was established based on a transcriptomic approach targeting pyloric, hepatic, and muscular tissues. Results in post-smolts showed that the pyloric caeca transcriptome is more sensitive to dietary Ax supplementation compared to the other tissues. Key genes sensitive to Ax supplementation could be identified, such as cd36 in pylorus, agr2 in liver, or fbp1 in muscle. The most modulated genes in pylorus were related to absorption but also metabolism of Ax. Additionally, genes linked to upstream regulation of the ferroptosis pathway were significantly modulated in liver, evoking the involvement of Ax as an antioxidant in this process. Finally, the muscle seemed to be less impacted by dietary Ax supplementation, except for genes related to actin remodelling and glucose homeostasis. In conclusion, the transcriptome data generated from this study showed that Ax dynamics in Atlantic salmon is characterized by a high metabolism during absorption at pyloric caeca level. In liver, a link with a potential of ferroptosis process appears likely via cellular lipid peroxidation. Our data provide insights into a better understanding of molecular mechanisms involved in dietary Ax supplementation, as well as its beneficial effects in preventing oxidative stress and related inflammation in muscle.

Digestible nutrient and energy values of corn and wheat glutens fed to Atlantic salmon (Salmo salar) are affected by feed processing method

The impact of feed processing on the digestibility of two major grain proteins fed to post-smolt Atlantic salmon (Salmo salar) was examined using a simple factorial experimental design of two protein types (wheat and corn gluten) and two feed processing methods (hot [cooking] extrusion and cold extrusion). A series of diets were each prepared from the same basal mash, including two basal diets (each diet was prepared using the same processing methods as the test diets) were also included in the experiment. Triplicate tanks of salmon (286 ± 20.9 g) were fed each diet for one week and then stripped of faeces, which was repeated two more times. Faeces, diets and ingredients were assessed for protein, amino acid, and energy digestibilities and by derivation the ingredient digestibilities for these parameters were also determined. Ingredient protein digestibility was affected by both ingredient type and feed processing method, with an interaction effect between parameters also present. Protein digestibilities were highest in diets that were cold extruded, with corn gluten protein digestibility being significantly affected by feed processing method, but wheat gluten comparatively less affected. Energy digestibilities typically reflected the protein digestibilities, but the interaction effect was not evident. The digestibility of the sum of amino acids in corn gluten was negatively affected by hot extrusion but this processing method had limited impact on wheat gluten digestibility. The digestibility of individual amino acids was highly variable between ingredients and processing methods, though was typically consistent with the digestibility observations of crude protein and sum of amino acids. Wheat gluten had superior digestibility characteristics than that of corn gluten across most parameters. This study demonstrates that the feed processing method has a clear influence on the nutritional value of corn gluten but in contrast has negligible effect on the digestibilities of wheat gluten.

Hypoxia does not change responses to dietary omega‐3 long‐chain polyunsaturated fatty acids, but rather reduces dietary energy demand by Atlantic salmon

Over 116 days, Atlantic salmon postsmolts of 183 ± 5 g were fed diets with high or low levels of lipid (230 or 180 g/kg) with high or low levels of omega-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFA; 14 or 7 g/kg). Fish were reared under hypoxic and normoxic conditions (6.7 or 8.0 mg/L), as an environmental stressor. Higher levels of lipid and n-3 in the diet increased final weight and weight gain, although no lipid x n-3 interaction was found across both environments. Hypoxia led to reduced growth, which can be explained by reduced feed intake, with no effects on FCR being observed. High lipid diets improved protein and energy retention in the fish carcass as well as improved the digestibility of lipid and LC-PUFA, including EPA and DHA. High n-3 diets also improved retention and digestibility of LC-PUFA, and transcriptomic analysis showed that the liver had reduced levels of expression of fatty acid synthesis genes, for example fads2d5 and elovl2 in those treatments. A clear relationship between performance and energy intake, independent of n-3 LC-PUFA intake, shows that energy demand under hypoxia was an over-riding feature of the nutritional responses in this study.

Thermal delousing in anaesthetised small Atlantic salmon (Salmo salar) post-smolts: A case study showing the viability of anaesthesia prior to delousing for improved welfare during treatment for salmon lice

AbstractDelousing treatment for salmon sea lice (Lepeophtheirus salmonis) is considered a significant welfare concern in farming of Atlantic salmon (Salmo salar), where both industry and legislative bodies prompt for better methods. Currently, the most common method is thermal delousing, where fish are crowded, pumped into a vessel and exposed to ~28-34°C for ~30 s. Physical collisions occurring as a result of a loss of behavioural control lead to acute stress. Crowding triggers vigorous escape behaviour as salmon respond not only to treatment but also to being channeled to and from the treatment zone. A sequence of events considered to cause mortality and poor welfare. The present case study was motivated by an urgent need for delousing in groups of small salmon post-smolts in experimental research. For this purpose, a simple, small-scale system for thermal delousing was constructed, including anaesthesia to alleviate behavioural responses. The anaesthetised fish showed little behavioural response to thermal treatment, strong appetite within hours, and negligible mortality. The described method is regarded as a welfare-friendly alternative to industrial delousing in smaller fish groups, for example, in experimental research. We would encourage detailed research aimed towards gaining a deeper understanding of the welfare effects of anaesthesia prior to treatment for delousing.

What is the limit of sustained swimming in Atlantic salmon post smolts?

A trend in Atlantic salmon aquaculture is to establish new production sites that are susceptible to extreme weather conditions; however, strong and persistent water currents may compromise fish welfare. Defining acceptable current conditions necessitates an assessment of sustained swimming abilities that are fuelled solely by aerobic metabolism and do not result in fatigue. In this study, the limit of sustained swimming was quantified with regards to both speed and time in Atlantic salmon of ~700 g and ~39 cm at 12°C by testing fish in groups of 10 in a large swim tunnel respirometer. First, critical swimming speed (Ucrit) (107 cm s-1) and minimum cost of transport (66 cm s-1) were measured. Sustained swimming trials at constant speeds were then performed based on a percentage of the group mean Ucrit (80, 85, 90, 95, 100 or 105%). Fish were forced to swim until they fatigued or until 72 h had passed. Surprisingly, most fish were able to sustain 80 and 85% Ucrit for 72 consecutive hours. However, at the highest speeds, fatigue was reached within the first 2 h. By categorizing fatigue times of individual fish into &lt;2, 2-72 or &gt;72 h, significant differences in relative swimming speeds were found that corresponded to 2.7, 2.5 and 2.2 body lengths s-1, respectively. These results document impressive sustained swimming capacities in farmed Atlantic salmon and add important temporal insights about ambient current limits with regards to fish welfare at exposed aquaculture sites.

Filtration, concentration and detection of salmonid alphavirus in seawater during a post-smolt salmon (Salmo salar) cohabitant challenge.

Currently, the prevalence of salmonid alphavirus (SAV) in Norwegian Atlantic salmon farms is largely surveyed via sacrificing fish and sampling of organ tissue on a monthly basis. However, a more cost-efficient, straightforward, rapid, reliable, reproducible and animal welfare friendly method based on the detection of SAV in water could be considered as an alternative method. In the present study, such a method was developed and optimized through a 6 wk cohabitant challenge trial, using post-smolt Atlantic salmon Salmo salar L challenged with high or low doses of SAV subtype 3 (SAV3). Tank water and tissue samples from cohabitant fish were collected at 16 time points. SAV3 was concentrated from the water by filtration, using either electronegative or electropositive membrane filters, which were subsequently rinsed with one of 4 different buffer solutions. SAV3 was detected first in tank water (7 d post-challenge, DPC), and later in cohabitant fish organ tissue samples (12 DPC). The electronegative filter (MF-Millipore™) and rinsing with NucliSENS® easyMAG® Lysis Buffer presented the best SAV3 recovery. A significant positive correlation was found between SAV3 in the tank water concentrates and the mid-kidney samples. Based on these results, detection of SAV3 in filtrated seawater is believed to have the potential to serve as an alternative method for surveillance of SAV in Atlantic salmon farms.

Wild Atlantic salmon enter aquaculture sea‐cages: A case study

AbstractThere are more than 3,000 Atlantic salmon aquaculture sea‐cages distributed along the coastline of Norway. Many of these sea‐cages are located along the migration routes of wild Atlantic salmon (Salmo salar) postsmolts. This study documents for the first time that wild Atlantic salmon postsmolts can enter sea‐cages stocked with farmed Atlantic salmon. In addition, wild sea trout (Salmo trutta) and salmon/trout hybrid postsmolts were found inside the sea‐cages. The extent of such “bycatch” in commercial aquaculture is vital knowledge for the conservation of Atlantic salmon and sea trout. Further studies are encouraged in order to evaluate the extent of this possible ghost fishing phenomena.

DNA Methylation Dynamics in Atlantic Salmon (Salmo salar) Challenged With High Temperature and Moderate Hypoxia

The marine environment is predicted to become warmer and more hypoxic, and these conditions may become a challenge for marine fish species. Phenotypically plastic responses facilitating acclimatization to changing environments can be mediated by DNA methylation through the modulation of gene expression. To investigate whether temperature and hypoxia exposure induce DNA methylation changes, we challenged post-smolt Atlantic salmon (Salmo salar) to increasing temperatures (12 → 20°C, 1°C week–1) under normoxia or moderate hypoxia (∼70% air saturation) and compared responses in the liver after 3 days or 4 weeks at 20°C. DNA methylation was studied in six genes related to temperature stress (cirbp, serpinh1), oxidative stress (prdx6, ucp2), apoptosis (jund), and metabolism (pdk3). Here, we report that exposure to high temperature, alone or combined with hypoxia, affected the methylation of CpG sites within different genomic regulatory elements around the transcription start of these temperature/hypoxia biomarker genes. Yet, we uncovered distinct CpG methylation profiles for each treatment group, indicating that each environmental condition may induce different epigenetic signatures. These CpG methylation responses were strongly dependent on the duration of stress exposure, and we found reversible, but also persistent, CpG methylation changes after 4 weeks of exposure to 20°C. Further, several of these changes in CpG methylation correlated with transcriptional changes, and thus, can be considered as regulatory epigenetic marks (epimarkers). Our study provides insights into the dynamic associations between CpG methylation and transcript expression in Atlantic salmon, and suggests that this epigenetic mechanism may mediate physiological acclimation to short-term and long-term environmental changes.

Dietary Lipid:Protein Ratio and n-3 Long-Chain Polyunsaturated Fatty Acids Alters the Gut Microbiome of Atlantic Salmon Under Hypoxic and Normoxic Conditions.

Researchers have adjusted dietary lipid:protein ratios and n-3 long-chain polyunsaturated fatty acids (LC-PUFA) to optimize the growth performance of Atlantic salmon. However, dietary impacts on the gut microbiome are lacking, especially under varying environmental conditions. To examine this response, post-smolt salmon (184 ± 5 g) were fed diets with lipid:protein ratios considered low (180, 570 g/kg) and high (230, 460 g/kg) along with low and high levels of n-3 LC-PUFA (7 or 14 g/kg) while fish were reared under low and high levels of dissolved oxygen (6.7 or 8.0 mg/L). At day 0, 35 and 116, digesta in the distal intestine were collected and analyzed for viable counts and 16S ribosomal RNA (rRNA) genes (V4 region) using Illumina MiSeq. The reduction in oxygen had negligible effects, except on viable plate counts of total bacteria and an initial effect on beta-diversity. In contrast, the high lipid (HL) diets had an increased alpha-diversity (e.g., Shannon and Chao-1) at day 0 and day 35 whereas high n-3 diets suppressed these indices at day 116. Generally, a reduction in alpha-diversity was observed over time and an interaction between lipid:protein ratio x n-3 was found. Between diets, beta-diversity and phyla abundance were similar as both Proteobacteria (44%) and Firmicutes (21%) dominated. However, at the genus level Aliivibrio, Streptococcus, Weissella, and Lactobacillus, were associated with low lipid (LL) diets while the high lipid diets were associated with less abundant bacteria, e.g., Chromohalobacter. At day 116, the relative abundance of the Tenericutes phylum increased 10-fold (36%). Fish fed the high lipid diet with high n-3 had reduced alpha-diversity, lowest abundance of lactic acid bacteria, and highest abundance of Mycoplasma, which may indicate a less healthy gut microbiome. Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) analysis revealed that saturated and unsaturated fatty acid biosynthesis pathways were several folds higher in fish fed the high lipid diet, possibly to compensate for the lack of dietary n-3. In summary, our results show that the viable plate counts, alpha-diversity, beta-diversity, and predictive function of gut bacteria in Atlantic salmon post-smolts are influenced by dietary lipid:protein ratio and n-3 LC-PUFA over several time points with little effect by dissolved oxygen.

Sea Lice (Lepeophtheirus salmonis) Infestation Reduces the Ability of Peripheral Blood Monocytic Cells (PBMCs) to Respond to and Control Replication of Salmonid Alphavirus in Atlantic Salmon (Salmo salar L.).

Here we have studied the impact of lice (Lepeophtheirus salmonis) infestation of donor fish on the ability of isolated peripheral blood monocytes (PBMCs) to control the replication of salmonid alphavirus (SAV) ex vivo. PBMCs were collected by Percoll gradients at eight and nine weeks post copepodid infestation of Atlantic salmon post smolt. Uninfested fish were controls. PBMCs were then infected ex vivo with SAV (subtype 3), and samples were collected for analysis at two, four, and six days post virus infection. Virus titer in the supernatant was assayed in CHH-1 cells, and in addition, the relative expression of the virus structural protein E2 and selected host antiviral genes, IRF9, ISG15, Mx, and IFIT5, were assayed using real-time PCR. Significantly higher virus replication was detected in cells collected from lice-infested fish compared to controls. Higher virus titer coincided with an inability to upregulate the expression of different immune genes, IFIT5, IRF9, and Mx. These findings point towards compromised ability of PBMCs from lice-infested fish to control virus replication, and, to our knowledge, is the first report showing the direct effect of lice infestation on the interplay between viruses and immune cells. There is a possible impact on the dynamic spread of viral diseases in the aquatic environment.

Salmon lice-induced mortality of Atlantic salmon during post-smolt migration in Norway

Abstract The expansion of salmonid aquaculture has resulted in environmental challenges, including salmon lice that may infest both farmed and wild fish. For wild Atlantic salmon post-smolts that migrate from their rivers to the ocean, the first phase of their journey in the coastal zone, where aquaculture occurs, is critical when considering lice exposure. To evaluate the lice influence during the post-smot migration we have developed a migration model. An archive with spatiotemporal concentrations of lice larvae in Norwegian coastal waters has been established using a combination of state-of-the-art hydrodynamic and lice biology models. To estimate lice-induced mortality of wild salmon from Norwegian rivers, the infestation level on the virtual post-smolts was calibrated to match that observed on wild post-smolts genetically assigned their rivers of origin. The lice infestation pressure was modelled on post-smolts from 401 rivers covering all of Norway. Based on this, aquaculture-produced salmon lice-induced mortality of wild salmon post-smolts was estimated as &amp;lt;10% for 179 rivers, 10–30% for 140 rivers, and &amp;gt;30% for 82 rivers in 2019. Estimated mortalities were used together with other data sets to evaluate aquaculture sustainability in Norway. The aquaculture regulatory system represents a globally leading example of science-based management that considers the environmental impact.

Effects of ozone on post-smolt Atlantic salmon (Salmo salar) performance, health, and maturation in freshwater recirculation aquaculture systems

Steroid hormones accumulate in recirculation aquaculture systems (RAS) and may influence the reproductive physiology of farmed fish. Ozone reduces hormone concentrations in freshwater RAS used to rear Atlantic salmon, but its effect on reproductive development is unknown. Accordingly, an 8-month trial was carried out to evaluate the growth, health, and maturation of post-smolt Atlantic salmon (296 ± 4 g initial weight) reared in six replicated freshwater RAS (9.5 m3 total volume) operated with or without ozone (N = 3/treatment). Residual ozone was controlled with an oxidation reduction potential (ORP) of 300–320 mV, and mean water temperature was maintained at 14.7 °C. Atlantic salmon growth was generally faster in ozonated RAS. Salmon from RAS with and without ozone weighed 2156 ± 101 and 1810 ± 15 g, respectively, by the end of the study. Caudal, anal, and pelvic fin damage was greater (P < 0.05) for salmon in ozonated RAS early in the trial but improved thereafter. No statistical differences in gill, skin, and skeletal muscle histopathology were observed between treatments at the end of the study. Waterborne estradiol, testosterone, and 11-ketotestosterone levels were periodically lower (P < 0.05) in ozonated RAS, but maturing salmon were more prevalent in these systems. At the end of the trial, percent maturation of salmon populations reared in RAS with and without ozone was 63 ± 7 and 48 ± 1%, respectively; however, maturity appeared to be related to fish size. Improved water quality was observed in ozonated RAS including reduced dissolved copper, iron, and zinc levels, total heterotrophic bacteria counts, and true color, and increased ultraviolet transmittance, which may have supported improved Atlantic salmon growth. Overall, ozone did not inhibit the onset or prevalence of Atlantic salmon maturation, but significant improvements in water quality and salmon growth performance resulted from its use.

135 Production of a fifty percent functional protein concentrate from the dry grind ethanol process and use of the product in diets for Atlantic salmon

Abstract The corn distilling industry is a major processor of grain, but the high fiber co-product (DDGS), has limited application in feed. Simple mechanical stillage separation downstream of fermentation produces a high protein (52.4 % DM), highly digestible, low crude fiber (4.4% DM) product containing approximately 25% DM spent brewer’s yeast (high density distillers’ protein: HDDP). Currently, approximately 300 ktons of HDDP are produced annually in the USA, and the volume will double in 2020. The effect of graded inclusion levels of HDDP on growth, feed efficiency, nutrient utilization, blood chemistry and gut histology of 525 post-smolt Atlantic salmon (initial body weight 304 ± 10.7g), randomly allocated to three tanks per treatment, was tested in a salt-water recirculating aquaculture system. One control diet with no HDDP was formulated to meet the nutrient requirements of Atlantic salmon. Four test diets were formulated to contain graded levels of HDDP at 5, 10, 15 and 20% respectively. HDDP partially replaced soy protein concentrate and corn protein concentrate in the diets. Salmon were hand-fed to satiety, 3 times daily during the 84-day trial. Throughout the trial the performance of fish on all treatments exceeded commercial growth rates with thermal growth coefficients (TGC) in excess of 0.160 and feed conversion efficiency of ≤ 1.0. Overall HDDP was a nutritious feed ingredient and had no significant impact on performance. Overall TGC was highest (0.200 over the 84-day trial period) in fish fed the diet containing 10% HDDP. Both villi length and villi width in the distal intestine of salmon fed diets containing HDDP tended to be higher than in the controls. Overall, HDDP derived from the dry grind ethanol process was a safe and nutritious novel feed ingredient for Atlantic salmon, and the potential beneficial effect on gut morphology merits investigation.