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The aim of this study was to assess whether activity and heart rate sensor implants can be used to measure stress and thus estimate one important welfare indicator for fish in aquaculture pens, and if such measurements correlate to physiological factors measured through blood sampling. The experiment consisted of two parts: i) a bio-logger study where implanted sensors were used to monitor activity and heart rates for fish undergoing stress (crowding); and ii) an analysis of blood constituents (cortisol, glucose, lactate, and chloride) of a second group of fish undergoing the same treatment. We found that activity measurements can be used to track high-impact stress events but may not be suitable to discern possibly nuanced reactions to stress impacts of lower magnitude. While heart rate was measured reliably, e.g., in showing clear circadian rhythms, it was no credible proxy for predicting stress in this study. Our results thus underline challenges observed in previous work around the use of heart rate as stress indicator, and imply that the translation of its meaning into a proxy for stress needs further work. Although tag-based monitoring of stress is not without its difficulties, studies such as this provide a wealth of information on salmon behaviour and physiology, and the links between these. [ABSTRACT FROM AUTHOR]

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

The feed legislation allows the use of fish protein hydrolysates in feed for the same species in which it came from, since enzymatic hydrolysis degrades the proteins and eliminates potential prions, which have caused disease in mammals, but not in fish. In this trial, we investigated the effects of partially replacing dietary fishmeal (FM) with salmon protein hydrolysate (FPH) on the intestinal gene expression and microbiota. Atlantic salmon post smolts were either fed a control diet containing 30% fishmeal (FM), a 20% FM diet with 9% salmon hydrolysate (FPH-09) or a 10% FM diet with 18% salmon hydrolysate (FPH-18), until doubling of weight. Gene expression analysis by RNA sequencing of pyloric caeca (PC), midgut (MG) and hindgut (HG) revealed a downregulation of immunological genes involved in inflammation in the intestine of FPH-18 fed salmon compared to salmon fed the FM control. The gene expression of paralogous peptide transporters (PepT) was analyzed by real time quantitative PCR in PC, anterior midgut (AMG), posterior midgut (PMG) and HG of salmon fed all the three diets. The PepT1b paralog had highest relative expression levels in PC and AMG, suggesting that PepT1b is most important for peptide uptake in the anterior intestine. PepT1a was also mainly expressed in the PC and AMG, but at lower levels than PepT1b and PepT2b in the AMG. The PepT2b paralog had high levels of expression in AMG, PMG and HG indicating that it contributed significantly to peptide uptake in the posterior part of the gastrointestinal tract. The gut microbiota in the mucosa and digesta of the MG and HG, were dominated by the phyla Cyanobacteria and Proteobacteria, but also Firmicutes were present. The only dietary effect on the microbiota was the higher prevalence of the phyla Spirochaetes in the mucosa of FPH-18 fed salmon compared to the FM fed salmon. In conclusion, replacing FM with salmon hydrolysate reduced the expression of inflammatory markers in the Atlantic salmon intestine suggesting improved health benefits. The reduced inflammation may be related to the reduced FM content, potentially bioactive peptides in the hydrolysate and/or the altered gut microbial composition. [ABSTRACT FROM AUTHOR]

The levels of eicosapentaenoic (EPA) and docosahexaenoic (DHA) in salmon fillets have decreased because of the progressive replacement of fish oil (FO). This study contributes to enabling the sustainable growth of aquaculture by confirming the effects of partially or fully replacing FO with microalgal oil (AO) on growth, muscle fatty acid profiles, and muscle quality of farmed Atlantic salmon. Crucially, this is now done throughout the entire post‐smolt production cycle and up to a harvest weight of 3 kg. Three experiments were performed using fish ranging from 145 g to 3 kg and testing different diets, replacing FO up to 100%. Zootechnical performance was similar among treatments in all experiments. Changing the lipid source in the diet resulted in EPA and DHA digestibility of greater than 96%. Sensory characteristics of raw fish fillets were similar among treatments, supporting a similar sensorial experience with the replacement of FO with no impact on consumers. Overall, results confirm that the AO tested here enables the sustainable growth of Atlantic salmon aquaculture by helping to maintain a level of EPA and DHA in the fish fillets, without detriment to zootechnical performance and sensory characteristics, while simultaneously contributing to a reduced marine footprint for aquafeeds. [ABSTRACT FROM AUTHOR]

Farmed Atlantic salmon reared under natural seasonal changes in sea-cages had an elevated consumption of antioxidants during spring. It is, however, unclear if this response was caused by the increase in day length, temperature, or both. The present study examined redox processes in Atlantic salmon that were reared in indoor tanks at constant temperature (9 °C) under a simulated natural photoperiod. The experiment lasted for 6 months, from vernal to autumnal equinoxes, with the associated increase and subsequent decrease in day length. We found that intracellular antioxidants were depleted, and there was an increase in malondialdehyde (MDA) levels in the liver and muscle of Atlantic salmon with increasing day length. Antioxidant enzyme activity in liver and muscle and their related gene profiles was also affected, with a distinct upregulation of genes involved in maintaining redox homeostasis, such as peroxiredoxins in the brain in April. This study also revealed a nuclear factor-erythroid 2-related factor 2 (Nrf2)-mediated oxidative stress response in muscle and liver, suggesting that fish integrate environmental signals through redox signaling pathways. Furthermore, growth and expression profiles implicated in growth hormone (GH) signaling and cell cycle regulation coincided with stress patterns. The results demonstrate that a change in photoperiod without the concomitant increase in temperature is sufficient to stimulate growth and change the tissue oxidative state in Atlantic salmon during spring and early summer. These findings provide new insights into redox regulation mechanisms underlying the response to the changing photoperiod, and highlight a link between oxidative status and physiological function. [ABSTRACT FROM AUTHOR]

Keywords: Atlantic salmon; nephrocalcinosis; radiology EN Atlantic salmon nephrocalcinosis radiology 1883 1888 6 11/11/22 20221201 NES 221201 INTRODUCTION Nephrocalcinosis is a common disorder in nurseries in Norway (Klykken, Reed, et al., 2022) and was reported as one of the main welfare challenges in farmed salmon by The Norwegian Fish Health Report of 2019 (Sommerset et al., 2020). Nephrocalcinosis in Atlantic salmon is mainly identified as amorphous carbonate apatite, a calcium-dominated mineral (Klykken, Reed, et al., 2022), and it has previously been demonstrated that this mineral composition is suitable for x-ray detection (Smith & Lehr, 1966). In conclusion, we are confident that radiology is a suitable diagnostic tool for assessing mineral deposits (amount and distributions) associated with nephrocalcinosis in farmed Atlantic salmon, with minimal risk to the operator when appropriate measures are taken. Regarding the future use of radiology to assess nephrocalcinosis, one should be aware of the limitations of the method, since soft tissue changes not including mineralization cannot be seen on radiographs. [Extracted from the article]

Nephrocalcinosis is a common disorder in farmed Atlantic salmon, but the consequences for the fish physiology are not well understood. We performed a transcriptome study in kidneys of Atlantic salmon (Salmo salar) smolts without and with severe chronic nephrocalcinosis (NC). The study revealed that numerous genes are differentially expressed in fish with NC compared with healthy salmon. The most evident changes in gene expression patterns in the NC group were a massive downregulation of metabolism and energy production, upregulation of signalling pathways important for tissue repair and function maintenance and upregulation of inflammatory responses. Overall, the extensive tissue damage and the gene regulation responses that affect salmon with severe nephrocalcinosis are highly likely to have dramatic consequences on fish survival. [ABSTRACT FROM AUTHOR]

Accumulating evidence indicates a close relationship between oxidative stress and growth rate in fish. However, the underlying mechanisms of this relationship remain unclear. This study evaluated the combined effect of dietary antioxidants and growth hormone (GH) on the liver and the muscle redox status of Atlantic salmon. There were two sequential experimental phases (EP) termed EP1 and EP2, each lasting for 6 weeks. In EP1, Atlantic salmon were fed either low-(L, 230 mg/kg ascorbic acid (Asc), 120 mg/kg α-tocopherol (α-TOH)), or high-(H, 380 mg/kg Asc, 210 mg/kg α-TOH)vitamin diets. The vitamins were supplemented as stable forms and the feeding was continued in EP2. In EP2, half of the fish were implanted with 3 μL per g body weight of recombinant bovine GH (Posilac®, 1 mg rbGH g BW−1) suspended in sesame oil, while the other half were held in different tanks and sham-implanted with similar volumes of the sesame oil vehicle. Here, we show that increasing high levels of vitamin C and E (diet H) increased their content in muscle and liver during EP1. GH implantation decreased vitamin C and E levels in both liver and muscle but increased malondialdehyde (MDA) levels only in the liver. GH also affected many genes and pathways of antioxidant enzymes and the redox balance. Among the most consistent were the upregulation of genes coding for the NADPH oxidase family (NOXs) and downregulation of the oxidative stress response transcription factor, nuclear factor-erythroid 2-related factor 2 (nrf2), and its downstream target genes in the liver. We verified that GH increases the growth rate until the end of the trail and induces an oxidative effect in the liver and muscle of Atlantic salmon. Dietary antioxidants do lower oxidative stress but have no effect on the growth rate. The present study is intended as a starting point to understand the potential interactions between growth and redox signaling in fish. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Domestication of animals imposes strong targeted selection for desired traits but can also result in unintended selection due to new domestic environments. Atlantic salmon (Salmo salmar) was domesticated in the 1970s and has subsequently been selected for faster growth in systematic breeding programmes. More recently, salmon aquaculture has replaced fish oils (FOs) with vegetable oils (VOs) in feed, radically changing the levels of essential long‐chain polyunsaturated fatty acids (LC‐PUFAs). Our aim here was to study the impact of domestication on metabolism and explore the hypothesis that the shift to VO diets has unintentionally selected for a domestication‐specific lipid metabolism. We conducted a 96‐day feeding trial of domesticated and wild salmon fed diets based on FOs, VOs or phospholipids, and compared transcriptomes and fatty acids in tissues involved in lipid absorption (pyloric caeca) and lipid turnover and synthesis (liver). Domesticated salmon had faster growth and higher gene expression in glucose and lipid metabolism compared to wild fish, possibly linked to differences in regulation of circadian rhythm pathways. Only the domesticated salmon increased expression of LC‐PUFA synthesis genes when given VOs. This transcriptome response difference was mirrored at the physiological level, with domesticated salmon having higher LC‐PUFA levels but lower 18:3n‐3 and 18:2n‐6 levels. In line with this, the VO diet decreased growth rate in wild but not domesticated salmon. Our study revealed a clear impact of domestication on transcriptomic regulation linked to metabolism and suggests that unintentional selection in the domestic environment has resulted in evolution of stronger compensatory mechanisms to a diet low in LC‐PUFAs. [ABSTRACT FROM AUTHOR]

Abstract The onset of first feeding is a critical period for Atlantic salmon (Salmo salar). The fish goes through a dramatic transition, from using the yolk sac as an energy and nutrient resource to rely on exogenous food. However, the digestive system of salmon is not fully developed at start feeding. This is especially true for digestion and absorption of dietary lipids. To optimize lipid composition of the initial feed for better growth and development of salmon, it is important to have a systemic understanding of lipid metabolism. The present study combines transcriptomics and lipid composition data to obtain an overview of how lipid metabolism pathways change when salmon switch from endogenous to exogenous feed. Transition to exogenous feeding had higher influence on gene expression and fatty acids composition in pyloric caeca relative to liver, suggesting metabolism is more responsive in pyloric caeca when diet switches. The pathways of phospholipid and lipoprotein synthesis were both up-regulated in pyloric caeca, while phospholipid content unchanged. Because phospholipids are a major component of intestinal lipoproteins, it suggests that a higher level of dietary phospholipids is required for optimal lipid transport at first feeding stages. De-novo cholesterol synthesis pathway was up-regulated in pyloric caeca after exogenous feeding, while a down-regulation of bile acid synthesis pathway was found in liver. This suggests a higher requirement of cholesterol in salmon fry after switching to exogenous feeding. The present study has provided new insights on the systemic changes of lipid synthesis and transport pathways in salmon fry when switching from endogenous to exogenous feeding. Highlights • We aim to understand lipid metabolism regulation when the fish switched from endogenous to exogeneous feeding. • Phospholipids and cholesterol synthesis increased after first feeding, suggesting a high requirement of the two lipids. • We combine fatty acids, lipid class and gene expression data to study the systemic regulation of lipid metabolism. • We introduce a novel "sum of transcripts" metric to overcome gene redundancy in transcriptomic data from polyploid genomes. [ABSTRACT FROM AUTHOR]

Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are essential fatty acids (EFA) vital for Atlantic salmon health, growth performance, and product quality. Yet, DHA and especially EPA are in short supply as ingredients for aquafeeds. Whilst the role of EFA in salmonid nutrition has been well studied, clear guidelines for aquaculture nutrition practitioners are still missing. This article addresses this gap by testing different EPA:DHA ratios (0.15, 0.55, and 0.98) when these two EFA represent at least 10% of the total pool of fatty acids in aquafeeds. Grow-out trials revealed no differences in zootechnical performance between fish fed the different diets during the initial eight weeks before vaccination challenge, nor on the subsequent three weeks post-vaccination for fish truly vaccinated or sham vaccinated (used as control groups for each of the three diets tested). Nonetheless, the FCR of vaccinated fish was significantly higher than sham vaccinated conspecifics, but diet yielded no significant effect. The expression of most genes screened (e.g., Elongation Factor 1α (Elf-1α), Interleukin 10 (IL10), Interleukin 8 (IL8), Tumor Necrosis Factor (TNFα)) was not significantly affected by vaccination or diet, while Viperine and Mx genes were upregulated in sham vaccinated fish fed the experimental diet with an EPA:DHA ratio of 0.55. The fatty acid composition of head kidney was affected by diet, namely EPA, but not DHA. The fatty acid profile of white muscle was also significantly affected by diet, with contrasting results for EPA and DHA; EPA content was higher for fish fed diets with higher EPA:DHA ratios and DHA levels were significantly higher (peaking at 16% of the total pool of fatty acids) when fish were provided with the diet featuring the lowest EPA:DHA ratio (0.15). Interestingly, fish fed the diet with the highest EPA:DHA ratio showed a lower number of wounded fish at the end of the grow-out period post-vaccination. Despite the reduction was not statistically significant, given the severe impact of wounded fish on salmon farming productivity, our results indicate that the partial replacement of fish oil with algal oil in salmon feed contributed to achieving a balanced EPA:DHA ratio, an adequate profile of Omega-3 long chain polyunsaturated fatty acids and improved the overall health and welfare of fish. This approach creates the opportunity to increase the productivity of fish farming operations and foster a more sustainable growth of the aquaculture industry. • Different dietary EPA:DHA ratios in iso -EPA + DHA diets do not influence zootechnical performance of Atlantic salmon. • Different dietary EPA:DHA ratios result in different muscle and head kidney fatty acid profile in Atlantic salmon. • EPA:DHA ratios can influence the health of Atlantic salmon. [ABSTRACT FROM AUTHOR]

Background: It has been suggested that the high phospholipid (PL) requirement in Atlantic salmon (Salmo salar) fry is due to insufficient intestinal de-novo synthesis causing low lipoprotein (LP) production and reduced transport capacity of dietary lipids. However, in-depth ontogenetic analysis of intestinal PL and LP synthesis with the development of salmon has yet to be performed. Therefore, in this paper we used RNA-Seq technology to investigate the expression of genes involved in PL synthesis and LP formation throughout early developmental stages and associate insufficient expression of synthesis pathways in salmon fry with its higher dietary PL requirement. There was a special focus on the understanding homologous genes, especially those from salmonid-specific fourth vertebrate whole-genome duplication (Ss4R), and their contribution to salmonid specific features of regulation of PL metabolic pathways. Salmon fry were sampled at 0.16 g (1 day before first-feeding), 2.5 and 10 g stages of development and transcriptomic analysis was applied separately on stomach, pyloric caeca and hindgut of the fish. Results: In general, we found up-regulated pathways involved in synthesis of phosphatidylcholine (PtdCho), phosphatidylethanolamine (PtdEtn), and LP in pyloric caeca of salmon between 0.16 and 10 g. Thirteen differentially expressed genes (q < 0.05) in these pathways were highly up-regulated in 2.5 g salmon compared to 0.16 g, while only five more differentially expressed (q < 0.05) genes were found when the fish grew up to 10 g. Different homologous genes were found dominating in stomach, pyloric caeca and hindgut. However, the expression of dominating genes in pathways of PL and LP synthesis were much higher in pyloric caeca than stomach and hindgut. Salmon-specific homologous genes (Ss4R) had similar expression during development, while other homologs had more diverged expression. Conclusions: The up-regulation of the de-novo PtdCho and PtdEtn pathways confirm that salmon have decreasing requirement for dietary PL as the fish develops. The similar expressions between Ss4R homologous genes suggest that the functional divergence of these genes was incomplete compared to homologs derived from other genome duplication. The results of the present study have provided new information on the molecular mechanisms of phospholipid synthesis and lipoprotein formation in fish. [ABSTRACT FROM AUTHOR]

New de novo sources of omega 3 (n-3) long chain polyunsaturated fatty acids (LC-PUFA) are required as alternatives to fish oil in aquafeeds in order to maintain adequate levels of the beneficial fatty acids, eicosapentaenoic and docosahexaenoic (EPA and DHA, respectively). The present study investigated the use of an EPA+DHA oil derived from transgenic Camelina sativa in Atlantic salmon (Salmo salar) feeds containing low levels of fishmeal (35%) and fish oil (10%), reflecting current commercial formulations, to determine the impacts on tissue fatty acid profile, intestinal transcriptome, and health of farmed salmon. Post-smolt Atlantic salmon were fed for 12-weeks with one of three experimental diets containing either a blend of fish oil/rapeseed oil (FO), wild-type camelina oil (WCO) or transgenic camelina oil (DCO) as added lipid source. The DCO diet did not affect any of the fish performance or health parameters studied. Analyses of the mid and hindgut transcriptomes showed only mild effects on metabolism. Flesh of fish fed the DCO diet accumulated almost double the amount of n-3 LC-PUFA than fish fed the FO or WCO diets, indicating that these oils from transgenic oilseeds offer the opportunity to increase the n-3 LC-PUFA in farmed fish to levels comparable to those found a decade ago. [ABSTRACT FROM AUTHOR]

The effect of adding 0%, 1%, 2% and 5% chitin from prawn shells in the diets for Atlantic cod, Atlantic halibut and Atlantic salmon on growth was investigated. Nutrient digestibility and feed utilization was investigated in salmon and cod. Atlantic cod grew from 186 ± 29 to 383 ± 78 g ( N = 960) over 13 weeks. Dietary chitin had no effect on length, weight, condition, liver size or specific growth rate (SGR). The apparent digestibility ( ADC) for protein ranged from 84.7% to 86.5%, lipid between 88.8% and 93.1% and dry matter from 96.1% to 96.6%. Feed utilization varied between 1.08 and 1.11 and was not correlated with dietary chitin content. Atlantic salmon tripled their weight from 199 ± 9 to 615 ± 75 g ( N = 480) during the 13 weeks. High inclusions of chitin (>1%) reduced both growth rate and condition. Protein and lipid ADC was negatively correlated with dietary chitin. Feed utilization ranged between 0.86 and 0.90 and was not significantly affected by dietary chitin. Faecal protein increased significantly with increasing dietary chitin, while faecal dry matter and lipid did not. Individually tagged Atlantic halibut grew from 1300 ± 470 to 2061 ± 714 g ( N = 70) during 6 months. Individual growth rates varied within each group from being slightly negative to 0.81%·day−1. Diet had no significant effect on growth rates. Atlantic cod and Atlantic halibut seems unaffected by up to 5% chitin additions in the diet, while chitin >1% of diet negatively affects growth and nutrient utilization in Atlantic salmon. [ABSTRACT FROM AUTHOR]

BACKGROUND Methods of stunning used in salmon slaughter are still the subject of research. Fish quality can be influenced by pre-, ante- and post-mortem conditions, including handling before slaughter, slaughter methods and storage conditions. Carbon monoxide ( CO) is known to improve colour stability in red muscle and to reduce microbial growth and lipid oxidation in live fish exposed to CO. Quality differences in Atlantic salmon, Salmo salar L., stunned by CO or percussion, were evaluated and compared by different techniques [near infrared reflectance spectroscopy ( NIRS), electronic nose ( EN), electronic tongue ( ET)] and sensory analysis. RESULTS Thawed samples, freeze-dried preparates and NIRS devices proved to be the most efficient combinations for discriminating the treatments applied to salmon, i.e. first the stunning methods adopted, then the back-prediction of the maximum time to reach rigor mortis and finally to correlate some sensory attributes. A trained panel found significant differences between control and CO-stunned salmon: reduced tactile crumbliness, reduced odour and aroma intensities, and reduced tenderness of CO-treated fillets. CO stunning reduced radiation absorbance in spectra of thawed and freeze-dried fillets, but not fillet samples stored in ethanol, where it may have interacted with myoglobin and myosin. CONCLUSIONS The good results in a rapid discrimination of thawed samples detected by NIRS suggest suitable applications in the fish industry. CO treatment could mitigate sensory perception, but consumer tests are needed to confirm our findings. © 2015 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

When Atlantic salmon parr migrate from fresh water towards the sea, they undergo extensive morphological, neural, physiological and behavioural changes. Such changes have the potential to affect their responsiveness to various environmental factors that impose stress. In this study we compared the stress responses in parr and post-smolt salmon following exposure to repeated chasing stress (RCS) for three weeks. At the end of this period, all fish were challenged with a novel stressor and sampled before (T 0 ) and after 1 h (T 1 ). Parr had a higher growth rate than post-smolts. Plasma cortisol declined in the RCS groups within the first week suggesting a rapid habituation/desensitisation of the endocrine stress axis. As a result of the desensitised HPI axis, RCS groups showed a reduced cortisol response when exposed to the novel stressor. In preoptic area (POA) crf mRNA levels were higher in all post-smolt groups compared to parr. 11βhsd2 decreased by RCS and by the novel stressor in post-smolt controls (T 1 ), whereas no effect of either stress was seen in parr. The gr s were low in all groups except for parr controls. In pituitary, parr controls had higher levels of crf1r mRNA than the other parr and post-smolt groups, whilst pomcb was higher in post-smolt control groups. Overall, 11βhsd2 transcript abundance in parr was lower than post-smolt groups; after the novel stressor pomc s, gr s and mr were up-regulated in parr control (T 1 ). In summary, we highlight differences in the central stress response between parr and post-smolt salmon following RCS. [ABSTRACT FROM AUTHOR]

High melatonin concentrations were expected to negatively affect Atlantic salmon appetite. Hence, individually kept Atlantic salmon postsmolts were subjected to continuous light (24:0, L:L) or natural daylight (12:12, L:D) and then given intraperitoneal implants of slow release melatonin in a 2 by 2 factorial design. Possible effects on food intake were monitored over three weeks. In addition, a plasma melatonin assessment test was run in parallel to monitor diurnal blood levels of melatonin through the trial. The surgical intervention was effective, leading to a 10x increase in mean melatonin levels when compared to control fish, but neither the implant nor the change in daylight had any significant effect on feed intake, at least in the short term. [ABSTRACT FROM AUTHOR]

This study investigated the production performance of the Atlantic salmon postsmolt ( Salmo salar L.) subjected to cyclic oxygen reductions (hypoxia) of varying severity. Triplicate groups ( N = 955) were kept at constant 80% O2 (control) or subjected to 1 h and 45 min of hypoxia (50, 60 or 70% O2, termed 80:70, 80:60 and 80:50 groups) every 6 h at 16°C for 69 days. Feed was provided in normoxia. One third of the fish were kept further for 30 days in normoxia to study possible compensatory growth. Cyclic hypoxia did not alter the oxygen uptake rates of fish, measured in night-time. Fish subjected to 50% and 60% O2 reduced feeding by 13% and 6% compared with the controls, respectively, with corresponding reductions in specific growth rates. Feed utilization was not reduced. Compensatory growth was observed in fish from the 80:50 group, but full compensation was not achieved. The main conclusions were that feeding in normoxia does not fully alleviate negative effects of cyclic hypoxia on feeding and growth, when oxygen is reduced to 60% or below in hypoxic periods, that feed utilization is maintained, and that compensatory growth may lessen negative effects. [ABSTRACT FROM AUTHOR]

Infectious pancreatic necrosis virus (IPNV) causes high incidence of disease in salmonids during the first period after SW transfer. During this period as well as during periods of stress, cortisol levels increase and indications of a relationship between IPNV susceptibility and cortisol have been suggested. The intestine is an entry route and a target tissue for IPNV displaying severe enteritis and sloughing of the mucosa in infected fish. The mechanisms behind effects of the virus on the intestinal tissue and the impact of cortisol on the effect remain unclear. In the present study, Atlantic salmon post smolts treated with or without slow release cortisol implants were subjected to a cohabitant IPNV challenge. Analysis of genes and proteins related to the innate and acquired immune responses against virus was performed 6 days post-challenge using qPCR and immunohistochemistry. An increased mRNA expression of anti-viral cytokine interferon type I was observed in the proximal intestine and head kidney as a response to the viral challenge and this effect was suppressed by cortisol. No effect was seen in the distal intestine. T-cell marker CD3 as well as MHC-I in both intestinal regions and in the head kidney was down regulated at the mRNA level. Number of CD8α lymphocytes decreased in the proximal intestine in response to cortisol. On the other hand, mRNA expression of Mx and IL-1β increased in the proximal intestine and head kidney in IPNV challenged fish in the presence of cortisol suggesting that the immune activation shifts in timing and response pathway during simulated stress. The present study clearly demonstrates that IPNV infection results in a differentiated epithelial immune response in the different intestinal regions of the Atlantic salmon. It also reveals that the epithelial immune response differs from the systemic, but that both are modulated by the stress hormone cortisol. [ABSTRACT FROM AUTHOR]

Stress in response to anesthesia with benzocaine, MS-222, metomidate and isoeugenol was studied in Atlantic salmon ( Salmo salar), Atlantic halibut ( Hippoglossus hippoglossus), and Atlantic cod ( Gadus morhua) with no concomitant stress from handling or confinement in association with anesthesia or sampling. All of the anesthetics tested induced a stress response in all species, displayed by a release of cortisol to the water. MS-222 anesthesia elicited the highest cortisol release rates, reaching maximum levels 0.5 h post-exposure and returning to basal levels after 3–4 h. Benzocaine anesthesia caused a bimodal response where the initial peak in cortisol release rate was followed by a second increase lasting towards the end of the trial (6 h). This bimodality was more profound in Atlantic salmon than in Atlantic halibut and Atlantic cod. Metomidate anesthesia induced the lowest release of cortisol of the agents tested in both Atlantic halibut and Atlantic cod, but resulted in a bimodal response in Atlantic salmon where the initial increase in cortisol release was followed by a larger increase peaking at 2–2.5 h post exposure before returning to basal levels after 5 h. The stress induced in Atlantic salmon by isoeugenol anesthesia resembled that of MS-222, but did not reach the same elevated level. Overall, the cortisol release was most profound in Atlantic salmon followed by Atlantic halibut and Atlantic cod. [ABSTRACT FROM AUTHOR]

Background: Fish farmed under high intensity aquaculture conditions are subjected to unnatural environments that may cause stress. Therefore awareness of how to maintain good health and welfare of farmed fish is important. For Atlantic salmon held in sea cages, water flow, dissolved oxygen (DO) levels and temperature will fluctuate over time and the fish can at times be exposed to detrimentally low DO levels and high temperatures. This experimental study investigates primary and secondary stress responses of Atlantic salmon post smolts to long-term exposure to reduced and fluctuating DO levels and high water temperatures, mimicking situations in the sea cages. Plasma cortisol levels and cortisol release to the water were assessed as indicators of the primary stress response and intestinal barrier integrity and physiological functions as indicators of secondary responses to changes in environmental conditions. Results: Plasma cortisol levels were elevated in fish exposed to low (50% and 60% saturation) DO levels and low temperature (9°C), at days 9, 29 and 48. The intestinal barrier function, measured as electrical resistance (TER) and permeability of mannitol at the end of the experiment, were reduced at 50% DO, in both proximal and distal intestine. When low DO levels were combined with high temperature (16°C), plasma cortisol levels were elevated in the cyclic 1:5 h at 85%:50% DO group and fixed 50% DO group compared to the control (85% DO) group at day 10 but not at later time points. The intestinal barrier function was clearly disturbed in the 50% DO group; TER was reduced in both intestinal regions concomitant with increased paracellular permeability in the distal region. Conclusions: This study reveals that adverse environmental conditions (low water flow, low DO levels at low and high temperature), that can occur in sea cages, elicits primary and secondary stress responses in Atlantic salmon post smolts. The intestinal barrier function was significantly affected by prolonged hypoxic stress even when no primary stress response was observed. This suggests that intestinal barrier function is a good experimental marker for evaluation of chronic stress and that it can be a valuable tool to study the impact of various husbandry conditions on health and welfare of farmed Atlantic salmon. [ABSTRACT FROM AUTHOR]

Abstract: For Atlantic salmon, the gastrointestinal tract is the site of food digestion and nutrient uptake, a regulatory site for ion and water balance as well as a barrier against invading pathogens. During the parr–smolt transformation and subsequent seawater (SW) transfer, major changes occur in the intestine. A global shortage of fish oils (FO) for feed production is estimated to appear within a few years, and vegetable oils (VO) are being considered as alternatives for FO in fish feed production. However, VO influences the fatty acid composition of the polar lipids of cell membranes in the intestine which can disturb intestinal functions. A VO-based diet during the parr–smolt transformation, which is a sensitive developmental period, may cause adverse effects. Therefore, Atlantic salmon parr were fed either sunflower oil (SO) or FO as the major lipid source during out-of-season light controlled parr–smolt transformation. At three time points gill Na+,K+-ATPase activity and plasma levels of cortisol and growth hormone were assessed. Intestinal epithelia were sampled for assessment of nutrient absorption and bacterial translocation using an Ussing chamber in vitro system. While both dietary groups showed plasma hormone profiles indicative of successful parr–smolt transformation, the SO-fed fish had consistently increased cortisol levels compared to the FO-fed fish. Translocation of pathogenic bacteria increased, probably due to disturbed barrier functions, during the parr–smolt transformation. However, the fish fed the SO-diet maintained a higher barrier function compared to FO-fed fish, an effect that may be beneficial to these fish. Nutrient uptake was less affected by smoltification. Fish fed the SO-diet had higher uptake rates of amino acids and free fatty acids during mid-smoltification than fish fed the FO-diet. The combined effects of barrier function and nutrient uptake may suggest a positive effect of including vegetable lipids in the diet during the parr–smolt transformation. However, the vegetable lipid diet also seemed to act as a stressor and elevated the basal cortisol levels, which may be of concern in the context of general fish health and welfare. [Copyright &y& Elsevier]

Atlantic salmon ( Salmo salar L.) were fed fishmeal protein for 46 days, and 500 g kg−1 of fishmeal protein substituted with meal from Northern krill ( Meganyctiphanes norvegica). No differences were observed in weight gain, length gain, feed conversion or specific growth rate between the groups that could be attributed to dietary manipulation. The adherent microbiota in the hindgut of the two rearing groups were further investigated. By substituting fishmeal with krillmeal, the total viable counts of aerobic and facultative aerobic bacteria colonizing the hindgut of Atlantic salmon increased from 8.5 × 104 to 2.2 × 106. Furthermore, dietary krillmeal affected the adherent hindgut microbiota. The Gram-positive bacteria Carnobacteria piscicola, Microbacterium oxydans, Microbacterium luteolum and Staphylococcus equorum spp. linens and the Gram-negatives Psychrobacter spp. and Psychrobacter glacincola were not isolated from hindgut of fish fed the krill diet. On the other hand, Pseudomonas fulgida, Pseudomonas reactans and Stenotrophomonas maltophila were not isolated from the control group fed fishmeal. Acinetobacter lwoffi, which is not normally found in the fish gut, was isolated from both feeding groups. Transmission electron microscopy showed bacteria-like profiles between the hindgut microvilli in both feeding groups indicating autochthonous microbiota. When fish were fed the krill diet, hindgut enterocytes were replete with numerous irregular vacuoles. These vacuoles were not observed in fish fed the fishmeal protein. [ABSTRACT FROM AUTHOR]

In fish, bacterial pathogens can enter the host by one or more of three different routes: (a) skin, (b) gills and (c) gastrointestinal tract. Bacteria can cross the gastrointestinal lining in three different ways. In undamaged tissue, bacteria can translocate by transcellular or paracellular routes. Alternatively, bacteria can damage the intestinal lining with extracellular enzymes or toxins before entering. Using an in vitro (Ussing chamber) model, this paper describes intestinal cell damage in Atlantic salmon (Salmo salarL.) caused by the fish pathogenAeromonas salmonicidassp.salmonicida, the causative agent of furunculosis. The in vitro method clearly demonstrated substantial detachment of enterocytes from anterior region of the intestine (foregut) upon exposure to the pathogen. In the hindgut (posterior part of the intestine), little detachment was observed but cellular damage involved microvilli, desmosomes and tight junctions. Based on these findings, we suggest thatA. salmonicidamay obtain entry to the fish by seriously damaging the intestinal lining. Translocation of bacteria through the foregut (rather than the hindgut) is a more likely infection route forA. salmonicidainfections in Atlantic salmon. [ABSTRACT FROM AUTHOR]

Crowding is a necessary operation for moving fish out of or between sea cages in Atlantic salmon farming. These operations consist of gradually reducing available volume in the nets to increase the biomass density. This is known to stress the fish, increase risk of injury, and can in extreme cases increase mortality rates. To reduce the negative impacts of crowding, the operation must be adjusted based on real-time monitoring of fish welfare. Today, this is mainly done by manually monitoring surface activity, as the high fish density limits the use of available tools. In this paper a new approach for monitoring was applied to crowding of meso-scale cages containing 40 fish each, using automatic detection of passive acoustic signatures. Four synchronised hydrophones were deployed and the acoustic signature was defined from the recordings. The automatic detection algorithm recorded an extreme increase in registered acoustic events during crowding, as high as 1000 events per 10 min period, compared to only 20 events per 10 min period on the day following crowding. Correlating the number of acoustic events to recorded heart rate and activity measures from implants in the salmon indicate that automatically registering acoustic events is a promising method for monitoring farmed fish. • Detection algorithm applied to monitor acoustic signature of Atlantic salmon during crowding. • Drastic increase of occurrences of acoustic events during crowding. • Increase in number of acoustic events correspond well with increased activity measurements. • Monitoring acoustic events are a promising method for monitoring stress in farmed fish. [ABSTRACT FROM AUTHOR]

The effect of carbon monoxide (CO) as stunning method in Atlantic salmon ( Salmo salar L.) on stress indicators (adrenaline, A; noradrenaline, NAD) and on fillets quality during the shelf life has been investigated. The CO was dissolved into tanks with salmon for 8 and 20 min to obtain fish groups CO8 and CO20, respectively. These groups were compared to a non-stressed control group (C). All the fish were hauled out from the tank and killed by percussion. Adrenaline content of CO20 group was 1.8 and 1.7-fold higher than CO8 and C groups respectively (P < 0.001), which exhibited similar values. Noradrenaline content was higher in CO20 than in C group (8.1 vs . 5.4 ng/ml plasma; P < 0.0001). The CO treatment resulted in a small significant increase in lightness and yellowness, not altering the overall “natural” colour of the fillet. CO treatment caused a rapid onset of rigor mortis and a small but significant increase in drip loss (P < 0.05). [ABSTRACT FROM AUTHOR]

Infectious pancreatic necrosis virus (IPNV) causes high incidence of disease in salmonids during the first period after SW transfer. During this period as well as during periods of stress, cortisol levels increase and indications of a relationship between IPNV susceptibility and cortisol have been suggested. The intestine is an entry route and a target tissue for IPNV displaying severe enteritis and sloughing of the mucosa in infected fish. The mechanisms behind effects of the virus on the intestinal tissue and the impact of cortisol on the effect remain unclear. In the present study, Atlantic salmon post smolts treated with or without slow release cortisol implants were subjected to a cohabitant IPNV challenge. Analysis of genes and proteins related to the innate and acquired immune responses against virus was performed 6 days post-challenge using qPCR and immunohistochemistry. An increased mRNA expression of anti-viral cytokine interferon type I was observed in the proximal intestine and head kidney as a response to the viral challenge and this effect was suppressed by cortisol. No effect was seen in the distal intestine. T-cell marker CD3 as well as MHC-I in both intestinal regions and in the head kidney was down regulated at the mRNA level. Number of CD8α lymphocytes decreased in the proximal intestine in response to cortisol. On the other hand, mRNA expression of Mx and IL-1β increased in the proximal intestine and head kidney in IPNV challenged fish in the presence of cortisol suggesting that the immune activation shifts in timing and response pathway during simulated stress. The present study clearly demonstrates that IPNV infection results in a differentiated epithelial immune response in the different intestinal regions of the Atlantic salmon. It also reveals that the epithelial immune response differs from the systemic, but that both are modulated by the stress hormone cortisol. [ABSTRACT FROM AUTHOR]

Abstract: The present investigation evaluated the effect of chitin (5% supplementation) on the adherent aerobic intestinal microbiota of Atlantic salmon (Salmo salar L.). One hundred and seventy three isolates were isolated but 34 isolates died prior to positive identification. Sixty four out of 139 autochthonous gut bacteria were further identified by 16S rRNA gene sequencing and further tested for protease, amylase, cellulase, phytase, lipase and chitinase activities. Moreover, the most promising enzyme-producing bacteria and intestinal lactic acid bacteria (LAB) were tested for in vitro growth inhibition of four important fish pathogens: Aeromonas salmonicida subsp. salmonicida, Vibrio (Listonella) anguillarum, Moritella viscosa and Carnobacterium maltaromaticum. Dietary chitin modulates the gut microbiota but not the portion of enzyme-producing gut bacteria. LAB were only isolated from fish fed the chitin supplemented diet and they were able to inhibit in vitro growth of 3 of the 4 pathogens. However, the most promising gut bacteria isolated in the present study with respect to enzyme production and in vitro growth inhibition showed high similarity to Bacillus thuringiensis by 16S rRNA gene sequencing. [Copyright &y& Elsevier]

Abstract: We compared behavioural and physiological responses and recovery time after different acute environmental challenges in groups of salmon parr. The fish were prior to the study conditioned to a flashing light signalling arrival of food 30s later to study if the strength of Pavlovian conditioned food anticipatory behaviour can be used to assess how salmon parr cope with various challenges. The effect on anticipatory behaviour was compared to the effect on feed intake and physiological responses of oxygen hyper-consumption and cortisol excretion. The challenges were temperature fluctuation (6.5C° over 4h), hyperoxia (up to 380% O2 saturation over 4h), and intense chasing for 10min. Cortisol excretion was only elevated after hyperoxia and chasing, and returned to baseline levels after around 3h or less. Oxygen hyper-consumption persisted for even shorter periods. Feed intake was reduced the first feeding after all challenges and recovered within 3h after temperature and hyperoxia, but was reduced for days after chasing. Food anticipatory behaviour was reduced for a longer period than feed intake after hyperoxia and was low at least 6h after chasing. Our findings suggest that a recovery of challenged Atlantic salmon parr to baseline levels of cortisol excretion and oxygen consumption does not mean full recovery of all psychological and physiological effects of environmental challenges, and emphasise the need for measuring several factors including behavioural parameters when assessing fish welfare. [Copyright &y& Elsevier]

Abstract: Despite gains in commercial salmonid aquaculture production by using underyearling smolts (0+), poor performance in seawater has been noted. This study assesses how artificial photoperiods in seawater may improve the performance. Seawater-transferred 0+ Atlantic salmon were exposed to natural light (NL) or continuous light (LL) from October to midsummer, or to LL from October to January followed by natural light (LL–NL), or NL from October to January and then LL to midsummer. All fish experienced natural light after midsummer. The photoperiods changed the seasonal growth pattern and harvest weights became significantly different (LL: 3445±46 g; NL–LL: 3207±45 g; LL–NL: 3092±56 g; NL: 2854±42 g). Growth of NL fish decreased from autumn through winter and increased in spring. LL fish grew better than NL fish until spring and was 21% heavier at slaughter. Switching from LL to NL in January reduced growth rate from March onwards to a level slightly lower than the seasonal growth pattern of the NL fish. The onset of light in January (NL–LL) resulted in a temporary decrease in growth for 7 weeks followed by a major weight increase with growth rate being significantly higher than LL fish from late April until October. NL–LL fish never managed to catch up with the LL fish, but were significantly larger than the NL fish. Changes in condition factor with light treatment demonstrated clearly the photoperiodic influence on the seasonal growth pattern. Two vaccines were used in all photoperiods. The fish given the vaccine that gave least adherences (lesion score 1.8 vs. 2.3) became 20% heavier than those given the other vaccine, and no interaction between photoperiod and vaccine was observed. Muscle lipid and astaxanthin contents in June were highest in LL fish (lipid: 9.1%; astaxanthin: 4.4 mg kg−1) and lowest in NL fish (lipid: 4.1%; astaxanthin: 2.6 mg kg−1). These differences largely disappeared by November, although fish exposed to light following seawater transfer (LL and LL–NL) had a tendency to contain higher levels of astaxanthin than those on natural light (NL and NL–LL). Both lipid and astaxanthin contents in fillet correlated positively with fish weight. The incidence of sexual maturation was 4% in LL and LL–NL, 1.5% in NL and 0% in NL–LL. In the seawater-phase of underyearling autumn-transferred smolts, we recommend using the NL–LL photoperiod regime. This light treatment gave a slightly smaller fish than LL at harvest, but there were no losses due to sexual maturation. [Copyright &y& Elsevier]

Farmed Atlantic salmon in sea cages experience natural seasonal changes in seawater temperature and photoperiod. Atlantic salmon have more oxidized tissues in spring and early summer, and this corresponds to the period of increasing day length, temperature, and growth rate. However, the molecular mechanisms underlying the redox metabolism of Atlantic salmon exposed to the interaction of seasonal cues remain unclear. This study aims to investigate the effect of seasonal changes in temperature and photoperiod on the redox metabolism at the molecular level of Atlantic salmon. Salmon reared in tanks were subjected to simulated natural (for farmed salmon in sea cages) photoperiod and temperature to mimic spring and summer (March to August). We found that the changing photoperiod and temperature, which were simulated to spring and summer conditions, influenced the redox metabolism of Atlantic salmon over the experimental period. We showed that increased utilization of tissue antioxidants such as vitamin C, vitamin E, and reduced glutathione in the spring was restored in August. The more reduced glutathione-based redox potentials and the low levels of malondialdehyde (MDA) in August in liver and muscle suggest lowered tissue oxidative activity at that time. We further revealed that the expression profiles of genes involved in growth hormone signaling and cell cycle regulation were correlated with oxidative stress patterns. Together, these promising results reveal the molecular mechanisms underlying the ecological implications of oxidative status. The study provides new insight into the possible role redox signaling plays in the growth regulation of fish to the seasonal shift in environmental factors. • We investigated the effect of seasonal changes in temperature and photoperiod on redox metabolism in Atlantic salmon. • The seasonal shifts induced tissue-specific and temporal antioxidant responses. • The changes in multiple gene expression involved in redox balance contribute to lowered tissue oxidative activity in autumn. • Redox-sensitive gene expression correlated with cell cycle regulation and GH–IGF signaling genes. • Seasonal variation in oxidative status was associated with growth and physiological performance. [ABSTRACT FROM AUTHOR]

Feeding unhydrolyzed protein to the same species from which it came from have caused prion disease in some mammals, but this has not been observed in fish. In this study, we characterized a salmon protein hydrolysate (FPH) for prion content and investigated how partially replacing fish meal with salmon hydrolysate, affected growth, digestibility and gut health of Atlantic salmon (Salmo salar). The salmon hydrolysate was analysed for prion content by shotgun and targeted proteomics, but no prions were found. Atlantic salmon post smolts were fed one of the following: a control diet containing 30% fish meal (FM), a 20% FM with 9% salmon hydrolysate diet (FPH-09) or a 10% FM with 18% salmon hydrolysate diet (FPH-18). Salmon fed the hydrolysate diets had higher specific growth rate over the first 25 days. The FPH-18 diet contained more digestible proteins and amino acids than the FM diet, and the ash digestibility increased linearly with the FPH content, indicating increased mineral uptake. Histological analysis of midgut and hindgut did not reveal any significant differences between the FM and FPH-18 diets, and the intestines were assessed to be normal and healthy. These results imply that salmon hydrolysate is a promising novel feed ingredient for Atlantic salmon, due to its excellent amino acid profile and high digestibility. • Salmon protein hydrolysate (FPH) is a novel feed ingredient for Atlantic salmon. • FPH has an excellent amino acid profile and feed stimulatory properties. • No salmon prions were found by proteomics analysis of the salmon hydrolysate. • Partially replacing fish meal with FPH increased the protein and ash digestibility. • Dietary FPH significantly increased the initial growth rate of post smolts. [ABSTRACT FROM AUTHOR]

Increased cortisol production and oxygen consumption are commonly used as indicators for stress in most fish species. For comparative studies measuring acute stress responsiveness, it is often assumed that the cortisol is sampled at peak response. However, the effect of acclimated temperature on cortisol response is largely unknown, and so is also the dynamics of oxygen uptake following stress. In the present study we acclimated Atlantic salmon post-smolt to four different temperature within the species relevant temperature spectrum (4, 8, 12 and 17 °C), and applied an acute stressor of 60 s of confinement. Cortisol, as measured in water, was sampled before and up to 360 min following the stressor, while oxygen consumption rates was estimated per minute. Basal cortisol production increased significantly with temperature, which must be considered when calculating the cortisol response per se. The cortisol response followed a Gaussian pattern, where the amplitude (max value) increased with temperature while the curve width (time before peak and recovery) decreased. Also, the total amount of cortisol released in response to the stressor increased with temperature. The cortisol peak at 4, 8, 12 and 17 °C was respectively measured after 123.75 ± 7.2, 67.5 ± 9.7, 56.25 ± 3.75 and 33.74 ± 3.75 min. The stress induced peak in oxygen uptake increased with temperature in an exponential manner, and both peak value and the total oxygen uptake above baseline levels was three times higher at 17 than at 12 °C, while the total oxygen uptake was similar between 4, 8, 12 °C. This strong difference in oxygen uptake between 12 and 17 °C was not reflected by the cortisol levels, and suggests that salmon are extra vulnerable for creating hypoxic conditions when stressed at high temperature. The current work suggests when to sample cortisol for attaining peak values at a given acclimated temperatures in salmon post-smolt. This should allow for better comparison of cortisol values between studies. [ABSTRACT FROM AUTHOR]

Using functional feed ingredients to increase the intestinal health of Atlantic salmon (Salmo salar) could allow greater variation and higher inclusion of plant-based proteins in the feed. This is beneficial both for the fish feed industry and fish welfare. Components with strong bioactive properties, such as fucoidans from marine macroalgae, have a great potential as a functional feed ingredient. In the present trial, we challenged Atlantic salmon (Salmo salar) post-smolts with 17.8% soya HP48, a diet that has been shown to cause low-level intestinal inflammation. Fucoidan from Undaria pinnatifida was included at 0, 1, or 3% (Control, FUC1, and FUC3, respectively) to study its ability to alleviate this low-level inflammation. The fish were fed the diets in triplicate tanks for 59 days. At the end of the experiment, the fish were euthanised and the mid- and hind intestine were sampled for morphological-, integrity- (Ussing chamber) and gene expressional- (RNAseq) assessments. Addition of 3% fucoidan lowered the protein digestibility of the feed, however, this did not result in significant differences in the growth parameters. The paracellular permeability of the hydrophilic marker 14C-mannitol tended to decrease with the addition of fucoidan in both tissue segments. The active transport of l -lysine in the mid intestine was significantly reduced in a dose-dependent manner of fucoidan. An anti-inflammatory effect of fucoidan was observed in the hind intestine with significant reductions in the stratum granulosum width and lamina propria height of fish fed FUC1 and FUC3 compared to the Control. This suggests that U. pinnatifida fucoidan can have positive effect on both intestinal integrity and immune regulation of Atlantic salmon (Salmo salar). • U. pinnatifida fucoidan was highly sulfated and contained fucose:galactose in a 3.9:1 ratio. • Fucoidan tended to increase intestinal integrity in a dose-dependent manner. • Morphological evaluation revealed lowered hind-intestinal inflammation in fucoidan diets. [ABSTRACT FROM AUTHOR]

Several major market operators argue that the current level of knowledge about quality is too scant to justify a switch to a large-scale production of triploid salmon. The aim of the present study was, therefore, to elucidate how rearing conditions (5, 10 and 15 °C) affect the flesh quality of triploid Atlantic salmon ( Salmo salar L., 1.6 ± 0.3 kg). As a reference, diploid salmon kept under equal conditions and with equal genetics were used. The main design discriminant was the holding temperature; increased temperature gave increased blood lactate, rigor index (I r ), drip loss (DL), content of astaxanthin and intensity of redness, but reduced muscle pH, cathepsin activity and fillet lightness. Salmon kept at 10 °C grew the fastest. It is concluded that ploidy gave less variation than temperature. Triploids were characterized by lower blood haematocrit (Hct) and I r , higher DL and collagenase activity, and on average, paler and less yellowish fillets. [ABSTRACT FROM AUTHOR]

The use of sterile triploids in Atlantic salmon aquaculture would mitigate the environmental risks associated with introgressive hybridization between escaped farmed and wild Atlantic salmon. However, production of farmed triploid salmon is limited due to reports of poorer growth and higher mortality when compared to diploids, in particular under sub-optimal environmental conditions. To address these concerns, we monitored triploid and diploid Atlantic salmon post-smolts at temperatures between 3 and 18 °C and 100% oxygen saturation (O 2 sat ), and additional periods of 60% O 2 sat (hypoxia) at 6 or 18 °C, respectively. Feed intake and oxygen consumption rate were monitored throughout the experimental period. Muscle and blood samples were collected at 100 and 60% O 2 sat at 6 and 18 °C for analysis of white muscle energy phosphates (creatine phosphate, adenosine triphosphate) and carbohydrate fuels (glucose, glycogen) as well as blood clinical chemistry (whole blood: hematocrit; plasma: Na + , K + , Cl − , glucose, lactate, pH, triacylglycerol). Mortality was similar between ploidies, but higher in triploids compared to diploids during reduced O 2 sat at 18 °C. Compared to diploids, triploids had higher feed intake (% biomass) at ≤ 9 °C, but lower feed intake at ≥ 15 °C. Feed intake peaked at 12 and 15 °C for triploids and diploids, respectively. Triploids progressively reduced feed intake with increasing temperature after peak feeding, indicating reduced scope for specific dynamic action with increasing water temperature. During hypoxia, triploids had lower feed intake than diploids at 6 and 18 °C. The difference in feed intake was not associated with any ploidy effect on body weight gain or feed conversion ratio, but triploids had greater body length growth compared to diploids. At ≥ 15 °C triploids consumed less oxygen than diploids. In the white musculature, the only observed difference between ploidies was a lower level of glycogen in triploids compared to diploids at 18 °C and 100% O 2 sat . In the blood plasma, the concentration of ions was lower and glucose level higher in triploids compared to diploids at 18 °C and 60% O 2 sat . The results of this study indicate that triploid Atlantic salmon post-smolts can substitute diploids, but are less tolerant to high seawater temperature and low O 2 sat . For sea-cage farming of triploid salmon post-smolts, this would favour production areas with maximum temperatures of 15 °C and sufficient oxygen. Statement of Relevance This study demonstrates that triploid Atlantic salmon post-smolts have lower temperature optima for feeding and growth than diploids, a similar physiological response to high temperatures, but higher mortality under suboptimal conditions. Consequently triploid Atlantic salmon post-smolts may be well suited for commercial farming in geographical regions with moderate water temperatures in the summer and autumn months. [ABSTRACT FROM AUTHOR]

Moderate levels of intestinal damage and inflammation are often seen in intensive fish aquaculture. The causes may be due to antinutrients from plant meals, stress or other causes. There is currently a lack of good models to explore these effects and so how to mitigate the consequences. Most studies have used full-fat soy or other compounds that cause intestinal damage that are likely not reversible. In this study we have explored the possibility of using soybean HP48, made from solvent extracted peeled soybeans, as a low-inflammation model in post-smolt Atlantic salmon, and then investigated whether supplementation of the probiotic Pediococcus acidilactici CNCM I-4622 – MA 18/5 M (Bactocell) could diminish this effect. The fish were fed triplicate diets. A Control diet containing 18.08% soy protein concentrate (SPC), a HP48 diet where most of the SPC was replaced by HP48 (5.00% SPC and 17.68% HP48), and a Bactocell diet that was identical to the HP48 diet but contained 0.03% Bactocell. After 10 weeks of feeding, the mid- and hind-intestinal health were assessed by histology, integrity (Ussing chamber) and gene expression (RNAseq). Transcriptomic and integrity data suggests that HP48 led to a disturbed mid-intestinal homeostasis with impaired cellular integrity and increased inflammation and cell turnover. Most of the transcriptomic effects were reversed with Bactocell including downregulation of immune genes and upregulation of transmembrane proteins such as type IV collagen, which is important in restoring epithelial homeostasis. In the hind-intestine, the HP48 diet led to deleterious morphological changes such as widening of lamina propria and stratum granulosum, disrupted mucosal folds, loss of absorptive vacuoles, and upregulation of several immune regulated genes and downregulation of genes involved in solute- and water transport. The intestinal integrity assessed by Ussing chamber was not affected. Bactocell supplementation did alleviate several of the morphological effects. However, it was not able to completely reverse the expression of immune- or transport related genes, suggesting a higher effect of probiotic supplement in the mid-intestine compared to the hind-intestine. This study demonstrates that the level of HP48 used here is sufficient to create low-level intestinal changes in Atlantic salmon, which is within range for functional feed ingredients to reverse. • HP48 caused transcriptional changes in the mid-intestine and low-level hind-intestinal inflammation. • Bactocell reversed the transcriptional changes in the mid-intestine caused by HP48. • Bactocell improved the hind-intestinal morphology but did not reverse gene expression of HP48. [ABSTRACT FROM AUTHOR]

The possibility to prepare for and respond to challenges in a propermanner is essential to cope with a changing environment, and learning allows fish to up or downregulate the stress response based on experience. The regulation of the response to predicted needs should be easier inmore predictable environments.Weexposed salmon parr to chasing of either 15 s (weak stressor) or 5min (strong stressor) twice daily for a 7-day learning period, with chasing either announced by a 30 s light signal (conditioned) or not announced (unconditioned). The behavioural response to the light signalwas different between the conditioned and unconditioned groups, demonstrating that conditioned groups associated the signal with chasing. We could, however, not demonstrate any effect on the stress response of anticipation. The fish habituated to repeated stress exposures with a similar decrease in oxygen hyperconsumption in all groups. Due to habituation, possible effects of predictable announcement of a stressor on the physiological stress response may not have been expressed in this study. Plasma cortisol concentrations 1 h after light signal and chasing the day after the training period was moderate in all groups although higher after 5 min chasing (13 ng ml-1) than 15 s chasing (7 ng ml-1). There was no physiological stress response after exposure to the light signal only after the learning period. We argue that the benefit of predictability of stressors is limited when the fish have no way to avoid the stressor. [ABSTRACT FROM AUTHOR]

It is well established that farmed Atlantic salmon (Salmo salar) need n3-highly unsaturated fatty acids (HUFA) in their diet to thrive and grow. However, the biological functions to the individual HUFAs may differ, implying that future supplementation could require fixed ratios for maximum benefit. The intestinal barrier is essential to fish health, and any disruption of the barrier can have detrimental effects. The current experiment was designed to examine the response of the intestinal hindgut when fed a low HUFA diet with 8.5 g/kg EPA + DHA (4.5% total fatty acid) or two high HUFA diets, with either high DHA (28.7 g/kg and 5.9% total fatty acid) or high EPA (25 g/kg and 14.2% total fatty acid). The diets were fed to Atlantic salmon post-smolt over 10 weeks and thereafter exposed to 3 weeks of chronic stress. After 10 weeks of feeding there were no differences in intestinal permeability and integrity, but intestinal morphology indicated increased intestinal health in the high EPA group. Gene expression also suggest that fish fed the high EPA diet had more regulation of pathways related to protein turnover compared to the high DHA fed fish. There was also indication of lower energy utilization in the low HUFA fed fish than high HUFA. Subjecting fish to 3 weeks of chronic stress led to a reduction in transepithelial resistance, increased ion flux and active l -lysine transport across the intestinal barrier in addition to a decrease in mucosal fold, enterocyte height and supranuclear vacuole density and an increase in thickness of the intestinal muscularis. After stress, the low HUFA group showed signs of inflammation with increased infiltration of MHCII positive cells. Gene expression also showed that low HUFA fed fish had a lower response to chronic stress compared to the high HUFA groups. Comparing fish fed either high DHA or EPA exposed to chronic stress showed few physical effects, but a lower density of supranuclear vacuoles and upregulation in immune-related gene expression indicate inflammation in the high DHA group. • DHA and EPA regulated gene expression differently in Atlantic salmon hindgut. • Low levels of dietary HUFA causes a decreased intestinal barrier after stress. • Chronic stress significantly affects the intestinal integrity in Atlantic salmon. [ABSTRACT FROM AUTHOR]

Atlantic salmon (Salmo salar L.) experience periodic drops in dissolved oxygen (O2) inside aquaculture sea cages. In order to evaluate whether fish function or welfare is compromised during such drops in O2 (termed hypoxia), it is necessary to establish the limit for acceptable O2 reductions; the hypoxia tolerance threshold. In the present study, effects of temperature (6, 12 and 18°C) and hypoxia acclimation (33days of hypoxic periods down to 50% O2 occurring every 6h at 16°C) on the routine oxygen consumption rate (ṀO2) and the limiting oxygen saturation (LOS, defined as the hypoxia tolerance threshold) were investigated in undisturbed, fed fish kept in groups with the aim of resembling commercial aquaculture conditions. ṀO2 was measured using open respirometry where a progressive decline in O2 was caused by fish O2 consumption during a period of low water turnover. LOS was defined as the O2 below which fish were no longer able to uphold routine ṀO2. Both ṀO2 and LOS were found to increase exponentially with temperature (Q10 =2.7 for ṀO2 and 1.8 for LOS), but no effect of hypoxia acclimation was found. The mean (±SE) LOS at 6, 12, 16 and 18°C was 30±1, 39±1, 47±1 and 55±2% of air saturation respectively. The variation in LOS within and across temperatures was to a large extent explained by variation in ṀO2 (R2 =0.93), suggesting that LOS increases with any factor that raises the metabolic rate of Atlantic salmon. This study provides aquaculturists and legislators with a lower limit for acceptable drops in O2 at temperatures relevant for the on-growing phase in Atlantic salmon aquaculture, and discusses the variation in LOS that can be expected at a given temperature. [ABSTRACT FROM AUTHOR]

Abstract: In order to investigate the effects of hypoxic periods on the feeding behaviour and physiology of Atlantic salmon (Salmo salar L.) post-smolts (237±7g), fish were kept at constant 90% O2 (control) or subjected to cyclic reductions in oxygen, from 90% O2 (termed normoxia) to 40, 50, 60 or 70% O2 (termed hypoxia) for 2h every 6h for 23days at 16°C (groups are denoted as 90:40, 90:50, 90:60, 90:70 and 90:90). Fish were fed to satiation three times per day, twice in hypoxia and once in normoxia. Blood samples were drawn during hypoxic periods on day 0, 7, 14 and 21 and analysed for haematocrit, haemoglobin concentration and plasma cortisol, chloride, lactate and glucose concentrations. During first exposure to hypoxia (day 0), plasma lactate was increased in 90:60, 90:50 and 90:40 groups, plasma cortisol was increased in 90:50 and 90:40 groups and plasma chloride was increased in the 90:40 group, indicating oxygen shortage and stress at oxygen saturations below 60% O2. On day 7, 14 and 21, there were no signs of stress, but plasma lactate levels remained increased in hypoxic periods in 90:40, 90:50 (all the days) and 90:60 groups (day 7 and 14), suggesting that the stress response was down-regulated in spite of a persisting oxygen shortage. Feed intake was reduced according to hypoxia severity in groups subjected to 40–60% O2 during the first meal of the day, and in all experimental groups (40–70% O2) during the third meal of the day. The effect of hypoxia on feed intake persisted throughout the experiment, but total daily feed intake was substantially increased in 90:40 and 90:50 groups during weeks 2 and 3 due to compensatory feeding in the normoxic feeding period. Present results suggest that 70% O2 may represent a threshold for reduced growth and that 60% O2 represents a minimum O2 saturation considering the welfare of Atlantic salmon post-smolts subjected to cyclic hypoxia at 16°C. [Copyright &y& Elsevier]

Abstract: In this study we evaluated Pavlovian conditioned food anticipatory behaviour as a potential indicator for stress in groups of Atlantic salmon, and compared this with the physiological stress responses of cortisol excretion into water and hyper-consumption of oxygen. We hypothesised that environmental stress would result in reduced feeding motivation. To assess this, we measured the strength of anticipatory behaviour during a period of flashing light that signalled arrival of food. Further, we expected that fish given a reduced food ration would be less sensitive to environmental stress than fish fed full ration. The fish responded to an acute temperature fluctuation with hyper-consumption of oxygen that decreased in line with the temperature, and elevated cortisol excretion up to 1h after the stressor. These physiological responses did not differ significantly between the food ration groups. The anticipatory behaviour was significantly reduced after the stressor and returned to control levels after 1 to 2h in the reduced ration group, but not until after 3 to 4h in the full ration group. Our results show that acute stress can be measured in terms of changes to feeding motivation, and that it is a more sensitive indicator of stress that influences the fish over a longer time period than measures of change in cortisol excretion. [Copyright &y& Elsevier]

Abstract: Infectious pancreatic necrosis virus (IPNV) is a viral disease that afflicts salmon aquaculture worldwide. Transmission of viral diseases may occur via the skin, gills or intestine but the main entry route for IPNV is not known. However, acute inflammation of the intestinal mucosa is an early symptom in infected fish which suggests transmission through an oral route. The main aim of this study is to determine if IPNV can translocate across the intestinal epithelium. It also aims to investigate how acute and chronic IPNV exposure as well as stress affects the physiological barrier functions of the intestinal epithelium. Possible translocation of IPNV across the intestinal mucosa as well as effects of virus on intestinal barrier function was measured in vitro, using the Ussing chamber technique. IPNV was translocated across both proximal and distal segments of the intestine with a higher rate in distal compared to proximal intestine. The translocated virions caused cytopathic effects on cultured Chinook salmon embryo cells (CHSE-214), proving viability and high virulence. Intestinal barrier function was disturbed as assessed by increased permeability for 14C-mannitol in the proximal region after exposure to IPNV in vitro. The same pattern was observed after prolonged exposure to IPNV in vivo. Further, the intestine appeared to respond with an increased mucus secretion, as indicated through increased TER after prolonged IPNV exposure. No additional effects of cortisol implantation on barrier function were observed. In conclusion, this study demonstrates that both proximal and distal intestine can be used by IPNV as a route of infection and that the intestinal barrier function is negatively affected by exposure to IPNV. [Copyright &y& Elsevier]

Interspecific hybridisation may improve the farm performance of sterile triploid salmonids via heterosis (i.e. hybrid vigour). We assessed growth over the final 293 days in seawater, and harvest quality, in diploid and triploid Atlantic salmon (Salmo salar) × brown trout (Salmo trutta) hybrids compared to diploid and triploid Atlantic salmon. We measured vertebral deformities, cataracts, flesh colour, gut mass, and body shape at harvest. In triploids, hybridisation had no effect on harvest size, vertebral deformities, cataracts, or body shape, but did improve fillet colouration (Mean digital SalmoFan™ score [95% CI]: 24.6 [24.4–24.9] and 26.0 [25.7–26.2] for triploid salmon and triploid hybrids, respectively) and lower relative gut size (34% lower). Compared to diploid salmon, triploid salmon were significantly heavier at harvest, triploid hybrids tended to be heavier (Post-hoc, least square means, p = 0.08), whereas diploid hybrids were 83% lighter (Mean mass [g] at harvest [95% CI]: 2676 [2470–2898], 3395 [3134–3679], 462 [401–534], and 3086 [2832–3363] for diploid salmon, triploid salmon, diploid hybrids, and triploid hybrids, respectively). However, both triploid groups had a significantly higher incidence of fish with one or more deformed vertebra (Mean % [95% CI]: 23 [14–35], 60 [47–71], 38 [20–60], and 44 [31–57] % in diploid salmon, triploid salmon, diploid hybrids, and triploid hybrids, respectively), more severe cataracts (Mean cataract score [95% CI]: 3.0 [2.7–3.3], 3.5 [3.2–3.8], 2.2 [1.7–2.6], 3.6 [3.3–4.0] for diploid salmon, triploid salmon, diploid hybrids, and triploid hybrids, respectively), and a smaller relative gut size (21% smaller) compared to diploid counterparts. In conclusion, triploid hybrids have no growth advantage over triploid salmon and suffer from similar welfare issues while only benefiting from increased fillet colour. • Hybridisation had no effect on harvest size, vertebral deformities, cataracts, or body shape in triploids • Triploid hybrids had better fillet colouration and a smaller gut than triploid salmon • Triploid salmon were heavier at harvest than diploid salmon • Triploids had more vertebral deformities and cataracts than diploid salmon • Diploid hybrids grew much slower than diploid salmon [ABSTRACT FROM AUTHOR]

Abstract: Probiotic bacteria increase the host health status and protect mucosal tissue against pathogen-caused damage in mammalian models. Using an in vitro (intestinal sac) method this study aimed to address (a) the in vitro ability of Lactobacillus delbrueckii subsp. lactis to remain in the gastrointestinal tract of Atlantic salmon (Salmo salar L.) and (b) its ability to prevent cellular damage caused by successive incubation with Aeromonas salmonicida subsp. salmonicida the causative agent of furunculosis. Short in vitro incubation of salmon foregut with (TRITC)-labelled L. delbrueckii subsp. lactis showed that the probiont was able to colonize the enterocyte surface as studied by confocal microscopy. Furthermore, foregut incubated with the probiotic bacteria only, resulted in a healthy intestinal barrier whereas exposure to A. salmonicida disrupted its integrity. However, pre-treatment of salmon intestine with L. delbrueckii subsp. lactis prevented Aeromonas damaging effects. These results are promising in the context of the use of non-autochthonous probiotic bacteria as prophylactic agents against fish bacterial infections in the gastrointestinal tract. [Copyright &y& Elsevier]

For a rapidly developing aquaculture industry where availability of raw materials for diet formulation are quickly changing it is fundamental to define what the dietary needs and benefits are. In farming of Atlantic salmon (Salmo salar), highly unsaturated fatty acids (HUFA) are known to be essential and a minimum dietary inclusion is needed. The aim of this study has been to map Atlantic salmon performance and midgut health towards dietary HUFAs under normal and challenging condition. Atlantic salmon post-smolt at 150 g were fed four experimental diets over a feeding period of 10 weeks up to a final weight of 377 g followed by three weeks of unpredictable chronic stress (UCS). The diets varied in their HUFA level, with either 28.7 g/kg DHA (HDHA), 25 g/kg EPA (HEPA), 21.3 g/kg ARA (HARA) or 8.5 g/kg EPA + DHA (LHUFA). After the feeding period all fish had more than doubled their weight and fish fed HARA showed a significant lower specific growth rate compared to all other diets. Diets had little effect on intestinal morphology, barrier and transport function. Intestinal polar lipid composition suggested higher lipid metabolism in fish feed LHUFA and transcriptome analysis confirm upregulated lipid metabolism and downregulated energy turn over. Comparing transcriptome profiles from HDHA to HEPA, more upregulated pathways are seen in fish fed HEPA, including metabolism and immunity. The fish feed HARA had downregulated turn-over and metabolism compared to fish fed HEPA. The UCS period resulted in zero growth and lower enterocyte height in all diet groups, and the intestinal barrier was reduced in the paracellular permeability to mannitol. Contradictory to previous studies, fish fed HDHA and HEPA responded to UCS with enhanced intestinal resistance. UCS also resulted in impaired intestinal transport by elevated ion flux and epithelial electrochemical gradient in fish fed LHUFA. Transcriptome pathway analysis indicated more cell turn over and lipid metabolism in LHUFA and HDHA. In conclusion, a low HUFA diet with 8.5 g/kg DHA + EPA can sustain growth and intestinal health under controlled condition, but the health is impaired after three weeks of chronic stress. Decreasing the n6/n3 ratio by increasing levels of EPA and DHA strengthens intestinal barrier in response to chronic stress. Increasing the ARA to HUFA ratio may have a negative effect on growth, but not on intestinal health. • High dietary n6/n3 andlow HUFA reduced Atlantic salmon intestinal health in response to chronic stress. • Exposing Atlantic salmon smolt to chronic stress caused a high allostatic load and decreased intestinal health. • High dietary ARA to HUFA had a negative effect on Atlantic salmon post-smolt growth. [ABSTRACT FROM AUTHOR]