Production Of Atlantic Salmon Research Articles

Impact of freshwater rearing history on Atlantic salmon gill response to viral stimulation post seawater transfer

Land-based recirculating aquaculture systems (RAS) have risen in prevalence in recent years for Atlantic salmon production, enabling intensive production which allows increased growth and environmental control, but also having the potential for reducing water use and eutrophication. The Atlantic salmon has an anadromous life history with juvenile stages in freshwater (FW) and on-growing in seawater (SW), enabled by a transformational process known as smoltification. The timing of smoltification and transfer of smolts from FW to SW is critical under commercial production with high mortalities during this period. The impact of FW rearing system on immune function following seawater transfer (SWT) is not well understood. In this study parr were raised in either RAS or a traditional open-LOCH system until smolting and then transferred to a common marine environment. Two-weeks post-SWT fish were immune stimulated with a viral mimic (poly I:C) for 24 h to assess the ability to mount an antiviral immune response, assessed by whole transcriptome analysis of gill tissue, an important immune organ in fish. We show that unstimulated smolts reared in the LOCH had higher immune gene expression than those reared in RAS as determined by functional analysis. However, following stimulation, smolts reared in the RAS mounted a greater magnitude of response with a suite of immune genes displaying higher fold induction of transcription compared to LOCH reared smolts. We suggest RAS smolts have a lower steady state immune-associated transcriptome likely due to an unvarying environment, in terms of environmental factors and lack of exposure to pathogens, which shows a compensatory mechanism following stimulation allowing immune ‘catch-up’ with those reared in the LOCH. Alternatively, the RAS fish are experiencing an excessive response to the immune stimulation.

Conceptualization of the Norwegian feed system of farmed Atlantic salmon

The total production of Norwegian Atlantic salmon is expected to increase considerably in the years to come. A majority of greenhouse gas emissions from aquaculture is accounted for by feed. To investigate and assess the sustainability and robustness of the feed system, a holistic perspective on the system is needed. We aim to conceptualize the current value chains of feed in Norway using the Food Systems Approach, existing literature, and stakeholder inputs. The Sustainable Development Goals include no specific mention of feed. Still, many Norwegian feed and animal producers link their sustainability work to these goals. This paper summarizes the sustainability perspectives of feed and animal producers in the aquaculture sector, as well as relevant background, regulations, and environmental and socio-economic drivers.

Validation and genetic parameters of the X-ray method for phenotyping individual feed intake in Atlantic salmon

Feed efficiency is a highly desirable breeding goal trait as it can potentially reduce the relative economic cost of feed and concurrently reduce the environmental footprint of fish production. However, recording feed intake is a bottleneck in Atlantic salmon production. We recorded feed intake in 700 Atlantic salmon parr from 34 full sibling families using the X-ray method, where fish were fed feed containing radio-opaque beads and subsequently X-ray imaged one time after a full meal corresponding to the daily ration. In parallel, we cultured siblings from the same 35 families in duplicate family tanks of 25 individuals per tank and recorded the daily feed intake of each family at the tank level, which is known as the gold standard tank-based method. The heritability estimate for daily feed intake in Atlantic salmon using the X-ray method was significantly different from zero (0.19 ± 0.06) and was genetically correlated to growth-related traits (rg = 0.48–0.81). Daily feed intake at the family level with the X-ray method was highly genetically correlated to the daily feed intake traits using the tank-based feeding method at 0.78–0.82, depending on whether the comparison was made at a common time, common weight, or cumulative feed intake for the entire period. Whilst the X-ray method holds promise for research on the genetic background of feed intake and feed efficiency, more studies are needed to investigate the feasibility during the sea phase of Atlantic salmon production.

Six decades of ecohydrological research connecting landscapes and riverscapes in the Girnock Burn, Scotland: Atlantic salmon population and habitat dynamics in a changing world

AbstractLong‐term data are crucial for understanding ecological responses to climate and land use change; they are also vital evidence for informing management. As a migratory fish, Atlantic salmon are sentinels of both global and local environmental change. This paper reviews the main insights from six decades of research in an upland Scottish stream (Girnock Burn) inhabited by a spring Atlantic salmon population dominated by multi‐sea‐winter fish. Research began in the 1960s providing a census of returning adults, juvenile emigrants and in‐stream production of Atlantic salmon. Early research pioneered new monitoring techniques providing new insights into salmon ecology and population dynamics. These studies underlined the need for interdisciplinary approaches for understanding salmon interactions with physical, chemical and biological components of in‐stream habitats at different life‐stages. This highlighted variations in catchment‐scale hydroclimate, hydrology, geomorphology and hydrochemistry as essential to understanding freshwater habitats in the wider landscape context. Evolution of research has resulted in a remarkable catalogue of novel findings underlining the value of long‐term data that increases with time as modelling tools advance to leverage more insights from “big data”. Data are available on fish numbers, sizes and ages across multiple life stages, extending over many decades and covering a wide range of stock levels. Combined with an unusually detailed characterization of the environment, these data have enabled a unique process‐based understanding of the controls and bottlenecks on salmon population dynamics across the entire lifecycle and the consequences of declining marine survival and ova deposition. Such powerful datasets, methodological enhancements and the resulting process understanding have informed and supported the development of fish population assessment tools which have been applied to aid management of threatened salmon stocks at large‐catchment, regional and national scales. Many pioneering monitoring and modelling approaches developed have been applied internationally. This history shows the importance of integrating discovery science with monitoring for informing policy development and assessing efficacy of management options. It also demonstrates the need to continue to resource long‐term sites, which act as a focus for inter‐disciplinary research and innovation, and where the overall value of the research greatly exceeds the costs of individual component parts.

Upcycling of carbon, nitrogen, and phosphorus from aquaculture sludge using the polychaete Hediste diversicolor (OF Müller, 1776) (Annelida: Nereididae)

IntroductionFocusing on circular bioeconomy and finding solutions for managing finite and scarce resources such as phosphorus are issues that need to be addressed across sectors to attain food security. Land-based aquaculture of Atlantic salmon (Salmo salar L.) smolt and post-smolt results in a large output of aquaculture sludge. These nutrient-rich side streams from aquaculture production constitute a valuable resource for cultivation of polychaetes Hediste diversicolor. The aim of this study was to evaluate the capacity of H. diversicolor to upcycle carbon (C), nitrogen (N), and phosphorus (P) contained in aquaculture sludge from Norwegian salmon production.Material and methodsWe investigated the effect of two diets, smolt sludge and post-smolt sludge, which were supplied at four different feed levels, on the gain of C, N, and P in H. diversicolor and established uptake rates for the upcycling of these nutrients. Additionally, we examined how different feed composition (type of diet) and supply (feel level) influenced C, N, and P content as well as the elemental ratios of H. diversicolor.Results and discussionPolychaetes fed with both types of sludge were shown to incorporate C, N, and P from their diets into biomass. Incorporation of C, N, and P in polychaete biomass was highest at the highest feed levels, following specific growth rates. Uptake of diet C, N, and P into polychaete biomass was similar for both diets and across feed levels. On average, C and N uptake rates amounted to 2–10% and 2–15%, respectively, while values for P uptake were lower at 0.5–1.5%. C, N, and P content of polychaetes was not affected by different diets or feed levels while the C:N ratio increased with increasing feed supply. Overall, we found that H. diversicolor can successfully take up nutrients contained in aquaculture sludge and thus can be beneficial for upcycling of side streams from Atlantic salmon production.

Atlantic salmon (Salmo salar) distribution and vertical size-stratification in a commercial sea cage: A case study

Biomass and size estimates of fish are most valuable information to assure optimal management in Norwegian Atlantic salmon production. Such estimates are largely based on models and small samples of few individuals, and improvements are required for better representativity. Advances in machine learning triggered fast development of automated size estimation using stereovision cameras. These measurement systems can result in precise measurements of individual fish. Nevertheless, fish behavior needs to be considered for a proper description of the true mean and variation of fish sizes of cage populations because salmon distribution is not homogeneous in sea cages. Most studies on salmon distribution were performed in relatively small sea cages and additional experiments at commercial scale are required to verify that previous findings are applicable under industrial conditions. In this case study, we monitored vertical and horizontal distributions of salmon in a commercial sea cage. Vertical size stratification was investigated using stereovision cameras, and salmon and growth-stunted fish abundances and swimming speed were measured using cameras recording simultaneously in 16 positions: four horizontal positions and four depths (1 m, 5–6 m, 9–11 m and 14–16 m), four times during one day. Our results suggest a heterogeneous vertical distribution with longer individuals found deeper in the sea cage at high abundance and swimming more slowly than smaller individuals, including growth-stunted fish, found in low abundance close to the surface. Cumulative mean fork-lengths per depth were compared to the estimated true mean fork-length for the whole population of the cage and results show that automatic biomass and size estimation based on a single depth likely results in biased size estimation for the cage population. On the contrary, horizontal distribution appeared homogeneous, and our data supports the assumption that fish were exhibiting a circular swimming pattern, as previously described in small sea cages and under slow current conditions. Our study adds data to currently still scarce knowledge about fish behavior and distribution at commercial scale and provides indications on the use of new technologies for biomass and size estimation. Further studies on longer timelines and different locations are necessary to further generalize behavioral models.

How Do Alternative Protein Resources Affect the Intestine Morphology and Microbiota of Atlantic Salmon?

The availability and cost of fishmeal constitute a bottleneck in Atlantic salmon production expansion. Fishmeal is produced from wild fish species and constitutes the major feed ingredient in carnivorous species such as the Atlantic salmon. These natural stocks are at risk of depletion and it is therefore of major importance to find alternative protein sources that meet the nutritional requirements of the Atlantic salmon, without compromising the animals' health. Terrestrial animal by-products have been used in aquaculture feed, but their use is limited by the lack of several essential amino acids and consumer acceptance. In the case of plant ingredients, it is necessary to take into account both their concentration and the extraction methodologies, since, if not dosed correctly, they can cause macro- and microscopic alterations of the structure of the gastrointestinal tract and can also negatively modulate the microbiota composition. These alterations may compromise the digestive functions, growth of the animal, and, ultimately, its well-being. An updated revision of alternative protein sources is provided, with the respective impact on the intestine health in terms of both morphology and microbiota composition. Such information may constitute the premise for the choice and development of Atlantic salmon feeds that guarantee fish health and growth performance without having a significant impact on the surrounding environment, both in terms of depletion of the fish's natural stocks and in terms of pressure on the terrestrial agriculture. The sustainability of aquaculture should be a priority when choosing next-generation ingredients.

Using skin mucus for the identification of ovulation biomarkers in North American Atlantic salmon (Salmo salar)

In Maine, North American Atlantic salmon production has experienced a 20% decrease in eye-up eggs, the point of embryo development where the black eye spot is visible. The maternal endocrine environment is suggested to be an important factor for ovulation and viable embryos but needs to be further investigated. Combining new sampling matrices (skin mucus) and advanced technologies (liquid chromatography tandem mass spectrometry (LC-MS/MS)) will advance the knowledge of the endocrine status in reproductively mature North American Atlantic salmon. The objectives of this study were to 1) identify mucus as a viable matrix to measure steroid hormones, 2) quantify steroid hormone profile of North American Atlantic salmon during ovulation and 3) compare hormone profiles of salmon with high and low eye-up rates. Mucus and plasma were collected from sexually mature female North American Atlantic salmon (n = 30). A group of females were sampled pre-ovulation (n = 9) and a separate group post-ovulation (n = 21) then analyzed by liquid chromatography tandem mass spectrometry (LC-MS/MS). Fish collected post-ovulation were slotted into groups based on eye-up rate, fish with ≥70% eye-up rate (high eye-up, n = 5) and fish with ≤70% eye up rate (low eye-up, n = 16). In mucus allopregnanolone (p = 0.01), 11-deoxycorticosterone (p = 0.05) and 11-deoxycortisol (p = 0.01) were significantly higher after ovulation. In plasma, allopregnanolone was significantly lower after ovulation (p = 0.01 and 17α, 20β-hydroxyprogesterone was significantly elevated (p = 0.05) after ovulation. Fish with a low eye-up rate had elevated mucus concentrations of corticosterone (p = 0.02). While fish with a high eye-up rate had elevated plasma testosterone concentrations (p = 0.04). Circulating androstenedione (r = 0.46, p = 0.03) and testosterone (r = 0.47, p = 0.03) were significantly correlated with eye-up rate. Mucosal concentrations of steroid hormone correlated with circulating concentrations of related steroids and reflect changes in reproductive physiology. The significant changes in mucosal and circulating steroid concentrations of the 5α reduced pregnane, allopregnanolone suggests a role of 5α-reduced pregnanes during ovulation in North American Atlantic salmon. To our knowledge this is the first time any 5α-reduced pregnane has been reported in teleosts. Mucosal concentrations of precursor glucocorticoids significantly elevated after ovulation combined with significant correlation with hydroxylated pregnanes suggests a dual mechanism needed for ovulation between glucocorticoids and pregnanes. Additionally, glucocorticoids and androgens appear to influence the viability of fertilized eggs highlighting the need for further research into the role's multiple hormones play in both oocyte maturation and embryo viability.

Water Flow Requirements of Post-smolt Atlantic Salmon (Salmo salar L.) Reared in Intensive Seawater Flow-through Systems: A Physiological Perspective

Environmental challenges related to open sea cage production of Atlantic salmon have sparked interest in developing commercial-scale semi-closed sea systems for post-smolt Atlantic salmon (100–1000 g). Determining the mass-specific water flow required by post-smolts will largely influence the design and dimensioning of such systems. In this experiment, post-smolts were exposed to four levels of specific water flow: 0.2, 0.3, 0.4, and 0.5 L kg fish−1 min−1. All treatments involved flow-through seawater with full oxygenation, a salinity of 34‰, and a mean temperature of 9.3 °C. The stocking density was kept stable at 75 kg m−3. Water pH decreased with reduced flow, while partial pressure of carbon dioxide (pCO2) and total ammonia nitrogen (TAN) in the water increased. The increase in water CO2 was reflected in the blood with increased pCO2, HCO3−, and decreased Cl− in the lowest water flow treatment (0.2 L kg fish−1 min−1), indicating a typical regulatory response to increased water CO2 over the eight-week experimental period. No negative effects on osmoregulation, external macroscopic welfare, or performance indicators were observed, suggesting that within the time period of this experiment, post-smolts can compensate for reductions in water flow down to 0.2 L kg fish−1 min−1. However, to avoid activating and exhausting potentially energy-costly physiological regulatory mechanisms, it is suggested to keep specific water flow above 0.3 L kg fish−1 min−1 in large-scale operations with semi-closed sea systems at intermediate temperatures.

Intestinal epigenotype of Atlantic salmon (Salmo salar) associates with tenacibaculosis and gut microbiota composition

It remains a challenge to obtain the desired phenotypic traits in aquacultural production of Atlantic salmon, and part of the challenge might come from the effect that host-associated microorganisms have on the fish phenotype. To manipulate the microbiota towards the desired host traits, it is critical to understand the factors that shape it. The bacterial gut microbiota composition can vary greatly among fish, even when reared in the same closed system. While such microbiota differences can be linked to diseases, the molecular effect of disease on host-microbiota interactions and the potential involvement of epigenetic factors remain largely unknown.The aim of this study was to investigate the DNA methylation differences associated with a tenacibaculosis outbreak and microbiota displacement in the gut of Atlantic salmon. Using Whole Genome Bisulfite Sequencing (WGBS) of distal gut tissue from 20 salmon, we compared the genome-wide DNA methylation levels between uninfected individuals and sick fish suffering from tenacibaculosis and microbiota displacement. We discovered >19,000 differentially methylated cytosine sites, often located in differentially methylated regions, and aggregated around genes.The 68 genes connected to the most significant regions had functions related to the ulcerous disease such as epor and slc48a1a but also included prkcda and LOC106590732 whose orthologs are linked to microbiota changes in other species. Although the expression level was not analysed, our epigenetic analysis suggests specific genes potentially involved in host-microbiota interactions and more broadly it highlights the value of considering epigenetic factors in efforts to manipulate the microbiota of farmed fish.

Reciprocal hybrids of Atlantic salmon (Salmo salar) x brown trout (S. trutta) confirm a heterotic response to experimentally induced amoebic gill disease (AGD)

Amoebic gill disease (AGD) affects global marine aquaculture production of Atlantic salmon, requiring costly reiterative treatment and negatively impacting fish performance and welfare. Although there has been gradual and ongoing progress in genetic selection to improve host resistance to the causative agent (Neoparamoeba perurans) there has been little focus on the response of interspecific hybrids to AGD challenge. Previous research has demonstrated that Atlantic salmon x brown trout hybrids had reduced requirement for freshwater bathing (based on gross gill signs) during chronic natural AGD exposure, yet there has been no histological or molecular evidence confirming differential host response or parasite abundance. In this study we exposed Atlantic salmon (SS), brown trout (TT) and their reciprocal interspecific hybrids (TS and ST) to a single laboratory challenge (∼700 amoebae.l−1 for 18 days) and compared the resultant infection and disease signs characteristic of AGD. Gill score was significantly higher in SS than in TT and hybrids. Copy number quantification of amoebae on gills was higher in salmon than in hybrids or trout but did not differ between hybrids and trout. Gill histopathology confirmed both an increased amoebae abundance and higher expression of host tissue reaction in SS with significantly higher percentages of lesions harboring hyperplastic lesions. Mid-parent and best-parent heterosis of resistance to N. perurans and host response (gill lesions) was confirmed but did not differ between hybrid crosses. Although limited to a single laboratory infection event, our results support previously reported observations (from natural infection/reinfection) of reduced AGD signs in trout and interspecies hybrids. We conclude that interspecies hybrids have potential to improve our understanding of salmonid resistance to amoebic branchitis and support future gene-based research toward fish disease management.

Algal oil gives control of long‐chain omega‐3 levels in full‐cycle production of Atlantic salmon, without detriment to zootechnical performance and sensory characteristics

AbstractThe 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.

Welfare and survival of lumpfish (Cyclopterus lumpus) in Norwegian commercial Atlantic salmon (Salmo salar) production

Lumpfish are currently used as a part of the overall strategy for the prevention and control of sea lice in Atlantic salmon farming in Norway. Their use as biological delousers is advantageous as it exposes salmon to very little stress and injuries. However, there is a growing concern and criticism about the welfare and survival of lumpfish in salmon farms. This study monitored the welfare and survival of lumpfish from four commercial salmon farms for 6 to 12 months in 2019–2021. Environmental and production conditions were also registered. Lumpfish welfare decreased during the study period, mainly related to eye and skin injuries. Mortality rate was low in the first few months after transfer to sea, but increased thereafter. Mechanical delousing affected the welfare and survival most negatively of all monitored external parameters. Even though diseases are often pointed out as the main factor for mortality of lumpfish in sea cages, it was not the case in the present study. However, there were indications that diseases are more likely to occur when lumpfish is already weakened by other factors such as mechanical delousing. One to two thirds of lumpfish were assessed as underweighted or emaciated at all time during the monitoring period, suggesting that the nutritional requirements of lumpfish are not fully met in sea cages.

The skin mucosal barrier of lumpfish (Cyclopterus lumpus L.) is weakened by exposure to potential aquaculture production-related stressors.

Various cleaner fish species, such as the lumpfish (Cyclopterus lumpus L.), are used in the sea cage production of Atlantic salmon (Salmo salar L.) as a control measure against the ectoparasitic salmon louse (Lepeophtheirus salmonis). Nonetheless, during severe lice infestation, alternative treatments are required to control parasitic burden. The aim of this study was to gain insight into how lumpfish skin responds to different chemicals used to treat parasites. The authors collected skin from lumpfish from both research facilities (tank-reared fish) and commercial production (cage-reared fish) and used operational welfare indicators, in vitro models, histology and transcriptomics to study how the skin responded to two anti-parasitic oxidative chemicals, hydrogen peroxide (H2 O2 ) and peracetic acid. Lumpfish sampled from the farm were classified as clinically healthy or weak based on their morbidity status, and fish from each category were used to gain insight into how the therapeutics affect the skin barrier. Differences between healthy and weakened (moribund) fish, and between treated fish from each of the two groups, were observed. Histological examination showed an overall reduced skin quality in fish characterized as moribund, including different grades of exposed bony plates. In vitro oxidant-treated lumpfish skin had reduced the migration capacity of keratocytes, a weakened epidermal barrier, and altered gene transcription, changes that are known predisposing factors to secondary infections. Skin from non-treated, healthy fish sampled from commercial farms exhibited similar features and attributes to oxidant-exposed tank-reared fish from a research facility, suggesting that apparently healthy cage-held lumpfish exhibited stress responses in the epidermal barrier. The results of the study outline the risks and consequences lumpfish can face if accidentally subjected to potential anti-parasitic oxidant treatments aimed at Atlantic salmon. It also strengthens the evidence behind the requirement that lumpfish should be removed from the cages before being potentially exposed to this type of treatment and outlines the potential risks of differing husbandry practices upon lumpfish health, welfare and resilience.

Evaluation of ME-PRO® and EnviroMeal Combinations as Partial and Complete Fish Meal Replacements in Diets for Juvenile Atlantic Salmon (Salmo salar) Reared in A Recirculating Aquaculture System

A feeding trial was conducted in a recirculation aquaculture system (RAS) to test the growth of juvenile Atlantic salmon (Salmo salar). A standard salmon diet (Control) was used as the template for two experimental diets that contained a combination of Black Soldier Fly (Hermetia illucens) larvae (BSFL) defatted meal (EnviroMeal) and fermented soy protein (MEPRO®). The two ingredients were combined to replace fish meal by 50 or 100% (MEP/Meal 50 and MEP/Meal 100) in the experimental diets. At the 12-week trial conclusion, all growth parameters were similar among the three treatments. The diet containing no fish meal, MEP/Meal 100, demonstrated slightly higher numeric growth performance compared to the Control and MEP/Meal 50 treatment. Similarly, a histological analysis of distal intestines and organosomatic indices showed no significant difference among treatments. All intestinal samples were healthy in appearance showing no apparent enteritis. The results of this study show a combination of fermented soy and BSFL meal may be a viable option in sustainable diets for commercial Atlantic salmon production.

Commercial aquaponic system developed for Atlantic salmon (Salmo salar) production in RAS together with vegetable production – a CO2 zero concept

ISHS XXXI International Horticultural Congress (IHC2022): International Symposium on Urban Horticulture for Sustainable Food Security (UrbanFood2022) Commercial aquaponic system developed for Atlantic salmon (Salmo salar) production in RAS together with vegetable production – a CO2 zero concept

Tenacibaculum ovolyticum 16S rDNA Quantitative-PCR Assay Development and Field Testing

In British Columbia (BC; Canada) Atlantic salmon (Salmo salar L.) production, Tenacibaculum members are associated with ‘mouthrot’ and disease identification is based on gross observation and clinical data. Genomic similarities (i.e., putative virulence factors) between T. ovolyticum and other better-characterized agents of mouthrot could imply potential pathogenicity. While T. ovolyticum has not been directly linked to salmon mortality events in BC, it has been isolated from diseased marine fish. To investigate T. ovolyticum’s pathogenicity in situ, a T. ovolyticum 16S rDNA qPCR assay targeting a ~155 bp amplicon was developed. The assay was used to screen 67 biotic and 33 abiotic samples collected from a BC Atlantic salmon (Salmo salar L.) net-pen site before, during, and after a mouthrot outbreak. The assay was specific, quantifiable and detectable for T. ovolyticum over 6-log and 8-log units, respectively. However, cycle quotients differed between the BC isolate and type strain of T. ovolyticum, suggesting that qualitative use of the qPCR assay in field samples would be more accurate. Only two out of 100 samples were T. ovolyticum-positive, indicating limited involvement in this particular outbreak. However, the ecological role of T. ovolyticum and its involvement in the pathogenesis of other mouthrot outbreaks in Atlantic salmon is unknown.

Utilization of feed resources in the production of Atlantic salmon (Salmo salar) in Norway: An update for 2020

The utilization of feed resources in Norwegian salmon farming has previously been reported for 2010, 2012 and 2016. This paper presents an update for 2020, giving an overview of the feed ingredients used and retention of nutrients in fillet and whole salmon for the entire Norwegian salmon production.A total of 1,976,709 tonnes of feed ingredients were used to produce 1,467,655 tonnes of salmon. The feed was produced from 22.4 % marine ingredients, 73.1 % vegetable ingredients and 4.1 % micro ingredients such as vitamin and mineral premixes, astaxanthin and crystalline amino acids. In addition, 0.4 %, or 8126 tonnes, of single cell protein, insect meal, fermented products and microalgae were used in salmon feeds. Norwegian marine protein and marine oil constituted 8.3 % of the ingredients. The remaining 91.7 % of the ingredients were imported. The feed conversion factor was 1.35 if calculated from feed ingredients ‘as is’, or 1.25 if calculated form ingredients on dry matter basis. The retention of energy, dry matter, protein, fat, EPA + DHA and phosphorus from feed was 39 %, 33 %, 34 %, 57 %, 49 % and 25 %, respectively, in whole salmon. In fillet, the corresponding retention rates were 25 %, 21 %, 25 %, 35 %, 32 % and 12 %, respectively.The feed ingredients used and the utilization of feed in 2020 resembled that of 2016, except that there was an increase in the amount produced in 2020 and a slight increase in the economic feed conversion ratio (eFCR).

Characteristics of lumpfish (Cyclopterus lumpus) with high cleaning efficacy in commercial Atlantic salmon (Salmo salar) production

Cleaner fish such as lumpfish (Cyclopterus lumpus) are widely used as a biological method for delousing in Atlantic salmon (Salmo salar) aquaculture. Previous studies have mainly focused on the number of salmon lice (Lepeophtheirus salmonis) per salmon or on the proportion of individuals grazing on sea lice (L. salmonis and Caligus elongatus) and reported large variations in cleaning efficacy. Understanding what parameters cause these differences in cleaning efficacy is crucial to optimize the use of lumpfish as a biological delouser. In addition, it is uncertain how many sea lice are commonly ingested per lumpfish, even though this constitutes decisive information in the use of lumpfish for delousing. This study focused on the impact of lumpfish weight, diet and sex on cleaning efficacy in commercial Atlantic salmon net pens. A total of 2104 lumpfish were sampled from 8 Norwegian salmon farms over 2 years. Weight and sex was determined for each individual. Stomach content was visually identified and categorized as sea lice, lumpfish feed, salmon feed, biofouling organisms and zooplankton. Proportions of lumpfish with sea lice in their stomachs varied from 0 to 47% (average of 8.7% for the whole study) and the number of ingested sea lice varied from 0 to 120 (average of 0.6) between Atlantic salmon farms and sampling dates. Our results suggested that estimating the average number of sea lice ingested per lumpfish is necessary to determine cleaning efficacy. Weight was found to be a determining factor as lumpfish >300 g were very unlikely to consume sea lice. Individuals with the highest cleaning efficacy were small (< 100 g) and fed on additional prey items, mainly biofouling organisms. Lumpfish sex did not influence cleaning efficacy. We developed a simple model based on logistic regression analysis to predict lumpfish predict cleaning efficacy. The model predicted that maintaining lumpfish in net pens at a relatively small size (< 300 g) may raise grazing up to >1 sea louse per lumpfish.

Temporal changes in skin and gill microbiomes of Atlantic salmon in a recirculating aquaculture system – Why do they matter?

Mucosal surfaces are key components of teleost health, providing defence against opportunistic pathogens and other insults. Maintaining the integrity of mucosal surfaces and their associated microbial communities, especially the gill and skin that have large surface areas exposed to the environment is essential. Production of Atlantic salmon in land-based recirculating aquaculture systems (RAS) has increased significantly in recent years as it allows greater control over stability of the environment in which fish are reared, reduces water demand and minimises environmental impacts. However, little is known about the impact of the RAS environment upon the temporal dynamics of skin and gill mucosal microbiomes. In this study we examined microbial communities in gill mucus, skin mucus and rearing water throughout freshwater (FW) RAS production, and at 1-week and 4-weeks following transfer to seawater (SW) in open cage production using 16S rRNA sequencing. Microbial diversity and richness in skin and gill mucus of fish reared in a RAS system were temporally dynamic. Dynamics in richness and diversity were similar in the two mucosal tissues, and to some extent also mirrored that of the surrounding water. Dysbiosis indicated by an abrupt decline in diversity during FW production coincided with an increase in the relative abundance of two taxa belonging to the RAS-biofilter-associated nitrogen-cycling genus Hydrogenophaga in RAS tank water and this was also observed in gill and skin mucus. Extensive overlap in core taxa was observed between gill and skin mucus, but host-specific cores were non-existent during the dysbiotic event with all cores present in the rearing water. Diversity remained stable during the transition from FW to SW, but distinct community composition and core taxa were observed in the two environments. Although RAS are closely controlled, significant temporal variation could be observed in temperature as well as levels of CO2 and nitrogen compounds, reflecting the increasing biological load within the system over time. The results presented here suggest that, in terms of microbiomes, dysbiosis may occur in both the RAS environment and fish mucosal surfaces over time, but microbial communities have the capability to recover.