Salmon Farming Research Articles

Assessment of Initial Investment Strategies for Different Farm-Scale Scenarios with Economic Cost Analyses in Offshore Salmon Farming

Abstract The simulation of investment strategies with different farm-scale scenarios has been evaluated for best management plan in cage farming business for the establishment of a salmon production with either full capacity or progressive investment. Economical revenues were analyzed with business risk assessment based on operating and fixed costs for each of the four scenarios. In the theoretical model projected for the stimulation of best management plans, structural elements for the construction of an offshore Turkish salmon farm in the Black Sea were designed and investment costs for an annual production capacity of 4,000 tons were re-scaled by 25, 50 and 75% reduction, corresponding to 3,000, 2,000 and 1,000 tons per year, respectively. Economic variables of operational costs were comparatively evaluated with the revenues and annual profit conditions by sales of harvested fish. The break-even points for all investment strategies with different farm-scale scenarios were remarkably lower (on average 302,574.7 kg/year) than the harvest yields from the farms (on average 3,702,857.1 kg/year). Based on break-even points and margin of safety (MOS over 85%), all farms gained net profits with low risks in the first year, whether the farm received full investment, or initiated business with reduced investment expenditures for a gradual and progressive expansion plan. Findings of this study exhibit useful indications for farm management in understanding conditions of a stepwise establishment of business plans for salmon farming in offshore conditions.

Seaweed Fly Larvae Cultivated on Macroalgae Side Streams: A Novel Marine Protein and Omega‐3 Source for Rainbow Trout

A nutritional bottleneck in salmonid aquaculture is the procurement of marine‐derived compounds, such as essential amino and fatty acids, including omega‐3 fatty acids, lysine, and methionine. Therefore, insects containing these compounds are highly promising as feed ingredients. The present study evaluates larvae of a “marine” insect (Coelopa frigida, the bristly‐legged seaweed fly larvae, SWFL) reared on brown algae side streams as a feed ingredient for rainbow trout (Oncorhynchus mykiss). SWFL contained, on a dry matter basis, 60% crude protein (CP), 3.5% lysine, and 1.5% methionine, as well as 17% lipids, including 4% eicosapentaenoic acid and docosahexaenoic acid. Four isoenergetic (ca. 23 MJ kg−1 gross energy) and isoproteic (ca. 45% CP) feeds were evaluated in a 10‐week feeding trial. The diets included a control containing 25% fish meal, a commercial reference, and two diets substituting 40% fish meal with either SWFL or partially defatted black soldier fly larvae (BSFL) meal (Hermetia illucens). SWFL‐fed fish displayed higher specific growth rates (SGR) compared to BSFL‐fed fish and similar SGR compared to control and reference diet‐fed fish. Feed intake in SWFL‐fed fish was higher than for the control and BSFL diets and similar to the reference diet. The feed conversion ratio of fish fed the BSFL and SWFL diets was higher compared to the control, suggesting lower bioavailability of both insect meals compared to fish meals. No difference in intestinal health parameters was noted between the insect diets and the control diet, indicating good intestinal health across all treatments. However, changes in electrogenic intestinal transport were observed between the SWFL and BSFL diets, illustrating the heterogeneous effect of different insect products. Overall, SWFL meal is a promising alternative marine feed ingredient, compatible with circular production systems, as it can be efficiently cultivated using marine side streams.

Countering salmon farming expansion: Network-making power in a nomadic marine space

Promoted by the state, and national and international companies, salmon farming has spread to the south of Chile over the last three decades. This expansion has been resisted by local groups as social and environmental impacts in expanded territories of production and processing have been identified. Informed by a counter-territorialisation and network theory lens, we analyse how strategies by the state and national and international companies to expand salmon aquaculture have been resisted by a global network led by the Indigenous nomadic Yagán people. Data was obtained through participant observation and interviews gathered during three periods of fieldwork in the Region of Magallanes. Our research shows how network-making power was employed to resist state territorialisation at sea to reconfigure spatial boundaries and power relations at the border of the Chilean state. These findings extend an understanding of marine counter-territorialisation and contribute to a reorientation of marine policies to recognise networked spatial claims and territorial rights of Indigenous people of the sea.

Novel large‐scale mapping highlights poor state of sea trout populations

Abstract The state of sea trout in 1251 Norwegian watercourses was assessed based on a scoring system for human pressures, abundance data, and local knowledge. Over 16,000 km of rivers and lakes were available to sea trout in these watercourses, spanning from the temperate to Arctic regions. Sea trout were classified to be in a good or very good state in fewer than 25% of the watercourses and in a poor or very poor state in almost 40%. Twenty‐nine watercourses had lost their sea trout populations. Salmon lice from aquaculture salmon farms had by far the largest adverse effect on sea trout among the human impact factors, both in the number of watercourses (83%) and river area affected (60%), and the total effect on sea trout abundance. Agriculture and hydropower production also had strong adverse impacts (35% and 19% of watercourses), but substantially lower than that caused by salmon lice. Culverts related to road crossings and other habitat alterations also had impacts on sea trout in many watercourses (27%). Exploitation of sea trout has been reduced in Norway in recent years, both in the marine and freshwater fisheries. Yet, the exploitation pressure was moderate or high in almost 14% of the watercourses where the state of sea trout was poor or very poor, suggesting a high potential for overexploitation in these. The state of sea trout was best in the northern sparsely populated areas. However, distribution of watercourses with sea trout in a poor or very poor state was more linked to aquaculture, agriculture, and hydropower production than human population density. The developed approach for large‐scale mapping of state and pressures, which is vital for prioritizing management measures, may inspire other nations in their conservation effort for this important species.

The heat is on: sensitivity of goldsinny wrasse to global climate change.

Unsustainable harvesting practices have drastically reduced fish populations globally and developments in aquaculture have increased. Unexpectedly, Atlantic salmon farming caused the opening of a new fishery in northern European countries, where previously unharvested mesopredatory species, like the goldsinny wrasse (Ctenolabrus rupestris), are captured for use as cleaner fish in pens along the coast and fjords. The goldsinny wrasse is widespread in coastal areas where it plays an ecologically important role as a predator of small invertebrates. Since climate change effects are particularly pronounced in coastal waters, it becomes urgent to understand how fish like the goldsinny will respond to global climate change, including the increasing frequency and intensity of marine heatwaves (MHWs), ocean freshening (OF) and ocean acidification (OA). To address this, we conducted a multi-stressor experiment exposing adult goldsinny to each stressor individually, as well as to all three combined. The results indicated that the goldsinny is highly affected by MHWs and extremely sensitive to a multi-stressor environment, with 34% and 53% mortality, respectively. Additionally, exposure to a MHW event, OF and multi-stressor conditions affected fish metabolism, with the highest standard metabolic- and maximum metabolic-oxygen consumption rates observed for the MHW treatment. Increases in oxidized glutathione (GSSG) and percent oxidized glutathione (% GSSG) in the livers, indicative of oxidative stress, were also seen in the MHW, OF and multi-stressor treatments. As a single stressor, OA showed no significant impacts on the measured parameters. This information is important for conservation of coastal marine environments, given the species' important role in shallow-water habitats and for management of goldsinny or other mesopredatory fish harvested in coastal ecosystems. The sensitivity of the goldsinny wrasse to future stressors is of concern, and any potential reductions in abundance as a result of climate change may lead to cascade effects with ecosystem-wide consequences.

Modelling the dispersion of infectious salmon anemia virus from Atlantic salmon farms in the Quoddy Region of New Brunswick, Canada and Maine, USA

Pathogen dispersal from infected aquaculture sites into the surrounding ocean poses risks of infection to wild and farmed species, but is difficult to predict. This study aimed to build a framework using an ocean circulation and a particle tracking model in conjunction with a dynamic infection model and a virus inactivation model to simulate the dispersal of the infectious salmon anemia virus (ISAV) from Atlantic salmon farms. Simulated particles were released from hypothetically infected farms and advected by modelled currents. Inactivation of viral cohorts by ambient ultraviolet radiation and natural microbial communities was simulated during advection. Simulations showed that ISAV concentration varied spatiotemporally with the progression of the outbreak, current speed and direction, tidal elevation amplitude, and environmental decay. Connectivity among aquaculture sites varied in relation to seaway distances, though simulations showed that connectivity can also be asymmetrical between farm sites. Sensitivity analyses showed that the dispersal of ISAV was moderately sensitive to uncertainty associated with the viral decay model, highlighting the importance of obtaining accurate estimates of inactivation rates of ISAV. This framework provides an approach to simulate waterborne viral transmission that considers the biology and epidemic features of significance for pathogens and the dynamic conditions of the ocean.

Development of commercial trout breeding in southern Russia in the context of the import substitution strategy

Aquaculture is the main promising direction for the development of the fisheries industry. Analysis of the general condition of fish breeding enterprises and the potential for expanding production shows that the growth trend of traditional for the southern regions pond fish breeding is weak. A significant problem for the development of aquaculture is the high price of fish products and, accordingly, low demand. A substantial reduction in the cost of fish production is currently unlikely to be achieved, so switching to more valuable fish varieties can stimulate consumption. To ensure the development of the fish products market and increase demand, entrepreneurs in southern Russia are improving technologies for growing such valuable fish varieties as salmonoids, in particular, rainbow trout. Studying the activities of trout farms requires taking into account which area of activity is prioritized. A farm can produce marketable fish or fish planting material, as well as execute both types of production. The work observes the organizational features of trout farms and promising directions of their development. Solving such key issues as the provision of qualified personnel, high-quality feed of domestic, preferably regional production, and provision of logistically affordable and high-quality planting material is the basis for achieving the goals of import substitution for high-quality fish products in Russia.

Histological examination of the young Oncorhynchus mykiss intestines using the feed with chelated and probiotic supplements.

Macronutrient and micronutrient deficiencies in the fish diet can affect fish growth rate, ability to resist disease, and fillet quality. Determination of effective dose of developed feed additives consisting of chelate compounds of biogenic elements and probiotic preparation based on Bacillus subtilis. Young rainbow trout were divided into four groups consisting of 100 fish each. The control group received standard food; the experimental groups received food with chelates and probiotics in different concentrations. At the end of the experiment (30 days), the middle intestine histology and morphometric parameters were studied. The use of chelated compounds alone affected the state of the intestinal villi and the infiltration of the epithelium by lymphocytes. The addition of a probiotic had a positive effect on the migration of immune cells in the intestinal villi; however, the probiotic in high concentrations contributed to a decrease in the number and area of goblet cells. Synergistic effects of chelated compounds and probiotic preparations on the morphometric parameters of the medium intestine were observed. In the proper doses, the studied feed additives might be recommended for rainbow trout farming under industrial aquaculture conditions.

Identification of new yeast strains, Candida zeylanoidesY12‐3 and Hyphopichia pseudoburtoniiY12‐1, from the intestinal tract of rainbow trout, Oncorhynchus mykiss, with potential probiotic characteristics

AbstractIn this study, 2 yeasts, Candida zeylanoides isolate Y12‐3 (MN073455.1) and Hyphopichia pseudoburtonii isolate Y12‐1 (MN073489.1), were isolated from rainbow trout hindguts. Their identity was confirmed by amplification of internal transcribed spacer (ITS) gene regions. Their in vitro probiotic properties showed that they were hydrophobic and did not inhibit bacterial growth. However, they displayed positive co‐aggregation with several bacterial pathogens. It was interesting that Y12‐1 and Y12‐3 isolates survived and grew well in bile salt concentrations ranging from 0.6% to 1.5% and at low pH conditions. After a 35‐day feeding trial, the results of dietary incorporation of the yeast isolates showed that serum myeloperoxidase activity was unchanged in the treated and control groups. Meanwhile, serum lysozyme activity in yeast groups was decreased significantly compared to the control. However, fish fed with Y12‐1 had higher total protein, albumin, and globulin than other groups. Total cholesterol levels were decreased significantly in yeast groups compared to the control. Interestingly, the Y12‐1 and Y12‐3 groups showed higher survival (69.05% and 80.95%) after the challenge with Lactococcus garvieae compared to the control (45.24%). In brief, the aforementioned findings showed that Y12‐1 and Y12‐3 strains could be potential probiotic candidates for use in rainbow trout farming.

On the prediction of SAV transmission among Norwegian aquaculture sites

Pancreas Disease (PD) is a viral disease that affects Atlantic salmon (Salmo salar) in Norwegian, Scottish and Irish aquaculture. It is caused by salmonid alphavirus (SAV) and represents a significant problem in salmonid farming. Infection with SAV leads to reduced growth, mortality, product downgrading, and has a significant financial impact for the farms. The overall aim of this study is to evaluate the effect of various factors on the transmission of SAV and to create a predictive model capable of providing an early warning system for salmon farms within the Norwegian waters. Using a combination of publicly available databases, specifically BarentsWatch, and privately held PCR analyses a feature set consisting of 11 unique features was created based on the input parameters of the databases. An ensemble model was developed based on this feature set using XG-Boost, Ada-Boost, Random Forest and a Multilayer Perceptron. It was possible to successfully predict SAV transmission with 94.4% accuracy. Moreover, it was possible to predict SAV transmission 8 weeks in advance of a ‘PD registration’ at individual aquaculture salmon farming sites. Important predictors included well boat movement, environmental factors, proximity to sites with a ‘PD registration’ and seasonality.

Гидробиоценозы озера Малое Янисъярви (Южная Карелия) в условиях товарного выращивания форели

Based on our own and literature data, the state of the ecosystem of Lake Maloe Yanisjarvi (South Karelia) in the conditions of industrial trout farming (since 2020) has been analyzed. The reservoir belongs to the mineralized (24.4-31.6 mg/l), calcium sulfate class. The chemical composition of the waters is not subject to significant fluctuations throughout the year. Among the forms of mineral nitrogen, nitrate and ammonium predominate (the maximum concentration noted is 0.12 mg/l). The total phosphorus content does not exceed 0.012 mg/l, mineral – 0.01 mg/l. Fluctuations in the concentration of dissolved oxygen are in the range of 7.0-9.1 mg/l. High flow rate (indicator of conditional water exchange 3.5 year-1) is the main stabilizing factor contributing to the preservation of the hydrochemical regime of the reservoir. In general, the water masses of Lake Maloe Yanisjarvi in their chemical composition meet the requirements for the aquatic environment in the cage cultivation of salmon. The data on the main hydrological and hydrobiological indicators of the lake are presented. According to the level of quantitative development of zooplankton in the summer-autumn period, the lake corresponds to the oligotrophic type with a biomass of up to 1 g/m3, benthos – to the α-mesotrophic type (2.8 g/m2). The reservoir belongs to the highest fishery category, according to literature data, valuable fish species (salmon, trout, whitefish and grouse) are noted as part of the ichthyofauna. Recommendations on the timing of the ecological expertise of the lake are given.

A mechanistic model approach to characterize suitable regions for Salmo salar aquaculture in the Yellow Sea under global warming

Global warming has a profound effect on aquaculture. Salmon aquaculture, as an emerging industry in China, is particularly vulnerable to climate change. For this reason, spatial planning with mechanistic understanding is essential for mitigating and adapting to the impacts of climate change. Through the use of dynamic energy budget models for Atlantic salmon (Salmo salar) with fine-scale environmental data under 0 m, 20 m, 40 m, and 60 m depth, this study established a framework for identifying optimal regions for salmon aquaculture in the Yellow Sea under current and two Shared Socioeconomic Pathway scenarios (SSP1-2.6 and SSP5-8.5) in the 2050s. These results suggest that most regions in the Yellow Sea under 40 m and 60 m depth are suitable for salmon farming at both current and future scenarios, the central region of the Yellow Sea under 20 m (38°N, 123°E) is the optimal site for salmon aquaculture in China. Overall, these findings provide valuable support for aquaculture management and can help stakeholders create an effective blueprint for adaptation strategies.

Molecular quantification of parasitic sea louse larvae depends on species and life stage.

Sea lice cause substantial economic and environmental harm to Norway's aquaculture industry and wild salmonid populations. Rapid, accurate quantification of lice larval densities in coastal waters remains the greatest bottleneck for providing empirical data on infestation risk within wild salmon habitats and aquaculture production regions. We evaluated the capability of droplet digital PCR (ddPCR) as an absolute quantification method for the planktonic stages of two parasitic louse species, Lepeophtheirus salmonis (Krøyer) and Caligus elongatus (von Nordman). Results demonstrated linear relationships between the DNA quantity measured and the number of spiked larvae for both species and life stages. However, L. salmonis contained a significantly greater number of DNA copies than C. elongatus individuals and for C. elongatus, nauplii displayed a significantly higher number of DNA copies than copepodids. Our results suggest that ddPCR can effectively enumerate louse larvae, but interpreting ddPCR results differ between the two louse species. Obtaining larval abundance estimates from marine plankton samples will depend on the nauplii to copepodid ratio for C. elongatus, but not for L. salmonis.

Andrographolide Alleviates Oxidative Damage and Inhibits Apoptosis Induced by IHNV Infection via CTSK/BCL2/Cytc Axis.

Infectious hematopoietic necrosis virus (IHNV) is an important pathogen that causes significant economic losses to salmon trout farming. Although vaccines have been invented for the treatment of IHNV, findings from our previous survey show that breeding enterprises and farmers require effective oral drugs or immune enhancers. However, studies on the development of oral drugs are limited. In the present study, we used bioinformatics methods to predict the protein targets of andrographolide (Andro) in IHNV. Cells were infected with IHNV, and the effect of andrographolide was explored by evaluating the expression levels of genes implicated in oxidative stress, activities of antioxidant enzymes, and the expression of genes implicated in apoptosis and necrosis. In the present study, cells were divided into NC, IHNV, IHNV+10 μM andrographolide, and IHNV+20 μM andrographolide groups. qRT-PCR was performed to determine the expression level of genes, and an antioxidant enzyme detection kit was used to evaluate the activities of antioxidant enzymes. Fluorescent staining was performed using a reactive oxygen species detection kit (ROS) and Hoechst 33342/PI double staining kit, and the mechanism of alleviation of apoptosis and oxidative stress andrographolide after IHNV infection was determined. The results indicated that andrographolide inhibits viral growth by binding to the NV protein of IHNV and increasing the antioxidant capacity of the body through the CTSK/BCL2/Cytc axis, thereby inhibiting the occurrence of IHNV-induced apoptosis. This is the first study to explore the antagonistic mechanism of action of andrographolide in alleviating IHNV infection. The results provide valuable information on alternative strategies for the treatment of IHNV infection during salmon family and provide a reference for the use of andrographolide as an antioxidant agent in agricultural settings.

Performance of biochemical tools as fish waste particle tracers in a dispersive marine system

As finfish aquaculture expands to more dispersive coastal environments, inputs of aquaculture-derived organic matter become more diffuse, but widespread. Significant amounts of organic material are likely to be exported beyond the near-farm area, where it may encounter sensitive habitats. Biochemical tracers of organic matter, such as stable isotopes and fatty acids may be useful tools for detecting diffuse waste deposition. We used numerical modelling of direct and resuspended farm waste deposition and empirical environmental measurements to evaluate a range of biochemical indicators (major nutrients, bulk stable isotopes, fatty acids, minor and trace elements) for their efficacy as particle tracers of fish waste around a shallow water (∼30 m) salmon farm, in a dispersive coastal farming area. We also compared their efficacy across a range of sampling approaches (in sediment trap material, sediment and Mytilus edulis as a bio-indicator). Elemental carbon, nitrogen and zinc indicators could accurately reflect predicted waste deposition close to the farm, but only terrestrial fatty acid indicators were able to reflect diffuse wastes farther afield suggesting they are more sensitive tracers of fish waste. Their performance as tracers also differed between sediment trap and sediment samples, with most performing better in sediment trap samples. Although translocated mussels showed evidence of fish waste assimilation in areas of high waste deposition, tissue concentrations of fish waste tracers correlated relatively poorly with modelled waste deposition. Our results highlight the sensitivity of terrestrial fatty acids as fish waste tracers for detecting diffuse waste deposition, and demonstrate that concentrations of a number of elements can be used for mapping acute waste deposition. Our findings can inform selection of biochemical tracers for improved monitoring and management of farm wastes in dispersive marine systems.

Evaluation of the protective efficiency of an autogenous Vibrio anguillarum vaccine in lumpfish (Cyclopterus lumpus) under controlled and field conditions in Atlantic Canada

Lumpfish (Cyclopterus lumpus) have become the predominant cleaner fish species used in North American salmon aquaculture. Vibrio anguillarum is a frequent pathogen of lumpfish in Atlantic Canada, and current vaccines against local isolates conferred low to moderate efficacy. This study evaluated the safety and efficiency of a V. anguillarum autogenous vaccine under controlled and field conditions. Two safety trials were conducted following the Canadian Food Inspection Agency (CFIA) regulations before field trial testing. The first safety trial was a common garden assay, and 250 PIT-tsgged lumpfish were used for five treatments per tank (PBS-negative control, Lab vaccine-positive control, autogenous intraperitoneal (IP) vaccine, autogenous dip vaccine, autogenous dip-IP boosted vaccine) in triplicates. Weight, gross pathology, and IgM titers were evaluated to determine the vaccine’s safety. After 10 weeks post-vaccination (wpv), lumpfish were bath-challenged with a lethal dose (1.24 x 106 CFU/mL) of V. anguillarum serotype O2. Survival rate, IgM titers, memory immune response, and cross-immune protection were evaluated. The second safety trial was conducted using a double vaccine dose in two groups, PBS and autogenous IP. The gross pathology score indicated a normal immune response without tissue damage, and no mortality nor fish health issues were observed in the immunized animals. The IP route of administration conferred the highest protection against the V. anguillarum challenge. The autogenous vaccine conferred long-term immunity but did not confer cross-protection against V. anguillarum serotype O1. To evaluate the efficiency of the autogenous vaccine under field conditions, 58,976 naïve lumpfish (8-10 g) were IP immunized with either the autogenous vaccine or the commercial Forte micro IV vaccine. After 7 wpv, the lumpfish were equally distributed into eight sea cages and co-cultivated with Atlantic salmon smolts (60,000 per cage). Lumpfish IgM titers, tissue bacterial loads, mortality, and sea lice count on salmon were monitored. The autogenous vaccine and Forte vaccine confer acceptable protection to the lumpfish in sea cages. No significant difference was observed between lumpfish vaccinated with autogenous and commercial vaccines under field conditions.

Modelling assessment of how small-scale vertical movements of infectious sea lice larvae can affect their large-scale distribution in fjordic systems

Sea lice are ectoparasites that can be found in high numbers in and around salmon farms, where they are a threat to fish health and can induce high aquacultural costs. Large numbers of suitable hosts facilitate the infection and subsequent release of their planktonic larvae in the surrounding environment where they can potentially infect wild salmonids, including migrating juvenile fish (smolts). Investigating sea lice spatial distribution is generally done using coupled hydrodynamic and particle tracking models. The quality of these numerical tools is critical to identify areas of higher infection risk to valuable wild salmon populations and thus support sustainable salmon aquaculture. While the transport of salmon lice is mainly affected by physical processes, biological behaviours such as vertical swimming can also play an important role. However, a review of previous sea lice studies shows no clear consensus on their swimming abilities and the parameters implemented in sea lice dispersion modelling. Here, we focus on the Diel Vertical Migration (DVM) behaviour, a vertical migration that sea lice perform within a daily cycle. Our sensitivity study of the infectious copepodid phase of sea lice highlights how their retention potential and spatial distribution within a water body are affected by their vertical swimming velocity and maximum swimming depth. In a fjordic system (Loch Linnhe on the West Coast of Scotland), the vertical position of sea lice can affect their horizontal trajectory due to the two-layer exchange flow of the estuarine circulation. At the surface, transport is mainly due to the wind driven circulation, and the residual seaward current. Lower in the water column, the saltier shelf water is drawn into the sea loch. This can potentially increase the retention of sea lice if they dive deep enough to reach those opposing subtidal currents. Therefore, lack of confidence in sea lice DVM parameterisation may introduce inaccuracy in modelled sea lice distribution. Effective sea lice management in aquaculture would benefit from more observational data like farm sea lice count, sea lice swimming laboratory observations, field observation of sea lice vertical distribution and accurate sea lice quantification in the field. This would help to reduce uncertainties derived from sea lice vertical swimming behaviour parameterisation in lice dispersal models.

New wine in old bottles: Modification of the Na+/K+‐ATPase enzyme activity assay and its application in salmonid aquaculture

AbstractThe Na+, K+ ATPase (NKA) enzyme is important to generate the transmembrane ion gradient in the gills, intestine, and kidneys, hence, is vital for secondary transport of fluids and different solutes in teleosts. Gill NKA enzyme activity is often used as a proxy for parr–smolt transformation (PST) during which anadromous salmonids prepare for seawater (SW). Increased intensification and production of larger smolts in modern salmonid aquaculture has resulted in reports of gill NKA activity being less reliable as a proxy for smolt quality. Consequently, changes in mRNA nka‐α1b/α1a ratios in gills are increasingly used as indicators of PST. However, nka isoform mRNA abundance may not reflect translation into the functional protein, nor the activity of the mature enzyme. This may limit the predictive power of molecular markers under certain environmental conditions, rearing regimes and biological scenarios. During PST, the osmoregulatory transformations necessary for SW tolerance and survival does not only occur in the gills. Equally important are the changes in ion transporting activities, including NKA activity, in the intestine and kidneys. However, to our knowledge, there are no previous studies addressing the timing and concurrent changes in NKA activity in the three osmoregulatory tissue during PST. Here we present modifications and optimization of the NKA enzyme activity protocols for gill, intestinal and kidney tissue and outline how to best utilize NKA activity measurements as part of a more holistic approach to evaluate overall smolt quality in modern aquaculture.

Systemic immune response of rainbow trout exposed to Flavobacterium psychrophilum infection

Bacterial cold-water disease (BCWD) caused by Flavobacterium psychrophilum is one of the most serious bacterial diseases leading to significant economic loss for rainbow trout (Oncorhynchus mykiss) aquaculture. However, little is known about the systemic immune response of rainbow trout against F. psychrophilum infection. This study investigated the immune response of rainbow trout to F. psychrophilum infection using multiple experiments, including bacterial load detection, phagocyte activity assessment, enzyme activity evaluation, and gene expression profiling. Results showed that the spleen index and intestinal pathogen load reached a peak at 3 days post-infection, with strong pro-inflammatory gene expression observed in rainbow trout. Leukocytes RBA and PKA were significantly elevated in the spleen, blood and intestine at 7 days post-infection. Heat map analysis demonstrated that the spleen had a more substantial pro-inflammatory response compared to the intestine post-infection and exhibited higher expression levels of immune-related genes, including IgM, il1β, il6, cd4, cd8a, cd8b, c1q, chathelicidin, inos, and lysozyme. Both Th1 and Th2 polarized responses in the spleen were activated, with Th2 (il4/13a, gata3) (FC > 4) being more intense than Th1 (tnfα, t-bet) (FC > 2). Tight junction proteins exhibited down-regulation followed by up-regulation post-infection. Collectively, the results of this study expand our current understanding of the immune response of rainbow trout post F. psychrophilum infection but also provide new avenues for investigation in salmonid aquaculture.

Antigenic similarities and clinical cross-protection between variant and classic non-viscous strains of Moritella viscosa in Atlantic salmon in Norway

Moritella viscosa (M. viscosa) is one of the major etiological agents of winter-ulcers in Atlantic salmon (Salmo salar) in Norway. Outbreaks of ulcerative disease in farmed fish occur across the North Atlantic region, causing reduced animal welfare and economical challenges, and are of hindrance for sustainable growth within the industry. Commercially available multivalent core vaccines containing inactivated bacterin of M. viscosa reduce mortality and clinical signs related to winter ulcer disease. It has previously been described two major genetic clades within M. viscosa, typical (hereafter referred to as classic) and variant, based on gyrB sequencing. In addition, there are phenotypical traits such as viscosity that may differ between different types of isolates. Western blot using salmon plasma showed that classic non-viscous strains are antigenically different from the classic viscous type included in core vaccines. Further, Western blot also showed that there are similarities in binding patterns between Norwegian variant and classic non-viscous isolates, indicating they may be antigenically related. Vaccination-challenge trials using Norwegian gyrB-classic non-viscous isolates of M. viscosa, demonstrate that the isolates from the classic clade that are included in current commercial multivalent core vaccines, provide limited cross protection against the emerging non-viscous strains. However, a vaccine recently approved for marketing authorization in Norway, containing inactivated antigen of a variant M. viscosa strain, demonstrates reduced mortality as well as clinical signs caused by infections with the classic non-viscous M. viscosa isolated from outbreaks in Norwegian salmon farms. The study shows that there are antigenic similarities between variant and classic non-viscous types of M. viscosa, and these similarities are mirrored in the observed cross-protection in vaccination-challenge trials.