Harald Sveier

Seaweed aquaculture has experienced significant expansion in recent decades, with global production reaching 34.7 million tonnes in 2020, driven by advancements in cultivation techniques and diverse commercial applications. Europe, and Scandinavian countries such as Norway, are seeing increasing interest. Norwegian seaweed farming is concentrated in the south, and although it faces unique challenges in the north it also has growth potential in northern sites. In this study, a comparison was made of growth rates and biochemical composition of Saccharina latissima grown on farms in southern (Bergen) and northern (Tromsø) Norway. Although, Bergen experiences higher temperatures but less daylight availability than Tromsø, the mean length of S. latissima sporophytes at the two sites did not show a statistically significant difference. Despite generally similar biomass production between the two sites, biochemical analysis revealed significant differences in protein and tissue nitrogen content, with Bergen having higher levels. Iodine content was not significantly different between the sites. This study showed relatively high single-season yields in both Bergen and Tromsø, with Tromsø potentially higher if optimal protocols are followed. Environmental factors like light and temperature significantly affect yields, with faster growth in the north most likely due to the 24-h light periods and northern sites also experience delayed biofouling. The study suggests strong commercial potential for seaweed aquaculture across Norway, with regional differences that can be strategically exploited.

Studying host–microbiota interactions through the perspective of the hologenome is gaining interest across all life sciences. Intestinal parasite infections are a huge burden on human and animal health; however, there are few studies investigating the role of the hologenome during parasite infections. We address this gap in the largest multi-omics fish microbiota study to date using natural cestode infection of farmed Atlantic salmon. We find a clear association between cestode infection, salmon lifetime growth, and perturbation of the salmon gut microbiota. Furthermore, we provide the first evidence that the genetic background of the host may partly determine how the gut microbiota changes during parasite-associated dysbiosis. Our study therefore highlights the value of a hologenomic approach for gaining a more in-depth understanding of parasitism.

Using low trophic marine resources such as sugar kelp (Saccharina latissimi) is of great interest to increase the circular food production in the ocean. Sugar kelp does, however, contain high levels of carbohydrates and iodine and does not have considerable levels of protein and lipids, which may make it less suitable as a feeding ingredient. A 10-week feeding trial was done to investigate the effect of graded dietary inclusion levels of fermented sugar kelp (FSK), on growth performance, digestibility, retention of nutrients, and mineral composition in postsmolt Atlantic salmon (Salmo salar L.). The experimental diets were made to simulate a standard grower feed for salmon postsmolts in SW with 63 plant-based ingredients vs 34 marine ingredients and increasing concentrations of FSK between 0 (control feed) and 4 of the diet. During the feeding trial, the weight gain and specific growth rate (SGR) decreased linearly with increasing dietary FSK levels, where the SGR was slightly reduced from 1.2 for the fish given the control feed to 1.1 in the fish given feeds containing 3 and 4 FSK. This resulted in a lower weight gain of up to 9 in the fish given 4 FSK compared to the control. Feed intake and feed conversion ratio were, however, similar in all diet groups, and FSK inclusion did not influence the digestibility of macronutrients or minerals, except for lipid. The reduced growth is likely related to a lower digestible energy level in the diets, and the retention of both lipids and energy was affected by FSK inclusion. Inclusion of FSK also influenced iodine availability and retention, as well as increasing iodine status in whole body and muscle in a dose-dependent manner until reaching a plateau, which corresponds to 124mgIkg⁻¹ WW (135mgIkg⁻¹ DW), at 3 FSK inclusion.

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.

Salmonids are important sources of protein for a large proportion of the human population. Interaction between the gut microbiota and host has been shown to affect the host phenotype in mammals, but relatively little is known about microbiota-host interaction in fish. Mycoplasma species are a major constituent of the gut microbiota of salmonids, often representing the majority of microbial cells. Despite the frequent reported dominance of intestinal Mycoplasma species, very little is known about their phylogenetic placement, functions and potential evolutionary relationships with their salmonid hosts.In this study, we utilise 2.9 billion metagenomic reads generated from 12 samples from three different salmonid host species to I) characterise and curate the first metagenome-assembled genomes (MAGs) of Mycoplasma dominating the intestines of three different salmonid species, II) establish the phylogeny of these salmonid candidate Mycoplasma species using known Mycoplasma genomes, III) perform a comprehensive pangenomic analysis of Mycoplasma, IV) decipher the putative functionalities of the salmonid MAGs and reveal specific functions expected to benefit the host.Our data provide a basis for future studies examining the composition and function of the salmonid microbiota, with a potential for being further exploited in order to increase animal health and growth in aquaculture.

Three feeds with different physical pellet quality but the same formulation were fed to Atlantic salmon for 97 days. Pellet quality was measured as bulk density, durability, fat leakage, hardness, water stability and porosity. The largest difference among the feeds was measured in hardness (201, 236 and 86 Newton for Diet 1, Diet 2 and Diet 3 respectively). The relative feed intake was highest in salmon fed Diet 2 and Diet 3 with no effects of pellet hardness. Growth and feed efficiency ratio were similar among all fish. The apparent digestibility of energy, dry matter, nitrogen and lipid was similar for all feeds, whereas the apparent digestibility of phosphorus and zinc was the lowest in Diet 3. Retention of energy, lipid and nitrogen was also similar for all feeds. Salmon fed Diet 1 and Diet 3 retained more phosphorus than those fed Diet 2. An increased retention of the digested zinc was found in salmon fed Diet 3. This study concludes that physical pellet quality affects feed intake and improve utilisation of feed in salmon if optimised properly. Moreover, pellet hardness can be optimised in commercial scale without compromising feed intake as it has no influence on feed intake.

The prevalence of type 2 diabetes (T2D) is low in populations with a high fish intake; however prospective studies with fish intake have shown positive, negative or no association between fish intake and the risk for T2D. The aim of this study was to investigate the effects of high intake of lean or fatty fish on glucose tolerance, leucocyte membrane fatty acid composition and leucocyte function in overweight/obese adults. In this randomised clinical trial, sixty-eight healthy overweight/obese participants consumed 750 g/week of either lean or fatty fish as dinners, or were instructed to continue their normal eating habits but to avoid fish intake (control group), for 8 weeks. Energy and macronutrient intake and physical activity were not changed within the groups during the study period. High intake of fatty fish, but not of lean fish, significantly improved glucose regulation 120 min postprandially (P=0·012), but did not affect fasting glucose concentration. A smaller increase in fasting to 120 min postprandial insulin C-peptide concentration was seen after fatty fish intake (P=0·012). Lean fish increased the DHA content in leucocyte membranes (P=0·010), and fatty fish increased the total content of n-3 PUFA (P=0·00016) and reduced the content of n-6 PUFA (P=0·00057) in leucocyte membranes. Lean and fatty fish intake did not affect phagocytosis of bacteria ex vivo. The findings suggest that high intake of fatty fish, but not of lean fish, beneficially affected postprandial glucose regulation in overweight/obese adults, and may therefore prevent or delay the development of T2D in this population.

Melanised focal changes (black spots) are common findings in the white skeletal muscle of seawater-farmed Atlantic salmon (Salmo salar). Fillets with melanised focal changes are considered as lower quality and cause large economic losses. It has been suggested that red focal changes (red spots) precede the melanised focal changes. In the present work, we examined different populations of captive and wild salmon for the occurrence of both types of changes, which were investigated for the presence of different viruses by immunohistochemistry and RT-qPCR. The occurrence of red or melanised foci varied significantly between the populations, from none in wild fish control group, low prevalence of small foci in fish kept in in-house tanks, to high prevalence of large foci in farm-raised salmon. Large amounts of Piscine orthoreovirus (PRV) antigen were detected in all foci. No other viruses were detected. Red focal changes contained significantly higher levels of PRV RNA than apparently non-affected areas in white muscle of the same individuals. Some changes displayed a transient form between a red and melanised pathotype, indicating a progression from an acute to a chronic manifestation. We conclude that PRV is associated with the focal pathological changes in the white muscle of farmed Atlantic salmon and is a premise for the development of focal melanised changes.