In the Northwest Atlantic Ocean, northern shrimp (Pandalus borealis) play key ecological roles as mid-trophic level consumers and as prey to higher-trophic level predators, including commercial fish species. However, the effects of changing environmental conditions and biological processes on trophic interactions in sub-Arctic ecosystems, particularly on lipid storage and nutrient transfer from intermediate to high trophic levels, remain unclear. Biochemical tracer methods (i.e., fatty acids and stable isotopes) were employed to study the trophic ecology and stage-specific nutritional condition of P. borealis across different spatial and seasonal scales. Trophic markers indicated significant contributions from both diatoms and zooplankton to the diet of P. borealis and highlighted the adaptability of this species to opportunistic feeding strategies based on sinking phytodetritus. Our results revealed a strong seasonality in the lipid composition of P. borealis, with lipid dynamics being highly influenced by environmental conditions and resource availability. The primary lipid classes in P. borealis were storage triacylglycerols, accounting for over 50% of lipids observed, followed by membrane phospholipids. Eggs from ovigerous females exhibited the highest concentrations of total lipids and essential fatty acids, such as omega-3 fatty acids, underscoring the important ecological role of eggs in sub-Arctic food webs by providing high-quality lipid sources. Additionally, our findings indicated an increase in the total lipid content of shrimp eggs from spring to summer, suggesting that the early stages of P. borealis are vulnerable to changes in the timing of seasonal primary production, when females store large reserves of energy-rich lipids. This study highlights the large seasonal and temporal variability in the nutritional status of P. borealis and underlines the importance of understanding lipid dynamics in assessing the resilience of populations to environmental changes.

This study was done to appraise the effects of the combination of dietary Gracilaria pulvinata and Sargassum ilicifolium on growth, immunity, and fatty acid profile in Asian seabass (Lates calcarifer). A total of 540 juveniles (36.06 ± 0.05 g) were stocked into eighteen 200 L tanks and divided into six experimental treatments, each in triplicate. Fish were fed diets containing 0 (control), 3% (SW3), 6% (SW6), 9% (SW9), 12% (SW12), and 15% (SW15) mixtures of both seaweeds powder in equal proportions (1 : 1) for 56 days. There was no improvement in weight gain parameters. Serum lysozyme and peroxidase activities in SW9 and SW12 treatments were significantly higher in compare to other treatments. The highest activities of skin mucus lysozyme, alkaline phosphatase, and total protease were observed in the SW12. Liver igf-1, il-1β, il-8, and lysozyme expression showed a rising trend up to SW9 and then decreased. Liver antioxidant enzymes activity and glutathione content showed a similar pattern of changes. Liver total antioxidant capacity was highest in the SW9 treatment, while the lowest value of liver malondialdehyde was observed in the 12% seaweed treatment. The amount of total n‐3 polyunsaturated fatty acids, especially docosahexaenoic acid, was higher in the SW12 and SW15 treatments in compare to others. Our findings suggest that adding 9%–12% of Gracilaria and Sargassum seaweed powder to the diet improves serum and mucosal immunity, antioxidant status, and fatty acid profile in L. calcarifer juveniles.

We used lipid, fatty acid, and stable isotope analyses to investigate variation, over nine months, in the trophodynamics of 10 dominant cryptofaunal, macroalgal/algal, and environmental components from two sites within a rhodolith (Lithothamnion glaciale) bed in southeastern Newfoundland (Canada). There was an overall shift from a diatom-based food web following the spring phytoplankton bloom to a kelp/algae-based food web during fall, accompanied by preferred use of EPA (20:5ω3) over DHA (22:6ω3) in most cryptofauna. The food web contained three trophic levels that encompassed: (1) direct feeding relationships from primary producers (e.g., rhodoliths, macroalgae) to second-order consumers (e.g., sea stars, polychaetes); (2) trophic subsidy from within and outside the rhodolith bed via settlement, resuspension, and consumption of macroalgal fragments and other detrital organic matter; and (3) strong pelagic/benthic coupling. Riverine input did not affect cryptofaunal diets, as shown by the lack of terrestrial biomarkers at the study site nearest to the riverine input, and there were minor differences in trophodynamics between both study sites. The present study’s findings, applicable to relatively broad spatial and temporal domains, as well as those of complementary studies of the same rhodolith bed, uncover high spatio-temporal stability of the rhodolith bed framework and of resident cryptofaunal abundance, diversity, and trophodynamics.

Mass mortality events (MMEs) are defined as the death of large numbers of fish over a short period of time. These events can result in catastrophic losses to the Atlantic salmon aquaculture industry and the local economy. However, they are challenging to understand because of their relative infrequency and the high number of potential factors involved. As a result, the causes and consequences of MMEs in Atlantic salmon aquaculture are not well understood. In this study, we developed a structural network of causal risk factors for MMEs for aquaculture and the communities that depend on Atlantic salmon aquaculture. Using the Interpretive Structural Modeling (ISM) technique, we analysed the causes of Atlantic salmon mass mortalities due to environmental (abiotic), biological (biotic) and nutritional risk factors. The consequences of MMEs were also assessed for the occupational health and safety of aquaculture workers and their implications for the livelihoods of local communities. This structural network deepens our understanding of MMEs and points to management actions and interventions that can help mitigate mass mortalities. MMEs are typically not the result of a single risk factor but are caused by the systematic interaction of risk factors related to the environment, fish diseases, feeding/nutrition and cage-site management. Results also indicate that considerations of health and safety risk, through pre- and post-event risk assessments, may help to minimize workplace injuries and eliminate potential risks of human fatalities. Company and government-assisted socio-economic measures could help mitigate post-mass mortality impacts. Appropriate and timely management actions may help reduce MMEs at Atlantic salmon cage sites and minimize the physical and social vulnerabilities of workers and local communities.

The immunomodulatory effects of omega-3 and omega-6 fatty acids are a crucial subject of investigation for sustainable fish aquaculture, as fish oil is increasingly replaced by terrestrial vegetable oils in aquafeeds. Unlike previous research focusing on fish oil replacement with vegetable alternatives, our study explored how the omega-6 to omega-3 polyunsaturated fatty acid (PUFA) ratio in low-fish oil aquafeeds influences Atlantic salmon's antiviral and antibacterial immune responses. Atlantic salmon were fed aquafeeds rich in soy oil (high in omega-6) or linseed oil (high in omega-3) for 12 weeks and then challenged with bacterial (formalin-killed Aeromonas salmonicida) or viral-like (polyriboinosinic polyribocytidylic acid) antigens. The head kidneys of salmon fed high dietary omega-3 levels exhibited a more anti-inflammatory fatty acid profile and a restrained induction of pro-inflammatory and neutrophil-related genes during the immune challenges. The high-omega-3 diet also promoted a higher expression of genes associated with the interferon-mediated signaling pathway, potentially enhancing antiviral immunity. This research highlights the capacity of vegetable oils with different omega-6 to omega-3 PUFA ratios to modulate specific components of fish immune responses, offering insights for future research on the intricate lipid nutrition-immunity interplay and the development of novel sustainable low-fish oil clinical aquaculture feeds.

Large-scale mortality events have occurred during the winter in Atlantic salmon sea cages in Eastern Canada and Iceland. Thus, in salmon held at 3 °C that were apparently healthy (i.e., asymptomatic) and that had ‘early’ and ‘advanced’ symptoms of ‘winter syndrome’/’winter disease’ (WS/WD), we measured hepatic lipid classes and fatty acid levels, and the transcript expression of 34 molecular markers of fatty liver disease (FLD; a clinical sign of WS/WD). In addition, we correlated our results with previously reported characteristics associated with this disease’s progression in these same individuals. Total lipid and triacylglycerol (TAG) levels increased by ~50%, and the expression of 32 of the 34 genes was dysregulated, in fish with symptoms of FLD. TAG was positively correlated with markers of inflammation (5loxa, saa5), hepatosomatic index (HSI), and plasma aspartate aminotransferase levels, but negatively correlated with genes related to lipid metabolism (elovl5b, fabp3a, cd36c), oxidative stress (catc), and growth (igf1). Multivariate analyses clearly showed that the three groups of fish were different, and that saa5 was the largest contributor to differences. Our results provide a number of biomarkers for FLD in salmon, and very strong evidence that prolonged cold exposure can trigger FLD in this ecologically and economically important species.

There is limited ability to biosynthesize long-chain omega-3 fatty acids such as EPA and DHA in food webs leading to humans. Seafood is the key source of ω3 LC-PUFA, with aquaculture expected to meet rising global demand; however, marine fish have a high dietary requirement for EPA and DHA themselves. This was traditionally met using unsustainable dietary fish oil and fish meal, but limited supply and environmental concerns have dictated research on replacements. Among the industrial sources of EPA and DHA, microalgae and especially thraustochytrids stand out as resources with high concentrations. Although unicellular, thraustochytrids are not microalgae as they are not photosynthetic but instead are microheterotrophs. This removes the light requirement and facilitates high yields of monoculture for the production of single-cell oils. The availability, in high concentrations, of usually one or the other essential fatty acid permits a calibration of the EPA and DHA dose, which is especially useful as their effects have mainly been considered together in medical and aquaculture research. EPA and DHA have different effects on cell function and are precursors of different bioactive compounds. Using thraustochytrids, microalgae, and heterotrophic dinoflagellates, the importance of DHA has been investigated. DHA was essential for optimizing the growth of the early life stages of scallops and finfish and was preferentially incorporated into fish membrane phospholipids. The production of microalgae and microheterotrophs can contribute to the treatment of wastewater and waste gas, further enhancing their sustainability and reducing the environmental costs of aquaculture.

The aim of this study was to evaluate the impacts of dietary Gracilaria spp. and Sargassum spp. on growth, immunity, antioxidant status, and fatty acid composition of Sobaity seabream (Sparidentex hasta). A total of 540 Sobaity seabream juveniles (19.6 ± 0.5 g) were stocked into 18 tanks (300 L) and divided into six groups (three replicates per group). Fish were fed diets containing 0 (control), 3

Polar marine ecosystems are undergoing major transformations due to climate change. Alterations of the physical and chemical growth conditions for plankton are likely to propagate through the food web, potentially having major consequences for the animals that Inuit harvest for subsistence. These alterations can impact the nutritional qualities of plankton through physiological responses or indirectly via changes in the taxonomic composition of assemblages. This study focuses on lipids, which provide a vital source of energy in cold waters, and on essential fatty acids (EFA), such as omega-3 and omega-6 FA, which are necessary for the function, growth, and reproduction of organisms. To better understand how EFA propagate and accumulate in the lower food web, we compared the fatty acid composition of phytoplankton and copepods across a large portion of the western Arctic. The bulk lipid profiles of copepod assemblages were determined largely by their taxonomic composition, but specific fatty acid groups (e.g., omega-6 and saturated fatty acids) exhibited strong correlations with water properties (e.g., pH, salinity). A comparative analysis of specific fatty acids suggests that the animals accumulate eicosapentaenoic acid (EPA) but metabolize its precursors, although these processes were not measured directly. The proportions of EPA, docosahexaenoic acid, and specific omega-7 FA (e.g., 16:1ω7) were much higher in copepods than in phytoplankton, and a fatty acid diatom marker accounted for over 45% of the fatty acid pool in copepods. The positive relationship between proportions of this marker in copepods and phytoplankton implies that the fatty acid content of copepods is influenced primarily by recent feeding. These results underscore the importance of long-lived subsurface chlorophyll maxima for trophic transfers of EFA in the strongly stratified waters of the Pacific-influenced sector of the Arctic Ocean and question the paradigm that copepods rely principally on brief surface blooms to rapidly store lipids for the following winter.

The continuous growth of aquaculture places a growing demand on alternative sources of fish oil (FO). Certain microorganisms provide a sustainable replacement for FO due to their content of EPA and DHA, which are essential for fish health. Appreciable evidence shows that changes in feeding sources may alter the nutritional components of salmon; however, the influence of diets on lipid species remains unclear. In this study, the identification and semi-quantification of lipid molecular species in salmon muscle during feeding with a microbial oil (MO) were carried out by focusing on triacylglycerol (TAG) and diacyl-phospholipid using shotgun-based mass spectrometry analysis. DHA in the MO diet was efficiently incorporated into phospholipid structures on feeding, followed by accumulation in salmon muscle. The MO diet elevated the level of certain EPA-containing TAGs, such as TAG C52:5 (16:0_16:0_20:5) and TAG C54:6 (16:0_18:1_20:5), indicating that the MO diet may be an excellent source for enhancement of the abundance of ω3 lipids. Further, prostaglandins (PGs) PGE2 and PGF3α were identified and quantified for the first time in salmonid tissue.

Microalgae are the main source of the omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), essential for the healthy development of most marine and terrestrial fauna including humans. Inverse correlations of algal EPA and DHA proportions (% of total fatty acids) with temperature have led to suggestions of a warming-induced decline in the global production of these biomolecules and an enhanced importance of high latitude organisms for their provision. The cold Arctic Ocean is a potential hotspot of EPA and DHA production, but consequences of global warming are unknown. Here, we combine a full-seasonal EPA and DHA dataset from the Central Arctic Ocean (CAO), with results from 13 previous field studies and 32 cultured algal strains to examine five potential climate change effects; ice algae loss, community shifts, increase in light, nutrients, and temperature. The algal EPA and DHA proportions were lower in the ice-covered CAO than in warmer peripheral shelf seas, which indicates that the paradigm of an inverse correlation of EPA and DHA proportions with temperature may not hold in the Arctic. We found no systematic differences in the summed EPA and DHA proportions of sea ice versus pelagic algae, and in diatoms versus non-diatoms. Overall, the algal EPA and DHA proportions varied up to four-fold seasonally and 10-fold regionally, pointing to strong light and nutrient limitations in the CAO. Where these limitations ease in a warming Arctic, EPA and DHA proportions are likely to increase alongside increasing primary production, with nutritional benefits for a non-ice-associated food web.

Lipids are key compounds in the transfer of energy and nutrients in marine food webs. Specifically, neutral lipids are the main reservoir of dietary energy in most marine animals and are often used as indicators of nutritional condition. In contrast, polar lipids, including acetone-mobile polar lipids and phospholipids, are key structural components of cell membranes. Here, we explored the fatty acid (FA) composition across the neutral and polar lipid fractions in benthic organisms belonging to five major phyla (Arthropoda, Cnidaria, Echinodermata, Mollusca, and Porifera), which were collected from a deep-water region in the Northwest Atlantic. Overall, the FA composition of acetone-mobile polar lipids (e.g., glycolipids) and phospholipids was more similar to each other and characterized by higher proportions of saturated FA (e.g., 16:0) compared to that of neutral lipids. This result reflected the different functions (structural vs storage) of these lipid fractions. Furthermore, independently of the taxon, monounsaturated FA (e.g., 16:1ω7, 18:1ω9) were dominant in neutral lipids, suggesting their preferential utilization for energy production. Whereas several species, including the gastropod Buccinum sp., retained the essential polyunsaturated FA (i.e., ω3 and ω6 FA) in their neutral lipids, others, such as the crustacean Pasiphaea tarda and the echinoderm Phormosoma placenta incorporated them into their polar lipids, pointing to differences in the metabolism of essential FA across species. These findings highlight the value of quantifying differences among lipid fractions. Last, the relatively high content of essential FA in neutral lipids of most species suggested a dietary surplus indicating a healthy, productive food web.

A 12-week feeding trial examined the dietary impact of replacing fishmeal (FM) with algal biomass (AB) derived from Pavlova sp. strain CCMP459 (Pav459) in Atlantic salmon diets. Three distinct diets were formulated: a control diet featuring 20% FM and 7% fish oil (FO), an experimental diet incorporating a 50:50 blend of FM and AB Pav459 and reduced FO (10% FM; 4.5% FO; 10% AB), and a second experimental diet with full replacement of FM with AB Pav459 and further reduction in FO (1.75% FO; 20% AB). Replacing FM with AB Pav459 showed no significant effects on the growth performance of Atlantic salmon. Fish across all diets exhibited growth exceeding 200% from their initial weight. Analysis of total lipid content after the 12-week trial revealed no significant differences among the diets. However, individual proportions of omega-3 (ω3) and omega-6 (ω6) fatty acids varied. Fatty acid profiling in muscle and liver tissues showed distinct compositions reflective of dietary treatments. Linoleic acid (LA) and α-linolenic acid (ALA) exhibited higher proportions in total fatty acids than in membrane lipids. Docosahexaenoic acid (DHA) emerged as the predominant fatty acid in the membranes of both liver and muscle tissues. Furthermore, an analysis of sterol composition in Pavlova and salmon muscle tissue showed the presence of important sterols, including conventionally animal-associated cholesterol. This emphasizes the suitability of microorganisms, such as Pav459, for synthesizing diverse nutrients. Stable isotope analysis demonstrated direct incorporation of eicosapentaenoic acid (EPA) and DHA from diets into salmon tissues. Notably, minimal biosynthesis from the precursor ALA was observed, reaffirming the utility of Pav459-derived fatty acids. The EPA+DHA proportions in the fillet consistently met daily human consumption requirements across all dietary conditions, supporting the use of Pav459 algal biomass as an alternative to FM.

An understanding of genetic differences in fitness-related traits for farm, wild, and hybrid Atlantic salmon (Salmo salar) is key for predicting impacts of aquaculture escapes on wild populations. Here we used lipid and fatty acid (FA) analyses to investigate differences in storage and foraging ability among Atlantic salmon juveniles of three cross types (farm, wild, and F1 hybrids), at the beginning and end of a common garden experimental release in the Newfoundland wild. We found differences in lipid class and FA profiles among cross types at both release and recapture, with farm fish being the most differentiated at recapture. In addition, low recapture levels of triacylglycerols and certain FAs indicative of freshwater prey suggest the possibility of a feeding disadvantage for farm fish. Overall, we show that lipid and FA profiles in juvenile salmon can change over just a short period of time even under favourable conditions in the wild, and farm fish may have genetic differences affecting energy acquisition and storage that could negatively impact their survival and fitness in the longer term.

The aim of this work was to evaluate the impact of adding Gracilaria spp. and Sargassum spp. to diets on growth performance and resistance to hypoxia stress in Asian seabass. The fish (36.06 ± 0.05 g) were stocked in 18 tanks (200 L), divided into six experimental groups and fed diets containing 0 (control), 3 % (SW3), 6 % (SW6), 9 % (SW9), 12 % (SW12) and 15 % (SW15) Gracilaria and Sargassum mixture in equal proportions for 56 days. Each group consisted of three tanks. Fish were exposed to air for 1 min (hypoxia) and the recovery rate of fish was monitored for 24 h. Results showed that final weight, weight gain, and specific growth rate (SGR) of fish fed the dietary seaweed mixture up to 12 % were significantly higher than fish fed 15 % seaweed powder. Fish fed the 9 % and 12 % seaweed mixture also showed a significantly lower feed conversion ratio (FCR) than the SW15 group. Serum cortisol was significantly higher in the control and lowest in the 12 % seaweed group 6 h post-stress. Hypoxia stress led to significant increases in cortisol values in all fish, but the dietary Gracilaria and Sargassum mixture significantly reduced cortisol values in the SW9 and SW12 groups at 24 h post-stress. Before and 1 h and 24 h after hypoxia, fish fed the 9 % and 12 % seaweed mixture showed significantly lower glucose than the SW15 and control groups. Moreover, serum lactate in the 6–12 % seaweed groups was significantly lower than the control fish at 24 h post-stress. Overall, dietary seaweed showed anti-stress properties and the dietary Gracilaria and Sargassum mixture at levels of 9–12 % increased resistance to hypoxia stress in fish. The present results showed that seaweed (Gracilaria and Sargassum mixture) up to 12 % level is useful in the diet of juvenile Asian seabass.

A 16-week feeding trial was conducted to investigate effects of replacing dietary fish oil (FO) with docosahexaenoic acid (DHA)-rich microbial oil (MO) from Schizochytrium sp. (T18) on membrane lipid composition of Atlantic salmon parr liver and muscle tissues. Four nutritionally balanced diets were formulated with varying levels of FO, MO, and canola oil (CO), including a control diet with 20% FO, a secondary control diet with 10% FO and 10% CO, and two experimental diets that completely replaced FO with a low (5%) and high (10%) proportion of MO. No significant differences were observed in growth parameters (81–98 g; weight gain), total lipid class composition, and total sterol content among the dietary treatments. However, there were significant differences in the proportions of individual ꞷ3 and ꞷ6 fatty acids in both liver and muscle tissues, reflecting the different dietary treatments. Notably, the presence of low eicosapentaenoic acid (EPA) in the MO diets did not affect the growth performance of the fish, suggesting a lower requirement for EPA in the diet and a greater necessity for DHA. The results also showed that DHA was present in very high proportions in the cellular membrane, particularly in muscle tissue, with low levels of linoleic acid and alpha-linolenic acid. Overall, the findings suggest that MO derived from Schizochytrium sp. (T18) could be a potential substitute for FO in the diet of farmed Atlantic salmon.

Abstract In the environment, algae are exposed to non-optimal conditions and adapt their physiology to cope with adverse conditions, such as limiting nutrients or excess contaminants. The present study evaluated the changes in photosynthetic parameters and lipid classes of the freshwater green microalga Ankistrodesmus densus exposed to nitrogen (N) limitation and cadmium (Cd) exposure. While N is required for the algal metabolism, Cd does not present known functions in freshwater microalgae. Our results indicate that the growth rate was more affected by metal than by the nutrient. At the same time, the quenchings, i.e., fractions of light energy driven to photochemical or non-photochemical processes of photosynthesis, were not affected under the N limitation. However, in the combination of the two stressors, the changes were more pronounced, suggesting a synergism in the growth rate, chlorophyll a production, photochemical quenching (qP), and effective quantum yield ((Y(II)). While Cd did not affect any lipid classes, the percentage of storage lipids (triacylglycerol) was increased under N limitation and in some of the combinations of N limitation and Cd. However, in the combination of the stressors, there were some non-linear changes in structural lipids (phospholipids) and a decrease in acetone mobile polar lipids. Our data indicate that the combination of the two stressors affected algal physiology with synergism in several parameters. However, the algal photoprotective mechanisms effectively avoided photodamage, as indicated by non-photochemical quenchings (qN and NPQ) and in the quantum yield related to regulated energy loss Y (NPQ) values.

We investigated the immunomodulatory effect of varying levels of dietary ω6/ω3 fatty acids (FA) on Atlantic salmon (Salmo salar) antibacterial response. Two groups were fed either high-18:3ω3 or high-18:2ω6 FA diets for 8 weeks, and a third group was fed for 4 weeks on the high-18:2ω6 diet followed by 4 weeks on the high-18:3ω3 diet and termed “switched-diet”. Following the second 4 weeks of feeding (i.e., at 8 weeks), head kidney tissues from all groups were sampled for FA analysis. Fish were then intraperitoneally injected with either a formalin-killed Renibacterium salmoninarum bacterin (5 × 107 cells mL−1) or phosphate-buffered saline (PBS control), and head kidney tissues for gene expression analysis were sampled at 24 h post-injection. FA analysis showed that the head kidney profile reflected the dietary FA, especially for C18 FAs. The qPCR analyses of twenty-three genes showed that both the high-ω6 and high-ω3 groups had significant bacterin-dependent induction of some transcripts involved in lipid metabolism (ch25ha and lipe), pathogen recognition (clec12b and tlr5), and immune effectors (znrf1 and cish). In contrast, these transcripts did not significantly respond to the bacterin in the “switched-diet” group. Concurrently, biomarkers encoding proteins with putative roles in biotic inflammatory response (tnfrsf6b) and dendritic cell maturation (ccl13) were upregulated, and a chemokine receptor (cxcr1) was downregulated with the bacterin injection regardless of the experimental diets. On the other hand, an inflammatory regulator biomarker, bcl3, was only significantly upregulated in the high-ω3 fed group, and a C-type lectin family member (clec3a) was only significantly downregulated in the switched-diet group with the bacterin injection (compared with diet-matched PBS-injected controls). Transcript fold-change (FC: bacterin/PBS) showed that tlr5 was significantly over 2-fold higher in the high-18:2ω6 diet group compared with other diet groups. FC and FA associations highlighted the role of DGLA (20:3ω6; anti-inflammatory) and/or EPA (20:5ω3; anti-inflammatory) vs. ARA (20:4ω6; pro-inflammatory) as representative of the anti-inflammatory/pro-inflammatory balance between eicosanoid precursors. Also, the correlations revealed associations of FA proportions (% total FA) and FA ratios with several eicosanoid and immune receptor biomarkers (e.g., DGLA/ARA significant positive correlation with pgds, 5loxa, 5loxb, tlr5, and cxcr1). In summary, dietary FA profiles and/or regimens modulated the expression of some immune-relevant genes in Atlantic salmon injected with R. salmoninarum bacterin. The modulation of Atlantic salmon responses to bacterial pathogens and their associated antigens using high-ω6/high-ω3 diets warrants further investigation.

An intact-cell meal produced from the marine microalga, Pavlova sp. CCMP459 (Pav459) cultivated in land-based enclosed photobioreactors, was investigated as a protein and lipid source in the diets for post-smolt Atlantic salmon (Salmo salar). The Pav459 meal contained 60.87% protein, 12.25% lipid, 2.86% EPA and 1.45% DHA. Growth performance and tissue fatty acid profiles of salmon (170.1 +/- 23.9 g/fish initial weight) were evaluated after being fed test diets for 12 weeks containing either 10% (Low Pav) or 20% (High Pav) Pav459 meal; relative to a fish meal and fish oil-based control diet. No significant differences (P > 0.05) were found in salmon comparing dietary treatments for weight gain (271.3-279.6 g/fish), specific growth rate (1.2%/day), or feed conversion ratio (0.9 g feed/g gain). Salmon fed diets containing Pav459 meal had a slightly higher condition factor (1.3) than salmon fed the control diet (1.2). Liver DHA + EPA were significantly higher in salmon fed the control diet (5.1 mg/g) than salmon fed diets containing 10-20% Pav459 meal (3.4-3.5 mg/g). There were no significant differences observed in fillet muscle DHA, EPA, and most fatty acids among salmon fish diets containing 10-20% Pav459 meal compared to salmon fed the control diet. Overall, the results from this study indicate that Pav459 marine microalgae meal is a good candidate source of protein and essential n-3 LC-PUFA in diets for farmed Atlantic salmon.

Coastal and estuarine food webs receive large inputs of both autochthonous and allochthonous detritus, which serves as an important dietary input for a variety of detritivorous and omnivorous organisms. Surfactants, which aid digestion by solubilizing hydrophobic lipids, are found in the gut-fluids of many fish and invertebrate consumers. To develop a biomimetic assay to explore how source of primary production and age may affect the bioavailability of nutritional lipids from detrital food sources, we assessed the capacity of a model surfactant, sodium taurocholate (STC), to solubilize fatty acids from three primary producers, a haptophyte (Isochrysis galbana), a rock-weed (Ascophyllum nodosum), and a marsh grass (Spartina alterniflora). Comparing lipids solubilized by a constant concentration of STC to traditional Folch-extracted yields, we assessed relative bioavailability of nutritional lipids from fresh and decayed material of each primary producer. We focused on the solubilization of storage triacylglycerols (TAG) and the fatty acid constituents of all lipids (FA). With a temperature of 5 ?C, 28.7 mM STC solubilized 44 +/- 12% of total FA from S. alterniflora and about half that fraction for I. galbana and A. nodosum after 15 h in the dark unstirred. In the form of TAG, STC solubilized 53 +/- 19% of pure triolein as a reference and similar proportions from S. alterniflora (56 +/- 19%) and I. galbana (48 +/- 2%) but only 9 +/- 3% from A. nodosum. Both approaches (TAG and FA) thus show significant differences in bioavailability among these three sources. Two months of decay had inconsistent effects on overall lipid yields but substantial effects on composition. Degradation led to decreased total phospholipids and long-chain polyunsaturated FA and increased break-down products (free FA and diacylglycerols), saturated and monounsaturated FA, and bacterial FA. Lower FA bioavailability and reduced degradation rates in A. nodosum may be due to its higher polyphenol and alginate concentrations. Although we mimicked only one component of the digestion process of lipids, this study represents a first step in developing a biomimetic assay to assess the relative bioavailability of nutritional lipids.