Due to a limited access to marine raw materials from capture fisheries, Atlantic salmon feeds are currently based on mainly plant ingredients (75%) while only 25% come from traditional marine ...ingredients including marine fish meal and fish oil. Thus, current feeds contain less of the essential omega-3 fatty acids. The aim of the study was to assess the impact of different omega-3 levels in fish feed on intestinal barrier and transporting functions of Atlantic salmon freshwater and seawater smolts. Atlantic salmon were fed three levels of omega-3 (2, 1 and 0.5%) and fish performance was followed through smoltification and the subsequent seawater acclimation. Intestinal barrier and transporting functions were assessed using Ussing chamber methodology and combined with transcript analysis of tight junction related proteins and ion transporters. A linear decrease in growth was observed with decreasing omega-3 levels. Low (0.5%) inclusion of omega-3 impaired the barrier function of the proximal intestine compared to 2% inclusion. Further, low levels of omega-3 decrease the transepithelial electrical potential across the epithelium indicating disturbed ion transport. It can be concluded that low dietary levels of omega-3 impair somatic growth and intestinal function of Atlantic salmon.
Limited availability of the n-3 fatty acids EPA and DHA have led to an interest in better understanding of the n-3 biosynthetic pathway and its regulation. The biosynthesis of alpha-linolenic acid to ...EPA and DHA involves several complex reaction steps including desaturation-, elongation- and peroxisomal beta-oxidation enzymes. The aims of the present experiments were to gain more knowledge on how this biosynthesis is regulated over time by different doses and fatty acid combinations. Hepatocytes isolated from salmon were incubated with various levels and combinations of oleic acid, EPA and DHA. Oleic acid led to a higher expression of the Δ6 fatty acid desaturase (fad) genes Δ6fad_a, Δ6fad_b, Δ6fad_c and the elongase genes elovl2 compared with cells cultured in medium enriched with DHA. Further, the study showed rhythmic variations in expression over time. Levels were reached where a further increase in specific fatty acids given to the cells not stimulated the conversion further. The gene expression of Δ6fad_a_and Δ6fad_b responded similar to fatty acid treatment, suggesting a co-regulation of these genes, whereas Δ5fad and Δ6fad_c showed a different regulation pattern. EPA and DHA induced different gene expression patterns, especially of Δ6fad_a. Addition of radiolabelled alpha-linolenic acid to the hepatocytes confirmed a higher degree of elongation and desaturation in cells treated with oleic acid compared to cells treated with DHA. This study suggests a complex regulation of the conversion process of n-3 fatty acids. Several factors, such as that the various gene copies are differently regulated, the gene expression show rhythmic variations and gene expression only affected to a certain level, determines when you get the maximum conversion of the beneficial n-3 fatty acids.
Plant-based food provides more ALA (α-linolenic acid) and less EPA (eicosapentaenoic acid) and DHA (docosahexanoic acid) than marine food. Earlier studies indicate that cetoleic acid (22:1
-11) ...stimulates the
-3 pathway from ALA to EPA and DHA. The present study aimed to investigate the dietary effects of camelina oil (CA) high in ALA and sandeel oil (SA) high in cetoleic acid on the conversion of ALA to EPA and DHA. Male Zucker fa/fa rats were fed a diet of soybean oil (Ctrl) or diets of CA, SA, or a combination of CA and SA. Significantly higher levels of DPA (docosapentaenoic acid) and DHA in blood cells from the CA group compared to the Ctrl indicate an active conversion of ALA to DPA and DHA. Increasing the uptake and deposition of EPA and DHA meant that a trend towards a decrease in the liver gene expression of
,
, and
along with an increase in the dietary content of SA was observed. However, 25% of the SA could be exchanged with CA without having a significant effect on EPA, DPA, or DHA in blood cells, indicating that bioactive components in SA, such as cetoleic acid, might counteract the inhibiting effect of the high dietary content of DHA on the
-3 biosynthetic pathway.
Aquaculture contributes to global food security but sustainable aquaculture development in terms of biodiversity impacts requires the establishement of viable solutions in replacement of the ...fisheries-based components in aquafeeds. In the current work, pit-tagged Atlantic salmon individuals were grown, from fresh water (18g body weight) to salt water in tanks (up to 800g body weight), on diets with low fish meal (10%) and 1-1.25% total n-3 LC-PUFA levels balanced acccross the experimental diets. Dietary n-3 LC-PUFAs were supplemented by 1) fish oil (FO), 2) Schyzochytrium limacinum biomass (ScB) or 3) a mix of the two (FO/ScB). Further, the fish from all treatments were mixed and redistributed in sea cages reared to slaughter (ca. 3kg body weight) on either FO or ScB. As fish oil was rich in both EPA and DHA and ScB was rich in DHA ands nearly devoid of EPA, the experimental diets differed significantly in DHA/EPA ratio (0.8 vs 10.5 in average for FO and ScB, respectively). ScB treatment fish grew to significantly higher body weight in the end of the experiment (2.8kg vs 3.3kg, for FO and ScB, respectively) but similar FCR, survival rate and biometric indexes as compared to the FO groups. ScB fish contained higher levels of EPA+DHA in the fillet but lower in the liver, and better fillet pigmentation already from the tank phase of the experiment as determined chemically, by salmonfan and a trained sensory panel, and lower prevalence of melanin spots at slaughter. The trained sensory panel found no differences in flavor or odour in the fillets from the different dietary groups, however fillets in the FO group were percieved as softer and juicier compared to ScB. The pre-diets up to 800 g body weight had minor effects on fish performance. Global transcriptomics in liver and intestinal tissues revealed significant dietary effects on the expression of immune modulating, as well as ion, lipid, protein and xenobiotic metabolism genes.
New protein sources in fish feed require the assessment of the carry-over potential of contaminants and anti-nutrients from feed ingredients into the fish, and the assessment of possible health risks ...for consumers. Presently, plant materials including wheat and legumes make up the largest part of aquafeeds, so evaluation of the transfer capabilities of typical toxic metabolites from plant-infesting fungi and of vegetable phytoestrogens into fish products is of great importance. With the aim of facilitating surveillance of relevant mycotoxins and isoflavones, we have developed and validated a multi-analyte LC-HRMS/MS method that can be used to ensure compliance to set maximum levels in feed and fish. The method performance characteristics were determined, showing high specificity for all 25 targeted analytes, which included 19 mycotoxins and three isoflavones and their corresponding aglycons with sufficient to excellent sensitivities and uniform analytical linearity in different matrices. Depending on the availability of matching stable isotope-labelled derivates or similar-structure homologues, calibration curves were generated either by using internal standards or by matrix-matched external standards. Precision and recovery data were in the accepted range, although they varied between the different analytes. This new method was considered as fit-for-purpose and applied for the analysis of customised fish feed containing wheat gluten, soy, or pea protein concentrate as well as salmon and zebrafish fed on diets with these ingredients for a period of up to eight weeks. Only mycotoxin enniatin B, at a level near the limit of detection, and low levels of isoflavones were detected in the feed, demonstrating the effectiveness of maximum level recommendations and modern feed processing technologies in the Norwegian aquaculture industry. Consequently, carry-over into fish muscle was not observed, confirming that fillets from plant-fed salmon were safe for human consumption.
Feed safety is a necessity for animal health and welfare as well as prerequisite for food safety and human health. Wheat gluten (WG) is considered as a valuable protein source in fish feed due to its ...suitability as a feed binder, high digestibility, good amino acid profile, energy density and most importantly, due to its relatively low level of anti-nutritional factors (ANFs). The main aim of this study was to identify the impact of dietary WG on salmon health by analysing growth, feed efficiency and the hepatic and intestinal transcriptomes. The fish were fed either control diet with fishmeal (FM) as the only source of protein or diets, where 15% or 30% of the FM were replaced by WG. The fish had a mean initial weight of 223 g and approximately doubled their weight during the 9-week experiment. Salmon fed on 30% WG showed reduced feed intake compared to the 15% and FM fed groups. The liver was the less affected organ but fat content and activities of the liver health markers in plasma increased with the inclusion level of WG in the diet. Gene expression analysis showed significant changes in both, intestine and liver of fish fed with 30% WG. Especially noticeable were changes in the lipid metabolism, in particular in relation to the intestinal lipoprotein transport and sterol metabolism. Moreover, the intestinal transcriptome of WG-fed fish showed shifts in the expression of a large number of genes responsible for immunity and tissue structure and integrity. These observations implied that the fish receiving WG-containing diet were undergoing nutritional stress. Overall, the study provided evidence that a high dietary level of WG can have a negative impact on the intestinal and liver health of salmon with symptoms similar to gluten sensitivity in humans.
Cultivation of lumpfish (Cyclopterus lumpus) as lice cleaner fish for salmon is now expanding. For successful cultivation of a new species, understanding the basic biology of digestive functions is ...vital to facilitate and optimize diet formulation. This paper presents results from two experiments conducted to deepen our knowledge on lumpfish intestine physiology. Experiment 1 was a 42-day feeding trial in which lumpfish were fed twelve different diets in the following ranges of macronutrients: Protein 43-68%, lipid 4-17%, and carbohydrate 6-17%. Intestinal tissue, gut content and liver were sampled from 6 fish per tank. The results showed that with increasing lipid level and corresponding decrease in protein level, there was a linear decrease in several of the observed biomarkers, including activity of brush border membrane digestive enzymes, expression of genes related to nutrient digestion and transport, ion exchange, immune regulation, and cell remodeling. Increased intracellular accumulation of lipid (steatosis) was observed in gut and liver with increasing dietary lipid level. Fewer effects were observed for increased dietary carbohydrate and corresponding decreased protein level. Experiment 2 was a two-week feeding trial for estimation of macronutrient digestibility in which lumpfish were fed three diets, all containing 55% crude protein, with lipid to carbohydrate ratio of the low lipid diet of 7.5%/18.3%, the medium lipid diet of 13.8%/14.6%, and high lipid diet of 18.1%/9.5%. Fecal samples were collected as pooled samples per tank. These results showed that fatty acid digestibility’s increased as dietary lipid level increased. Of note, starch digestibility decreased greatly as starch level increased, whereas protein digestibility did not change as lipid or starch level varied. Taken together, the present studies indicated that increasing lipid level in the diet with corresponding decrease in protein level affects digestion, absorption, and immune responses in the lumpfish intestine. Variation in dietary carbohydrate to protein level showed less effects, possibly due to low starch digestibility which makes the variation in available carbohydrates much less than the variation in the analysed level of dietary carbohydrates.
The aim of the present research was to investigate the potential use of the phototrophic microalgae Phaeodactylum tricornutum (P. tricornutum) as a fish meal replacement in diet for Atlantic salmon, ...Salmo salar. Two experiments were designed with fish meal based control diets and dried whole cells P.tricornutum replacing fishmeal in the ratios 3%, 6% and 12% (experiment one) and 3 and 6% (experiment two). Experiment one was a digestibility study lasting for 21days, investigating effects of inclining level of P. tricornutum on apparent digestibility (ADC) of nutrients and energy. Experiment two was investigating ADC's of nutrients and energy, growth performance and nutrient retention in salmon fed for 82days. The results from experiment one showed a linear reduction in ADC of dry matter (DM; P=0.02), lipid (P<0.0001), and protein (P=0.04) with increasing level of algae biomass in the diet. The ADC of starch increased (P<0.05) with algae inclusion level in both experiments. For experiment two, no effects were observed on digestibility of DM, lipid, protein, energy or ash, with 3 and 6% algae replacing fish meal. Neither was growth or feed conversion affected by 3 and 6% algae replacing fish meal. Increasing inclusion level of algae biomass caused an increase in whole body lipid. The ADC of saturated fatty acids was higher in fish fed 3% alga biomass compared to the 6% group. There was no difference in ADC or retention of n-3 fatty acids. In conclusion, the two experiments showed that P. tricornutum can replace up to 6% of the fish meal without adverse effects on nutrient digestibility, utilization of the feed and growth performance.
Microalgae are potential omega-3-contributing feed ingredients
•The potential of whole cell microalgae Phaeodactylum tricornutum was investigated as a feed ingredient for Atlantic salmon.•Increasing dietary levels of algae from 0-12% gave a linear reduction in digestibility of dry matter, lipid, and protein.•Algae can replace up to 6 % of the fishmeal without adverse effects on digestibility, FCR and growth of Atlantic salmon.
Vegetable oils, typically high in
n
−
6 fatty acids, are necessary alternatives in fish feed production. Such oils have been tested in salmonid diets with good growth results, but with major changes ...in lipid composition. The aim of this study was to provide information regarding the effect of the higher dietary
n
−
6/
n
−
3 fatty acid ratio caused by vegetable oil on growth, chemical composition and bone development, on eicosanoid production and on formation and mineralization of bone.
A feeding experiment was carried out in juvenile Atlantic salmon (
Salmo salar). Groups of fish (1.28
g) were fed diets added fish oil (FO) or soybean oil (SO) as the main lipid source through the 174
days long experimental period with sampling points at days 0, 31, 53, 96, 136 and 174 up to smoltification. Subsequently, fish performance was observed after 2, 8 and 18
months in sea water.
Weight was significantly higher in the fish oil group (95.4
g) than in the soybean oil group (87.4
g) after the 174
days experimental period. This difference developed during short day treatment prior to smoltification, and the fish oil group had a significantly higher growth rate (TGC) during this period (1.62 vs 1.45). Whole body mineral analysis displayed low levels of Ca (2400 and 3500
mg
kg−1) and P (3200 and 3900
mg
kg−1) in all samples. The corresponding Ca:P ratio ranged from 0.74 to 0.91. On day 136 the level of Ca, and Ca/P ratio, were significantly higher in the fish oil group than in the soybean oil group. There was a significant increase in
n
−
6 fatty acids and decrease in
n
−
3 fatty acids in the soybean oil group compared to the fish oil group for both TAG and PL in vertebrae. Individual variation was large in plasma prostaglandin E
2 (PGE
2), and at day 174 the trend was towards a higher level in the soybean oil group. Radiography analyses demonstrated a distinctive pattern of development of spinal pathology with time and fish size, similar in both groups. Hyper dense vertebrae dominated at earlier stages, fusion-type malformations dominated at harvest size. The histological examination of the vertebrae revealed no differences between treatments.
The results suggest that vegetable oil as a replacement for fish oil influence the arachidonic acid level in phospholipids of vertebrae, may slightly increase production of PGE
2 in blood, and reduce vertebrae mineralization around the sensitive smoltification phase. These trends did not lead to any detectable skeletal malformations. Differences in growth and vertebrae mineralization observed around smoltification disappeared during the seawater phase.
Bacterial protein meal (BPM) produced on natural gas was evaluated with respect to growth, nutrient digestibilities, feed conversion ratios, sensory quality, and histopathological indices in Atlantic ...salmon in saltwater. In the extruded diets, experimentally produced BPM accounted for 0, 10, or 20% of the ingredients or 0, 17.2, or 33.1% of dietary nitrogen, replacing high-quality fish meal. Each diet was fed to two groups of salmon with a mean initial weight of 1.4 kg for 5 months. The pens were organized in two randomized blocks. One block was located with one side of the pens exposed to the open sea. The other block was completely surrounded by other pens. During the experiment, the salmon increased to approximately 3.6–3.9 kg in weight. Analysis of variance revealed no significant (
P>0.05) differences in growth, but regression analysis showed that fish weights at 2 and 5 months and growth rates for the whole experiment were slightly reduced with increasing content of BPM. No significant effects of diet were seen on dressed-out carcass, liver, or intestine to body weight percentages. Carcass and visceral fat and dry matter contents decreased with increasing dietary BPM. There was a trend (0.10≤
P<0.05) that apparent digestibilities of nitrogen, fat, and energy were reduced when substituting fish meal with BPM, while the nitrogen retention was not significantly affected. Flesh carotenoid concentration and colour were not significantly affected by dietary composition, nor were any differences seen for sensory characteristics related to taste, smell or texture. Histological examination did not reveal abnormalities, or signs of allergic reaction against BPM components, and hematocrit values were within normal ranges. Significant block effects were seen for chemical composition of viscera, and digestibilities of nitrogen, fat, and energy.
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