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Systematic granulomatosis is a chronic disease that affects the majority of farmed meagre (A. regius). Nutritional imbalances and overcrowding can increase the risk to suffer oxidative stress, and consequently impact the incidence of granulomatosis. In order to evaluate this, juvenile meagre were fed five isolipidic (16.7 %) and isoproteic (49.6 %) fish meal and fish oil-based feeds prepared by adding different levels of vitamin C, minerals (Mn, Zn, Se) with constant vitamin E and K (300 and 35 mg kg-1, respectively): Diet KEC (100 mg kg-1C), Diet KEC+Mn/Zn/Se (100 mg kg-1C, 40 mg kg-1Mn, 200 mg kg-1Zn, 1.5 mg kg-1Se), Diet KECC (600 mg kg-1C), Diet KECCC (1,200 mg kg-1C), Diet KECCCC (3,200 mg kg-1C). All diets were tested at 3.20 kg m-3, but diets KECC and KECCCC was also tested at 6.20 kg m-3. Growth performance was only affected by stocking density, being lower at high density. Percentage of fish with granulomas was significantly lower in fish fed with the highest dietary vitamin C contents (KECCC and KECCCC) at low density. TBARS content was correlated with the percentage of granulomas in liver (R2=0.9439, y=0.003x-0.1242) denoting the involvement of an imbalance oxidative status in the appearance of granulomas. The present results show that high levels of vitamin C (1,200-3,200 mg kg-1C) and low stock density (3.20 kg m-3) favours the growth of juvenile meagre, reducing the lipid peroxidation indicators and decreasing the incidence of granulomas, which confirms that this pathology is mostly triggered by deficiency of antioxidant nutrients, particularly vitamin C.

There is an increased use of vegetable oils containing n-6 fatty acids (FA) in aquafeeds, and several trials indicate that there might be an increased requirement of EPA and DHA for Atlantic salmon when they are fed higher dietary n-6 FA. With a limited supply of EPA and DHA for production of aquafeeds, it is important to know how to efficiently use these FA to maintain growth and health of the fish. In the present trial, three diets containing equal amounts of n-3 FA (about 7·7 % of total FA) and different n-6:n-3 FA ratios (about 1, 2 and 6), as well as one diet with n-6:n-3 FA ratio at about 1 but twice as much n-3 FA, were fed to Atlantic salmon. Despite constant dietary n-3, increasing dietary n-6 led to significantly reduced n-3 in tissue polar lipids. Interestingly, EPA was significantly reduced while DHA was not. Maintaining a stable n-3 content in the polar lipids when increasing dietary n-6 FA was only obtained by simultaneously increasing the dietary n-3 content and with this maintaining the same n-6:n-3 FA ratio. Polar lipid n-6 FA in tissues thus primarily reflected the dietary n-6:n-3 FA ratio and not the absolute dietary n-6 FA content. Neutral lipids, on the other hand, reflected the dietary absolute levels of both n-3 and n-6 FA. This study indicates that a better use of dietary EPA is achieved by keeping the dietary n-6:n-3 FA ratio low.

Meagre (Argyrosomus regius) is a promising new aquaculture species, however with some bottlenecks to high-scale commercial production. One of those constraints are the scarce information about its nutritional requirements, which difficult the production of optimized diets and can lead to pathological alterations in liver, such as hepatic steatosis. Furthermore, meagre production is widely affected by granulomatosis, an infectious or non-infectious disease that may compromise fish performance and appearance. The cause of non-infectious granulomatosis is still unclear, but nutritional deficiencies are potential explanations. Since essential fatty acids are nutrients required to sustain vital functions, growth, but also immune status and disease resistance, the present work evaluated, in a 30-day feeding trial, the effect of 5 dietary n-3 long-chain polyunsaturated fatty acid levels (0.8, 1.4, 2.0, 2.6 and 3.5% in dry weight of the diet) on liver health status of meagre fingerlings. Fish fed the lowest n-3 LC-PUFA diets (0.8 and 1.4%) showed a higher hepatosomatic index, as well as a higher hepatic lipid infiltration, which resulted in severe hepatic steatosis. Oleic acid and docosahexaenoic acid were the most important fatty acids driving the variability of meagre hepatic fatty acid composition and, consequently, hepatic histological alterations. Although fatty acid composition of phospholipids was less affected by the dietary n-3 LC-PUFA, meagre fed 0.8% n-3 LC-PUFA tended to present lower levels of essential fatty acids and higher levels of oleic acid in polar lipids. Moreover, the diet with the lowest n-3 LC-PUFA content (0.8%) led to a higher incidence of hepatic granulomas, suggesting a possible relation between essential fatty acid deficiency and hepatic granulomatosis in meagre. These results suggest that the inclusion of vegetable oils in diets for meagre fingerlings should be taken with careful, guaranteeing that, at least, 2.0% DW of n-3 LC-PUFA is available in feeds, in order to maintain the normal hepatic function in meagre.

The aim of the study was to investigate the influence of dietary level and ratio of n-6/n-3 fatty acids (FA) on growth, disease progression and expression of immune and inflammatory markers in Atlantic salmon (Salmo salar) following challenge with Paramoeba perurans. Fish (80 g) were fed four different diets with different ratios of n-6/n-3 FA; at 1.3, 2.4 and 6.0 and one diet with ratio of 1.3 combined with a higher level of n-3 FA and n-6 FA. The diet with the n-6/n-3 FA ratio of 6.0 was included to ensure potential n-6 FA effects were revealed, while the three other diets were more commercially relevant n-6/n-3 FA ratios and levels. After a pre-feeding period of 3 months, fish from each diet regime were challenged with a standardized laboratory challenge using a clonal culture of P. perurans at the concentration of 1,000 cells L−1. The subsequent development of the disease was monitored (by gross gill score), and sampling conducted before challenge and at weekly sampling points for 5 weeks post-challenge. Challenge with P. perurans did not have a significant impact on the growth of the fish during the challenge period, but fish given the feed with the highest n-6/n-3 FA ratio had reduced growth compared to the other groups. Total gill score for all surfaces showed a significant increase with time, reaching a maximum at 21 days post-challenge and declined thereafter, irrespective of diet groups. Challenge with P. perurans influenced the mRNA expression of examined genes involved in immune and inflammatory response (TNF-α, iNOS, IL4-13b, GATA-3, IL-1β, p53, COX2 and PGE2-EP4), but diet did not influence the gene expression. In conclusion, an increase in dietary n-6/n-3 FA ratio influenced the growth of Atlantic salmon challenged with P. perurans; however, it did not alter the mRNA expression of immune genes or progression of the disease.

Earlier studies have indicated that a high inclusion of n-6 fatty acids (FA) in feeds for Atlantic salmon can affect the stress response. To test this hypothesis, Atlantic salmon (Salmo salar) were fed diets containing varying dietary n-6/n-3 FA ratios and different absolute levels of n-6 and n-3 FAs. The fish were divided into two different stress challenge groups, where one group was exposed to three weekly hypoxia challenges for 4 weeks (repeated stress), while one group was left undisturbed. At the end of the experiment, both groups were exposed to an acute stressor (lowering of water level). Thus, effects of the diets on acute stress, repeated stress and the combined effect of these could be investigated. In general, there were few effects of the repeated stress, while fish in all diet groups responded strongly to the acute stress based on several stress markers. Dietary n-6/n-3 ratio did not affect growth, all fish appeared phenotypically healthy, and all groups were able to mount an acute stress response. However, there was an interaction between diet and repeated stress on cortisol response after acute stress, possibly indicating altered hypothalamic-pituitary adrenal axis reactivity in fish fed high n-6/n-3 FA ratio. Hepatic levels of prostaglandin D2 (PGD2) and leukotriene B4 responded differently to acute stress depending on the dietary n-6/n3 FA ratio, indicating an altered acute stress response. Additionally, increasing the dietary n-6/n-3 FA content led to higher levels of PGD2 and PGE2 as well as higher liver triacylglycerol. In summary, the results suggest that increasing the dietary n-6/n-3 FA ratio in salmon feeds can affect the way they respond to stressors in an aquaculture setting, possibly affecting the fish robustness.

PurposeTo explore whether high intake of cod or salmon would affect gut microbiota profile, faecal output and serum concentrations of lipids and bile acids.MethodsSeventy-six adults with overweight/obesity with no reported gastrointestinal disease were randomly assigned to consume 750 g/week of either cod or salmon, or to avoid fish intake (Control group) for 8 weeks. Fifteen participants from each group were randomly selected for 72 h faeces collection at baseline and end point for gut microbiota profile analyses using 54 bacterial DNA probes. Food intake was registered, and fasting serum and morning urine were collected at baseline and end point.ResultsSixty-five participants were included in serum and urine analyses, and gut microbiota profile was analysed for 33 participants. Principal component analysis of gut microbiota showed an almost complete separation of the Salmon group from the Control group, with lower counts for bacteria in theBacteroidetesphylum and theClostridialesorder of theFirmicutesphyla, and higher counts for bacteria in theSelenomonadalesorder of theFirmicutesphylum. The Cod group showed greater similarity to the Salmon group than to the Control group. Intake of fibres, proteins, fats and carbohydrates, faecal daily mass and output of fat, cholesterol and total bile acids, and serum concentrations of cholesterol, triacylglycerols, non-esterified fatty acids and total bile acids were not altered in the experimental groups.ConclusionA high intake of cod or salmon fillet modulated gut microbiota but did not affect faecal output or serum concentrations of lipids and total bile acids.Clinical trial registrationThis trial was registered at clinicaltrials.gov as NCT02350595.

A well-balanced diet adapted to fulfil the specific nutritional requirements of greater amberjack (Seriola dumerili) would contribute to optimize reproduction and spawning quality. The main objective of the present study was to examine the effects of supplemental histidine, taurine and protein in broodstock diets, on egg quality of greater amberjack. Twelve broodstocks were distributed in three 40 m3 circular tanks and fed three different diets, one high in histidine, another in taurine and the third one in protein contents. Overall the best spawning quality was obtained histidine levels were elevated from 1 to 1.5%, increasing the relative fecundity, fertilization rates, egg viability, hatching rates, larval survival, egg protein contents, and egg and larval size, denoting the importance of this amino acid for embryo and larval development. The increase of taurine from 0.3 to 1.1% in diets for greater amberjack increased the relative fecundity in comparison to fish fed higher protein levels. Fertilization rates tend to increase with the elevation of dietary taurine and were not significantly different from those of broodstock fed higher histidine levels. Besides, dietary taurine increased egg diameter and taurine contents. Increase in dietary protein contents from 51 to 56% lead to an increase protein content in egg, as well as a larger yolk sac volume, but did not improve any of the spawning quality parameters. In conclusion, the results of this study have pointed out the importance of raising histidine contents in broodstock diets from 1 to 1.5% to optimize the reproductive performance of greater amberjack. Besides, the study showed that taurine levels in broodstock diets increased fecundity, maintaining good fertilization rates, but further studies must be conducted to determine the optimum taurine dietary levels.

Systemic granulomatosis is a growing disease with a high morbidity, which affects to the majority of farmed meagre (Argyrosomus regius). The impossibility of isolating any infectious agents has hypothesized a nutritional origin of the disease. In order to try to elucidate the nutritional origin of granulomas, juvenile meagre were fed for 15 weeks with six diets containing different levels of vitamin E and C and with or without addition of vitamin K: Diet 0 (basal premix, no K, 150 mg kg‐−1 E, 20 mg kg‐−1 C), K (added 23 mg kg‐−1 K), EC (300 mg kg‐−1 E, 70 mg kg‐−1 C), KEC (23 mg kg‐−1 K, 300 mg kg‐−1 E, 70 mg kg‐−1 C), EECC (450 mg kg‐−1 E, 230 mg kg‐−1 C) and KEECC (23 mg kg‐−1 K, 450 mg kg‐−1 E, 230 mg kg‐−1 C). The diet EC significantly increased meagre growth in terms of final weight and length. Fish fed the highest levels of vitamin E and C presented lower percentage of granulomas in liver and heart than fish fed diet 0. The scored severity of granulomatosis in liver and kidney (main affected organs) tended to be lower with dietary increase of vitamin E, C and addition of vitamin K (from 1.83 diet 0 to 1.3 diet KEECC and from 0.91 diet 0 to 0.39 diet KEECC). In liver, the diet KEECC significantly increased catalase expression compared with diet 0. In kidney tnfα expression was significantly up-regulated in fish fed diet EECC and KEECC. In heart, low vitamin E and C levels (300 and 70 mg kg‐−1, respectively) significantly increased superoxide dismutase and glutathione peroxidase expression and high addition increased the expression of tnfα and cox-2 (0 or 23 mg kg‐−1 K, 450 mg kg‐−1 E and 230 mg kg‐−1 C, diet EECC and KEECC). The results show that combination of high dietary content of vitamin K and antioxidant vitamins E and C (23, 450 and 230 mg kg‐−1, respectively) influenced in the incidence of the granulomatosis, which suggests that this pathology could be mediated by nutritional factors.

The establishment of well-balanced diets that meet nutrient requirements is important to optimize a large-scale production of new aquaculture species. This is the case of meagre (Argyrosomus regius), a promising new aquaculture species, with great potential owing to its high growth rate, feed efficiency and easy adaptation to captivity. Knowledge on the nutritional requirements of this species is still scarce, namely regarding essential fatty acids, which are required to sustain growth, development, immune status and survival. A feeding trial was performed with meagre fingerlings (2.8 g ± 0.23) testing 5 increasing dietary n-3 LC-PUFA levels (0.8, 1.4, 2.0, 2.6 and 3.6% DM) with the purpose of evaluating the n-3 LC-PUFA requirements for fast growth of meagre fingerlings. Meagre reflected very high specific growth rates (4.1 to 4.6%) and low feed conversion ratios (0.7 to 0.8), thus highlighting its great potential for aquaculture production. Fish fed 0.8% n-3 LC-PUFA showed the lowest growth, which was significantly improved by increasing the dietary n-3 LC-PUFA levels up to 2.0–2.6%. DHA and ARA were preferentially retained over EPA in whole fish body. Fish fed 0.8% n-3 LC-PUFA showed an up-regulation of fads2 and elovl5 relative gene expressions. Thus, meagre seems to have active Δ6 desaturases and Elovl5, but their activities being insufficient to produce DHA and EPA from PUFA precursors to sustain fast growth, at least under the experimental conditions tested. Young meagre shows a typical marine requirement for n-3 LC-PUFA, estimated to be, at least, 2.0% DM of the diet.

The increasing use of plant-based ingredients in aquafeeds for Atlantic salmon has led to increasing feed concentrations of plant sterols (phytosterols) combined with decreasing concentrations of cholesterol. Questions have been raised regarding how this may affect performance, health and lipid metabolism in a carnivorous fish species adapted to a high cholesterol diet in nature, and whether phytosterols could be involved in the liver lipid accumulation commonly observed in salmon fed diets with high content of vegetable oils. A feeding trial with 9 diet groups with varying additions of phytosterols and cholesterol was conducted at two temperatures (6 and 12 °C). Fish grew from an initial weight of ~ 250 g to a final weight of ~ 900 g. Overall, the addition of phytosterols and/or cholesterol within the range tested (1353–3147 mg kg− 1 phytosterols, 867–3153 mg kg− 1 cholesterol and phytosterol:cholesterol ratios of 0.7–3.2) exhibited few effects on fish performance, lipid metabolism and health. The main hypothesis regarding phytosterols or phytosterol:cholesterol ratio affecting liver lipid accumulation appears to be false. However, dietary cholesterol did increase muscle pigmentation at both temperatures, while fillet dry matter and hepatosomatic index were also increased by dietary cholesterol at 12 °C. Dietary cholesterol also had some minor effects on the fatty acid composition of liver polar lipids, probably mediated by LXR. In general, more effects were seen from variations in dietary cholesterol compared to phytosterols. The current trial is the first to feed salmon graded levels of phytosterols, cholesterol and their ratio without changing the dietary fatty acid composition, and thereby isolating the effects of dietary sterols.

As fish oil is an increasingly limited input-factor, content of the n-3 fatty acids eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3) is being gradually reduced in feeds for farmed salmon, and consequences for fish health and fillet quality need to be addressed. In the present study, Atlantic salmon (Salmo salar L.) were fed two levels of EPA and DHA through the seawater rearing period from six weeks after smolt transfer (~ 150 g) until harvest (~ 5000 g). The trial was conducted under commercial production conditions, with triplicate net pens used for each diet group. The control (standard) diet contained 8% EPA + DHA of total fatty acids (FAs, 26 g kg− 1 feed), while the low n-3 diet contained 6% EPA + DHA of FAs until 1200 g body weight and 4.5% in following feeds, averaging out to 5% of FAs (16 g kg− 1 feed) during the entire production cycle. Growth performance and measured health parameters including cataract, liver lipid accumulation and vaccine side-effects did not differ significantly between the two diet groups. Through the production period, the fish faced stressful and challenging conditions such as five treatments against sea lice (one oral and four bath treatments), as well as an outbreak of pancreas disease and considerable mortality from gill infections. Despite this, mortality did not differ significantly between the diet groups, indicating that fish fed low dietary n-3 FAs were equally robust as fish fed the standard diet. Quality classification at slaughter did not reveal any diet effects, and neither did sensory evaluation of the fish fillets. As expected, the fillet FA profile differed, with 5.4% EPA + DHA of total FA (0.9 g 100 g− 1) in the fillet of fish fed the low n-3 diet and 7.5% (1.3 g 100 g− 1) in fish fed the standard diet. The fish fed low EPA + DHA showed a higher frequency of fillet melanin spots, 28.2%, compared to 21.5% in the salmon fed the standard diet, possibly related to dietary FA composition affecting inflammatory processes. Statement of relevance Supply of fish oil is limiting growth of the salmon industry

Atlantic salmon (Salmo salar) were fed five graded levels of eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3), from 1.4 to 5.2% of total fatty acids (FA, 5–17 mg kg−1 feed), and grew from ~160 g to ~3000 g, with the period from 1450 g onwards conducted both at 6 °C and at 12 °C. All fish appeared healthy, and there were no diet-related differences in haematological or plasma parameters, as well as intestinal histological or gut microbiota analysis. Fish reared at 6 °C had higher accumulation of storage lipids in the liver compared to fish reared at 12 °C. Liver lipids also increased with decreasing dietary EPA + DHA at 6 °C, while there was no such relationship at 12 °C. Gene expression of SREBP1 and 2, LXR, FAS and CPT1 could not explain the differences in liver lipid accumulation. In liver polar lipids, DHA was found to be reduced when dietary EPA + DHA was

This study investigated whether retention of n-3 fatty acids (FAs) is influenced by the levels of dietary monounsaturated (MUFA)-, saturated (SFA)- and n-6 FAs. The feeding trial used a mixture design, with rapeseed-, palm (PO)- and soybean oil (SO), providing high levels of MUFA, SFA and n-6 FAs, respectively, while 18:3n-3, eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3) were kept constant. Furthermore, a diet group with high SO and reduced 18:3n-3 was included in addition to the mixture design. There were no differences in growth or proximate composition, but the PO diet gave reduced FA digestibility and increased feed conversion ratio. All diet groups had a net production of DHA, shown by retention values >100% (133%–177%). High dietary n-6 FAs of up to 43% of FAs (18:2n-6/18:3n-3 ratio 8.6) did not negatively affect DHA retention, but rather had a small positive impact. High levels of substrate (dietary 18:3n-3 at ~10% of FAs) did not enhance DHA retention compared to 5% 18:3n-3. This is a highly significant finding for the aquaculture industry, allowing for greater flexibility in the choice of lipid sources to replace fish oil in salmon feeds.

The present study was conducted to evaluate the effects on Atlantic salmon hepatic lipid metabolism when fed diets with increasing substitution of fish oil (FO) with a vegetable oil (VO) blend. Four diets with VOs replacing 100, 90, 79 and 65 % of the FO were fed for 5 months. The levels of eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acid (DHA; 22:6n-3) in the experimental diets ranged from 1.3 to 7.4 % of fatty acids (FAs), while cholesterol levels ranged from 0.6 to 1.2 g kg(-1). In hepatocytes added [1-(14)C] α-linolenic acid (ALA, 18:3n-3), more ALA was desaturated and elongated to EPA and DHA in cells from fish fed 100 % VO, while in fish fed 65 % VO, ALA was elongated to eicosatrienoic acid (ETE; 20:3n-3), indicating reduced Δ6 desaturation activity. Despite increased desaturation activity and activation of the transcription factor Sp1 in fish fed 100 % VO, liver phospholipids contained less EPA and DHA compared with the 65 % VO group. The cholesterol levels in the liver of the 100 % VO group exceeded the levels in fish fed the 65 % VO diet, showing an inverse relationship between cholesterol intake and liver cholesterol content. For the phytosterols, levels in liver were generally low. The area as a proxy of volume of lipid droplets was significantly higher in salmon fed 100 % VO compared with salmon fed 65 % VO. In conclusion, the current study suggests that suboptimal dietary levels of cholesterol in combination with low levels of EPA and DHA (1.3 % of FAs) can result in minor metabolic perturbations in the liver of Atlantic salmon.

Dietary lipids and fatty acids composition play an important role in the reproductive processes, embryo development and larval survival in marine fish. Long-chain polyunsaturated fatty acids (LC-PUFA) are especially important for egg and larval quality. The main objective of the present study was to evaluate the effects of increasing dietary n-3 LC-PUFA levels on spawning performance and egg quality of greater amberjack (Seriola dumerili). Sixteen mature broodfish were distributed in four 40 m3 circular tanks and fed four diets containing different levels of n-3 LC-PUFA: diet D1 with 1% of the dry weight basis (dw), diet D2 with 1.7% dw, diet D3 with 2.3% dw and diet D4 with 3% dw. The fecundity was significantly higher (P

Post-smolt Atlantic salmon (Salmo salar) were fed with standard feed added one of five concentrations of either pure deoxynivalenol (DON; 0.5–6 mg/kg) or pure ochratoxin A (OTA; 0.2–2.4 mg/kg), or no added toxins for up to 8 weeks. Performance effects (feed intake, feed efficiency, gain, length and condition factor), various clinical biochemical parameters, packed cell volume and vaccination response against Aeromonas salmonicidae were all inversely correlated with DON dose, whereas relative liver weight increased with DON dose. In fish fed OTA, however, the effects at the doses tested were rather small. We observed no effects of OTA exposure on performance parameters, but some clinical biochemical parameters tended to increase with OTA dose primarily at 3 weeks, and compared with controls OTA exposure caused increased mRNA expression of two immune markers in the spleen. No liver histopathological effects were found from DON or OTA exposure. For DON, we derived a BMDL20 of 0.3 mg/kg feed for reduced total protein in plasma, a BMDL5 of 0.5 mg/kg feed for reduced condition factor, and a NOAEL of 1 mg/kg feed for DON. For OTA, a BMDL or NOAEL could not be derived (>2.4 mg/kg).

Consumption of fatty acids from fishes is widely regarded as beneficial for preventing cardiovascular disorders. Nevertheless, salmonids themselves are victims of vascular diseases. As the pathogenesis and nature of these changes are elusive, they are here addressed using novel morphological and transcriptional approaches. Coronary arteries of wild Atlantic salmon Salmo salar L., (n = 12) were investigated using histological and immunohistochemical techniques, and RT-qPCR was employed to investigate expression of stretch-induced genes. In an experimental trial, fish were fed diets with different fatty acids composition, and histological features of the coronary arteries (n = 36) were investigated. In addition, the heart fatty acid profile (n = 60) was analysed. There were no differences in morphological or immunological features between wild fish and groups of experimental fish. Arteriosclerotic lesions consisted of smooth muscle cells in dissimilar differential stages embedded in considerable amounts of extracellular matrix in a similar fashion to what is seen in early stages of human atherosclerosis. No fat accumulations were observed, and very few inflammatory cells were present. In affected arteries, there was an induction of stretch-related genes, pointing to a stress-related response. We suggest that salmon may have a natural resistance to developing atherosclerosis, which corresponds well with their high investment in lipid metabolism.

Post-smolt Atlantic salmon (Salmo salar) were fed standard feed with added 2 or 6 mg kg–1 pure deoxynivalenol (DON), 0.8 or 2.4 mg kg–1 pure ochratoxin A (OTA), or no added toxins for up to 8 weeks. The experiments were performed in duplicate tanks with 25 fish each per diet group, and the feed was given for three 2-h periods per day. After 3, 6 and 8 weeks, 10 fish from each diet group were sampled. In the following hours after the last feeding at 8 weeks, toxin elimination was studied by sampling three fish per diet group at five time points. Analysis of DON and OTA in fish tissues and plasma was conducted by liquid chromatography-mass spectrometry and high-pressure liquid chromatography with fluorescence detection, respectively. DON was distributed to the liver, kidney, plasma, muscle, skin and brain, and the concentrations in liver and muscle increased significantly from 3 to 8 weeks of exposure to the high-DON diet. After the last feeding at 8 weeks, DON concentration in liver reached a maxim...

Adult Atlantic salmon (Salmo salar; approximately 800 g start weight) were fed diets with a high replacement of fish meal (FM) with plant proteins (70% replacement), and either fish oil (FO) or 80% of the FO replaced by olive oil (OO), rapeseed oil (RO) or soybean oil (SO) during 28 weeks in triplicate. Varying the lipid source only gave non-significant effects on growth and final weight. However, a significantly reduced feed intake was observed in the SO fed fish, and both feed utilization and lipid digestibility were significantly reduced in the FO fed fish. Limited levels of dietary 18:3n-3, precursor to EPA and DHA, resulted in no net production of EPA and DHA despite increased mRNA expression of delta-5-desaturase and delta-6-desaturase in all vegetable oil fed fish. Net production of marine protein, but not of marine omega-3 fatty acids, is thus possible in Atlantic salmon fed 80% dietary vegetable oil and 70% plant proteins resulting in an estimated net production of 1.3 kg Atlantic salmon protein from 1 kg of FM protein. Production of one 1 kg of Atlantic salmon on this diet required only 800 g of wild fish resources (Fish in - Fish out

A two-compartmental model for the kinetics of carry-over of the brominated flame retardant α-hexabromocyclododecane (HBCD) from feed to the fillet of farmed harvest-sized Atlantic salmon (Salmo salar L.) was developed. The model is based on a fat compartment for storage of the lipophilic α-HBCD and a central compartment comprising all other tissues. Specific for this model is that the salmon has a continuous growth and that fillet contaminant levels are explained by both the fat and the central compartments. The uptake and elimination kinetics are obtained from experimental data where consumer sized (start weight approximately 1 kg) Atlantic salmon was fed α-HBCD spiked feed (280 ± 11 µg kg−1) for 2 months followed by a depuration period of 3 months. The model was used to simulate the HBCD feed-to-fillet transfer in Atlantic salmon under realistic farming conditions such as the seasonal fluctuations in feed intake, growth and fillet fat deposition. The model predictions gave fillet concentrations of 0.2–1.8 µg kg−1 depending on the level of fish oil inclusion in the salmon diets when using fish oil with high POP background levels. Model simulations show that currently farmed Atlantic salmon can contribute to a maximum of 6% of the estimated provisional food reference dose for HBCD.

Atlantic cod (Gadus morhua), initial weight 15 g, were fed ten experimental diets for 15 weeks. The diets were based on a mixture of plant proteins (PP) and fish meal (FM), where PP constituted 65% of dietary protein. PP mixtures were chosen to reach as low levels of lysine and methionine as possible. The diets were supplemented with increasing amounts of lysine (19.2–31.9 g kg−1 diet) or methionine (9.4–12.3 g kg−1 diet), in a regression design. No growth difference among diet groups was found in the plant-based diets. Increased dietary lysine resulted in decreased liver size, plasma triacylglycerol concentration (TAG) and lipid productive value (LPV). Methionine additions did not result in changed Hepatosomatic index (HSI), LPV or plasma TAG. Feed conversion ratio (FCR) and protein utilization were neither affected by lysine nor methionine. Plasma and muscle concentrations of free lysine and methionine correlated with dietary levels 5-h post feeding. Overall conclusion was that cod maintain growth rates in plant-based diets if dietary protein was high, without additional supplements of crystalline lysine or methionine. Lysine intake significantly influenced lipid metabolism, showing the necessity to add lysine in plant protein-based diets to hinder increased lipid deposition. No such effects were found because of lack of methionine additions.

Impaired growth, immunity, and intestinal barrier in mammals, poultry, and carp have been attributed to the mycotoxin deoxynivalenol (DON). The increased use of plant ingredients in aquaculture feed implies a risk for contamination with mycotoxins. The effects of dietary DON were explored in 12-month-old Atlantic salmon (Salmo salar) (start weight of 58 g) that were offered a standard feed with non-detectable levels of mycotoxins (control group) or 5.5 mg DON/kg feed (DON group). Each group comprised two tanks with 25 fish per tank. Five fish from each tank were sampled eight weeks after the start of the feeding trial, when mean weights for the control and DON groups were 123.2 g and 80.2 g, respectively. The relative expression of markers for three tight junction proteins (claudin 25b, occludin, and tricellulin) were lower, whereas the relative expression of a marker for proliferating cell nuclear antigen was higher in both the mid-intestine and the distal intestine in fish fed DON compared with fish from the control group. The relative expression of markers for two suppressors of cytokine signaling (SOCS1 and SOCS2) were higher in the distal intestine in fish fed DON. There was no indication of inflammation attributed to the feed in any intestinal segments. Our findings suggest that dietary DON impaired the intestinal integrity, while an inflammatory response appeared to be mitigated by suppressors of cytokine signaling. A dysfunctional intestinal barrier may have contributed to the impaired production performance observed in the DON group.

Farmed Atlantic cod ( Gadus morhua L.) is known to grow large liver, while muscle growth is preferred. Therefore, the main focus of this feeding trial was to find a strategy to achieve reduced liver size without compromising total growth, feed utilization, digestibility of nutrients or fish health. All experimental diets held a similar protein to energy (P:E) ratio, but indigestible fibre was added to dilute total energy. Two basal diet mixtures had increasing α-cellulose levels (0, 6, 12 and 18%). The basal diet mixtures consisted of either 50% plant ingredients plus 50% fish meal as protein sources (PP), or 100% fish meal (FM). The initial average cod live weight was 139 ± 4 g, and the feeding trial lasted for 97 days. All diet groups showed good growth and feed utilization, both in combination with FM and PP. Increased dietary α-cellulose did, however, result in increased feed intake and similar protein and energy intakes in all treatments, concluding that the cod adjusted its feed intake to both protein and energy levels in the diet to maintain growth. Digestibility of fat and dry matter decreased with increased α-cellulose. Liver index (HSI), protein digestibility and protein retention was not affected by α-cellulose. None of the haematological or clinical parameters in blood and plasma were affected by dietary treatment, and close to no mortality was registered in the experiment. The results show that cod is able to adjust its feed, protein and energy intake to maintain growth. Adding α-cellulose to diets can therefore not be used as a strategy to reduce liver size, at least not when offering cod a feeding regime to satiation.

The nutritional requirement for n-3 long-chain PUFA in fast-growing Atlantic salmon (Salmo salar) during grow out in the sea is not well documented. Diets were formulated with levels of EPA (20 : 5n-3) and DHA (22 : 6n-3) ranging from 1·3 to 7·4 % of fatty acids (4–24 g/kg feed). Two long-term trials were conducted through the seawater phase, the first at 6 and 12°C, and the second at 12°C. In the first trial, growth at both temperatures was significantly lower in fish fed 1·4 % EPA+DHA of total fatty acids compared with the 5·2 % EPA+DHA group. In the second trial, growth was significantly lower in fish fed 1·3 and 2·7 % compared with 4·4 and 7·4 % EPA + DHA. Fatty acid composition in the fish reflected diet composition, but only after a 7-fold increase in body weight did the fatty acid profile of the fish stabilise according to dietary fatty acids (shown for EPA and DHA). The retention efficiency of DHA increased with decreasing dietary levels, and was 120–190 and 120–200 % in trials 1 and 2, respectively. The retention efficiency of EPA was lower (60–200 %), and values >100 % were only achieved at the lowest dietary levels in both trials. Temperature did not affect fatty acid retention efficiency. These results suggest that Atlantic salmon have a specific requirement for EPA + DHA >2·7 % of fatty acids for optimal long-term growth in seawater, and that short-term growth trials with less weight increase would not show these effects.

Replicate groups of Atlantic cod were fed 5 diets in which fish meal protein was replaced with 25% (25 PP), 50% (50 PP), 75% (75 PP) and 100% (100 PP) of a plant protein mixture containing 50% wheat gluten, 36% soy protein concentrate and 14% bioprocessed soybean meal. After 28 weeks, fish were sacrificed and analysed for growth, feed conversion, nutrient digestibility (see [Hansen, A.-C., Rosenlund, G., Karlsen, Ø., Koppe, W., Hemre, G.-I., Accepted for publication. Total replacement of fish meal with plant proteins in diets for Atlantic cod (Gadus morhua L.) I: Effects on growth and protein retention. Aquaculture]) and health status. Except for small reductions in the mean cell volume and haemoglobin content of red blood corpuscles, health indicators in blood and plasma were mostly unaffected by diet. Although the apparent digestibility coefficient (ADC) of nutrients was only marginally affected by diet [Hansen, A.-C., Rosenlund, G., Karlsen, Ø., Koppe, W., Hemre, G.-I., Accepted for publication. Total replacement of fish meal with plant proteins in diets for Atlantic cod (Gadus morhua L.) I: Effects on growth and protein retention. Aquaculture], faeces moisture content increased non-linearly peaking in fish fed the 100 PP diet where dry matter was only 11% compared to 18% in the control fish. This indicates a progression towards a diarrhoea-like condition in 100 PP fish. Feeding plant proteins did not affect gut relative weight but did affect intestinal morphology. In particular, there was a general increase in cellularity of the lamina propria and a modest goblet cell hypertrophy and hyperplasia which peaked in fish fed the 100 PP diet. More severe enteritis-like conditions were rare and found in only two fish fed the 100 PP diet. The dietary effect on goblet cells may be caused by phytate or fibres rather than the primary enteritis-inducing compounds found in untreated soybean meal. Hindgut segments seemed to be more affected than midgut thus suggesting an up-concentration of the causative agents of intestinal alteration in hindgut regions. Soyasaponins were not degraded during gut transit although the various conjugates were hydrolysed increasing the level of un-conjugated soyasaponins in the faeces. The intestinal level of heat shock protein 70 (HSP70) was unaffected by diet except in one replicate pen of fish fed the 100 PP diet where expression increased fourfold compared to the other replicate and other diets. The reason for this remains obscure. In conclusion, the plant ingredients used in the present study appear not to affect cod health to any major degree when used to replace up to 75% of fish meal protein. An increase to 100% may induce enteritis-like conditions in the guts of some fish and also activate HSP70 stress-gene mRNA expression in the intestine. © 2007. 156195/129 This work was supported by the Research Council of Norway (grant # 156195/129). Jacob Wessels at NIFES is acknowledged for excellent technical assistance. We are also grateful for the dedicated and invaluable assistance of Anne Karin Nyheim, Trygve Knag and Helen Olsen at the MIC Platform at Haukeland, Bergen for their efforts during processing of the histological samples.

A regression design with increasing levels of a plant protein mixture replacing fish meal in diets for Atlantic cod, was used to elucidate effects on growth, feed utilization (FCR), digestibility (ADC), and retention of nutrients (PER, PPV and HSI). The plant protein diets contained soybean meal, soy protein concentrate and wheat gluten meal, all of high quality, and were added crystalline methionine and lysine to achieve levels of indispensable amino acids for maximizing growth in other fish species. Initial fish weight was 1652 ± 6 g (mean ± SEM) and the experiment lasted for 28 weeks from December 2004. High growth (SGR 0.31–0.35) and feed utilization (FCR 1.06–1.26) were obtained up to 50% plant protein inclusion. Above this inclusion level, growth (SGR 0.30–0.14) and feed utilization (FCR 1.42–2.71) were reduced. None of the diets affected whole body, liver or muscle proximate compositions. Hepatosomatic index was not effected by diet up to 75% plant protein (HSI 12.7–14.3), but was significantly lower for the 100% plant protein diet group (HSI 10.1–11.4). Plasma and muscle free amino acid pools, sampled 5 h post-feeding, partly reflected diet amino acid composition. Reduced protein retention was found as dietary plant protein increased (PPV 0.45–0.16 and PER 2.11–0.73), however without any reductions in apparent digestibility coefficients. There was a decrease in vitamin B12 concentrations in the diets (120–10 μg kg− 1) as inclusion of plant protein increased, but no specific deficiency symptoms were detected in the fish. Furthermore, the sufficiency of dietary methionine supply in the highest replacement groups, can be questioned based on low levels in the muscle free amino acid pool. Overall conclusion is a great potential for using quite high inclusions of plant proteins in cod diets, provided that the plant ingredients are of high quality.

Atlantic cod ( Gadus morhua ) has been a new candidate for aquaculture for some decades in countries around the North Atlantic Ocean. Greatest interest in developing a cod farming industry is found in Norway, Canada and the United Kingdom as well as in Iceland and the USA (north east). Modern hatchery methods for cod using cultivated plankton such as rotifers and Artemia were first described in 1984, but it took more than 15 years of dedicated research and development before these efforts now are being translated into up scaled hatchery protocols. Protocols for keeping reproductive stocks of Atlantic cod under different photoperiods have been established resulting in year around production of fertilised eggs. Hatcheries commonly keep 3–5 different stocks to achieve this. The relationship between brood stock nutrition, external cues and reproductive performance is largely unknown and should be studied further. Cod larvae have a very high growth potential (> 20% day − 1 ), they are aggressive feeders and can be cannibalistic if food availability is sub optimal. Both temperature and light are found to influence growth in larval cod. Research has addressed cod larval nutrition, both qualitative and quantitative requirements. Also, development of feeds and feeding strategies that would allow early weaning onto inert diets has been a primary objective in cod juvenile production research. Using a diet designed to support larval requirements, weaning can start from 15–20 days post hatch. This strategy has resulted in satisfactory growth and survival without use of Artemia , thus reducing the dependency on live feeds. Huge variation in survival and a high incidence of deformities have been reported in hatchery-reared cod juveniles. These observations have been ascribed partly to unfavourable environmental conditions (gas super-saturation) and the problem has to a large extent been solved. Methods to produce large numbers of cod juveniles have been implemented in several Atlantic countries in recent years, and present hatchery capacities can support an annual production of several hundred thousand tons of farmed cod. Common practices in cod hatcheries are presented and future perspectives on cod juvenile production are discussed.

Atlantic cod were fed 7 different diets from August 2001 to June 2002 varying in protein (range 36–66% of feed), lipid (10–28% of feed) and starch (4–19% of feed) concentration. These dietary treatments were duplicated in netpens with continuous light from metal halogen lamps mounted above surface and under natural light conditions. None of the diets resulted in impaired health of the fish measured as mortality or increased plasma levels of organ specific transaminases or glucose. A few fish in the groups under continuous light conditions spawned during the experimental period while all cod under natural light conditions spawned during spring 2002. Use of continuous light from August 2001 delayed spawning for most of the cod by at least 4 months, this even though the fish was farmed under continuous light from February to August 2001. Spawning decreased final weight in all groups irrespective of diet composition. Postponed sexual maturation will allow continuous growth and thus the cod to reach market size before first spawning. Increased dietary protein increased growth irrespective of light treatment. Liver indices were negatively correlated with increased dietary protein: lipid (P : L) ratio. These results were not affected by spawning. Investment in maturation measured as gonad index in March for the groups kept under natural light conditions was also negatively correlated with increased P : L ratio. Consequently, groups fed diets with the highest dietary protein had the smallest livers and gonads. The present study confirms that dietary protein is the main driver of growth in cod whereas energy deposition is more closely related to dietary lipid content.

This experiment evaluated the nutritional value of extracted soybean meal (SBM) for on-grown Atlantic cod, and if this was improved by bioprocessing into a product with reduced contents of antinutrients (BPSBM). Three iso-nitrogenous and iso-energetic extruded diets contained no soy (FM control), or 24% of total protein from either soy product. Each diet was fed to duplicate groups of 534 g (1-year old) and 1750 g (2-year old) cod in sea pens equipped with feed waste collectors. The experiment lasted 84 feeding days, the fish were weighed at days 48 and 84, and fish were sampled at days 0 and 87 to budget protein and energy utilisation by comparative slaughter. At day 48 faeces was collected for estimation of macronutrient, energy, and amino acid digestibility. The 1-year old cod reached weights ranging from 916 to 984 g, while the 2-year olds reached weights ranging from 2490 to 2644 g. There was no effect of age-class on growth rate estimated as TGC, but relative feed intake (% of BW) and FER were higher in the 1-year olds. Digestibility and retention of macronutrients were not affected by size. Still, the digestibility of most amino acids and the retention of several digested amino acids were highest in the 2-year olds. The body lipid content was similar in all groups, and did not change. There was no effect of diet on weight gain within age-classes, nor any general effect of diet on growth rate estimated as TGC. The digestibility of amino acids and the lipid was reduced when feeding the SBM and BPSBM diets, but cod of both age-classes compensated for this by increased feed intake and gastrointestinal growth, resulting in lower FER and reduced protein retention. Similar growth and body composition when feeding all diets and similar macronutrient and protein utilisation when feeding SBM and BPSBM showed that Atlantic cod have relatively high tolerance for dietary SBM.

Currently, Atlantic cod (Gadus morhua) is the primary species being developed for commercial culture, with activities concentrated around the North Atlantic. In addition, closed life cycles have been established for haddock (Melanogrammus aeglefinus), pollock (Pollachius pollachius), and hake (Merluccius australis), but production of these species (in Canada, Spain, and Chile) is rather modest. In the short- to medium-term, Atlantic cod will be the dominant gadoid species in culture, and it is believed that production can reach levels similar to those of farmed salmon within the next 15–20 years. This development is possible because methods for year-round production of juveniles and significant hatchery capacity have been established. Also, there is a demand for farmed cod to fill the gap between increasing market needs and diminishing supply from fisheries. However, challenges must be met if cod farming is to reach its anticipated potential. Juvenile production must become more reliable in terms of survival and quality. For the on-growing phase, the supply of cost-efficient feeds produced from sustainable raw materials is of utmost importance. Consumer markets need to be developed with an emphasis on quality and food safety. Relatively little is known about health management for gadoid species.

Juvenile Atlantic cod (Gadus morhua) were fed extruded feeds formulated to contain 360–660 g kg−1 protein, 80–280 g kg−1 lipid and 80–180 g kg−1 starch at feeding frequencies of either once per day or every second day to satiation. The trial was conducted at 8 °C and lasted for 28 weeks during which fish were weighed five times at regular intervals. Sampling for proximate analysis was performed at the start, after 12 weeks and at the end of the trial. Fish grew from an average weight of 192 g to between 750 and 866 g, with growth being negatively affected by low dietary protein concentration. High dietary starch concentrations had some negative effects on growth, whereas changes in dietary fat concentration had no significant effect on growth. Liver indices (at the end of the experiment) varied between 80 and 170 g kg−1, and there was a negative correlation between the ratio of protein to fat and liver index. Feed conversion ratio (FCR) ranged between 0.74 and 0.88, and feed utilization improved with increasing concentrations of dietary protein and fat. Increasing dietary starch concentrations resulted in poorer feed utilization. To achieve good growth and protein retention, and avoid excessive liver size in juvenile cod, feeds should contain 500–600 g kg−1 crude protein, 130–200 g kg−1 lipid and

As the supply of marine fish oil is becoming a limiting factor in the production of Atlantic salmon (Salmo salar), new diets and alternative sources of energy are being tested. Plant oils are natural potential candidates to replace fish oil, but the different levels of essential polyunsaturated fatty acids may influence the health and growth of salmon. In this study, we have investigated the resistance to transport stress and bacterial infection, phagocytic activity in head kidney macrophages and eicosanoid metabolism in salmon fed three different diets. In high-energy fishmeal based diets, 50% and 100% of the supplementary fish oil (FO) was replaced with soybean oil (SO). The three dietary groups were fed for 950 day-degrees at 5 � C (27 weeks) and 12 � C (11 weeks) before challenging the fish with Aeromonas salmonicida, analyzing the lipid composition of head kidney and examining macrophage function in vivo and in vitro. Dietary fatty acids affected the lipid composition of the kidney. The level of eicosanoid precursor’s 20:4n-6 and 20:3n-6 were 3 and 7-fold higher in the 100% SO group compared with the FO group. The total fraction of n-3 lipids in kidney was 19% in the SO group, compared to 16% and 12% in the 50% or 100% SO groups, respectively. However, the production of leucotriene B4 (LTB) and prostaglandin E2 (PGE) immunoreactive materiel from exogenously added arachidonic acid in head kidney macrophages was only affected by the composite diet (increased) at 5 � C. In addition, the phagocytic activity of kidney macrophages in vivo and in vitro was not affected by diet. No effect of diet was observed on transport stress or susceptibility to a bacterial infection with Aeromonas salmonicida. Atlantic salmon therefore seems to tolerate a diet solely based on soybean oil as lipid source, without any detrimental effects on growth, health and immune functions.

Effect of season and diet on muscle composition were evaluated in farmed Atlantic cod (Gadus morhua L.), fed varying levels of macro-nutrients, and kept at two different light regimes during 1 year grow-out in sea-cages. The cod were fed seven different diets varying in protein, lipid and starch, in a mixture design. The diets spanned 4–20% starch, 8–26% lipid and 36–66% protein. Each dietary regime was subjected to two different light regimes: continuous light (24 h), or natural light (August 2001 to June 2002). Fish subjected to natural light started to mature in December/January and spawning was more or less completed during March/April. No maturation was registered in the continuous light groups at this point. No variation was found in muscle dry matter, protein or lipid concentration as a consequence of the dietary or light regime variations, except for the groups spawning in March. Glycogen varied from 1 to 6.5 mg g−1 wet weight, without any correlation to the present dietary variations. At the June 2002 sampling all groups given a natural light regime showed almost twice the concentration of muscle glycogen compared with fish subjected to continuous light. Such clear results were not measured at the December or March samplings. Increased dietary lipid resulted in lowered muscle vitamin E concentration. A strong covariation between muscle vitamins C and E was found at all samplings, and these showed a negative correlation towards eicosapentaenoic (EPA) and docosahexaenoic acid (DHA), and the ratio n-3/n-6 in muscle. The highest dietary vitamin E resulted in the lowest muscle vitamin C concentrations. All dietary lipid added was identical and of marine origin; in addition, the wheat added as a starch source summed up parts of the dietary lipid fraction, resulting in slightly decreased sum of polyenes in the diets holding the highest levels of wheat. The lean cod muscle consists almost solely of membrane lipids. These were, however, highly influenced by the dietary lipid composition, especially as concerned the different monoenes. Two of the diets showed tendencies to increased thiobarbituric acid-reactive substances (TBARS). This was not reflected in the muscle concentrations of vitamins E or C, and did not result in any changes in muscle TBARS values at any of the samplings, except for the fish spawning in March. The water-soluble fraction of the muscle protein, pH range from 4.5 to 6, did show a difference in structure when comparing our experimental cod to wild cod. We could also identify a differential pattern between some of the experimental groups. The method used to identify this was, however, not quantitative, and further studies are needed. Taste panel evaluation and shear force measurements after final sampling in June concluded with minor differences between muscles from the different diet groups, except for fish given one diet with relatively high protein, intermediate lipid and low starch levels. Fish kept at continuous light was described as less firm (texture) compared with fish kept at natural light, explained partly by the different size of these two categories of fish. In conclusion, both diet and season (spawning or not) did influence several of the measured muscle parameters.

The aim of the study was to investigate the replacement of fish oil by vegetable oils and the effects of a washout with a return to fish oil on growth performances and lipid metabolism. Three experimental fish meal-based isonitrogenous (crude protein content: 57.5%) and isolipidic (crude lipid content: 16.5%) diets were formulated containing either 9% of added fish oil (FO), soybean oil (SO), or linseed oil (LO). Each diet was distributed to triplicate groups of 25 marketable size turbot (initial body weight of 579 g) grown in seawater at water temperature of 17 °C. Fish were fed once a day to visual satiety. At the end of the growth trial, which lasted 13 weeks, all groups of turbot were fed with FO diet for 8 weeks. The growth of turbot was high, but the incorporation of vegetable oils in the diets resulted in a slight decrease in growth as compared to those fed with fish oil-based diet. Feed and protein efficiency and whole body composition were not affected by dietary lipid sources. Total lipid content was low in the muscle of turbot (below 2%); ventral muscle being fatter than dorsal muscle. Liver and muscle fatty acid (FA) composition reflected dietary FA composition. Liver and muscle of fish fed with SO diet were rich in 18:2n-6, whereas those of fish fed with LO diet were rich in 18:3n-3. Liver and muscle of fish fed with SO and LO diets had lower levels of 20:5n-3 and 22:6n-3 in comparison to those of fish fed with FO diet. In turbot, hepatic lipogenic enzyme activities were low and not influenced by dietary lipid source. At the end of the second period, after transfer to FO-based diets, muscle FA composition of fish fed previously with SO and LO diets were still different to those of fish fed with FO diet. The values of 18:2n-6 and 18:3n-3, respectively, were lower than the values found at the end of the growth period, but higher than those of fish fed with FO diet. An increase of FA levels, characteristic of fish oil, was observed in the liver and muscle of fish previously fed with vegetable oils. Data obtained show that replacement of fish oil by vegetable oils is possible with negligible impact on growth performance of turbot, that dietary lipids are an effective vector to influence the nutritional quality of finished product, and that a duration of 8 weeks is not sufficient to bring the FA profile of turbot of this size back to that of fish fed with fish oil over the whole period.

The uncertain supply and variable price of fish oil warrants the investigation of other sources of energy in salmon diets. A study was done to test the effects on growth, feed utilization, tissue fatty acid composition, heart histology and standard oxygen consumption of replacing 50% or 100% of the supplementary fish oil (FO) with soybean oil (SO) in high energy, fish meal-based diets for Atlantic salmon smolts. Triplicate groups of fish were tested for approximately 950 day-degrees (DD) at both 5 (initial weight, 108 g) and 12 °C (initial weight, 118 g). The salmon tripled their weight during the trial. Total feed intake and growth were significantly greater in the groups fed the 100% FO diet compared with those fed the 50% SO diet, with the 100% SO-fed groups in the middle. Feed efficiency ratios were not affected by dietary treatment or water temperature. No histological pathologies were found in heart tissue of salmon sampled at the end of the trial. Neither diet nor temperature affected whole body composition or lipid content in the heart of fish sampled at the end of the trial. Standard oxygen consumption was significantly lower in salmon fed the 50% SO diet (83±2 mg O 2 kg −1 h −1 ) compared with fish fed the 100% FO and 100% SO diets (90±2 and 92±2 mg O 2 kg −1 h −1 , respectively). In general, the levels of the individual fatty acids in the triacylglyerol fraction of the heart and fillet lipids showed either no response or a linear response to the corresponding fatty acids in the diets. Thus, no relationship was evident between the tissue fatty acid levels and oxygen consumption. This study showed that Atlantic salmon grow well and with high efficiency on high energy, fish meal-based diets containing up to 100% supplementary soybean oil. No evidence of detrimental effects of the soybean oil on the health of the fish was found.

Background Fish meal and fish oil are increasingly replaced by ingredients from terrestrial sources in the feeds for farmed salmonids due to expanding production and reduced availability of marine feed raw material. Fish oil that is rich in n-3 polyunsaturated fatty acids is considered beneficial to human health in general and to prevent intestinal inflammation and carcinogenesis in particular. In contrast, n-6 fatty acids that are present in many vegetable oils have been associated with increased risk of colitis and colon cancer in rodents and humans, as well as lowered transcription levels of certain stress and antioxidant-related genes in Atlantic salmon. The aim of the present study was to investigate the intestinal health in Atlantic salmon fed with different vegetable oils as partial substitutes of fish oil in the diet. A feed trial lasting for 28 weeks included one reference diet containing fish oil as the sole lipid source and three diets where 80% of the fish oil was replaced by a plant oil blend with either olive oil, rapeseed oil or soybean oil as the main lipid source. These plant oils have intermediate or low n-3/n-6-ratios compared to fish oil having a high n-3/n-6-ratio. The protein and carbohydrate fractions were identical in all the feeds. Results Morphometric measurements showed significantly shorter folds in the mid intestine in all groups fed vegetable oils compared to the group fed fish oil. In the distal intestine, the complex folds were significantly shorter in the fish fed soybean oil compared to the fish fed rapeseed oil. Histological and immunohistochemical examination did not show clear difference in the degree of inflammation or proliferation of epithelial cells related to dietary groups, which was further confirmed by real-time RT-PCR which revealed only moderate alterations in the mRNA transcript levels of selected immune-related genes. Conclusions Shortened intestinal folds might be associated with reduced intestinal surface and impaired nutrient absorption and growth, but our results suggest that partial substitution of dietary fish oil with vegetable oils does not have any major negative impact on the intestinal health of Atlantic salmon.

The present study investigates the impact of replacing at least 50% of the fish oil in high-energy salmon diets with other types of oils. Triplicate groups of Atlantic salmon (Salmo salar L.) were fed six diets differing only in dietary lipid source for 12 months in sea water. The experimental oils were combinations of fish oil and one or two of the following oils: rapeseed, soybean, linseed, palm or poultry oil. Fish oil constituted 40%−50% of the oil mixtures. The fish grew from an average weight of 120 g to 2000 g during the 12 month trial. Except for minor differences in the lipid concentration of trimmed fillets, no significant effects of dietary lipid source were found on growth, survival, body traits or fillet quality. The main dietary effect was observed in the muscle fatty acid composition, which clearly reflected that of the diets. These results show that high-energy diets where 50%−60% of the fish oil is replaced by other lipid sources can produce similar results to diets containing 100% fish oil during the grow out phase of Atlantic salmon in sea. The importance of fillet fatty acid composition on processing and sensory characteristics requires further evaluations.

Rotifers, Brachionus plicatilis, fed baker's yeast and a lipid emulsion (High DNA Super Selco, INVE Aquaculture NV Systems SA, Belgium), were harvested and fed Isochrysis galbana for 72 h, the nutrient composition was analysed during this period. The enrichment effect on the rotifers following transfer to I. galbana was most pronounced for ascorbic acid and thiamin. I. galbana seemed to contribute very little as a source of the lipid-soluble vitamins. Most of the minerals and trace elements were unaffected by the transfer to I. galbana, but Fe, Mn, As and Cd increased, Cu and Ni decreased whereas the effect on Cr and Mo were uncertain. The fatty acid composition of the rotifers changed towards the composition of I. galbana during the experimental period. Intermediate glycogen levels were measured in the rotifers at all sampling times. With the exception of lysine, serine and proline, all amino acid levels seemed to be unaffected by the transfer to I. galbana. This study showed that transfer of rotifers to microalgae (I. galbana) feeding had a positive effect on nutritional value. Macronutrients were maintained at adequate levels, and algal feeding improved the nutritional quality of rotifers with respect to water-soluble vitamins. Changes in rotifer nutrient composition are discussed in relation to nutritional requirements of fish larvae.

Background To ensure sustainable aquaculture, fish derived raw materials are replaced by vegetable ingredients. Fatty acid composition and contaminant status of farmed Atlantic salmon (Salmo salar L.) are affected by the use of plant ingredients and a spillover effect on consumers is thus expected. Here we aimed to compare the effects of intake of Atlantic salmon fed fish oil (FO) with intake of Atlantic salmon fed a high proportion of vegetable oils (VOs) on development of insulin resistance and obesity in mice. Methodology/principal findings Atlantic salmon were fed diets where FO was partly (80%) replaced with three different VOs; rapeseed oil (RO), olive oil (OO) or soy bean oil (SO). Fillets from Atlantic salmon were subsequently used to prepare Western diets (WD) for a mouse feeding trial. Partial replacement of FO with VOs reduced the levels of polychlorinated biphenyls (PCB) and dichloro-diphenyl-tricloroethanes (DDT) with more than 50% in salmon fillets, in WDs containing the fillets, and in white adipose tissue from mice consuming the WDs. Replacement with VOs, SO in particular, lowered the n−3 polyunsaturated fatty acid (PUFA) content and increased n−6 PUFA levels in the salmon fillets, in the prepared WDs, and in red blood cells collected from mice consuming the WDs. Replacing FO with VO did not influence obesity development in the mice, but replacement of FO with RO improved glucose tolerance. Compared with WD-FO fed mice, feeding mice WD-SO containing lower PCB and DDT levels but high levels of linoleic acid (LA), exaggerated insulin resistance and increased accumulation of fat in the liver. Conclusion/Significance Replacement of FO with VOs in aqua feed for farmed salmon had markedly different spillover effects on metabolism in mice. Our results suggest that the content of LA in VOs may be a matter of concern that warrants further investigation.

Diets with increasing levels of potato and maize starch were fed to duplicate groups of maturing cod, Gadus morhuaL., from June 1991 to January 1992.The level of starch in the diet did not influence feed conversion factors, broodfish growth or gonadal development. Low levels of fillet glycogen were measured at all samplings, without variations according to dietary starch, or to developmental stage of the brood fish. During the reproductive phase no decreases were measured in relative liver size or liver protein, lipid or glycogen, indicating no net use of stored energy from the liver to build up gonads as long as the fish was offered feed. The variations in dietary starch vs. protein did not alter the composition of gonad dry matter, protein, lipid or glycogen levels. However, dry matter and protein levels increased during maturation in all groups. Plasma glucose levels were within normal ranges in all dietary groups at all sampling times, indicating no negative effects of high levels of dietary starch in brood fish, as also confirmed by stable and normal haematocrit, red blood cell count, and mean cell volume in blood. Haemoglobin, mean cell haematocrit and mean cell haemoglobin concentration decreased during the reproductive phase. Serum haemolytic complement activity did not vary between dietary treatments. Glycogen, dry matter, protein and lipid levels in eggs did not vary between dietary treatments of brood fish. Very low levels of glycogen were measured, suggesting that this energy reserve was of minor importance. Dry matter and lipid levels were quite stable in relation to egg developmental stage: protein levels decreased from day 0 until hatching.

The present study assessed differences in fecundity and egg quality from Atlantic cod Gadus morhua fed isoproteic diets containing 13% fat (low fat, LF) or 20% fat (high fat, HF) and either stressed or left unstressed as a control over the spawning season. Each diet was fed to triplicate groups of G. morhua from June 2009, through to first maturation and spawning. In January 2010 sub-groups of G. morhua were moved to land-based spawning tanks where the experimental trial was carried out. At the start of the experiment, G. morhua fed the high-fat diet were significantly larger than G. morhua fed low-fat diet. These differences were maintained through the spawning season, although with a loss of mass in both dietary groups. Relative fecundity through the season was significantly lower in stressed G. morhua fed LF compared to unstressed G. morhua fed the same diet. Stressed G. morhua had a higher variability in weekly amount of eggs spawned, spawning occurred more irregularly, and the spawning period lasted longer than in unstressed G. morhua. Several egg quality variables were also affected: eggs from G. morhua fed LF and exposed to stress had lower fertilization and hatching rates compared to the unstressed G. morhua fed the same diet as well as all G. morhua fed HF. Gadus morhua fed a low-fat diet appeared less tolerant to stress than fish fed a high-fat diet.

The effects of dietary vitamin C on maturation and egg quality of cod Gadus morhua L. have been investigated. The broodstock groups were fed three different levels of vitamin C mixed into a commercial dry pellet. The experimental feeding started three months prior to the spawning season. Naturally spawned eggs were collected and analyzed with regard to viability, biochemical composition and physical characteristics. Differences in free amino acid profile, egg strength and neutral buoyancy were found, whereas no effects on vital parameters, such as fertilization rate and survival rate, were detected.

1. 1. Plaice (Pleuronectes platessa L.) with an initial weight of 2.9 ± O.6 g were fed diets containing 0, 200 and 2000 mg ascorbic acid (AA)/kg feed for 250 days after a depletion period of four months. 2. 2. Significant differences between the AA deficient and the AA supplemented groups were seen in growth (P < O.001), mortality, hepatosomatic index (P

Background In a previous study, a group of coronary heart disease (CHD) patients exhibited positive cardioprotective effects of fatty acids derived from a diet of farmed Atlantic salmon fed fish oil (Seierstad et al. 2005). This follow-up study examines these patients for plasma exposure to selected organic and inorganic contaminants found in seafood that may detract from the benefits of eating oily fish. Methods The study design was from Seierstad et al. (2005), where 58 patients were allocated into three groups consuming 700 g week−1 of differently fed Atlantic salmon (Salmo salar) fillets for 6 weeks: 100% fish oil (FO), 100% rapeseed oil (RO), or 50% of each (FO/RO). Results Different fillets showed graded levels (FO > FO/RO > RO) of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), dioxin-like polychlorinated biphenyls (DLPCBs), indicator PCBs, polybrominated diphenyl ethers (PBDEs), and arsenic (As). Mercury (Hg) and lead (Pb) levels were similar across the three types of fillets. After 6 weeks of consumption, patient levels of PCDDs, DLPCBs, and PCBs in plasma decreased as the dietary intake of these contaminants increased. Plasma PBDEs only showed increases for the FO patients. Levels of inorganic contaminants in plasma showed only slight changes over the study period. Conclusions These results show a reduction in the use of marine oils in fish feed reduces organic contaminant levels in farmed salmon while still providing a good dietary source of marine fatty acids.

The present study investigated the short-term (5 months) effect of replacing dietary marine oils with vegetable oils on the development of arteriosclerotic changes in the heart of Atlantic salmon, Salmo salar. The experiment was performed as a randomized observer-blinded and controlled trial. Farmed Atlantic salmon were randomly sampled from a study population containing 900 individuals. The salmon were divided into three groups and given diets with either 100% fish oil (Diet 1), a 50/ 50% mixture of fish oil and rapeseed oil (Diet 2) or 100% rapeseed oil (Diet 3). Ten sexually immature salmon from each dietary group were sampled in March and August 2002. Additionally, 47 sexually mature wild salmon were randomly collected in mid-September 2001. Serial histological sections were taken from the bulbus arteriosus and ventricle wall for histopathological evaluation of the coronary arteries and myocardium. No significant differences in mean coronary changes recorded by the main variable mean range lesion (MRL) were detected between the groups in March or August. MRL increased significantly between March and August with Diet 2 (P < 0.01), was nearly significant with Diet 3 (P ¼ 0.06) and was unchanged with Diet 1. This pattern coincided with the Diet 2 group having the highest increase in heart weight. MHC class II immunoreactive cells in the coronary changes were detected in sections from one individual in each group. Heart weight was the most dominant variable in the data set and explained linearly 15.5% of the variation in MRL. Body weight, fish length and heart weight were all significantly, positively and linearly correlated to MRL. The Diet 2 group had the highest growth rate and also exhibited a significant increase in MRL. The possible influence of diet composition on weight gain and MRL needs to be further elucidated. Increase in heart weight seems to be the dominating predictor of the appearance of MRL in Atlantic salmon. However, the present results cannot exclude the possibility that differences in fatty acid composition of fish feed can influence the development of arteriosclerotic changes in Atlantic salmon.

Assimilation and elimination rate constant of dietary polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and dioxin-like polychlorinated biphenyls (DLPCBs) with a World Health Organization toxic equivalency factor (WHO-TEF) were estimated in market-size Atlantic salmon (Salmo salar) using fish that were previously fed vegetable oil-based (low in PCDD/Fs and DLPCBs) or fish oil-based (high in PCDD/Fs and PCBs) diets. At the start of the kinetic trial, half the fish that were fed fish oils were fed vegetable oil feeds and inverted (cross-over design) for five months. The assimilation efficiencies of the PCDD/F congeners were more variable (3-89%) and, generally, were lower than those of the DLPCBs (70-80%). Among the PCDD/F congeners, the assimilation efficiency of the most toxic tetra- and pentachlorinated PCDD/Fs was greater than that of higher-chlorinated PCDD/Fs. Elimination rates for DLPCBs were higher than those for PCDD/Fs. Lower-chlorinated PCDDs had a lower elimination rate than the higher-chlorinated PCDDs, but no differences were observed among PCDF congeners or DLPCB congeners. Kinetic parameters were used to predict the level of WHO-TEF dioxins and DLPCBs in Atlantic salmon reared in a large-scale facility under commercial conditions. Predictions were based on preanalyzed levels of these organochlorines in feeds with three different replacement levels (0, 30, and 60%) of vegetable oil. A simple one-compartmental, first-order kinetic model was used to predict the level of sum WHO toxic equivalents for PCDD/Fs and DL-PCBs. The predicted values varied by 0 to 11% from the measured values in the commercially reared salmon.

Cultures of the rotifer Brachionus plicatilis (200 ind./ml, 0.5 μg dry weight/ind.) pre-fed on yeast and capelin oil (10:1 w/w) were given different enriched diets and harvested after 24 h. The fatty acid composition of the rotifers was affected by that of the feed. The highest level of n−3 highly unsaturated fatty acids (HUFA) 38%) and 22:6 n−3 (19%) was obtained after enrichment of the rotifers fed with squid meal. A positive relation was found between the n−3 HUFA in the enrichment diet and that of the rotifers (P < 0.05, t-test). The cultivation feed of the rotifers may nevertheless be more important for the n−3 HUFA level than the enrichment feed. Starvation for 49 h did not change the fatty acid composition of the rotifers.

Saithe (Pollachius virens) and rainbow trout (Salmo gairdneri) were fed diets containing increasing levels from 12 to 60% of protein energy relative to metabolizable energy for 8 and 3 weeks, respectively. Ribosomes were isolated from skeletal muscle tissue and the rate of protein synthesis in vitro determined. Ribosomal capacity for protein synthesis per g wet weight of muscle tissue was significantly correlated (p