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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.

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.

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.

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.

The use of plant-based feeds has introduced undesirables, such as pesticides, that have previously not been associated with seawater farming of fish species such as Atlantic salmon. Earlier wide-scope chemical screening showed that the organophosphate (OP) pirimiphos-methyl (PM-m) is one of the most prevalent pesticides present in commercially produced Atlantic salmon feed. Information on the safe upper limit of background levels of PM-m in Atlantic salmon feeds with regards to possible adverse effect on fish health is lacking. Therefore, Atlantic salmon (132 ± 25 g) were fed graded levels of PM-m spiked feeds (0, 0.35, 1.5, 5, and 22 mg kg−1) in triplicate for 3 months. Adverse effects were assessed on OP target toxic exposure such as plasma choline esterase (ChE), and secondary toxic responses such as lipid metabolism and oxidative stress, as well as general adverse effect parameters (plasma biochemistry, haematology, and growth). Safe limits were set by model-fitting the effect data in a dose-response (lower bound) bench mark dose (BMDL) regression analysis. Fish fed 1.5 mg kg−1 and higher had a significant (p

Atlantic salmon (Salmo salar) were fed diets with the three vegetable oils, rapeseed oil (RO), palm oil (PO) and soybean oil (SO), in a mixture design for 12 weeks. The diets contained high levels of monounsaturated fatty acids (mainly 18:1n-9), saturated fatty acids (mainly 16:0) and n-6 fatty acids (mainly 18:2n-6), respectively. The dietary content of 20:4n-6 (arachidonic acid, ARA), 20:5n-3 (eicosapentaenoic acid, EPA) and 22:6n-3 (docosahexaenoic acid, DHA) was similar in all diets. The aim was to investigate how dietary 18:1n-9, 16:0 and 18:2n-6 affect the fatty acid composition of salmon tissues, as well as the lipid metabolism and the fish health through lipid-derived compounds such as eicosanoids. Dietary 18:2n-6 had a clear impact on the fatty acid profile of polar lipids, and caused an increase in ARA levels combined with a concomitant decrease in EPA levels, indicating a direct replacement effect. There was a gradient among the tissues, where the dietary effects were most pronounced in liver polar lipids, followed by heart polar lipids and erythrocytes, while retina and brain were the most conserved. The DHA level in polar lipids was highly conserved. Eicosanoid levels in liver were affected by diets, but did not directly reflect the content of precursor fatty acids in the cell membranes, indicating a more complex relationship. Profiling of the main metabolites of the liver revealed distinct differences between fish fed RO and PO compared to fish fed SO, where the latter had reduced levels of both free carnitine and several acylcarnitines. The accumulation of triacylglycerol in the liver also varied between the diet groups, with the level of dietary saturated fat (16:0) appearing to be the variable in the design explaining most of the variation.

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

The aim of this study was to compare how different dietary vegetable oil n-6/n-3 ratios affect gene responses involved in inflammation, signaling pathways, fatty acid synthesis and oxidation, oxidation and apoptosis as well as eicosanoid production in salmon head kidney tissues and isolated head kidney leukocytes. Salmon smolts (200 g) were fed four different diets where the main lipid components were palm oil (n-6/n-3 ratio = 0.7), rapeseed oil (n-6/n-3 ratio = 0.9), and soybean oil (n-6/n-3 ratio = 2.4) and a high soybean oil diet with an n-6/n-3 ratio = 4. Both head kidney tissue and leukocytes isolated from head kidneys were sampled from the four diets, but from different fish. Leukocytes isolated from the head kidneys were seeded into culture wells and added lipopolysaccharide (LPS) to induce inflammatory responses. Controls without LPS were included. Head kidney leukocytes and the tissues should have the same phenotype reflecting the different diets. Interleukin 1β (IL-1β) transcription was elevated in head kidney tissue and especially in LPS treated leukocytes isolated from soybean oil (n-6/n-3 = 2.4) fed salmon, which confirmed the suitability of the in vitro model in this experiment. Leukocytes, treated with LPS, and isolated from salmon fed the soybean oil diet (n-6/n-3 = 2.4) also upregulated tumor necrosis factor alpha (tnf-α), cyclooxygenase (cox2), prostaglandin D and E synthase (ptgds, ptges), fatty acyl synthase (fas), 5 and 6 desaturases (5des, 6 des) and a fatty acid translocase protein (cd36) when compared to the other diets. The results suggest that diets with a specific n-6/n-3 ratio influence the transcription of pro-inflammatory genes and may be cross-linked to transcription of selected fatty acid metabolism genes. Salmon fed the palm oil diet (n-6/n-3 = 0.7) showed a lower expression of inflammatory genes. Instead, peroxisome proliferator activated receptor β1 (pparβ1), acyl coenzyme A (aco), apoptosis regulator (bax) and superoxide dismutase (sod) were upregulated in leukocytes in vitro, while head kidney tissue transcription of a dendritic marker (cd83) was lower than measured in tissues from fish fed the other diets. The concentration of LTB4 (10-20 ng/mL) were relatively constant in leukocyte supernatants, all diets. Head kidney leukocytes from soybean oil (n-6/n-3 = 2.4) fed fish produced LPS induced PGE2 (mean 0.5 ng/mL) while leukocytes isolated from palm oil diet (n-6/n-3 = 0.7) secreted very high amounts of LTB5 (50-70 ng/mL). In addition, equal amounts of LPS induced PGE2 and PGE3 (mean 0, 5 ng/mL) were produced, indicating that the n-6/n-3 ratio of this saturated fatty acid may have a specific impact on eicosanoid production in the head kidney of salmon.

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.

By feeding Atlantic salmon diets with 64% of the fish oil (FO) replaced by vegetable oil, and with decreasing fishmeal (FM) inclusion levels from 213, 178 and 143 g kg−1 (accumulated level during the seawater phase) in a full-scale experiment producing 3.1 thousand tonnes fish, no significant negative effects on fish performance, health and product quality were observed. All dietary groups showed, however, moderate intestinal inflammation. Reduced growth and feed efficiency were seen with decreasing fishmeal inclusion levels. Two dietary groups demonstrated net marine protein production, while none of the groups showed net fish production (FIFO ≥1.65) due to the equal low FO inclusion. High plant oil level gave lower fillet level of persistent organic pollutants (POPs) compared with the levels surveyed on the Norwegian market. The study gave predictable incorporation rates of essential n-3 long-chain fatty acids in the fillet. Cooked salmon fillet from all dietary groups showed minor differences in sensory quality. Based on the present full-scale production results, dietary FM inclusion down to 160 g kg−1 (accumulated) during the seawater phase, concurrent to replacing ~70% of the FO with a suitable plant oil, is not regarded to represent any risk to fish performance, health or quality.

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

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.

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.

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.

This paper reports on the use of plant protein in cod diets, and where corn gluten meal, soybean meal, a mixture of these, or a mixture of wheat gluten meal and soy protein concentrate, substituted fish meal in a regression design up to 440 g kg−1 plant ingredients. Feeding lasted for a period of 20 weeks. High growth rates were obtained, and fish were able to maintain growth in all groups by increasing feed intake when plant proteins exerted high amounts of the protein fraction. This was confirmed by increased feed conversion ratio (FCR) values. The apparent digestibility measured by means of faecal stripping, showed high apparent digestibility coefficients (ADC) for fat, starch and protein. Small decreases in protein ADC and larger decreases in fat ADC were observed with high levels of plant protein ingredients. No histopathological changes were found, neither in liver nor in the different sections of the gastrointestinal (GI) tract, for any of the diet groups. Expression of stress genes (heat shock protein 70 and 90 (HSP70 and HSP90)) in liver showed no response to high levels of plant protein. Invasion of gut-bacteria in the distal part of the GI tract was substantial, but independent of diet level of plant ingredients. Gut evacuation analysis showed that the time for a meal to pass through the stomach and the GI tract was more than 72 h, with no variation dependent on diet plant protein level. The major conclusion is that cod shows a high tolerance to the plant protein sources investigated in this experiment, and consequently that Atlantic cod safely can be fed diets holding up to 440 g kg−1 of the present investigated plant protein ingredients without any adverse effects on intestinal or liver function. There seems to be no gain if feeding frequency exceeds more than one large meal every 24 h at 6–7°C.

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.

To determine the effect of long term feeding of diets with high levels of vegetable oils gilthead seabream juveniles were fed for 7 months with several diets containing vegetable oils at two inclusion levels. Anchovy oil was the only lipid source of FO (fish oil) diet, whereas in diets 60RO, 60LO and 60SO, 60% of fish oil was substituted by rapeseed (RO), linseed (LO) or soybean (SO) oils, respectively, and 80% was substituted by linseed or soybean oils in diets 80LO and 80SO. Afterwards, all fish were fed only a fish oil diet to determine the progressive evolution of fillet fatty acid profiles, since fish muscle fatty acid composition changes by feeding vegetable oils affecting its nutritional value for human health. Results showed that substitution by vegetable oils of up to 60% fish oil in diets for gilthead seabream does not affect growth and feed utilization even after a long feeding period. However, 80% substitution of fish oil significantly reduced growth. Feeding vegetable oils reduced muscle contents of docosahexaenoic acid (DHA) and arachidonic acid (ARA) to a lower degree than their reduction in the diet, denoting their importance, reduction of eicosapentaenoic acid (EPA) in muscle being more pronounced. Moreover, re-feeding with a FO diet for 60 days effectively recovered muscle DHA and ARA contents, whereas those of EPA were not recovered even after 90 days. Linoleic acid was strongly retained even after “wash out”. Fish fillets were very well accepted by the panel of judges. Dietary soybean oil inclusion produced significantly less shiny and less hard fillets, but more juicy and adhesive than FO fillets, with a slight earthy flavour when fish were fed 80SO diet. However linseed oil inclusion only increased shininess when fish were fed 80LO diet. A significantly higher chroma value was obtained for 80LO fish fillets, although it was not noticeable to the human eye.

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

This study evaluated the effects of fish oil (FO) replacement by vegetable oils [soybean oil (SO), rapeseed oil (RO), linseed oil (LO)] and subsequent feeding with FO on the liver morphology of sea bream. A short-term trial (3 months) and long-term trial (6 months) were carried out feeding sea bream with the following experimental diets: FO100%; SO60% + FO40%; RO60% +FO40%; LO60% + FO40%; SO + RO +LO60% + FO40%. Finally, all groups from the long-term trial were fed with FO100% for 95 days (washout period). Liver samples were taken for histological and biochemical studies. In both the short- and long-term trials, livers of sea bream fed LO60% and SO + RO + LO60% showed a similar hepatic morphology to that observed in fish fed FO100%. In contrast, sea bream fed SO60% showed an intense steatosis, with foci of swollen hepatocytes containing numerous lipid vacuoles. After the washout period, a considerable reduction of the cytoplasmic vacuolation and the lipid vacuole accumulation were observed in the livers of fish fed the different experimental diets. The results of this study suggested that the type of non-essential fatty acid, characteristic of vegetable oils, induces the appearance of steatosis in the following order: linoleic acid > linolenic acid > oleic acid. However, the liver alterations found during the experimental periods with vegetable oils are reversible when the fish are re-fed with a balanced diet (FO100%), indicating the non-pathological character of these histological changes.

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.

Due to its traditionally good availability, digestibility and high content of n − 3 HUFA, fish oil is the main lipid source in fish feeds. However, world demand for this product has grown significantly in recent years, whereas its production, based on fisheries landings, is static. The purpose of the present study was to assess the effect of partial replacement of fish oil in compound diets for gilthead seabream and seabass, by several vegetable oil sources, on growth, dietary fatty acid utilization and flesh quality. Five iso-energetic and isoproteic experimental diets were formulated (25% lipid content). Fish oil was the only added lipid source in the control (FO) diet, and it was included in the other experimental diets at a level high enough (40% of FO diet) to keep the n − 3 HUFA levels well over 3% in order to cover the essential fatty acid requirements of these species. Fish oil was replaced by soyabean oil (SO), rapeseed oil (RO) and linseed oil (LO) or a mixture (Mix) of them. Feed intake in all dietary groups was in the range of results obtained for commercial diets in both species, and growth and feed utilization were very good. The results show that, providing a minimum content of essential fatty acids in the diet, it is possible to replace up to 60% of the fish oil by SO, LO and RO or a mixture of them in diets for seabream and seabass, without compromising fish growth. Fatty acid composition of liver and muscle reflected that of the diet, but utilization of dietary lipids differed between these two tissues and was also different for the different fatty acids. Despite reduction in dietary saturated fatty acids by the inclusion of vegetable oils, their levels in fish liver were as high as in fish fed the fish oil diet, whereas, in muscle, levels were reduced according to that in the diet. Linoleic and linolenic acids were accumulated in the liver proportionally to their levels in the diet, suggesting a lower oxidation of these fatty acids in comparison to other 18C fatty acids. Regarding eicosapentaenoic acid (20 : 5n − 3; EPA), docosahexaenoic acid (22 : 6n − 3; DHA) and arachidonic acid (20 : 4n − 6; ARA), these essential fatty acids were reduced in the liver at a similar rate, whereas DHA was preferentially retained in the muscle in comparison with the other fatty acids, denoting a higher oxidation particularly of EPA, in the muscle. Some other PUFA increased despite their low dietary levels in seabream fed LO diets and in seabass fed SO diet, suggesting the stimulation of delta-6 and delta-5 desaturase activity in marine fish. Despite differences in fatty acid composition, fillet of fish fed vegetable oils was very well accepted by trained judges when assessed cooked.

The aim of the present study was to evaluate the morphological changes in the intestine of gilthead seabream fed different lipid sources. Five experimental diets containing 22% lipid and 45% crude protein were formulated: the control diet included fish oil as the only lipid source, whereas the other four diets contained linseed, soybean or rapeseed oils at two different levels of fish oil substitution, 60% or 80%. Gilthead seabream juveniles of 79 g mean body weight were fed the experimental diets for 3 months. At the end of experiment, samples of anterior intestine were taken for ultrastructural study. A morphometric study was performed to complete the morphological results. Irreversible tissue damages (necrosis or cell degeneration) could not be found in the intestinal epithelium of fish, regardless the diet fed. Microvillis were well developed, among which some absorptive vesicles were observed in fish from all diets. The major ultrastructural differences in the enterocytes of fish fed different diets were the accumulation of supranuclear lipid droplets and the formation of lipoproteins. Lipid droplet accumulation was increased by the percent of fish oil replaced. The morphometric study revealed that the cellular space occupied by lipid droplets was 2.3 times higher when fish were fed a diet containing linseed or soybean oils at a 60% replacement level than in the control fish, whereas in fish fed the vegetable oils at a 80% replacement level and rapeseed at 60% it was 5 times higher than in the control fish. In the intercellular spaces and lamina propria two different classes of lipoproteins in relation to their size were found: very low density lipoproteins (VLDL) of 30 to 85 nm in diameter and chylomicrons (QM) of over 100 nm. Fish fed a soybean oil diet, particularly at a 60% replacement level, exhibited a much higher accumulation of these granules in dilated intercellular spaces. The rest of experimental groups showed chylomicrons as the main lipoprotein. These results are discussed in relation to fatty acid compositions and cellular mechanisms involved in lipid absorption.

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 aim of the present study was to determine the impact of replacing at least 50% of the fish oil by alternative lipid sources in diets for rainbow trout on growth, lipid digestibility, fatty acid profiles of liver and muscle and tissue histology. Four experimental diets were formulated combining two fish oils (capelin and anchovy) with different vegetable oils (soybean, rapeseed, palm and olive) and one type of animal fat (lard), in order to obtain 60% to 80% fish oil replacement. A fifth diet prepared with pure fish oil (capelin oil) served as control. The diets were fed to apparent satiation twice a day to triplicate groups of 30 rainbow trout with an initial weight of 250 g for 64 days at 12 °C. Growth was good (TGC 3 3.7–3.9) and independent of diet. Final body weight was on average 760 g. Feed conversion ratios (FCR) ranged from 0.72 to 0.79. The only significant difference in FCR was found in the group fed an olive oil–lard combination replacing 80% of the fish oil. This diet also had a lower apparent lipid digestibility (79% vs. 91–94% for the rest of the diets). The liver and muscle fatty acid compositions were similar within groups and reflected that of the diets. But, tissue levels of 20:5 n −3 were lower and levels of 22:6 n −3 were higher than their respective dietary percentages. Histologically, a supranuclear accumulation of lipid droplets was observed in the intestinal cells of some of the groups fed diets supplemented with vegetable oils. Similarly, livers from these groups showed large amounts of lipid droplets within the hepatocytes. The present results suggest that most of the fish oil can be replaced by the alternative sources tested without compromising growth and feed utilisation. However, the histological changes observed suggest an impact of dietary lipid source on the transport and/or metabolism of fat in the fish. This requires further investigation.

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.

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.

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.

The objective of the present study was to investigate the development of intimal changes of coronary arteries over the lifetime of farmed Atlantic salmon, Salmo salar L., fed either a 100% fish oil or a 100% vegetable oil blend. The study was performed as a randomized observer blinded controlled trial with parallel group design. At the start of the project, the fish were divided in two groups and sampled at five different time points throughout their life span. The total study sample consisted of 259 healthy fish. Serial sections were taken from the coronary artery lying on the bulbus arteriosus for histopathological evaluation and for area measurements using semi-quantitative and quantitative methods. The earliest onset of vascular changes was detected in fish from both groups in the freshwater stage prior to smoltification. The mean range lesion (MRL), used to describe the severity of the lesions observed, increased significantly for both groups from sea transfer throughout the study period. Comparison of the two groups based on the overall material corrected for time of sampling did not show any difference (P = 0.20) between the two groups with regard to MRL. The percentage lumen loss (PLL) measured by a quantitative method and used as a measure to indicate lesion severity showed an incremental, non-significant increase from week 72 to week 92 and further to week 115 in both diet groups during the seawater phase. Comparison of the groups corrected for time of sampling indicated a difference of PLL in favour of VO (P = 0.02). Heart weight, body weight and body length were all positively and significantly correlated to Log MRL. The partial correlation analysis indicated that heart weight was the most dominant variable in the set. Early vascular changes were found in the major bifurcation of the coronary artery at the apex and beyond the flow divider into the daughter branches. The latter represented the dominant changes and were found throughout the entire lifecycle of the fish. Increasing in size over time they formed pads or cushions that were regularly located close to the outer walls of the bifurcation. The origin of the cells forming the intimal thickening has not been conclusively determined, but immunohistochemical findings indicate a smooth muscle cell origin, possibly of a myointimal type. Our findings suggest there is no correlation between diet and intimal changes. The severity of the changes, MRL and PLL, of the coronary vessels correlate with heart weight and fish weight growth and growth rate and mechanical factors are implicated in intimal development, but rather than being induced by external injury due to the location of the coronaries, haemodynamic factors and low shear stress are proposed as the main mechanism behind these changes.

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.

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.

Few ingredients allow the complete replacement of fish meals (FM) and fish oils (FO) in aquaculture feeds without affecting fish performance or fillet nutritive value. This is due to the adequate content of essential nutrients, including the n-3 long-chain polyunsaturated fatty acids (n-3 LC PUFA), and the unique high palatability of FM and fish oil. Some microalgae present abundant amounts of these fatty acids, for instance docosahexaenoic acid (DHA). Therefore, the aim of the present study was to evaluate the effect of two different microalgae products, one providing DHA and eicosapentaenoic acid (EPA, 20:5n-3; ED diet), and the other one DHA and n-6 docosapentaenoic acid (DPA, 22:5n-6; DD diet), in combination with poultry oil and rapeseed oil, as total replacers of fish oil, at two different dietary fish meal contents (15 and 7.5%). The effects of these dietary oil combinations on performance, composition and nutritive quality indexes of gilthead sea bream (Sparus aurata) juveniles were studied and compared against a positive control diet (FO) and two negative control diets (PO diets), one for each dietary fish meal content tested, giving in total 7 experimental diets. Both microalgae products in combination with poultry and rapseed oils were able to completely replace fish oil in practical diets with 15% FM without affecting growth performance, utilization of dietary fatty acids or the nutritional quality of fish fillet for the consumer. On the contrary, PO alone was not able to completely replace fish oil and negatively affected fish performance, in relation to an insufficient dietary n-3 LC-PUFA content. A similar decrease in growth performance was also observed with the reduction of the dietary FM content to 7.5%. In conclusion, both oils from microalgae, providing either DHA and EPA or DHA and n-6 DPA, were effective n-3 LC-PUFA sources for sea bream juveniles and allowed complete replacement of fish oil in combination with more cost-effective lipid sources, such as poultry and rapeseed oils.