Effect of dietary fish meal and fish oil replacement on lipogenic and lipoprotein lipase activities and plasma insulin in gilthead sea bream (Sparus aurata)

The effects of a double replacement of fish oil (FO) and fish meal (FM) by dietary vegetable ingredients in juvenile gilthead sea bream (Sparus aurata L. 1758) on some indices of lipid metabolism and plasma insulin levels were analysed. Four experimental diets with a replacement of 75% of FM by plant proteins (PP) were administered. Added oil was either FO (75PP/FO diet), or a vegetable oil mix (VO), replacing 33%, 66% or 100% of FO (75PP/33VO, 75PP/66VO, 75PP/100VO diets). Another diet with 50% of substitution of FM by PP and with 100% of VO was also tested (50PP/100VO diet). Final body weight was similar in all diet groups, except for the 75PP/100VO group, which presented lower values. Circulating insulin levels increased with feed administration in all groups and no differences between diets were observed, with the exception of the 75PP/FO group, which presented higher plasma insulin values. In adipose tissue, glucose‐6‐phosphate dehydrogenase and malic enzyme activities decreased with the inclusion of vegetable oil, especially 5 h after feeding. Diet had no significant effect on the hepatic activity of either enzyme. Lipoprotein lipase activity decreased in white muscle and adipose tissue with the replacement of fish oil in 75PP diets, 5 h after feeding. In conclusion, the use of a combined replacement of fish oil and fish meal by vegetable ingredients in gilthead sea bream permits satisfactory growth, with moderate changes in tissue lipogenesis and lipid uptake.     

Effects of fish oil replacement by vegetable oil blend on digestive enzymes and tissue histomorphology of European sea bass (<Emphasis Type="Italic">Dicentrarchus labrax</Emphasis>) juveniles

The impact of replacing circa 70 % fish oil (FO) by a vegetable oil (VO) blend (rapeseed, linseed, palm oils; 20:50:30) in diets for European sea bass juveniles (IBW 96 ± 0.8 g) was evaluated in terms of activities of digestive enzymes (amylase, lipase, alkaline phosphatase, trypsin and total alkaline proteases) in the anterior (AI) and posterior (PI) intestine and tissue morphology (pyloric caeca—PC, AI, PI, distal intestine—DI and liver). For that purpose, fish were fed the experimental diets for 36 days and then liver and intestine were sampled at 2, 6 and 24 h after the last meal. Alkaline protease characterization was also done in AI and PI at 6 h post-feeding. Dietary VO promoted higher alkaline phosphatase activity at 2 h post-feeding in the AI and at all sampling points in the PI. Total alkaline protease activity was higher at 6 h post-feeding in the PI of fish fed the FO diet. Identical number of bands was observed in zymograms of alkaline proteases of fish fed both diets. No alterations in the histomorphology of PC, AI, PI or DI were noticed in fish fed the VO diets, while in the liver a tendency towards increased hepatocyte vacuolization due to lipid accumulation was observed. Overall, and with the exception of a higher intestine alkaline phosphatase activity, 70 % FO replacement by a VO blend in diets for European sea bass resulted in no distinctive alterations on the postprandial pattern of digestive enzyme activities and intestine histomorphology.     

Validation of processed animal proteins (mono‐PAPS) in experimental diets for juvenile gilthead sea bream (Sparus aurata L.) as primary fish meal replacers within a European perspective

Experimental diets were formulated to evaluate a “pure” poultry meat meal (PMM) source in diets formulated for juvenile gilthead sea bream (Sparus aurata L.). The digestible protein contribution of fish meal in a control diet was substituted by 25%, 50% and 75% of a processed poultry meat meal (PMM) on a digestible crude protein (DCP) basis and by 5% and 10% for an enzyme‐treated feather meal (EFM) and also a spray‐dried haemaglobin meal (SDHM), respectively. In a consecutive trial, diets were designed to assess the value of a “pure” (defatted) poultry protein substituting the fish meal (FM) protein content. Experimental diets included: a control diet, two test diets where 75% of FM was replaced by a full‐fat PMM (PMM75) or a defatted grade of PMM (dPMM75) and two test diets where 50% of FM was substituted for defatted PMM (dPMM50) or a 50:50 blend of soya bean meal and defatted PMM (SBM/dPMM) to produce a composite product. This soya bean/dPMM blend was tested to enhance the nutritional value of this key plant ingredient commonly employed in sea bream diets that can be deficient in specific amino acids and minerals. In the first trial, gilthead sea bream grew effectively on diets containing up to the 75% replacement of FM attaining a mean weight of 63.6 g compared to 67.8 g for the FM control fed group. For the consecutive trial, the fishmeal‐based control diet yielded the highest SGR followed by dPMM50 and SBM/dPMM blend inclusion but was not significant. Carcass FA profiles of gilthead sea bream conformed to the expected changes in relation to the dietary FA patterns, with the 18:1n‐9 representative of the poultry lipid signature becoming more apparent with PMM inclusion. The ratio of n‐3/n‐6 fatty acids was greatly affected in sea bream fed the full‐fat PMM at 75% inclusion due to fish oil exclusion. Defatted dPMM, however, allowed more of the fish oil to be used in the diet and reducing this latter effect in sea bream carcass, hence restoring the higher total omega‐3 HUFA fatty acids namely EPA and DHA and n‐3/n‐6 ratio. It is concluded that poultry meat meal can be modestly incorporated into formulated diets for sea bream and can be used in conjunction with soya bean meal without any fundamental changes in performance and feed efficiency.     

Histological alterations in the liver of sea bream, Sparus aurata L., caused by short- or long-term feeding with vegetable oils. Recovery of normal morphology after feeding fish oil as the sole lipid source

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.     

The influence of dietary fish oil replacement with mixture of vegetable oils on reproductive performance,immune responses and dynamic of fatty acids during embryogenesis in Oncorhynchus mykiss

A 90‐day feeding trial was carried out to examine the influence of fish oil (FO) substitution with blends of vegetable oils (VOs) on reproductive efficiency of female brooders and fluctuation in fatty acid (FA) profile of embryos in Oncorhynchus mykiss. A basal diet was formulated in which 20% (80FO/20VO), 50% (50FO/50VO), 75% (25FO/75VO) and 100% (100VO) of FO were replaced by mixture of VO. Reproductive performance of brooders was not affected by drastic alternations in FA profile of diets. The level of saturated and monounsaturated FAs (MUFAs) significantly increased, whereas the levels of long‐chain polyunsaturated FAs (LC‐PUFAs), mainly docosahexaenoic acid, profoundly decreased during embryogenesis. The concentrations of MUFA and n?6 PUFA increased in the eggs with increasing the incorporation of VO mixture in diets; however, the concentration of LC‐PUFA and n?3/n?6 PUFA ratio decreased. Haematological parameters and humoral immune responses including total immunoglobulin content, lysozyme and alternative complement pathway activities in brooders fed with the experimental diets did not statically different. In summary, incorporating mixture of various VO sources especially linseed and sunflower oils as good sources of α‐linolenic and linoleic acids, respectively, along with low levels of residual fat from fish meal in diet suggested a good strategy for providing the appropriate essential FA requirements of O. mykiss brooders for their successful reproduction.     

Optimum selenium levels in diets high in plant‐based feedstuffs for gilthead sea bream (Sparus aurata) fingerlings

Substitution of marine ingredients (FM‐FO) by plant protein and oil sources can modify selenium (Se) levels in feeds. Se plays an important role in the antioxidative defence by forming part of selenoproteins. Se requirements of gilthead sea bream are not accurately determined; therefore, this study was conducted to define Se supplementation levels in low FM‐FO practical diets for sea bream fingerlings. A plant‐based diet containing 0.45 mg Se/kg diet was used as the basal diet. Four other diets were supplemented to contain 0.68, 0.86, 1.00 or 1.70 mg Se/kg diet, supplied as sodium selenite. Sea bream, weighing 12.6 ± 1.4 g, were distributed in triplicate groups per diet and fed for 42 days. Se supplementation up to 1.00 mg Se/kg significantly improved the growth of sea bream, whereas further increase up to 1.70 mg Se/kg diet reduced growth. The results of this study suggest that the optimum dietary levels of sodium selenite in diets with low FM‐FO with basal levels of 0.45 mg Se/kg are around 0.94 mg Se/kg to promote growth of gilthead sea bream juveniles. On the contrary, dietary levels of 1.70 mg Se/kg were found to be excessive and caused growth reduction, increased catalase expression and hydropic degeneration in the liver.     

Vegetable oil blend as alternative lipid resources in diets for gilthead seabream, Sparus aurata

The recent decreasing worldwide supplies of marine oils have forced the aquaculture industry to investigate alternative lipid sources for use in marine fish feeds. The aim of this study was to determine the impact of dietary replacement of fish oil by vegetable oils on gilthead seabream (Sparus aurata) growth performance, nutritive utilization, body composition, and fatty acid profile as well as feed cost. Two dietary vegetable oil (VO) mix blends (VO1 and VO2) in which: sunflower (SO), cottonseed (CO) and linseed (LO) for VO1 or soybean oil (SBO) for VO2, were tested as 60% fish oil (FO) substitutes versus the 100% FO control or reference diet (FO). Three iso-proteic (46% CP) and iso-lipidic (18%) experimental diets were hand fed, twice a day, 6 days a week to apparent visual satiety to triplicate groups of seabream growers (average initial weight, 130.9 ± 3.44 g), until fish reached market size (300–400 g/fish) after 20 weeks at mean ambient temperature 27.0 ± 1.8°C. All experimental diets were well accepted by seabream growers regardless of the different lipid sources used, as overall mean feed intake (FI) and daily intake (DFI) were not significantly different (P > 0.05) among dietary treatments. In terms of growth performance, fish fed VO1 diet (with LO) exhibited a relatively lower, but significant (P < 0.05), total weight gain (WG) than fish fed all FO diet (FO). However, mean value of WG of fish fed either vegetable oil-tested diet was nonsignificantly different. Feeding seabream growers vegetable oil (VO) diets (VO1 or VO2) had no significant effect on specific growth rate (SGR), daily weight index (DWI), or feed conversion ratio (FCR) among dietary treatments. Consumption of VO for 20 weeks did not significantly alter the major nutrient composition of fish, but the muscle fatty acid (FA) profile was significantly altered compared to the reference FO diet. Comparatively reduced levels of eicosapentaenoic acid (EPA) and docosahexaenoic acids (DHA), as well as elevated levels of linoleic and linolenic acids (LA and LNA) compared with fish fed the FO were noticed. In terms of economics, 17 or 20% reduction in Kg feed cost was obtained for diets VO1 or VO2, respectively. In terms of growth performance and cost, VO2 diet showed slight relative superiority over VO1 diet. However, in terms of liver structure morphology, VO1 diet (with LO) has resulted in less fat-infiltration and altered hepatic cells than VO2 (with SBO). As these traits do not affect yield or the price paid for the fish, VO2 diet has therefore been considered better than VO1 as complementary lipid sources for gilthead seabream grower diets.     

植物油替代鱼油对虹鳟、花鲈和大黄鱼组织结构的影响

以初始体重分别为(11.24±0.07 g)、(18.60±0.36 g)和(8.93±0.21 g)的虹鳟、鲈鱼和大黄鱼幼鱼为研究对象,用植物油(亚麻籽油:豆油=1:1)分别替代0%(FO,对照组)、50%(FV)和100%(VO)的鱼油来配制三种等氮(粗蛋白含量为41%)等脂(粗脂肪含量为12%)的实验饲料。通过投喂实验探讨不同植物油替代鱼油水平对虹鳟(淡水鱼)、鲈鱼(广盐性鱼类)和大黄鱼(海水鱼)肝脏和肠道组织结构的影响差异。70 d投喂实验后发现,随着替代水平增加虹鳟、鲈鱼和大黄鱼的肝细胞中脂肪滴累积程度逐渐增高,相同替代水平下肝细胞中脂肪滴累积程度为大黄鱼>鲈鱼>虹鳟;肠道组织中杯状细胞随植物油替代水平升高而增多,而在大黄鱼全植物油组出现脂肪滴累积和上皮细胞死亡现象。以上结果表明植物油替代鱼油对虹鳟组织结构影响最小对大黄鱼影响最大。     

Replacement of fish oil with vegetable oil blends in feeds for greater amberjack (Seriola dumerili) juveniles: Effect on growth performance,feed efficiency,tissue fatty acid composition and flesh nutritional value

This study was undertaken to assess the effects of fish oil (FO) substitution by a mixture of alternative vegetable oils (VO) on Seriola dumerili culture performance. A 154‐day feeding experiment was conducted using juveniles (39.2 ± 1.6 g average weight). Three isolipidic and isoenergetic meal‐based diets were formulated varying their lipid component. The control diet contained 100% FO (FO100), whereas diets VO50 and VO100 included 1/2 of oil blend and all the oil from blend of palm oil (PO) and linseed oil (LO) as substitute for FO, respectively. Dietary regime did not significantly affect growth performance, biometric indices, feed efficiency, plasma chemistry and liver and muscle lipid contents. Nonetheless, dietary VO inclusion impacted on the fatty acid profile of target tissues, especially in the liver. Fatty acid profiles of the fillets reflected those of the dietary oils except that there was apparent selective utilization of palmitic acid (C16:0) and oleic acid (C18:1n‐9) and apparent selective retention of long‐chain polyunsaturated fatty acids, especially eicosapentaenoic acid (EPA, C20:5n‐3) and docosahexaenoic acid (DHA, C22:6n‐3). The nutritional value and the potential ability to prevent the development of coronary heart diseases of the flesh lipid fraction decreased with gradual FO substitution.     

Linseed oil inclusion in sea bream diets: effect on muscle quality and shelf life

Dietary lipid source in aquaculture has become a central topic in research whilst natural resources availability diminishes. Hence, to weigh up and forecast consumers impressions, the impact of partial (70%) and complete (100%) dietary replacement of fish oil (FO) by linseed oil (LO) on sensory and quality attributes was studied during the edible shelf life of gilthead sea bream (Sparus aurata). Physico‐chemical parameters (pH, torrymeter, total volatile basic nitrogen, thiobarbituric acid reactive substances and texture), and sensory analysis, both in cooked and raw fish were carried out during 17 days of ice storage. Throughout ice storage, feeding with LO diets, TBARS values remained lower on muscle than those found when feeding FO control diet. On freshly caught fish (day 0 of ice storage), statistically significant dietary texture variations were recorded on cooked fillet fed FO diet. No sensory differences on Quality Index Method, sensory profile or Torry scheme were found with partial or total LO replacement diets.     

Inter-individual variation in total fatty acid compositions of flesh of Atlantic salmon smolts-fed diets containing fish oil or vegetable oil

Fish such as Atlantic salmon (Salmo salar L.) are a natural source of n‐3 highly unsaturated fatty acids (HUFA) eicosapentaenate (EPA; 20:5n‐3) and docosahexaenoate (DHA; 22:6n‐3), which are essential for protecting humans against cardiovascular diseases. Thus, flesh n‐3 HUFA level is a trait of considerable importance in farmed fish, particularly now that the fishmeal and fish oil (FO) components of traditional aquaculture diets have to be replaced by more sustainable alternatives including plant meals and vegetable oils (VO). The present study aimed to characterize the inter‐individual variation in this trait in a single strain of Atlantic salmon. Fish were grown for 12 weeks on either an FO diet, or a diet with 100% of the FO replaced by a VO blend containing rapeseed, linseed and palm oils, flesh n‐3 HUFA content and composition determined, and the variation between individuals characterized. The results showed that, irrespective of diet, variation exists in the content of n‐3 HUFA in the flesh of individual salmon, showing that individual animals can display an enhanced ability to maintain high levels of n‐3 HUFA in their flesh. The pros and cons of defining the trait on a qualitative or quantitative basis are discussed.     

Effects of dietary lipid level and vegetable oil on fatty acid metabolism in Atlantic salmon (Salmo salar L.) over the whole production cycle

Changes in fatty acid metabolism in Atlantic salmon (Salmo salar) induced by vegetable oil (VO) replacement of fish oil (FO) and high dietary oil in aquaculture diets can have negative impacts on the nutritional quality of the product for the human consumer, including altered flesh fatty acid composition and lipid content. A dietary trial was designed to investigate the twin problems of FO replacement and high energy diets in salmon throughout the entire production cycle. Salmon were grown from first feeding to around 2 kg on diets in which FO was completely replaced by a 1:1 blend of linseed and rapeseed oils at low (14–17%) and high (25–35%) dietary oil levels. This paper reports specifically on the influence of diet on various aspects of fatty acid metabolism. Fatty acid compositions of liver, intestinal tissue and gill were altered by the diets with increased proportions of C₁₈ polyunsaturated fatty acids and decreased proportions of n-3 highly unsaturated fatty acids (HUFA) in fish fed VO compared to fish fed FO. HUFA synthesis in hepatocytes and enterocytes was significantly higher in fish fed VO, whereas β-oxidation was unaltered by either dietary oil content or type. Over the entire production cycle, HUFA synthesis in hepatocytes showed a decreasing trend with age interrupted by a large peak in activity at seawater transfer. Gill cell prostaglandin (PG) production showed a possible seasonal trend, with peak activities in winter and low activities in summer and at seawater transfer. PG production in seawater was lower in fish fed the high oil diets with the lowest PG production generally observed in fish fed high VO. The changes in fatty acid metabolism induced by high dietary oil and VO replacement contribute to altered flesh lipid content and fatty acid compositions, and so merit continued investigation to minimize any negative impacts that sustainable, environmentally-friendly and cost-effective aquaculture diets could have in the future. Abbreviations: FO - fish oil; HUFA - highly unsaturated fatty acids acids (carbon chain length ≥C ₂₀ with ≥3 double bonds); LO - linseed oil; RO - rapeseed oil; VO - vegetable oil. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of high-level fish meal replacement by plant proteins in gilthead sea bream (Sparus aurata) on growth and body/fillet quality traits

Juvenile gilthead sea bream (initial body weight ca. 100 g) were reared in an indoor flow through marine water system for 1 year. Fish were fed two isoenergetic [19.2 kJ g⁻¹ dry matter (DM)] and isoproteic (426 g kg⁻¹ DM) diets either based on fish meal (diet FM) or on a mixture of plant protein sources (diet PP), replacing 75% of fish meal protein. The growth trial was conducted in duplicate, two tanks for each dietary treatment. Growth performance and feed utilization were registered. Fillet quality parameters were evaluated and sensory analyses on cooked fillet were performed. Both groups had similar weight gain and specific growth rates. Feed intake was higher in sea bream fed diet FM (0.48 versus 0.44), while feed efficiency and protein efficiency ratio were significantly higher in sea bream fed PP (0.83 versus 0.77 and 2.0 versus 1.76, respectively). Sea bream fed diet FM had a lower hepatosomatic index (0.80 versus 0.87%), and a higher fillet yield (45.9 versus 44.9%). The fillet from sea bream fed diet FM had higher moisture (696 versus 682 g kg⁻¹), lower lipid levels (91 versus 100 g kg⁻¹) with higher levels of n‐3 polyunsaturated fatty acids (PUFA) and monounsaturated fatty acids (MUFA), while the PP fed sea bream presented a higher level of PUFA n‐6. There were minor differences in muscle free amino acid levels between the two diet groups. As regards sensory evaluation of cooked fillet, the judges were unable to discriminate the two dietary groups of fish. Summarizing, the results demonstrate the possibility to use diets containing high levels (750 g kg⁻¹) of plant ingredients in gilthead sea bream without affecting growth performance and with minor effects on quality traits of commercial size sea bream.     

Impact of Dietary Oil Source on the Shelf-Life of Gilthead Seabream (Sparus aurata)

Gilthead seabream were fed two diets containing 100% fish oil (FO) or a 75% vegetable oil blend (VO) (50/50 soybean and rapeseed oil) in order to study the effect on shelf life. The fish were stored at 4 ± 1ºC for 0, 7, 14, and 21 days. Physicochemical, microbiological, and sensory analyses were performed. The fatty acid composition of muscle reflected the profile of dietary lipids. A smaller quantity of highly unsaturated fatty acids (HUFAs) in the VO group resulted in lower lipid oxidation. In this group, lower thiobarbituric acid reactive substances (TBARS) values were observed during the storage and an increase in saturated fatty acid (SFAs) occurred later than in the group FO. Higher water holding capacity (WHC) of muscle was also observed in the VO group. A higher redness (a* value) was observed in the VO group, although discoloration occurred with the same intensity in both groups. Despite the differences among groups observed in psychrophilic and Pseudomonas counts and in some sensory attributes, shelf-life was equal for both groups.     

Total Replacement of Dietary Fish Oil with a Blend of Vegetable Oils in the Marine Herbivorous Teleost,Siganus canaliculatus

To investigate the feasibility of total replacement of dietary fish oil (FO) with vegetable oils (VOs) and the optimal dietary polyunsaturated fatty acid (PUFA) level in the marine herbivorous teleost Siganus canaliculatus, six isonitrogenous (32%) and isolipidic (8%) diets were formulated. Control diet used FO as lipid source, whereas diets VO1–VO5 contained various blends of palm, soybean, rapeseed, and linseed oils, in which the dietary PUFA levels were 42.0, 38.2, 33.8, 29.9, and 27.1%, respectively. After S. canaliculatus juveniles were fed with the diets for 9 wk, their growth performance exhibited no significant difference among the dietary groups. The tissue fatty acid (FA) profiles in liver and fillet generally reflected the dietary FA compositions and showed no significant difference among the VO dietary groups. The results suggest that dietary FO can be replaced completely by VO, without affecting their growth performance. Concerning the effects of the dietary FA profile on the survival rate, hepatosomatic index and viscerosomatic index, and PUFA composition in fillets, diets VO1 and VO2 were more favorable compared with diets VO3–VO5. Considering the availability and cost of the VOs, diet VO2 was recommended for practical use in S. canaliculatus.     

Fish proteins not lipids are the major nutrients limiting the use of vegetable ingredients in catfish nutrition

The objective of this study was to determine the major nutrient limiting growth and lipid metabolism in African catfish fed diets composed of vegetable ingredients. Four diets were formulated from contrasted meal (fish meal: FM; vegetable meal: VM) and oil (fish oil: FO; vegetable oil: VO) sources. Replacement of FO by VO did not affect specific growth rate (SGR) and feed efficiency, whereas lower values were recorded in the case of FM replacement. LC‐PUFAs muscle contents were higher in fish fed control FMFO diet than in fish fed vegetable ingredients. However, the decrease in docosahexaenoic acid (DHA) concentration in FMVO group was limited compared to VM groups despite the same low DHA level in those three diets. These results may suggest an activation of LC‐PUFA biosynthesis from PUFA precursors brought with vegetable oils in FMVO group. This hypothesize is reinforced by the significant stimulation of elovl5 gene expression in liver and intestine from fish fed FMVO. Therefore, this study demonstrated that African catfish is able to bioconvert LC‐PUFAs at a significant biological level when FO is replaced by VO whereas the use of plant proteins has strong detrimental effects on growth performances.     

Preliminary evaluation of pea seed meal in diets for gilthead sea bream (Sparus aurata) juveniles

Juvenile gilthead sea bream with a mean initial body weight of 5 g were fed for 12 weeks with experimental diets containing 10% and 20% fishmeal protein (sole protein source in the control diet) replaced by processed pea seed meals. The processed pea seed meals were dehulled, defibred, extruded and microground pea seed meal (PSM1) or whole pea treated by infrared radiation and ground (PSM2). Apparent digestibility coefficients of the experimental diets were determined in a separate trial. At the end of the growth trial there were no significant differences in growth performance, feed utilization or whole-body composition among experimental groups. There were no differences in apparent protein digestibility among experimental groups (except for fish fed PSM1 at the lowest inclusion level). Both dry matter and energy digestibility of the diets, including PSM2 and with the highest inclusion level of PSM1, were significantly lower than those of the control diet. The results of this study suggest that pea seed meal may replace up to 20% fishmeal protein in diets for gilthead sea bream juveniles without affecting fish performance. Further studies should focus on technological treatments to increase utilization of pea seed meal carbohydrate, as both apparent dry matter and energy digestibility were affected by dietary inclusion level and by pea seed meal processing method.     

Reducing the levels of dioxins and dioxin-like PCBs in farmed Atlantic salmon by substitution of fish oil with vegetable oil in the feed

Atlantic salmon were fed extruded diets based on either 100% fish oil (FO) or 100% vegetable oil blend (VO) substitution for 22 months. A total of seven distinct feeding periods were studied that incorporated higher levels of dietary oil inclusion, and larger pellet size as fish size increased. Whole fish levels of polychlorinated dibenzo‐p‐dioxins and dibenzofurans (PCDD/F) and dioxin‐like PCBs (DLPCB) were analysed at the beginning and end of each of the seven feeding periods. The PCDD/F and DLPCB concentrations in the FO diets increased from 2.43 to 4.74 ng WHO‐TEQ kg^?1 (TEQ, toxic equivalents), while VO diets decreased from 1.07 to 0.33 WHO‐TEQ kg^?1 as oil inclusion increased. Partial least square regression analyses identified feed concentration, growth rate and feed utilization, but not variations in lipid content, as factors significantly affecting fish PCDD/F and DLPCB levels. Accumulation efficiencies for DLPCB (740 ± 90 g kg^?1) were significantly (P < 0.01) higher than for PCDD/F (430 ± 60 g kg^?1), explaining the increasing dominance of DLPCB levels over PCDD/F levels in whole fish (DLPCB : PCDD/F ratio of 2.4 ± 0.1 for both VO and FO fed fish) compared with feed (DLPCB : PCDD/F ratio of 1.5 and 0.34 for FO and VO feed respectively). Vegetable oil substitution significantly reduced the level of PCDD/F and DLPCB (eightfold and twelve‐fold, respectively) in the fillet of a 2 kg salmon, but, also negatively affected beneficial health components such as fillet n‐3/n‐6 fatty acid ratio.