Effects of diets rich in linoleic (18:2n - 6) and α-linolenic (18:3n - 3) acids on the growth, lipid class and fatty acid compositions and eicosanoid production in juvenile turbot (Scophthalmus maximus L.)

Nrf2 pathway in vegetable oil-induced inflammation of large yellow croaker (Larimichthys crocea)

This study was conducted to investigate the effects and regulation of dietary vegetable oil (VO, enriched with α-linolenic acid [ALA] and linoleic acid [LNA]) on the nuclear factor erythroid 2-related factor 2 (Nrf2) and nuclear factor-κB (NF-κB) pathways in large yellow croaker. In vivo study showed that the VO diet significantly decreased the activity of antioxidant enzymes and antioxidant enzyme-related mRNA expression in the liver tissue, in comparison with the fish oil (FO) diet (P < 0.05). The suppression of antioxidant capacity might be due to the decrease of nuclear Nrf2 protein translocation, Nrf2 binding to antioxidant response element (ARE) sequences, and subsequently, antioxidant genes transcription as electrophoretic mobility shift assay (EMSA) and luciferase assay showed. VO-derivated ALA and LNA exerted a lower antioxidant capacity than FO-derivated DHA and EPA, characterized by significantly lower nucleus Nfr2 protein expression but significantly higher ROS production values in primary hepatocytes (P < 0.05). The pro-inflammatory genes (tumor necrosis factor α [TNFα] and interleukin 1β [IL1β]) expression was significantly higher in the liver tissue of fish fed the VO diet which might be due to the activation of the NF-κB pathway (P < 0.05). Knockdown of the Nrf2 gene negatively affected the anti-inflammatory effect of fatty acids by increasing the expression of TNFα and the IL1β gene and nuclear p65 protein (P < 0.05). In general, the results indicated that dietary vegetable oil decreased antioxidant capacity but induced inflammatory responses through the Nrf2/NF-κB pathway.

Increasing dietary n-6 fatty acids while keeping n-3 fatty acids stable decreases EPA in polar lipids of farmed Atlantic salmon (Salmo salar)

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

Effect of replacement of dietary fish oil with four vegetable oils on prostaglandin E2 synthetic pathway and expression of inflammatory genes in marine fish Larimichthys crocea

As a lipid mediator with important immune function, prostaglandin E₂ (PGE₂) has been widely studied in mammals, whereas its synthetic pathway and immune function in fish have yet to be fully studied. To investigate the regulation of PGE₂ synthetic pathway and inflammatory genes expression by dietary different oils and the underlying relationship, a 10-week feeding experiment and an immune challenge were carried out in marine fish Larimichthys crocea. Replacement of dietary fish oil (FO) with four vegetable oils (VO), including soybean oil, linseed oil, palm oil, and olive oil, all reduced PGE₂ levels, and the decrease of arachidonic acid (ARA, substrate for PGE₂) could account for this decline. Meanwhile, the expression of PGE₂ synthesis related genes was basically upregulated, which seemed to be a feedback regulation, but it cannot compensate the deficiency of ARA. In addition, mRNA expression of inflammatory genes, including interleukin (IL)-1β, IL-6, tumor necrosis factor (TNF)α and interferon (IFN)γ was all upregulated in four VO groups compared with FO group, which was the opposite of PGE₂ levels. To verify the inflammatory regulation of PGE₂, an immune challenge was conducted, and PGE₂ alleviated LPS-induced expression of inflammatory genes, including IL-6, TNFα and IFNγ, and the similar downregulation of toll-like receptor (TLR) genes expression revealed that TLR signaling pathway participated in the anti-inflammatory regulation of PGE₂. In conclusion, replacement of dietary FO with four VO (lack of ARA) reduced the levels of PGE₂ that could alleviate LPS-induced inflammatory genes expression via TLR signaling pathway, which could be one of the reasons that VO induced inflammation in marine fish.

Effect of plant-based diets with varying ratios of ω6 to ω3 fatty acids on growth performance, tissue composition, fatty acid biosynthesis and lipid-related gene expression in Atlantic salmon (Salmo salar)

Little is known about how variation in omega-6 to omega-3 (ω6:ω3) fatty acid (FA) ratios affects lipid metabolism and eicosanoid synthesis in salmon, and the potential underlying molecular mechanisms. The current study examined the impact of five plant-based diets (12-week exposure) with varying ω6:ω3 (0.3-2.7) on the growth, tissue lipid composition (muscle and liver), and hepatic transcript expression of lipid metabolism and eicosanoid synthesis-related genes in Atlantic salmon. Growth performance and organ indices were not affected by dietary ω6:ω3. The liver and muscle FA composition was highly reflective of the diet (ω6:ω3 of 0.2-0.8 and 0.3-1.9, respectively) and suggested elongation and desaturation of the ω3 and ω6 precursors 18:3ω3 and 18:2ω6. Furthermore, proportions of ω6 and ω3 PUFA in both tissues showed significant positive correlations with dietary inclusion (% of diet) of soy and linseed oils, respectively. Compound-specific stable isotope analysis (CSIA) further demonstrated that liver long-chain polyunsaturated fatty acid (LC-PUFA) synthesis (specifically 20:5ω3 and 20:4ω6) was largely driven by dietary 18:3ω3 and 18:2ω6, even when 20:5ω3 and 22:6ω3 were supplied at levels above minimum requirements. In addition, significant positive and negative correlations were identified between the transcript expression of LC-PUFA synthesis-related genes and liver ω6 and ω3 LC-PUFA, respectively, further supporting FA biosynthesis. Liver ω3 LC-PUFA also correlated negatively with the eicosanoid synthesis-related transcripts pgds and cox1. This is the first study to use CSIA, hepatic transcriptome, and tissue lipid composition analyses concurrently to demonstrate the impact of plant-based diets with varying ω6:ω3 on farmed Atlantic salmon.

Molecular characterization and tissue distribution of carnitine palmitoyltransferases in Chinese mitten crab Eriocheir sinensis and the effect of dietary fish oil replacement on their expression in the hepatopancreas

The carnitine palmitoyltransferase (CPT) family includes CPT 1 and CPT 2 that transport long-chain fatty acids into the mitochondrial compartment for β-oxidation. In this study, three isoforms (CPT 1α, CPT 1β and CPT 2) of the CPT family were cloned from Chinese mitten crab (Eriocheir sinensis) and their complete coding sequences (CDS) were obtained. Sequence analysis revealed deduced amino acid sequences of 915, 775 and 683 amino acids, respectively. Gene expression analysis revealed a broad tissue distribution for all three isoforms, with high CPT 1α and CPT 2 mRNA levels in the hepatopancreas of males and females. In males, CPT 1β was highly expressed in gill, heart, brain ganglia and muscle, while in females, CPT 1β-mRNA levels were relatively high in muscle, hepatopancreas and ovary tissue. The effects of dietary fish oil replacement on the expression of the three CPT isoforms in the hepatopancreas during gonadal development were investigated using five experimental diets formulated with replacement of 0, 25, 50, 75 and 100% fish oil by 1:1 rapeseed oil: soybean oil. The results showed that Diets 2# and 5# yielded higher CPT 1α and CPT 2 mRNA expression in males (P < 0.05), while in females, expression of all three CPT isoforms increased then declined in the hepatopancreas with increasing dietary fish oil replacement. The observed changes in CPT gene expression varied in different isoforms and gender, suggesting the three CPT genes might play different roles in fatty acid β-oxidation in E. sinensis.

Supplementation of arachidonic acid rich oil in European sea bass juveniles (Dicentrarchus labrax) diets: Effects on leucocytes and plasma fatty acid profiles, selected immune parameters and circulating prostaglandins levels

The main objective of this study was to assess the effects of graded levels of dietary arachidonic acid (ARA), supplemented from alternative sources, on fatty acid composition of plasma and head kidney leucocytes of European sea bass (Dicentrarchus labrax). For that purpose, sea bass juveniles were fed four diets containing graded levels of ARA as follows: 0.5% (ARA0.5), 1% (ARA1), 2% (ARA2) and 4% (ARA4) during 60 days. At the end of the feeding trial fatty acid profiles of plasma and head kidney leucocytes were analyzed. Besides, plasma prostaglandins levels, head kidney leucocytes respiratory burst activity; peroxidase activity and phagocytic index were assayed. Reducing dietary ARA levels below 1% markedly reduced European sea bass growth performance. However, fish fed diet ARA0.5 tried to compensate this dietary ARA deficiency by a selective deposition of ARA on plasma and head kidney leucocytes, reaching similar levels to those fish fed diet ARA1 after 60 days of feeding. Nevertheless, head kidney phagocytic capacity was reduced as dietary ARA content in relation not only to variations on membrane composition but also to changes on fish basal prostaglandins levels. Results obtained demonstrated the importance to supply the necessary quantity n-6 LC-PUFA, and not only n-3 LC-PUFA levels, in European sea bass diets, in relation to not only growth performance but also immune system function.

Influence of the marine feeding area on the muscle and egg fatty-acid composition of Atlantic salmon Salmo salar spawners estimated from the scale stable isotopes

Fatty acids in muscle tissue and eggs of female Atlantic salmon Salmo salar spawners were analysed to evaluate the dietary quality of their final feeding areas in the Baltic Sea. The final likely feeding area was identified by comparing stable carbon and nitrogen isotope composition of the outermost growth region (final annulus) of scales of returned S. salar with that of reference S. salar caught from different feeding areas. Some overlap of stable-isotope reference values among the three areas, in addition to prespawning fasting, decreased the ability of muscle tri-acylglycerols to discriminate the final likely feeding area and the area's dietary quality. Among three long-chained polyunsaturated fatty acids, docosahexaenoic acid (DHA; 22:6n-3), eicosapentaenoic acid (EPA; 20:5n-3) and arachidonic acid (ARA; 20:4n-6), the proportions of ARA in total lipids of spawning S. salar muscle and eggs showed a significant negative correlation with increasing probability of S. salar having returned from the Baltic Sea main basin (i.e. the Baltic Sea proper). The results suggest that ARA in muscle and eggs is the best dietary indicator for dietary characteristics of final marine feeding area dietary characteristics among S. salar in the Baltic Sea.

Effects of dietary linseed oil on innate immune system of Eurasian perch and disease resistance after exposure to Aeromonas salmonicida achromogen

This study was designated to investigate the effects of dietary fish oil (FO diet) replacement by linseed oil (LO diet) on regulation of immune response and disease resistance in Eurasian perch (Perca fluviatilis). A control diet containing fish oil (FO = cod liver oil) and characterized by high levels of n-3 high LC-PUFA (6% EPA, 7.5% of total fatty acids (FAs)) was compared to linseed oil diet (LO diet) composed of low LC-PUFA contents (1% EPA, 2.3% DHA of total FAs) but high C18 fatty acids levels. The experiment was conducted in quadruplicate groups of 80 fish each. After 10 weeks of feeding, the innate immune status was evaluated in various organs (liver, spleen, and head-kidney) (feeding condition). Two days later, a bacterial challenge was performed on fish from 2 rearing conditions: fish infected with Aeromonas salmonicida (bacteria condition) and fish injected with sterile medium but maintained in the same flow system that fish challenged with bacteria (sentinel condition). Three days after injection of bacteria, a significant decrease of lymphocyte, thrombocyte and basophil populations was observed while neutrophils were not affected. In addition, plasma lysozyme activity and reactive oxygen species production in kidney significantly increased in fish challenged with A. salmonicida while the plasma alternative complement pathway activity was not affected. Increase of plasma lysozyme activity as well as reactive oxygen species production in spleen and kidney of sentinel fish suggest that these immune defenses can also be activated, but at lower bacteria concentration than infected fish. No differences in leucocyte populations, plasma lysozyme and alternative complement pathway activities were observed between dietary treatments. Similarly, expression of genes related to eicosanoid synthesis in liver were not affected by the dietary oil source but were strongly stimulated in fish challenged with A. salmonicida. These findings demonstrated that the use of linseed oil does not deplete the innate immune system of Eurasian perch juveniles.

Dietary Linseed Oil Reduces Growth While Differentially Impacting LC-PUFA Synthesis and Accretion into Tissues in Eurasian Perch (Perca fluviatilis)

The aim of this study was to evaluate the impact of replacing dietary fish oil (FO) with linseed oil (LO) on growth, fatty acid composition and regulation of lipid metabolism in Eurasian perch (Perca fluviatilis) juveniles. Fish (17.5 g initial body weight) were fed isoproteic and isoenergetic diets containing 116 g/kg of lipid for 10 weeks. Fish fed the LO diet displayed lower growth rates and lower levels of DHA in the liver and muscle than fish fed the FO diet, while mortality was not affected by dietary treatment. However, DHA content recorded in the liver and muscle of fish fed the LO diet remained relatively high, despite a weight gain of 134 % and a reduced dietary level of long-chain polyunsaturated fatty acids (LC-PUFA), suggesting endogenous LC-PUFA biosynthesis. This was supported by the higher amounts of pathway intermediates, including 18:4n-3, 20:3n-3, 20:4n-3, 18:3n-6 and 20:3n-6, recorded in the liver of fish fed the LO diet in comparison with those fed the FO diet. However, fads2 and elovl5 gene expression and FADS2 enzyme activity were comparable between the two groups. Similarly, the expression of genes involved in eicosanoid synthesis was not modulated by dietary LO. Thus, the present study demonstrated that in fish fed LO for 10 weeks, growth was reduced but DHA levels in tissues were largely maintained compared to fish fed FO, suggesting a physiologically relevant rate of endogenous LC-PUFA biosynthesis capacity.

Dietary Mannan Oligosaccharides: Counteracting the Side Effects of Soybean Meal Oil Inclusion on European Sea Bass (Dicentrarchus labrax) Gut Health and Skin Mucosa Mucus Production?

The main objective of this study was to assess the effects of 4 g kg(-1) dietary mannan oligosaccharides (MOS) inclusion in soybean oil (SBO)- and fish oil (FO)-based diets on the gut health and skin mucosa mucus production of European sea bass juveniles after 8 weeks of feeding. Dietary MOS, regardless of the oil source, promoted growth. The intestinal somatic index was not affected, however dietary SBO reduced the intestinal fold length, while dietary MOS increased it. The dietary oil source fed produced changes on the posterior intestine fatty acid profiles irrespective of MOS dietary supplementation. SBO down-regulated the gene expression of TCRβ, COX2, IL-1β, TNFα, IL-8, IL-6, IL-10, TGFβ, and Ig and up-regulated MHCII. MOS supplementation up-regulated the expression of MHCI, CD4, COX2, TNFα, and Ig when included in FO-based diets. However, there was a minor up-regulating effect on these genes when MOS was supplemented in the SBO-based diet. Both dietary oil sources and MOS affected mean mucous cell areas within the posterior gut, however the addition of MOS to a SBO diet increased the mucous cell size over the values shown in FO fed fish. Dietary SBO also trends to reduce mucous cell density in the anterior gut relative to FO, suggesting a lower overall mucosal secretion. There are no effects of dietary oil or MOS in the skin mucosal patterns. Complete replacement of FO by SBO, modified the gut fatty acid profile, altered posterior gut-associated immune system (GALT)-related gene expression and gut mucous cells patterns, induced shorter intestinal folds and tended to reduce European sea bass growth. However, when combined with MOS, the harmful effects of SBO appear to be partially balanced by moderating the down-regulation of certain GALT-related genes involved in the functioning of gut mucous barrier and increasing posterior gut mucous cell diffusion rates, thus helping to preserve immune homeostasis. This denotes the importance of a balanced dietary n-3/n-6 ratio for an appropriate GALT-immune response against MOS in European sea bass juveniles.

From egg to hatchling: preferential retention of fatty acid biomarkers in young-of-the-year Port Jackson sharks Heterodontus portusjacksoni

The muscle and liver fatty acid composition of young-of-the-year (YOY) Port Jackson sharks Heterodontus portusjacksoni were investigated to determine the effects of a known dietary lipid source v. maternal input as demonstrated by egg yolk fatty acid profiles. Ten Heterodontus portusjacksoni egg yolks were collected in situ and compared with four hatched H. portusjacksoni fed a known diet in a controlled feeding experiment of 185 days. This study demonstrated that fatty acids are probably conservatively transferred from egg yolks to YOY H. portusjacksoni, while diet did not have a large effect on the fatty acid composition of the liver or muscle.

Effects of graded levels of arachidonic acid on the reproductive physiology of Senegalese sole (Solea senegalensis): Fatty acid composition, prostaglandins and steroid levels in the blood of broodstock bred in captivity

Previous studies on Senegalese sole (Solea senegalensis) indicated that cultured broodstock (first generation, G1) have lower tissue levels of arachidonic acid (20:4n-6, ARA) than wild counterparts. ARA is metabolized to form prostaglandins (PGs) that are involved in steroid production and follicle maturation in fish. In the present study the effects of different dietary levels of ARA on blood lipid and fatty acid composition, prostaglandin (PGF2α, PGF3α, PGE2 and PGE3) levels and plasmatic steroid levels (11-ketotestosterone, 11-KT, testosterone, T and estradiol, E2) in G1 Senegalese sole were studied. For this purpose, 12 groups of ten fish (1:1 male and female), were fed six diets (each diets was fed to two groups) with different dietary ARA levels over nine months (diets A=0.7, B=1.6, C=2.3, D=3.2, E=5.0, F=6.0% ARA). ARA and CHOL levels in blood showed a significant increase in an ARA dose related manner (P<0.05) whereas EPA and EPA/ARA ratio were reduced. In males, steroid (11-KT and T) levels increased significantly with increasing dietary ARA in a dose dependent manner, whereas in females E2 did not show any change related to dietary ARA content. Plasma concentration of 3-series PGs (i.e., PGE3 and PGF3α) were reduced in parallel to increased ARA levels in blood (P<0.05) and levels of PGs 3-series were always higher than 2-series PGs (PGE2 and PGF2α). In conclusion there is an effect of dietary ARA on steroid production of Senegalese sole males, which might have important consequences in the reproduction of cultured fish.

Enhanced intestinal epithelial barrier health status on European sea bass (Dicentrarchus labrax) fed mannan oligosaccharides

The study assesses the effects of dietary mannan oligosaccharides (MOS) in European sea bass (Dicentrarchus labrax) posterior intestinal lipid class composition and its possible relation to the potential prostaglandins production and Gut Associated Lymphoid Tissue (GALT) stimulation. Fish were fed 4 g kg(-1) MOS (Bio-Mos(®) Aquagrade, Alltech, Inc., USA) for eight weeks. Fish fed MOS presented higher (P ≤ 0.05) weight gain, total length, and specific and relative growth rates than fish fed the control diet. Stimulated posterior gut of fish fed MOS showed higher (P ≤ 0.05) prostaglandins production than fish fed the control diet. Lipid class analyses of posterior gut revealed a reduction (P ≤ 0.05) in the neutral lipid fraction in fish fed MOS compared to fish fed the control diet, particularly due to a reduction (P ≤ 0.05) in triacylglycerols content. The polar lipid fraction increased (P ≤ 0.05) in fish fed MOS compared to fish fed the control diet, mainly due to an increase (P ≤ 0.05) in phosphatidylethanolamine and phosphatidylcoline contents. Light microscopy of posterior gut revealed increased number or goblet cells as well as higher level of infiltrated eosinophilic granulocytes for fish fed MOS. Transmission electron microscopy qualitative observations revealed a better preserved cytoarchitecture of the intestinal epithelial barrier in the posterior gut of fish fed MOS. Posterior gut of fish fed MOS presented more densely packed non-damaged enterocytes, better preserved tight junctions structure, healthier and more organized microvilli, and a higher presence of infiltrated lymphocytes and granulocytes compared fish fed the control diet. The present study indicates that dietary MOS enhances European sea bass posterior gut epithelial defense by increasing membrane polar lipids content in relation to a stimulation of the eicosanoid cascade and GALT, promoting posterior gut health status.

Total substitution of fish oil by vegetable oils in Senegalese sole (Solea senegalensis) diets: effects on fish performance, biochemical composition, and expression of some glucocorticoid receptor-related genes

To study the substitution of fish oil by vegetable oils in fish diets, juveniles Senegalese sole (Solea senegalensis) were fed diets (56 % crude protein, 12 % crude lipid) containing either linseed (100LO) or soybean (100SO) oils in comparison with a 100 % fish oil-based diet (100FO) for 90 days. Samples of muscle, liver, and intestine were collected for biochemical analysis and for glucocorticoid receptor-related genes, including GR1 and GR2, and the associated heat shock proteins HSP70, HSP90AA, and HSP90AB. Besides, basal levels of plasma cortisol were also determined. After the feeding period, a stress test, consisting on 5 min of net chasing, was applied to a selected population of each dietary group. Total replacement of fish oil by vegetable oils did not induced changes in fish growth and performance, but affected fatty acid profile of muscle, liver, and intestine, reflecting those tissues the characteristic fatty acids of each type of dietary oil. A tendency to conserve the ARA/EPA ratio could be observed in the different tissues, despite of the level of these fatty acids in diet. Chasing stress induced an increase of muscle GR1 and a reduction in intestinal GR2 relative expressions at any of the experimental diets assayed. In liver, chasing stress induced an increase in both GR1 and GR2 gene expression in fish fed fish oil diets. Similarly, chasing stress induced an increase of muscle HSP70 and decrease of HSP90AB in liver at any of the experimental diet assayed. Besides, vegetable oils decreased the expression of HSP70 in intestine, being the relative expression of liver HSP90AA increased by the inclusion of linseed oil in the diet, at any of the experimental conditions assayed.

Teleost fish larvae adapt to dietary arachidonic acid supply through modulation of the expression of lipid metabolism and stress response genes

Dietary fatty acid supply can affect stress response in fish during early development. Although knowledge on the mechanisms involved in fatty acid regulation of stress tolerance is scarce, it has often been hypothesised that eicosanoid profiles can influence cortisol production. Genomic cortisol actions are mediated by cytosolic receptors which may respond to cellular fatty acid signalling. An experiment was designed to test the effects of feeding gilthead sea-bream larvae with four microdiets, containing graded arachidonic acid (ARA) levels (0·4, 0·8, 1·5 and 3·0 %), on the expression of genes involved in stress response (steroidogenic acute regulatory protein, glucocorticoid receptor and phosphoenolpyruvate carboxykinase), lipid and, particularly, eicosanoid metabolism (hormone-sensitive lipase, PPARα, phospholipase A2, cyclo-oxygenase-2 and 5-lipoxygenase), as determined by real-time quantitative PCR. Fish fatty acid phenotypes reflected dietary fatty acid profiles. Growth performance, survival after acute stress and similar whole-body basal cortisol levels suggested that sea-bream larvae could tolerate a wide range of dietary ARA levels. Transcription of all genes analysed was significantly reduced at dietary ARA levels above 0·4 %. Nonetheless, despite practical suppression of phospholipase A2 transcription, higher leukotriene B4 levels were detected in larvae fed 3·0 % ARA, whereas a similar trend was observed regarding PGE2 production. The present study demonstrates that adaptation to a wide range of dietary ARA levels in gilthead sea-bream larvae involves the modulation of the expression of genes related to eicosanoid synthesis, lipid metabolism and stress response. The roles of ARA, other polyunsaturates and eicosanoids as signals in this process are discussed.

Effects of the total replacement of fish-based diet with plant-based diet on the hepatic transcriptome of two European sea bass (Dicentrarchus labrax) half-sibfamilies showing different growth rates with the plant-based diet

Background

Efforts towards utilisation of diets without fish meal (FM) or fish oil (FO) in finfish aquaculture have been being made for more than two decades. Metabolic responses to substitution of fishery products have been shown to impact growth performance and immune system of fish as well as their subsequent nutritional value, particularly in marine fish species, which exhibit low capacity for biosynthesis of long-chain poly-unsaturated fatty acids (LC-PUFA). The main objective of the present study was to analyse the effects of a plant-based diet on the hepatic transcriptome of European sea bass (Dicentrarchus labrax).

Results

We report the first results obtained using a transcriptomic approach on the liver of two half-sibfamilies of the European sea bass that exhibit similar growth rates when fed a fish-based diet (FD), but significantly different growth rates when fed an all-plant diet (VD). Overall gene expression was analysed using oligo DNA microarrays (GPL9663). Statistical analysis identified 582 unique annotated genes differentially expressed between groups of fish fed the two diets, 199 genes regulated by genetic factors, and 72 genes that exhibited diet-family interactions. The expression of several genes involved in the LC-PUFA and cholesterol biosynthetic pathways was found to be up-regulated in fish fed VD, suggesting a stimulation of the lipogenic pathways. No significant diet-family interaction for the regulation of LC-PUFA biosynthesis pathways could be detected by microarray analysis. This result was in agreement with LC-PUFA profiles, which were found to be similar in the flesh of the two half-sibfamilies. In addition, the combination of our transcriptomic data with an analysis of plasmatic immune parameters revealed a stimulation of complement activity associated with an immunodeficiency in the fish fed VD, and different inflammatory status between the two half-sibfamilies. Biological processes related to protein catabolism, amino acid transaminations, RNA splicing and blood coagulation were also found to be regulated by diet, while the expression of genes involved in protein and ATP synthesis differed between the half-sibfamilies.

Conclusions

Overall, the combined gene expression, compositional and biochemical studies demonstrated a large panel of metabolic and physiological effects induced by total substitution of both FM and FO in the diets of European sea bass and revealed physiological characteristics associated with the two half-sibfamilies.

Effects of dietary lipids on tissue fatty acids profile, growth and reproductive performance of female rice field eel (Monopterus albus)

The effects of different lipids on tissue fatty acid profile and reproductive performance in female rice field eel were investigated in this study. Virgin female eels were fed with six diets containing different lipids (diets FO, LO, SO, PO and PL with fish oil, linseed oil, soybean oil, peanut oil and pork lard, respectively; diet APO with arachidonic acid and peanut oil). The results showed that there were positive correlations between the contents of 18:2n-6, 18:3n-3, arachidonic acid (ARA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in the tissues of eels and those of the corresponding fatty acids in their diets. The specific growth rate of eels fed with diet PO was the lowest and significantly lower than that of FO and SO. Gonad of eels fed with diets PO and PL showed hypogonadism. The long chain polyunsaturated fatty acids (LC-PUFA) can be synthesized by eels, but the quantity was not enough to meet their reproduction requirement completely. The fatty acid desaturation, rather than elongation probably was one of the limiting factors. Addition of proper amount of ARA in diet was favorable to the increase of the hatching rate of fertilized eggs, while EPA and DHA in diet were beneficial to the increase of the survival rate of larva. Both n-3PUFA and a suitable n-6/n-3PUFA ratio were necessary for growth and reproduction of eels.

Application of nonparametric multivariate analyses to the authentication of wild and farmed European sea bass (Dicentrarchus labrax). Results of a survey on fish sampled in the retail trade

The aim of this study was to apply biometric measurements and analyses of proximate composition, fatty acid composition, and ratios of stable isotopes of carbon (δ(13)C) and nitrogen (δ(15)N) in muscle tissue to reliably differentiate between wild and farmed European sea bass (Dicentrarchus labrax). Farmed (n = 20) and wild (n = 19) European sea bass were purchased between March and May 2008 and used as standard samples. In the same months, a survey was conducted to evaluate the truthfulness of the statements on the labels of European sea bass sold in retail markets (declared farmed n = 34 and declared wild n = 33). In addition, data from the literature (reference) were employed to build the profile type of wild and farmed European sea bass. Primarily, an exploration and comparison of the analytical data of the standard data set based on principal component analysis and permutation test were performed. Afterward, an inferential statistical approach based on nonparametric combination test methodology (NPC) was applied on standard samples to check its suitability in discriminating the production method. This multivariate statistical analysis selected 30 variables on a total of 36 available. The validation of standard fish data set was accomplished by a novel nonparametric rank-based method according to profile type (just 1 misclassification over 39 samples). Both the NPC test and nonparametric rank-based method were then applied to survey fishes using the selected variables with the aim to classify the individual European sea bass as "true farmed" or "true wild". The former test segregated 10 fishes over 33 declared wild, whereas the results obtained by the nonparametric rank-based method showed that 11 of 33 declared wild European sea bass samples could be unquestionably attributed to the wild cluster. Moreover, considering the comparative contribution of profile type, a few surveyed farmed samples were ascribed to the wild cluster.

Regulation of growth, fatty acid composition and delta 6 desaturase expression by dietary lipids in gilthead seabream larvae (Sparus aurata)

The Delta6 and Delta5 desaturases and elongases show only very limited activity in marine fish, and little is known of the possibility of enhancing Delta6 desaturase gene expression in these fish. The use of plant oils in marine fish diets is limited by their lack of n-3 highly unsaturated fatty acids (HUFA) despite an abundant content of the 18C fatty acid precursor linoleic and alpha-linolenic acids. The objective of the present study was to determine the ability of larval gilthead seabream to utilize vegetable oils and assess the nutritional regulation of Delta6 desaturase gene expression. Seventeen-day-old gilthead seabream larvae were fed during a 17-day period with one of four different microdiets formulated with either sardine fish oil (FO), soybean, rapeseed or linseed oils, respectively, or a fifth diet containing defatted squid meal and linseed oil. Good larval survival and growth, both in terms of total length and body weight, were obtained by feeding the larvae either rapeseed, soybean or linseed oils. The presence of vegetable oils in the diet increased the levels of 20:2n-9 and 20:2n-6, 18:2n-9, 18:3n-6, 20:3n-6 and 20:4n-6, in larvae fed rapeseed and soybean oils in comparison to those fed FO. In addition, a sixfold increase in the relative expression of Delta6 desaturase-like gene was found in larvae fed rapeseed and soybean oils, denoting the nutritional regulation of desaturase activity through its gene expression in this fish species. However, feeding linseed oil did not increase the expression of the Delta6 desaturase gene to such a high extent.

Effects of partial substitution of dietary fish oil with blends of vegetable oils, on blood leucocyte fatty acid compositions, immune function and histology in European sea bass (Dicentrarchus labrax L.)

Within a decade or so insufficient fish oil (FO) will be available to meet the requirements for aquaculture growth. Consequently, alternative sources are being investigated to reduce reliance on wild fish as a source of FO. Vegetable oils (VO) are a feasible alternative to FO. However, it is important to establish that alternative dietary lipids are not only supplied in the correct quantities and balance for optimal growth, but can maintain immune function and prevent infection, since it is known that the nutritional state of the fish can influence their immune function and disease resistance. A way of maintaining immune function, while replacing dietary FO, is by using a blend of VO rather than a single oil. In this study, juvenile European sea bass (Dicentrarchus labrax) were fed diets with a 60 % substitution of FO with a blend of rapeseed, linseed and palm oils. Two oil blends were used to achieve a fatty acid composition similar to FO, in terms of energy content, and provide a similar balance of SFA, MUFA and PUFA. Fish were fed the diets for 64 weeks, after which time growth and fatty acid compositions of liver and blood leucocytes were monitored. The impact of the dietary blends on selected innate immune responses and histopathology were also assessed, together with levels of plasma prostaglandin E2. The results suggest that potential exists for replacing FO with a VO blend in farmed sea bass feeds without compromising growth, non-specific immune function or histology.

Partial replacement of dietary fish oil with blends of vegetable oils (rapeseed, linseed and palm oils) in diets for European sea bass (Dicentrarchus labrax L.) over a long term growth study: effects on muscle and liver fatty acid composition and effectiveness of a fish oil finishing diet

Triplicate groups of European sea bass (Dicentrarchus labrax L.), of initial mass 5 g, were fed one of three practical type diets for 64 weeks. The three diets differed only in the added oil and were 100% fish oil (FO; diet A), 40% FO/60% vegetable oil blend (VO; diet B) where the VO blend was rapeseed oil, linseed oil and palm oil in the ratio 10/35/15 by weight and 40% FO/60% VO blend (diet C) where the ratio was 24/24/12 by weight. After final sample collection the remaining fish were switched to a 100% FO finishing diet for a further 20 weeks. After 64 weeks fish fed 60% VO diet B had significantly lower live mass and liver mass than fish fed diets A and C although SGR, FCR and length were not different between groups. There were no differences in any of the above parameters after either 14 or 20 weeks on the FO finishing diet. Fatty acid compositions of flesh were correlated to dietary fatty acids although there was selective retention of docosahexaenoic acid (22:6n-3; DHA) regardless of dietary input. Inclusion of dietary VO resulted in significantly reduced flesh levels of DHA and eicosapentaenoic acid (20:5n-3; EPA) while 18:1n-9, 18:2n-6 and 18:3n-3 were all significantly increased in fish fed the 60% VO diets. Fatty acid compositions of liver showed broadly similar changes, as a result of dietary fatty acid composition, as was seen in flesh. However, the response of flesh and liver to feeding a FO finishing diet was different. In flesh, DHA and EPA values were not restored after 14 or 20 weeks of feeding a FO finishing diet with the values in fish fed the two 60% VO diets being around 70% of the values seen in fish fed FO throughout. Conversely, and despite liver DHA and EPA levels being reduced to only 40% of the value seen in fish fed 100% FO after 64 weeks, the levels of liver DHA and EPA were not significantly different between treatments after feeding the FO finishing diet for 14 weeks. However, a 200 g portion of sea bass flesh, after feeding the experimental diets for 64 weeks followed by a FO diet for 14 weeks, contained 1.22 and 0.95 g of EPA+DHA for fish fed FO or 60% VO, respectively. Therefore, sea bass grown for most of the production cycle using diets containing 60% VO can still contribute a significant quantity of healthy n-3 HUFA to the human consumer.

Effect of dietary lipids on plasma fatty acid profiles and prostaglandin and leptin production in gilthead seabream (Sparus aurata)

The aim of this study was to investigate the effects of different levels of substitution of fish oil by vegetable oils rich in oleic, linoleic and linolenic acids on gilthead seabream plasma and leukocyte fatty acid compositions and prostaglandin (PG) and leptin production. Juvenile seabream of 24 g initial body mass were fed four iso-energetic and iso-proteic experimental diets for 281 days. Fatty acid composition of plasma lipids was markedly affected by the inclusion of vegetable oils (VO). ARA (arachidonate), EPA (eicosapentaenoate) and DHA (docosahexaenoate) were preferentially incorporated into polar lipids of plasma, and DHGLA (di-homogammalinoleate) accumulated with increased vegetable oil inclusion. Dietary treatments resulted in alterations of DHGLA/ARA ratios, but not ARA/EPA. ARA-derived PGE(2) production in plasma was not affected by vegetable oils, in agreement with similar eicosanoid precursor ratio (ARA/EPA) in leukocytes total lipids and plasma phospholipids among fish fed with the different dietary treatments. Feeding vegetable oils leads to a decrease in plasma EPA which in turn reduced plasma PGE(3) concentration. Moreover, PGE(3) was the major prostaglandin produced in plasma of fish fed fish oil based diet. Such findings point out the importance of EPA as a precursor of prostaglandins in marine fish, at least for the correct function of the blood cells, and correlates well with the predominant role of this fatty acid in immune regulation in this species. A negative correlation was found between plasma PGE(2) and leptin plasma concentration, suggesting that circulating levels of leptin may act as a metabolic signal modulating PGE(2) release. The present study has shown that increased inclusion of vegetable oils in diet for gilthead seabream may profoundly affect the fatty acid composition of plasma and leukocytes, specially HUFA (highly unsaturated fatty acids), and consequently the production of PGE(3), which can be a major PG in plasma. Alteration in the amount and type of PG produced can be at least partially responsible for the changes in the immune system and health parameters of fish fed diets with high inclusion of VO.

Beneficial effects of a diet rich in a mixture of n - 6/n - 3 essential fatty acids and of their metabolites on cyclosporine - nephrotoxicity

In this study we investigated the role of a mixture of n-6/n-3 essential fatty acids, in the cyclosporine model nephrotoxicity. Administration of cyclosporine in rats decreased creatinine clearance and provoked body weight loss, but it did not induce proteinuria and did not alter the urine volume. These changes were associated with decreased urinary ratios of prostaglandin E/thromboxane B and prostaglandin I/thromboxane B excretions. Light microscopic sections showed that 100% of the animals were affected by histological tubular lesions on their kidneys. Administration of cyclosporine to animals fed for 3 months on standard chow containing a mixture of n - 6/n - 3 essential fatty acids, restored creatinine clearance, augmented urine volume and prevented body weight loss. The improvement of renal function was accompanied by increased urinary ratios of prostaglandin E/thromboxane B and prostaglandin I/thromboxane B excretions. Light microscopic sections showed that only 40% of the animals demonstrated histological tubular lesions, of minor importance, to their kidneys. Our results suggest that the metabolites of arachidonic acid can play important role in the development of cyclosporine-nephrotoxicity because they increase the levels of thromboxane A and that the enhanced synthesis of prostaglandins (E) and (I) induced by a mixture of n - 6/n - 3 essential fatty acids, could play a beneficial role in the prevention of this renal dysfunction.

Beneficial effects of a diet rich in a mixture of n - 6/n - 3 essential fatty acids and of their metabolites on cyclosporine - nephrotoxicity

In this study we investigated the role of a mixture of n-6/n-3 essential fatty acids, in the cyclosporine model nephrotoxicity. Administration of cyclosporine in rats decreased creatinine clearance and provoked body weight loss, but it did not induce proteinuria and did not alter the urine volume. These changes were associated with decreased urinary ratios of prostaglandin E/thromboxane B and prostaglandin I/thromboxane B excretions. Light microscopic sections showed that 100% of the animals were affected by histological tubular lesions on their kidneys. Administration of cyclosporine to animals fed for 3 months on standard chow containing a mixture of n - 6/n - 3 essential fatty acids, restored creatinine clearance, augmented urine volume and prevented body weight loss. The improvement of renal function was accompanied by increased urinary ratios of prostaglandin E/thromboxane B and prostaglandin I/thromboxane B excretions. Light microscopic sections showed that only 40% of the animals demonstrated histological tubular lesions, of minor importance, to their kidneys. Our results suggest that the metabolites of arachidonic acid can play important role in the development of cyclosporine-nephrotoxicity because they increase the levels of thromboxane A and that the enchanced synthesis of prostaglandins (E) and (I) induced by a mixture of n - 6/n - 3 essential fatty acids, could play a beneficial role in the prevention of this renal dysfunction.

A thromboxane A(2) system in the Atlantic stingray, Dasyatis sabina

Thromboxane B(2)(TXB(2)) is the stable metabolite of thromboxane A(2)(TXA(2)) and thromboxane B(2)-like immunoreactivity (iTXB(2)) has been identified in the plasma of the Atlantic stingray, Dasyatis sabina (0.57+/-0.03 ng/ml). Plasma levels of iTXB(2) increase if the blood is allowed to clot (3.0+/-0.27 ng/ml). When clotting occurs in the presence of indomethacin, this increase is partially inhibited (1.5+/-0.17 ng/ml), indicating the presence of a cyclooxygenase activity. Radioligand binding analysis using the TXA(2) analog [125I]BOP in isolated kidney membranes revealed a receptor of K(d)=2.88+/-0.51 nM and B(max)=25.6+/-5.9 fmol/mg protein. [125I]BOP binding was displaced by the TXA(2) receptor (TP receptor) agonists U46619 (IC(50)=106.4+/-15.7 nM) and U44069 (IC(50)=88.7+/-13.0 nM), and the antagonist SQ29548 (IC(50)=51.0+/-12.9 nM). Binding was also displaced stereoselectively by the antagonists (-)L657925 (IC(50)=18.9+/-3.8 nM) and (+)L657926 (IC(50)=2025+/-280 nM). Tissue bath studies revealed that U46619, a stable TXA(2) mimetic, elicited concentration-dependent contractions in the ventral aorta which were inhibited in a concentration-dependent manner by the TP receptor antagonist SQ29548. Using a human TP receptor riboprobe, Northern blotting of mRNA isolated from the stingray kidney identified transcripts of 2.8 and 6kb. The 2.8kb transcript is similar to a 2.8kb transcript found in human cells or tissues, but the 6kb transcript may be unique. These data indicate the presence of a TXB(2)-like substance in the blood, a TP receptor in the kidney, TXA(2) biological activity in the ventral aorta, and expression of a TP receptor-like gene.

The esterification and modification of n-3 and n-6 polyunsaturated fatty acids by hepatocytes and liver microsomes of turbot (Scophthalmus maximus)

The present study was undertaken to establish whether the formation of 22:6n-3 from 18:3n-3 and/or 20:5n-3 can occur in turbot liver and if this conversion is consistent with the operation of a Delta4 desaturase-independent pathway. At the same, time the effects of feeding a diet devoid of long chain polyunsaturated fatty acids (PUFA) on the patterns of esterification and modification of 18:3n-3, 20:5n-3 and 18:2n-6 by turbot hepatocytes and liver microsomes were examined. For this purpose, two groups of fish (25-30 g) were employed: one was fed a commercial diet containing fish oil (FO) and thus rich in long chain n-3 PUFA and the other was fed an experimental diet based on olive oil (OO). After 5 months of feeding, hepatocytes and liver microsomes isolated from individuals in the two groups of fish were incubated with [1-(14)C]-PUFA [either 18:3n-3, 20:5n-3 or 18:2n-6]. After 3 h of incubation, most radioactivity from all three radiolabelled substrates incorporated into lipids by hepatocytes and microsomes was recovered in the original substrate. The formation of desaturation products of n-3 radiolabelled substrates was higher in hepatocytes isolated from OO-fed than FO-fed fish. Small amounts of radiolabelled 22:6n-3 were formed from [1-(14)C]18:3n-3 and [1-(14)C]20:5n-3, but only by hepatocytes from fish fed OO, which also synthesised a small amount of radiolabelled 24:6n-3 from 14C-20:5n-3. Elongation products predominated over desaturation products in hepatic microsomes from both groups of fish studied, particularly in microsomes from fish fed FO. The results confirm that regardless of the long chain PUFA content of the diet, the production of 22:6n-3 in turbot liver from 18:3n-3 and/or 20:5n-3, and of 20:4n-6 from 18:2n-6, is very limited. The presence of radiolabelled 24:6n-3 in microsomes coupled with the absence of radiolabelled 22:6n-3 suggests that the formation of 22:6n-3 that does occur in turbot liver cells, may involve C24 intermediates and peroxisomal beta-oxidation.

Phospholipid fatty acid and lipid peroxidation in liver microsomes from guinea pigs fed oil related to the toxic oil syndrome

The potential effects of oil specimens both related and unrelated to cases of Toxic Oil Syndrome (TOS) on the phospholipid fatty acid composition, some antioxidant enzyme activities, and lipid peroxidation in guinea pig liver microsomes were investigated. For 4 weeks, animals were fed diets supplemented with either oil related to cases of TOS or control oil, previously heated or not. In all cases, the fat diet produced the incorporation of approximately 7% of linoleic acid exclusively in the phosphatidylethanolamine (PE) of liver microsomes. A pronounced increase in lipid peroxidation products, measured as malondialdehyde (MDA) and 4-hydroxyalkenals, was detected in animals fed nonheated control oil. Heated oil diets produced significant increases in superoxide dismutase and glutathione peroxidase activities with concomitant decreases in the lipid peroxidation status. Heated oils also increased the oleic/stearic acid ratio in the phosphatidylserine plus phosphatidylinositol (PS + PI) fraction. This ratio was also increased in the same fraction from animals fed non heated case oil. The study shows that case oil produces a decrease in the lipid peroxidation products with minimal alterations in phospholipid fatty acid composition of liver microsomes, which is dependent rather on the composition of dietary fat than on toxic effects.

Growth, mortality, tissue histopathology and fatty acid compositions, eicosanoid production and response to stress, in juvenile turbot fed diets rich in gamma-linolenic acid in combination with eicosapentaenoic acid or docosahexaenoic acid

Three diets containing either borage oil (BO) and southern hemisphere fish oil Marinol (MO), or BO and tuna orbital oil (TO), or a northern hemisphere fish oil (FO) were fed to duplicate groups of turbot (Scophthalmus maximus) of initial mean weight 1.2 g for a period of 12 weeks. The BO/MO and BO/TO diets were enriched in gamma-linolenic (18:3n-6, GLA) and eicosapentaenoic (20:5n-3, EPA) acids, and GLA and docosahexaenoic acid (22:6n-3, DHA), respectively. No differences were observed in final weights or growth rates, either between duplicate tanks or between dietary treatments. Half of the FO-fed fish sampled showed a histopathological lesion indicative of lipoid liver degeneration while the other treatments only showed a slight incidence of the same pathology. The fatty acid compositions of carcass and tissues broadly reflected the dietary input. In general, fish fed the BO/MO diet had increased levels of 18:2n-6, 18:3n-6, 20:3n-6 and 20:5n-3, but a lower level of 22:6n-3, compared to fish fed FO. In fish fed the BO/TO diet, levels of 18:2n-6, 18:3n-6, 20:3n-6 and 20:4n-6 were increased while levels of 20:5n-3 and 22:5n-3 were reduced, compared to fish fed FO. Concentrations of thromboxanes B (TXB) and leukotrienes B (LTB), derived from 20:4n-6 and 20:5n-3, were measured in plasma and stimulated blood cells. Levels of TXB2 were greatest in fish fed the BO/TO diet compared to both other treatments, while LTB4 was decreased in fish fed the BO/MO diet compared to both other treatments. In a stress test which involved anaesthesia followed by measurement of recovery times, fish fed the BO/MO diet had significantly lower recovery times compared to fish fed the FO diet.

Effects of dietary gamma-linolenic acid-rich borage oil combined with marine fish oils on tissue phospholipid fatty acid composition and production of prostaglandins E and F of the 1-, 2- and 3-series in a marine fish deficient in delta5 fatty acyl desaturase

The effects of gamma-linolenic acid-rich borage oil (BO), in combination with different marine oils, namely an eicosapentaenoic acid (EPA) rich oil (MO) or a DHA-rich oil (TO), on tissue fatty acid composition and prostaglandin production were investigated in turbot, a species which lacks appreciable delta5 fatty acyl desaturase activity. The juvenile turbot grew well on the experimental diets and there were no significant differences in final weights between dietary treatments. Irrespective of the marine oil component, both the BO-containing diets increased tissue phospholipid levels of 18:2n-6 and 18:3n-6, and their respective elongation products, 20:2n-6 and 20:3n-6, compared to fish fed a control diet containing a standard Northern hemisphere fish oil. Both the BO-containing diets increased the production of 1-series prostaglandins (PG), this being observed across all tissues investigated with PGF and especially PGE. The BO/MO diet also reduced 20:4n-6 in tissue phospholipids without affecting 20:5n-3, whereas the BO/TO combination decreased 20:5n-3 but increased 20:4n-6. The production of 2-series and 3-series PGs was also altered by the dietary treatments but the changes were less dependent upon the tissue levels of their respective precursor fatty acids, 20:4n-6 and 20:5n-3. The BO-containing diets had very significant effects on gross fatty acid compositions of the phospholipids including increased proportions of saturated fatty acids and n-6 polyunsaturated fatty acids (PUFA) and decreased proportions of monounsaturated fatty acids and n-3 PUFA. Overall, this study shows that eicosanoid production in turbot tissues can be influenced by dietary fatty acids, not only by changes in the absolute and relative levels of specific eicosanoid precursor PUFA in tissue phospholipids, but also by general effects on membrane composition, structure and function induced by gross fatty acid compositional changes.

Diets rich in eicosapentaenoic acid and gamma-linolenic acid affect phospholipid fatty acid composition and production of prostaglandins E1, E2 and E3 in turbot (Scophthalmus maximus), a species deficient in delta 5 fatty acid desaturase

Duplicate groups of juvenile turbot, (Scophthalmus maximus), were fed diets containing either Marinol K (MO), a marine fish oil rich in eicosapentaenoic acid (EPA; 20:5, n-3) or borage oil (BO), rich in gamma-linolenic acid (GLA; 18:3, n-6), for a period of 12 weeks. Individual phospholipid fatty acid compositions from hearts of fish fed BO had significantly more 18:2, n-6, GLA, 20:2, n-6, dihomo-gamma-linolenic acid (DHGLA; 20:3, n-6) and total n-6 polyunsaturated fatty acids (PUFA), but significantly less arachidonic acid (AA; 20:4, n-6), compared to fish fed MO. In both phosphatidylcholine (PC) and phosphatidylethanolamine (PE) from heart, the DHGLA was increased by over 50-fold in fish fed BO while AA was reduced by over two-thirds, compared to fish fed MO. In brain, EPA was the major C20 PUFA, i.e. potential eicosanoid precursor in all phospholipids from fish fed MO, with the EPA level being twice that of AA in brain phosphatidylinositol (PI). DHGLA was the major C20 PUFA in all phospholipid classes from fish fed BO. In kidney and gill, EPA was the predominant C20 PUFA in all phospholipid classes, except PI, in fish fed MO. In kidney of fish fed BO, DHGLA was the major C20 PUFA in all phospholipid classes, except PE. In gill of fish fed BO, DHGLA was the major C20 PUFA in all phospholipid classes, including PI, where DHGLA was over 2.5-fold greater than AA. In homogenates of heart, kidney and gill from BO-fed fish the prostaglandin E1 (PGE1) concentration was significantly increased compared to MO-fed fish. In heart and kidney homogenates from fish fed MO the PGE3 concentration was significantly increased compared to fish fed BO. The ratio of PGE2/PGE1 was significantly reduced in brain, heart, kidney and gill homogenates from fish fed BO compared to those fed MO.

Effects of dietary borage oil [enriched in γ-linolenic acid,18:3(n-6)] or marine fish oil [enriched in eicosapentaenoic acid,20:5(n-3)] on growth, mortalities, liver histopathology and lipid composition of juvenile turbot (Scophthalmus maximus)

A marine fish oil, Marinol K (MO) and borage oil (BO) were used to formulate diets relatively rich in eicosapentaenoic acid [EPA; 20:5(n-3)] and γ-linolenic acid [GLA; 18:3(n-6)], respectively. The diets were fed to duplicate groups of juvenile turbot (Scophthalmus maximus) of initial weight 1.4 g for a period of 12 weeks. No differences were observed in final weights either between duplicate tanks or between dietary treatments. Mortalities in the MO-fed group were significantly greater than in the BO-fed group. In the MO-fed group, 7 out of 12 fish sampled for histological analysis showed a pronounced liver histopathology whereas only 1 of 12 fish sampled in the BO-fed group showed slight pathology. EPA levels were increased 2.2-fold and its elongation product, 22:5(n-3), was increased 1.8-fold while arachidonic acid [AA; 20:4(n-6)] was decreased by 30% in MO-fed fish compared to the initial carcass composition. GLA was increased 53-fold and its elongation product dihomo-γ-linolenic acid [DHGLA; 20:3(n-6)] was increased 16-fold while AA was reduced by 90% in BO-fed fish compared to the initial carcass composition. The amount of triacylglycerol in liver of BO-fed fish was significantly greater than levels in MO-fed fish. The fatty acid compositions of individual phospholipids from liver showed marked differences between dietary treatments. Fish fed MO had significantly higher levels of the (n-3) polyunsaturated fatty acids (PUFA), 20:5(n-3), 22:5(n-3) and 22:6(n-3), and also significantly more 20:4(n-6) compared to BO-fed fish which had significantly higher 18:2(n-6), 18:3(n-6), 20:2(n-6) and 20:3(n-6). The composition of liver phosphatidylinositol was particularly unusual in BO-fed fish having DHGLA as the major C20 PUFA which was 2.2-fold greater than AA and 3.9-fold greater than EPA. This study demonstrates that the carcass composition of turbot can be altered, by means of dietary lipids, to contain increased levels of EPA and DHGLA which would be of potential benefit in human as well as in fish nutrition. However, caution should be exercised when using very highly unsaturated oils relatively rich in EPA which may generate histopathological lesions in the fish.