Hepatic Fatty Acid and Transcriptome Profiles during the Transition from Vegetable- to Fish Oil-Based Diets in Rainbow Trout (Oncorhynchus mykiss)

A finishing diet strategy is effective at increasing fillet long-chain n-3 fatty acid content in fish consuming sustainable plant oil-based diets. This study investigates the outcomes of a fish oil finishing diet upon the hepatic fatty acid and transcriptome profile in rainbow trout (Oncorhynchus mykiss). Fish were placed on one of three feeding treatments: (1) FO: a fish oil (FO) diet for 20 weeks, (2) VO/FO: a vegetable oil (VO) diet during weeks 1-12 then the FO diet for 8 weeks, or (3) VO/fd/FO: the VO diet between weeks 1-12, 2 weeks of feed deprivation, then the FO diet for 6 weeks. Hepatic fatty acid and transcriptome profiles were analyzed at week 12, 14, and 20. Hepatic fatty acid profiles at week 12 were similar to dietary profiles; transcriptomic analyses indicated 131 differentially regulated genes (DEG) between VO- and FO-fed fish, characterized by VO-induced up-regulation of cholesterol and long-chain fatty acyl-CoA synthesis and oxidation-reduction processes. At week 14, the hepatic fatty acid profile was similar between VO/FO and FO, although concentrations of 18:3n-3 remained higher in the VO/FO group. Thirty-three DEG were detected at week 14 with enrichment of genes associated with extracellular matrix assembly, supporting liver remodeling during the early finishing diet period. Only five DEG were detected at week 20 between VO/FO and FO. Collectively, these findings suggest that it takes several weeks for liver to reach a homeostatic state, even after the hepatic fatty acid equilibration following a finishing diet.

Plasma biochemistry, gene expression and liver histomorphology in common carp (Cyprinus carpio) fed with different dietary fat sources

Demand for omega-3 long chain polyunsaturated fatty acids has become global challenge for aquaculture and different components have been used to increase nutritional value of fillets. The aim of this study was to evaluate influences of feeds on zootechnical parameters, biochemical plasma parameters, expression of lipid-dependent genes, hepatocyte histomorphologies, and fatty acid profiles in common carp fillets. We compared a control diet (CTRL), mimicking a commercial feed formulation for common carp, with three diets containing blends of vegetable oils and a DHA-rich alga (Schizochytrium sp.) included at 3.125% (CB1) or 1.563% (CB2), and 2.1% salmon oil (CB3). The study revealed no differences in final body weight of fish fed CB1-3 diets in comparison with significantly lower CTRL. Concentrations of all biochemical parameters in plasma increased gradually in fish fed CB1-3 diets when compared to CTRL diet, with exception of triacylglycerol levels. Expression of hepatic fas, elovl-5a and pparα genes increased significantly in fish fed CB1 and CB2. Additionally, eicosapentaenoic (EPA) and docosahexaenoic acid (DHA) accumulation in muscle tissue was directly proportional to the amounts supplied in the diets. Our study revealed that carp fillet profiles can be manipulated for DHA and EPA-contents using enriched diets, depending on the source of fat.

Interaction between dietary fatty acids and genotype on immune response in Atlantic salmon (Salmo salar) after vaccination: A transcriptome study

A pivotal matter to aquaculture is the sourcing of sustainable resources as ingredients to aquafeeds. Levels of plant delivered oils as source of fatty acids (FA) in aquafeeds have reached around 70% resulting in reduced levels of long-chain omega-3 polyunsaturated fatty acids (LC n-3 PUFA), such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), in salmon fillet composition. EPA and DHA can modulate inflammation and immune response, so it is crucial to understand how fish immune response is affected by low LC n-3 PUFA diet and if this diet can have a detrimental effect on vaccine response. Atlantic salmon (Salmo salar) can produce EPA/DHA from α-linolenic acid (ALA) and this endogenous capacity can be explored to develop families with higher tolerance to low LC n-3 PUFA diets. Here we analyze innate and adaptive immune response in Atlantic salmon to a commercial vaccine after being fed low levels of EPA and DHA, and we also compare three strains of salmon selected by their endogenous capacity of synthesizing LC- n-3 PUFA. A total of 2,890 differentially expressed genes (DEGs) were identified (p-value adjusted < 0.1) when comparing vaccinated fish against control non-vaccinated. Gene ontology (GO) and KEGG analysis with 442 up/downregulated genes revealed that most DEGs were both related to immune response as well as part of important immune related pathways, as "Toll-like receptor" and "Cytokine-Cytokine interaction". Adaptive response was also addressed by measuring antigen specific IgM, and titers were significantly higher than in the pre-immune fish at 62 days post-immunization. However, diet and strain had no/little effect on vaccine-specific IgM or innate immune responses. Atlantic salmon therefore display robustness in its response to vaccination even when feed low levels of LC n-3 PUFA.

Dietary Buglossoides arvensis Oil as a Potential Candidate to Substitute Fish Oil in Rainbow Trout Diets

The utilization of vegetable oils in salmonid diets substantially decreased the body content of omega-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFA), and thus the product quality for human consumption. Therefore, new ingredients for aquaculture feeds are needed that maximize the deposition of health-promoting n-3 LC-PUFA. This study investigated Buglossoides arvensis (Ahiflower) oil, a plant oil rich in alpha-linolenic acid (18:3n-3, ALA) and stearidonic acid (18:4n-3, SDA), as a source of n-3 fatty acids in rainbow trout (Oncorhynchus mykiss) nutrition. Rainbow trout (87.4 ± 0.6 g) were fed for 56 days. The oils of the control diet (FV) were substituted by Ahiflower oil at 33%, 66%, and 100% (A33, A66, A100). Dietary Ahiflower oil increased the final body weights of fish. mRNA steady state levels of fatty acyl desaturase 2a (delta-6) (fads2a(d6)) and 2b (delta-5) (fads2b(d5)) as well as carnitine palmitoyl transferase 1 a (cpt1a) were not altered by dietary treatments. In contrast, cpt1c mRNA steady state levels were significantly downregulated in samples of fish fed A66 and A100. Significantly higher eicosapentaenoic acid (20:5n-3, EPA) and docosahexaenoic acid (22:6n-3, DHA) levels were found in the liver and significantly higher EPA levels in the fillet of rainbow trout of A66 and A100 compared to FV. The content of DHA in fillets of fish fed Ahiflower oil was not significantly different to fish fed FV. Thus, high dietary amounts of Ahiflower oil can compensate for reduced dietary EPA and DHA levels.

Time-course microarray analysis for identifying candidate genes involved in obesity-associated pathological changes in the mouse colon

Background

Obesity is known to increase the risk of colorectal cancer. However, mechanisms underlying the pathogenesis of obesity-induced colorectal cancer are not completely understood. The purposes of this study were to identify differentially expressed genes in the colon of mice with diet-induced obesity and to select candidate genes as early markers of obesity-associated abnormal cell growth in the colon.

Methods

C57BL/6N mice were fed normal diet (11% fat energy) or high-fat diet (40% fat energy) and were euthanized at different time points. Genome-wide expression profiles of the colon were determined at 2, 4, 8, and 12 weeks. Cluster analysis was performed using expression data of genes showing log₂ fold change of ≥1 or ≤−1 (twofold change), based on time-dependent expression patterns, followed by virtual network analysis.

Results

High-fat diet-fed mice showed significant increase in body weight and total visceral fat weight over 12 weeks. Time-course microarray analysis showed that 50, 47, 36, and 411 genes were differentially expressed at 2, 4, 8, and 12 weeks, respectively. Ten cluster profiles representing distinguishable patterns of genes differentially expressed over time were determined. Cluster 4, which consisted of genes showing the most significant alterations in expression in response to high-fat diet over 12 weeks, included Apoa4 (apolipoprotein A-IV), Ppap2b (phosphatidic acid phosphatase type 2B), Cel (carboxyl ester lipase), and Clps (colipase, pancreatic), which interacted strongly with surrounding genes associated with colorectal cancer or obesity.

Conclusions

Our data indicate that Apoa4, Ppap2b, Cel, and Clps are candidate early marker genes associated with obesity-related pathological changes in the colon. Genome-wide analyses performed in the present study provide new insights on selecting novel genes that may be associated with the development of diseases of the colon.

Electronic supplementary material

The online version of this article (doi:10.1186/s12263-016-0547-x) contains supplementary material, which is available to authorized users.

Technological trends and market perspectives for production of microbial oils rich in omega-3

In recent years, foods that contain omega-3 lipids have emerged as important promoters of human health. These lipids are essential for the functional development of the brain and retina, and reduction of the risk of cardiovascular and Alzheimer's diseases. The global market for omega-3 production, particularly docosahexaenoic acid (DHA), saw a large expansion in the last decade due to the increasing use of this lipid as an important component of infant food formulae and supplements. The production of omega-3 lipids from fish and vegetable oil sources has some drawbacks, such as complex purification procedures, unwanted contamination by marine pollutants, reduction or even extinction of several species of fish, and aspects related to sustainability. A promising alternative system for the production of omega-3 lipids is from microbial metabolism of yeast, fungi, or microalgae. The aim of this review is to discuss the various omega-3 sources in the context of the global demand and market potential for these bioactive compounds. To summarize, it is clear that fish and vegetable oil sources will not be sufficient to meet the future needs of the world population. The biotechnological production of single-cell oil comes as a sustainable alternative capable of supplementing the global demand for omega-3, causing less environmental impact.

Echium oil increased the expression of a Δ4 Fads2 fatty acyl desaturase and the deposition of n-3 long-chain polyunsaturated fatty acid in comparison with linseed oil in striped snakehead (Channa striata) muscle

Despite the potential of vegetable oils as aquafeed ingredients, a major drawback associated with their utilization is the inferior level of beneficial n-3 long-chain polyunsaturated fatty acids (LC-PUFA). Echium oil (EO), which is rich in stearidonic acid (SDA, 18:4n-3), could potentially improve the deposition of n-3 LC-PUFA as the biosynthesis of LC-PUFA is enhanced through bypassing the rate-limiting ∆6 desaturation step. We report for the first time an attempt to investigate whether the presence of a desaturase (Fads2) capable of ∆4 desaturation activities and an elongase (Elovl5) will leverage the provision of dietary SDA to produce a higher rate of LC-PUFA bioconversion. Experimental diets were designed containing fish oil (FO), EO or linseed oil (LO) (100FO, 100EO, 100LO), and diets which comprised equal mixtures of the designated oils (50EOFO and 50EOLO) were evaluated in a 12-week feeding trial involving striped snakeheads (Channa striata). There was no significant difference in growth and feed conversion efficiency. The hepatic fatty acid composition and higher expression of fads2 and elovl5 genes in fish fed EO-based diets indicate the utilization of dietary SDA for LC-PUFA biosynthesis. Collectively, this resulted in a higher deposition of muscle eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3) compared to LO-based diets. Dietary EO improved the ratio of n-3 LC-PUFA to n-6 LC-PUFA in fish muscle, which is desirable for human populations with excessive consumption of n-6 PUFA. This study validates the contribution of SDA in improving the content of n-3 LC-PUFA and the ratio of EPA to arachidonic acid (ARA, 20:4n-6) in a freshwater carnivorous species.

Opportunities to enhance alternative sources of long-chainn-3 fatty acids within the diet

Health benefits or advocated health benefits of long-chain (LC)n-3 PUFA are better known by medical doctors as well as by consumers, so that consumption increases. In addition, the development of aquaculture requires more fishmeal and fish oil. Humanisation of care of companion animals is also associated with addition of LCn-3 PUFA in pet foods. The risk of the increased demand for LCn-3 PUFA is the excess harvesting of natural sources, especially of marine origin (oily fishes, krill). In order to improve sustainability, alternative sources of LCn-3 PUFA have been developed. These alternative sources are: (a) terrestrial plants naturally or genetically enriched in stearidonic acid (SDA), which bypasses the first limiting step of (i.e. ∆6 desaturase) of the biosynthesis of LCn-3 PUFA; (b) single-cell oils rich in LCn-3 PUFA (microalgae,Escherichia coli) and krill. Currently, plants rich in SDA are expensive, metabolic engineering is unfavourably accepted by consumers in many countries, cultivation of microalgae is very expensive even though their ability (for some of them) to synthesise biofuels could induce a decrease in industrial costs, and Antarctic krill harvest must be restricted. Thus, it is difficult to predict their real development in the future.

DHA-containing oilseed: a timely solution for the sustainability issues surrounding fish oil sources of the health-benefitting long-chain omega-3 oils

Benefits of long-chain (≥C20) omega-3 oils (LC omega-3 oils) for reduction of the risk of a range of disorders are well documented. The benefits result from eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA); optimal intake levels of these bioactive fatty acids for maintenance of normal health and prevention of diseases have been developed and adopted by national and international health agencies and science bodies. These developments have led to increased consumer demand for LC omega-3 oils and, coupled with increasing global population, will impact on future sustainable supply of fish. Seafood supply from aquaculture has risen over the past decades and it relies on harvest of wild catch fisheries also for its fish oil needs. Alternate sources of LC omega-3 oils are being pursued, including genetically modified soybean rich in shorter-chain stearidonic acid (SDA, 18:4ω3). However, neither oils from traditional oilseeds such as linseed, nor the SDA soybean oil have shown efficient conversion to DHA. A recent breakthrough has seen the demonstration of a land plant-based oil enriched in DHA, and with omega-6 PUFA levels close to that occurring in marine sources of EPA and DHA. We review alternative sources of DHA supply with emphasis on the need for land plant oils containing EPA and DHA.

Polycyclic aromatic hydrocarbon degradation of phytoplankton-associated Arenibacter spp. and description of Arenibacter algicola sp. nov., an aromatic hydrocarbon-degrading bacterium

Pyrosequencing of the bacterial community associated with a cosmopolitan marine diatom during enrichment with crude oil revealed several Arenibacter phylotypes, of which one (OTU-202) had become significantly enriched by the oil. Since members of the genus Arenibacter have not been previously shown to degrade hydrocarbons, we attempted to isolate a representative strain of this genus in order to directly investigate its hydrocarbon-degrading potential. Based on 16S rRNA sequencing, one isolate (designated strain TG409(T)) exhibited >99% sequence identity to three type strains of this genus. On the basis of phenotypic and genotypic characteristics, strain TG409(T) represents a novel species in the genus Arenibacter, for which the name Arenibacter algicola sp. nov. is proposed. We reveal for the first time that polycyclic aromatic hydrocarbon (PAH) degradation is a shared phenotype among members of this genus, indicating that it could be used as a taxonomic marker for this genus. Kinetic data for PAH mineralization rates showed that naphthalene was preferred to phenanthrene, and its mineralization was significantly enhanced in the presence of glass wool (a surrogate for diatom cell surfaces). During enrichment on hydrocarbons, strain TG409(T) emulsified n-tetradecane and crude oil, and cells were found to be preferentially attached to oil droplets, indicating an ability by the strain to express cell surface amphiphilic substances (biosurfactants or bioemulsifiers) as a possible strategy to increase the bioavailability of hydrocarbons. This work adds to our growing knowledge on the diversity of bacterial genera in the ocean contributing to the degradation of oil contaminants and of hydrocarbon-degrading bacteria found living in association with marine eukaryotic phytoplankton.

Algiphilus aromaticivorans gen. nov., sp. nov., an aromatic hydrocarbon-degrading bacterium isolated from a culture of the marine dinoflagellate Lingulodinium polyedrum, and proposal of Algiphilaceae fam. nov

A strictly aerobic, halotolerant, Gram-stain-negative, rod-shaped bacterium, designated strain DG1253T, was isolated from a laboratory culture of the marine dinoflagellate Lingulodinium polyedrum (CCAP 1121/2). The strain was able to degrade two- and three-ring polycyclic aromatic hydrocarbons. It exhibited a narrow nutritional spectrum, preferring to utilize aliphatic and aromatic hydrocarbon compounds and small organic acids. Cells produced surface blebs and contained a single polar flagellum. The predominant isoprenoid quinone of strain DG1253T was Q-8. The fatty acid profile was dominated by C18 : 1ω7c. The mean DNA G+C content of strain DG1253T was 63.6±0.25 mol%. 16S rRNA gene sequence analysis placed this organism within the order Xanthomonadales of the class Gammaproteobacteria . Its closest relatives included representatives of the Hydrocarboniphaga – Nevskia – Sinobacter clade (≤89.9 % 16S rRNA gene sequence similarity) in the family Sinobacteraceae . On the basis of distinct phenotypic and genotypic characteristics, strain DG1253T is considered to represent a novel species of a new genus in the class Gammaproteobacteria , for which the name Algiphilus aromaticivorans gen. nov., sp. nov. is proposed. The type strain of the type species, Algiphilus aromaticivorans, is DG1253T ( = ATCC BAA-2243T = DSM 24793T). In addition, a new family, Algiphilaceae fam. nov., is proposed to accommodate the genus Algiphilus.

Polycyclovorans algicola gen. nov., sp. nov., an aromatic-hydrocarbon-degrading marine bacterium found associated with laboratory cultures of marine phytoplankton

A strictly aerobic, halotolerant, rod-shaped bacterium, designated strain TG408, was isolated from a laboratory culture of the marine diatom Skeletonema costatum (CCAP1077/1C) by enrichment with polycyclic aromatic hydrocarbons (PAHs) as the sole carbon source. 16S rRNA gene sequence analysis placed this organism within the order Xanthomonadales of the class Gammaproteobacteria. Its closest relatives included representatives of the Hydrocarboniphaga-Nevskia-Sinobacter clade (<92% sequence similarity) in the family Sinobacteraceae. The strain exhibited a narrow nutritional spectrum, preferring to utilize aliphatic and aromatic hydrocarbon compounds and small organic acids. Notably, it displayed versatility in degrading two- and three-ring PAHs. Moreover, catechol 2,3-dioxygenase activity was detected in lysates, indicating that this strain utilizes the meta-cleavage pathway for aromatic compound degradation. Cells produced surface blebs and contained a single polar flagellum. The predominant isoprenoid quinone of strain TG408 was Q-8, and the dominant fatty acids were C(16:0), C(16:1) ω7c, and C(18:1) ω7c. The G+C content of the isolate's DNA was 64.3 mol% ± 0.34 mol%. On the basis of distinct phenotypic and genotypic characteristics, strain TG408 represents a novel genus and species in the class Gammaproteobacteria for which the name Polycyclovorans algicola gen. nov., sp. nov., is proposed. Quantitative PCR primers targeting the 16S rRNA gene of this strain were developed and used to show that this organism is found associated with other species of marine phytoplankton. Phytoplankton may be a natural biotope in the ocean where new species of hydrocarbon-degrading bacteria await discovery and which contribute significantly to natural remediation processes.

Omega-3 fatty acid supplementation and cardiovascular disease

Epidemiological studies on Greenland Inuits in the 1970s and subsequent human studies have established an inverse relationship between the ingestion of omega-3 fatty acids [C(20-22) ω 3 polyunsaturated fatty acids (PUFA)], blood levels of C(20-22) ω 3 PUFA, and mortality associated with cardiovascular disease (CVD). C(20-22) ω 3 PUFA have pleiotropic effects on cell function and regulate multiple pathways controlling blood lipids, inflammatory factors, and cellular events in cardiomyocytes and vascular endothelial cells. The hypolipemic, anti-inflammatory, anti-arrhythmic properties of these fatty acids confer cardioprotection. Accordingly, national heart associations and government agencies have recommended increased consumption of fatty fish or ω 3 PUFA supplements to prevent CVD. In addition to fatty fish, sources of ω 3 PUFA are available from plants, algae, and yeast. A key question examined in this review is whether nonfish sources of ω 3 PUFA are as effective as fatty fish-derived C(20-22) ω 3 PUFA at managing risk factors linked to CVD. We focused on ω 3 PUFA metabolism and the capacity of ω 3 PUFA supplements to regulate key cellular events linked to CVD. The outcome of our analysis reveals that nonfish sources of ω 3 PUFA vary in their capacity to regulate blood levels of C(20-22) ω 3 PUFA and CVD risk factors.

Echium oil provides no benefit over linseed oil for (n-3) long-chain PUFA biosynthesis in rainbow trout

The implementation of alternative lipid sources for use in aquaculture is of considerable interest globally. However, the possible benefit of using stearidonic acid (SDA)-rich fish oil (FO) alternatives has led to scientific confusion. Two hundred and forty rainbow trout (Oncorhynchus mykiss) were fed 1 of 4 diets (3 replicate tanks/treatment) containing either FO, linseed oil (LO), echium oil, or mixed vegetable oil (72% LO, 23% sunflower oil, and 6% canola oil) as the dietary lipid source (16.5%) for 73 d to investigate the competition and long-chain PUFA (LC-PUFA) biosynthesis between the fatty acid substrates α-linolenic acid (ALA) and SDA. SDA was more efficiently bioconverted to LC-PUFA compared with ALA. However, when the dietary lipid sources were directly compared, the increased provision of C18 PUFA within the LO diet resulted in no significant differences in (n-3) LC-PUFA content compared with fish fed the other diets. This study therefore shows that, rather than the previously speculated substrate competition, the limiting process in the apparent in vivo (n-3) LC-PUFA biosynthesis appears to be substrate availability. Rainbow trout fed the SDA- and ALA-rich dietary lipid sources subsequently had similar significant reductions in (n-3) LC-PUFA compared with fish fed the FO diet, therefore providing no additional dietary benefit on (n-3) LC-PUFA concentrations.

Porticoccus hydrocarbonoclasticus sp. nov., an aromatic hydrocarbon-degrading bacterium identified in laboratory cultures of marine phytoplankton

A marine bacterium, designated strain MCTG13d, was isolated from a laboratory culture of the dinoflagellate Lingulodinium polyedrum CCAP1121/2 by enrichment with polycyclic aromatic hydrocarbons (PAHs) as the sole carbon source. Based on 16S rRNA gene sequence comparisons, the strain was most closely related to Porticoccus litoralis IMCC2115(T) (96.5%) and to members of the genera Microbulbifer (91.4 to 93.7%) and Marinimicrobium (90.4 to 92.0%). Phylogenetic trees showed that the strain clustered in a distinct phyletic line in the class Gammaproteobacteria for which P. litoralis is presently the sole cultured representative. The strain was strictly aerobic, rod shaped, Gram negative, and halophilic. Notably, it was able to utilize hydrocarbons as sole sources of carbon and energy, whereas sugars did not serve as growth substrates. The predominant isoprenoid quinone of strain MCTG13d was Q-8, and the dominant fatty acids were C(16:1ω7c), C(18:1ω7c), and C(16:0). DNA G+C content for the isolate was 54.9 ± 0.42 mol%. Quantitative PCR primers targeting the 16S rRNA gene of this strain showed that this organism was common in other laboratory cultures of marine phytoplankton. On the basis of phenotypic and genotypic characteristics, strain MCTG13d represents a novel species of Porticoccus, for which the name Porticoccus hydrocarbonoclasticus sp. nov. is proposed. The discovery of this highly specialized hydrocarbon-degrading bacterium living in association with marine phytoplankton suggests that phytoplankton represent a previously unrecognized biotope of novel bacterial taxa that degrade hydrocarbons in the ocean.

Effects of dietary fish oil replacement with flaxseed oil on tissue fatty acid composition and expression of desaturase and elongase genes

BACKGROUND

This study was conducted to evaluate the effects of total or partial substitution of dietary fish oil (FO) by flaxseed oil (FlaxO) in Jade Tiger hybrid abalone on fatty acid composition of muscle, gonad and digestive gland, and the expression of desaturase and elongase genes. Abalone were fed five different experimental diets in which FO (control diet) was serially replaced by 25%, 50%, 75% and 100% FlaxO respectively.

RESULTS

Muscle, gonad and digestive gland of abalone fed the control diet and the diets containing 25%, 50% and 75% FlaxO showed significantly higher (P < 0.05) levels of eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA) and docosahexaenoic acid (DHA) compared to those fed the 100% FlaxO. The results also showed that Δ-6 desaturase and elongase gene expression in muscle was increased in a graded manner by increasing dietary FlaxO. The expression of both genes was higher in abalone fed the FlaxO-substituted diets compared to the abalone fed FO.

CONCLUSION

The replacement of FO with FlaxO in commercial abalone diets at levels of 25-75% can improve the composition of health-benefiting n-3 polyunsturated fatty acids in tissues of cultured hybrid abalone, and achieve similar outcomes to FO supplementation.

Up-regulated desaturase and elongase gene expression promoted accumulation of polyunsaturated fatty acid (PUFA) but not long-chain PUFA in Lates calcarifer, a tropical euryhaline fish, fed a stearidonic acid- and γ-linoleic acid-enriched diet

The limited activity of Δ6 fatty acid desaturase (FAD6) on α-linolenic (ALA, 18:3n-3) and linoleic (LA, 18:2n-6) acids in marine fish alters the long-chain (≥C(20)) polyunsaturated fatty acid (LC-PUFA) concentration in fish muscle and liver when vegetable oils replace fish oil (FO) in aquafeeds. Echium oil (EO), rich in stearidonic acid (SDA, 18:4n-3) and γ-linoleic acid (GLA, 18:3n-6), may enhance the biosynthesis of n-3 and n-6 LC-PUFA by bypassing the rate-limiting FAD6 step. Nutritional and environmental modulation of the mechanisms in LC-PUFA biosynthesis was examined in barramundi, Lates calcarifer , a tropical euryhaline fish. Juveniles were maintained in either freshwater or seawater and fed different dietary LC-PUFA precursors present in EO or rapeseed oil (RO) and compared with FO. After 8 weeks, growth of fish fed EO was slower compared to the FO and RO treatments. Irrespective of salinity, expression of the FAD6 and elongase was up-regulated in fish fed EO and RO diets, but did not lead to significant accumulation of LC-PUFA in the neutral lipid of fish tissues as occurred in the FO treatment. However, significant concentrations of eicosapentaenoic acid (EPA, 20:5n-3) and arachidonic acid (ARA, 20:4n-6), but not docosahexaenoic acid (DHA, 22:6n-3), appeared in liver and, to a lesser extent, in muscle of fish fed EO with marked increases in the phospholipid fraction. Fish in the EO treatment had higher EPA and ARA in their liver phospholipids than fish fed FO. Endogenous conversion of dietary precursors into neutral lipid LC-PUFA appears to be limited by factors other than the initial rate-limiting step. In contrast, phospholipid LC-PUFA had higher biosynthesis, or selective retention, in barramundi fed EO rather than RO.

Dietary fish oil supplements increase tissue n-3 fatty acid composition and expression of delta-6 desaturase and elongase-2 in Jade Tiger hybrid abalone

This study was conducted to investigate the effects of fish oil (FO) supplements on fatty acid composition and the expression of ∆6 desaturase and elongase 2 genes in Jade Tiger abalone. Five test diets were formulated to contain 0.5, 1.0, 1.5, 2.0 and 2.5% of FO respectively, and the control diet was the normal commercial abalone diet with no additional FO supplement. The muscle, gonad and digestive glands (DG) of abalone fed with all of the five test diets showed significantly high levels of total n-3 polyunsaturated fatty acid (PUFA), eicosapentaenoic acid (EPA), docosapentaenoic acid n-3 (DPAn-3), and docosahexaenoic acid (DHA) than the control group. In all three types of tissue, abalone fed diet supplemented with 1.5% FO showed the highest level of these fatty acids (P < 0.05). For DPAn-3 the higher level was also found in muscle and gonad of abalone fed diet supplemented with 2% FO (P < 0.05). Elongase 2 expression was markedly higher in the muscle of abalone fed diet supplemented with 1.5% FO (P < 0.05), followed by the diet containing 2% FO supplement. For ∆6 desaturase, significantly higher expression was observed in muscle of abalone fed with diet containing 0.5% FO supplement (P < 0.05). Supplementation with FO in the normal commercial diet can significantly improve long chain n-3 PUFA level in cultured abalone, with 1.5% being the most effective supplementation level.

Effect of feeding Atlantic salmon (Salmo salar L.) a diet enriched with stearidonic acid from parr to smolt on growth and n-3 long-chain PUFA biosynthesis

Vegetable oils (VO) have become the predominant substitute for fish oil (FO) in aquafeeds; however, the resultant lower content of n-3 long-chain ( ≥ C20) PUFA (n-3 LC-PUFA) in fish has put their use under scrutiny. The need to investigate new oil sources exists. The present study tested the hypothesis that in Atlantic salmon (Salmo salar L.), a high intake of stearidonic acid (SDA) from Echium oil (EO) would result in increased n-3 LC-PUFA biosynthesis due to a lower requirement for Δ6 desaturase. Comparisons were made with fish fed on diets containing rapeseed oil (RO) and FO in freshwater for 112 d followed by 96 d in seawater. EO fish had higher whole-carcass SDA and eicosatetraenoic acid (ETA) in freshwater and prolonged feeding on the EO diet in seawater resulted in higher SDA, ETA, EPA and docosapentaenoic acid (DPA) compared with RO fish. Fatty acid mass balance of freshwater fish indicated higher biosynthesis of ETA and EPA in EO fish compared with fish fed on the other diets and a twofold increase in n-3 LC-PUFA synthesis compared with RO fish. In seawater, n-3 biosynthetic activity was low, with higher biosynthesis of ETA in EO fish and appearance of all desaturated and elongated products along the n-3 pathway. SDA-enriched VO are more suitable substitutes than conventional VO from a human consumer perspective due to the resulting higher SDA content, higher total n-3 and improved n-3:n-6 ratio obtained in fish, although both VO were not as effective as FO in maintaining EPA and DHA content in Atlantic salmon.

Long-chain omega-3 oils-an update on sustainable sources

Seafood is currently the best and generally a safe source of long-chain (LC, (≥C(20)) omega-3 oils amongst the common food groups. LC omega-3 oils are also obtained in lower amounts per serve from red meat, egg and selected other foods. As global population increases the opportunities to increase seafood harvest are limited, therefore new alternate sources are required. Emerging sources include microalgae and under-utilized resources such as Southern Ocean krill. Prospects for new land plant sources of these unique and health-benefiting oils are also particularly promising, offering hope for alternate and sustainable supplies of these key oils, with resulting health, social, economic and environmental benefits.

Lipid digestion and absorption in early life: an update

PURPOSE OF REVIEW

To highlight our understanding of digestion and absorption of dietary lipids in newborn infants, and specifically how these processes differ from those in children and adults.

RECENT FINDINGS

The intestinal concentration of pancreatic triglyceride lipase (PTL) and bile salts is lower in newborns compared to later in life. Instead the PTL-related protein 2 and bile salt-stimulated lipase (BSSL) are the key enzymes secreted from pancreas, which in concerted action with gastric lipase operate to achieve efficient fat absorption during infancy. BSSL is also present in human milk which affects fat absorption and growth in breast-fed preterm infants. Under conditions of low luminal bile salt concentrations fat absorption is likely to occur from liquid crystalline product phases, which may result in absorption from an extended part of the small intestinal mucosal surfaces compared to adults. Chylomicron assembly and secretion also seem to adapt to the specific situation of the newborn.

SUMMARY

Both fat digestion and product absorption are different in newborn infants compared to adults; other lipases are used for digestion and different physical-chemical phases may be used for product absorption. Why these differences occur is still an unsolved question of considerable importance to neonatal nutrition.

Effect of diet, sex and age on fatty acid metabolism in broiler chickens:n-3 andn-6 PUFA

The PUFA metabolism in broiler chicken was studied through the whole body fatty acid balance method. Four dietary lipid sources (palm fat, Palm; soyabean oil, Soya; linseed oil, Lin; fish oil, Fish) were added at 3 % to a basal diet containing 5 % palm fat. Diets were fed to female and male birds from day 1 to either day 21 or day 42 of age. Birds fed the Lin diet showed a significantly higher 18 : 2n-6 accumulation compared with the other diets (85·2v.73·6 % of net intake), whereas diet did not affect 18 : 3n-3 accumulation (mean 63 % of net intake). Bioconversion of 18 : 2n-6 significantly decreased in the order Palm>Lin>Soya>Fish (4·7, 3·9, 3·4 and 1 % of net intake, respectively). The 18 : 3n-3 bioconversion on the Palm and Soya diets was similar and significantly higher than in broilers on the Lin diet (9·1v.5·8 % of net intake). The β-oxidation of 18 : 2n-6 was significantly lower on the Lin diet than on the other diets (10·8v.23·3 % of net intake), whereas β-oxidation of 18 : 3n-3 was significantly higher on the Fish diet than on the other diets (41·5v.27·3 % of net intake). Feeding fish oil suppressed apparent elongase and desaturase activity, whereas a higher dietary supply of 18 : 3n-3 and 18 : 2n-6 enhanced apparent elongation and desaturation activity on the PUFA involved in then-3 andn-6 pathway, respectively. Accumulation of 18 : 2n-6 and 18 : 3n-3 increased and β-oxidation decreased with age. Sex had a marginal effect on the PUFA metabolism.

n-3 Oil sources for use in aquaculture--alternatives to the unsustainable harvest of wild fish

The present review examines renewable sources of oils with n-3 long-chain (> or = C20) PUFA (n-3 LC-PUFA) as alternatives to oil from wild-caught fish in aquafeeds. Due to the increased demand for and price of wild-caught marine sources of n-3 LC-PUFA-rich oil, their effective and sustainable replacement in aquafeeds is an industry priority, especially because dietary n-3 LC-PUFA from eating fish are known to have health benefits in human beings. The benefits and challenges involved in changing dietary oil in aquaculture are highlighted and four major potential sources of n-3 LC-PUFA for aquafeeds, other than fish oil, are compared. These sources of oil, which contain n-3 LC-PUFA, specifically EPA (20:5n-3) and DHA (22:6n-3) or precursors to these key essential fatty acids, are: (1) other marine sources of oil; (2) vegetable oils that contain biosynthetic precursors, such as stearidonic acid, which may be used by fish to produce n-3 LC-PUFA; (3) single-cell oil sources of n-3 LC-PUFA; (4) vegetable oils derived from oil-seed crops that have undergone genetic modification to contain n-3 LC-PUFA. The review focuses on Atlantic salmon (Salmo salar L.), because it is the main intensively cultured finfish species and it both uses and stores large amounts of oil, in particular n-3 LC-PUFA, in the flesh.