Cholestane as a digestibility marker in the absorption of polyunsaturated fatty acid ethyl esters in Atlantic salmon

Digestibility of Conventional and Novel Dietary Lipids in Channel Catfish Ictalurus punctatus

Lipid and fatty acid digestibility is presumably high in Channel Catfish, but data is lacking. We determined the lipid and fatty acid digestibility of traditional and alternative dietary lipids in Channel Catfish to inform lipid choice for commercial diets. Six diets contained 4% of different lipids: soybean oil (SBO), soybean oil containing conjugated linoleic acids (CLA-SBO), catfish offal oil (COO), flaxseed oil (FXO), menhaden fish oil (MFO) and poultry fat (PF). Diets were fed to Channel Catfish (150-200 g) maintained at 26.5 °C in each of six 110 L aquaria. Six hours post-prandial, feces were collected for analysis. Total lipid, crude protein and fatty acids of lyophilized feces were analyzed, and apparent digestibility coefficients (ADCs) were calculated. ADCs of lipid, saturated and monounsaturated fatty acids, linoleic acid and protein digestibility were similar among diets. CLA isomers (cis-9, trans-11 (84.1%) and trans-10, cis-12 (90%)) in the CLA-SBO diet were highly digestible. Oleic acid digestibility was highest in the PF diet. ADC was high for α-linolenic acid in the FXO diet, and for arachidonic acid and n-3 LC-PUFA in the MFO diet. Overall, total lipid digestibility was high, but ADCs of individual fatty acids differed by source.

Microalgal polyunsaturated fatty acids: Hotspots and production techniques

Algae play a crucial role in the earth’s primary productivity by producing not only oxygen but also a variety of high-value nutrients. One such nutrient is polyunsaturated fatty acids (PUFAs), which are accumulated in many algae and can be consumed by animals through the food chain and eventually by humans. Omega-3 and omega-6 PUFAs are essential nutrients for human and animal health. However, compared with plants and aquatic sourced PUFA, the production of PUFA-rich oil from microalgae is still in the early stages of exploration. This study has collected recent reports on algae-based PUFA production and analyzed related research hotspots and directions, including algae cultivation, lipids extraction, lipids purification, and PUFA enrichment processes. The entire technological process for the extraction, purification and enrichment of PUFA oils from algae is systemically summarized in this review, providing important guidance and technical reference for scientific research and industrialization of algae-based PUFA production.

Nutrients and Energy Digestibility of Microalgal Biomass for Fish Feed Applications

Aquafeed accounts for at least 75–90% of aquaculture’s operating costs. Traditional aquafeed ingredients such as fishmeal, fish oil, and soybean meal are unsustainable; further, their increasing cost necessities developing alternative feed ingredients. Microalgae-based aquafeed is not only environmentally friendly, but it can also be cost-effective with proper optimization. In addition, the nutrition profile of microalgae is similar to that of many fishes. The digestibility of a feed is one of the most important factors to consider in feed formulation. A highly digestible feed can lower production costs, reduce feed waste, and reduce the risk of eutrophication. This review discusses the digestibility of various nutrients such as protein, lipid, carbohydrate, amino acids, and fatty acids (including omega-3 fatty acids), dry matter, and energy of various microalgae in fish. Other commonly used aquafeed ingredients were also compared to microalgae in terms of nutrient and energy digestibility in fish. The intrinsic characteristics of microalgae, biomass pretreatment, and feed preparation methods are all discussed as factors that contribute to the nutrient and energy digestibility of microalgae in fish. Furthermore, methods for increasing the digestibility of microalgal biomass in fish are suggested. Finally, the review concludes with the challenges and prospects of using microalgae as a fish feed in terms of digestibility.

Visualization of dietary docosahexaenoic acid in whole-body zebrafish using matrix-assisted laser desorption/ionization mass spectrometry imaging

Zebrafish models have been developed for several studies involving lipid metabolism and lipid-related diseases. In the present study, the migration of dietary docosahexaenoic acid (DHA) in whole-body zebrafish was estimated by stable-isotope tracer and matrix-assisted laser desorption/ionization mass spectrometry imaging. Administration of 1-¹³C-2,2-D₂-labeled DHA ((+3)DHA) ethyl ester to male zebrafish was conducted to evaluate its accumulation, migration, and distribution in the body. The (+3)DHA content in the body of zebrafish after administering (+3)DHA for 10 and 15 d was significantly higher than that in the control group. (+3)DHA was observed as a constituent of phosphatidylcholine (PC) in the intestine of zebrafish that were administered (+3)DHA for 5 and 10 d. (+3)DHA-containing PC tended to accumulate in the intestines of zebrafish administered (+3)DHA for 1 d, indicating that recombination of (+3)DHA from ethyl ester to PC occurs quickly at intestine. After administration for 15 d, (+3)DHA-containing PC accumulated in the intestine, liver, and muscle of whole-body zebrafish. In contrast, (+3)DHA-containing PC was not detected in the brain. These results showed that dietary DHA is initially constructed into PC as a structural component of intestinal cell membranes and gradually migrates into peripheral tissues such as muscle.

Effect of Substituting Fish Oil with Camelina Oil on Growth Performance, Fatty Acid Profile, Digestibility, Liver Histology, and Antioxidative Status of Red Seabream (Pagrus major)

Simple Summary

The shortage of natural resources, prices, and high demand for fish oil has encouraged the use of non-traditional ingredients in aquafeed. The search for an alternative lipid source in aquafeeds has seen terrestrial vegetable oils at the epicenter of various flagship aqua-feed research. Herein, we investigated the effects of substituting fish oil (FO) with camelina oil (CO) on growth performance, fatty acid profile, digestibility, liver histology, and antioxidative status of red seabream (Pagrus major). After 56 days of the feeding trial, the results suggested that FO can be replaced with CO in the feeds of farmed red seabream without compromising growth, blood chemistry, digestibility, and overall health status.

Abstract

A 56-day feeding trial to evaluate the responses of red seabream (initial weight: 1.8 ± 0.02 g) to the substitution of fish oil (FO) with camelina oil (CO) at different ratios was conducted. The control diet formulated at 46% CP (6F0C) contained only FO without CO; from the second to the fifth diet, the FO was substituted with CO at rates of 5:1 (5F1C), 4:2 (4F2C), 3:3 (3F3C), 2:4 (2F4C), and 0:6 (0F6C). The results of the present study showed that up to full substitution of FO with CO showed no significant effect on growth variables BW = 26.2 g–28.3 g), body weight gain (BWG = 1275.5–1365.3%), specific growth rate (SGR = 4.6–4.7), feed intake (FI = 25.6–27.8), feed conversion ratio (FCR = 1.0–1.1), biometric indices condition factor (CF = 2.2–2.4), hepatosomatic index (HSI = 0.9–1.1), viscerasomatic index (VSI = 7.5–9.5), and survival rates (SR = 82.2–100) with different FO substitution levels with CO. Similarly, there were no significant differences (p < 0.05) found in the whole-body composition except for the crude lipid content, and the highest value was observed in the control group (291 g/kg) compared to the other groups FO5CO1 (232 k/kg), FO4CO2 (212 g/kg), FO2CO4 (232 g/kg) and FO0CO6 (244 g/kg). Blood chemistry levels were not influenced in response to test diets: hematocrit (36–33%), glucose (Glu = 78.3–71.3 mg/dL), total protein (T-pro = 3.1–3.8 g/dL), total cholesterol (T-Chol = 196.0–241 mg/dL), blood urea nitrogen (BUN = 9.0–14.6 mg/dL), total bilirubin (T-Bil = 0.4–0.5 mg/dL), triglyceride (TG = 393.3–497.6 mg/dL), alanine aminotransferase test (ALT = 50–65.5 UL/L), aspartate aminotransferase test (AST = 38–69.3 UL/L). A remarkable modulation was observed in catalase (CAT) and superoxide dismutase (SOD) activities in the liver, as CAT and SOD values were lower with the complete FO substitution with CO (0F6C), and the highest values were observed in the control and (4F2C). This study indicates that red seabream may have the ability to maintain LC-PUFAs between tissues and diets, and CO substitution of FO could improve both lipid metabolism and oxidation resistance as well as maintain digestibility. In conclusion, dietary FO can be replaced up to 100% or 95% by CO in the diets of red seabream as long as n-3 HUFA, EPA, and DHA are incorporated at the recommended level.

Apparent Digestibility of Macronutrients and Fatty Acids from Microalgae (Schizochytrium sp.) Fed to Rainbow Trout (Oncorhynchus mykiss): A Potential Candidate for Fish Oil Substitution

Simple Summary

Aquaculture is the world’s fastest growing sector of the global food system. Aquaculture feed producers are seeking substitutes for fishmeal and fish oil to develop more sustainable feeds. Marine microalgae show promise as potential ingredients in aquafeeds; however, the literature lacks data on the digestibility and availability of macronutrients and individual fatty acids for omega 3-rich microalgal biomass, Schizochytrium spp., in rainbow trout. This is an important gap to fill because, among marine microalgae, this species is the most frequently used in fish feed, particularly as a dietary supplement or mixed with other ingredients; digestibility data would guide more judicious inclusion of this microalga biomass. High digestibility of macronutrients, energy and fatty acids showed that Schizochytrium spp. is a high-quality substitute for fish oil and potential candidate as a supplement of LC-PUFA in trout feed with vegetable oils. Digestibility is influenced by temperature and several trials have shown increased macronutrient digestibility with increasing temperature. There is an urgent need to determine the effect of temperature on lipid and fatty acid digestibility. We found that the digestibility of nutrients in rainbow trout maintained at 8 °C or 15 °C was not significantly different. However, the digestibility of DHA omega 3 was significantly higher at 8 °C than at 15 °C.

Abstract

Aquaculture feed formulation has recently turned its focus to reduce the reliance on marine-derived resources and utilise alternative feedstuffs, as an approach to improve the environmental sustainability of the aquaculture sector. The fish oil market is highly volatile, and availability of this commodity is continuously decreasing for use in aquaculture. Currently, a growing number of commercial efforts producing microalgae are providing omega 3-rich oil for sustainable aquaculture feed. This study was focused to determine the nutrient digestibility of a marine microalga, Schizochytrium spp., which is rich in docosahexaenoic acid (DHA) and long-chain polyunsaturated fatty acids (LC-PUFA), as a novel dietary lipid source that could be utilized effectively by rainbow trout (Oncorhynchus mykiss). A whole-cell Schizochytrium spp. biomass was used in the digestibility experiment at two different temperatures, 8 °C and 15 °C. No significant differences were detected between the two temperatures for the apparent digestibility coefficients (ADCs) of the dry matter (94.3 ± 4.9%), total lipids (85.8 ± 0.0%), crude proteins (89.5 ± 1.8%), energy (83.1 ± 1.7%) and fatty acids (85.8 ± 7.5%). The ADCs of the nutrients, energy, DHA and other fatty acids showed that Schizochytrium spp. is a high-quality candidate for fish oil substitution and supplement of LC-PUFA in fish feed with vegetable oils.

Digestion, Absorption, and Metabolism Characteristics of EPA-Enriched Phosphoethanolamine Plasmalogens Based on Gastrointestinal Functions in Healthy Mice

EPA-enriched phosphoethanolamine plasmalogens (EPA-pPE), widely present in marine creatures, is a unique glycerophospholipid with EPA at the sn-2 position of the glycerol backbone. EPA-pPE has been reported to exhibit numerous distinctive bioactivities. However, the digestion, absorption, and metabolism characteristics of EPA-pPE in vivo are not clear, which restrict the molecular mechanism analysis related to its distinctive activities. The aim of the present study was to illustrate the digestion, absorption, and metabolism characteristics of EPA-pPE by lipid analysis in serum, intestinal wall, and content after oral administration of EPA-pPE emulsion. Results showed the EPA percentage of total fatty acids in serum was increasing over time, with two peaks at 5 and 10 h by 1.89 ± 0.2 and 2.58 ± 0.27, respectively, and then fell from 1.89 ± 0.17 at 10 h to 1.35 ± 0.16 at 16 h. In small intestinal content, EPA-pPE was hydrolyzed to lyso-phospholipids and EPA by phospholipases A2 and the vinyl ether bond was retained at the sn-1 position. The released EPA could be quickly taken up into the enterocytes and enter circulation. The comparison of simulated digestion in vitro showed that the distinct digestion and absorption process of EPA-pPE was a unique phenomenon. EPA could be retained in serum at a high level for a substantial period of time, which suggested that EPA-pPE was not just a short-lived circulating molecule.

Oil from transgenic Camelina sativa containing over 25 % n-3 long-chain PUFA as the major lipid source in feed for Atlantic salmon (Salmo salar)

Facing a bottleneck in the growth of aquaculture, and a gap in the supply and demand of the highly beneficial n-3 long-chain PUFA (LC-PUFA), sustainable alternatives to traditional marine-based feeds are required. Therefore, in the present trial, a novel oil obtained from a genetically engineered oilseed crop, Camelina sativa, that supplied over 25 % n-3 LC-PUFA was tested as a sole dietary-added lipid source in Atlantic salmon (Salmo salar) feed. Three groups of fish were fed three experimental diets for 12 weeks with the same basal composition and containing 20 % added oil supplied by either a blend of fish oil and rapeseed oil (1:3) (COM) reflecting current commercial formulations, wild-type Camelina oil (WCO) or the novel transgenic Camelina oil (TCO). There were no negative effects on the growth, survival rate or health of the fish. The whole fish and flesh n-3 LC-PUFA levels were highest in fish fed TCO, with levels more than 2-fold higher compared with those of fish fed the COM and WCO diets, respectively. Diet TCO had no negative impacts on the evaluated immune and physiological parameters of head kidney monocytes. The transcriptomic responses of liver and mid-intestine showed only mild effects on metabolism genes. Overall, the results clearly indicated that the oil from transgenic Camelina was highly efficient in supplying n-3 LC-PUFA providing levels double that obtained with a current commercial standard, and similar to those a decade ago before substantial dietary fishmeal and oil replacement.

Transepithelial transfer of phenanthrene, but not of benzo[a]pyrene, is inhibited by fatty acids in the proximal intestine of rainbow trout (Oncorhynchus mykiss)

The inclusion of vegetable oils in aquafeeds introduces contaminating polycyclic aromatic hydrocarbons (PAHs) in salmonids. Since lipophilic PAHs solubilize in micelles composed of lipids, bile salts and fatty acids, dietary lipid composition can alter intestinal transepithelial PAH transfer. We studied the uptake of two PAHs, viz. benzo[a]pyrene (BaP) and phenanthrene (PHE), in rainbow trout (Oncorhynchus mykiss) intestine. We also investigated the effects of two fatty acids, viz. fish oil-derived eicosapentaenoic acid (EPA, 20:5n-3) and vegetable oil-derived oleic acid (18:1n-9) on intestinal uptake. Radiolabeled PAHs were solubilized in micelles composed of tritiated EPA and oleic acid, respectively, and administrated to intestinal segments mounted in Ussing chambers. In the absence of micelles, PHE accumulation was two times higher than BaP in the mucosal and serosal layers of proximal and distal intestine. Administration of PHE in micelles composed of oleic acid resulted in a 50% lower accumulation of PHE in the mucosal layers of the proximal intestine compared to EPA-composed micelles. Accumulation of EPA and oleic acid in the proximal intestinal mucosa correlated negatively with the transepithelial transfer of these fatty acids across the proximal intestinal epithelium. Transepithelial PHE transfer across the proximal intestine was reduced by 30% in co-exposure with EPA-composed micelles compared to 80% with oleic acid micelles. BaP was not transferred across the intestine. We conclude that the lipid composition of an aquafeed is an important determinant of PAH bioavailability. Therefore, lipid composition should be an important consideration in choosing vegetable oils as alternatives for fish oil in aquafeeds.

Fatty acid alterations in the detritivorous Prochilodus lineatus promoted by opportunistic feeding on sewage discharges in the Río de la Plata estuary

Muscle fatty acid profiles and PCB contents of the detritivorous species Prochilodus lineatus and its diet (stomach contents, settling particles and sediments) were analysed from reference and polluted areas of the Paraná-Rio de la Plata basin, to evaluate the alterations produced by opportunistic feeding on sewage discharges. Overall muscle fatty acid composition was dominated by saturated and monounsaturated 16 and 18 carbon (18 C-FA) components with reduced long-chain polyunsaturated fatty acids (LC-PUFA). Compared to sediments, settling particles and stomach contents were enriched in lipids and had a similar fatty acid composition. Opportunistic feeding on sewage detritus at Buenos Aires resulted in enhanced PCB and triglyceride accumulation, with higher proportions of 18 C-FA and lower proportions of 16:1 and LC-PUFA compared to fish from northern pristine reaches of the basin. Mid-Paraná showed intermediate values reflecting mixing of the North stock with migrating Buenos Aires P. lineatus identified by their lipid and contaminant profile. According to multivariate analyses, this geographical variation of fatty acid composition was strongly influenced by PCB concentration. Prochilodus lineatus assimilates the energy subsidy of sewage inputs through enhanced lipogenesis with dominant 18 C-FA and significant amounts of valuable LC-PUFA. This lipid alteration facilitates the bioaccumulation of PCBs which in turn may reinforce the adipogenic effect of sewage feeding.

The effect of dietary lipid composition on the intestinal uptake and tissue distribution of benzo[a]pyrene and phenanthrene in Atlantic salmon (Salmo salar)

Uptake of polycyclic aromatic hydrocarbons (PAHs) across the intestine is suggested to occur in association with dietary lipids. Partial replacement of fish ingredients by vegetable ingredients in aquafeeds has led to increased levels of PAHs in marine farmed fish. We therefore investigated, intestinal uptake, tissue distribution and PAH metabolism after a single dose of (14)C-benzo[a]pyrene (BaP) or (14)C-phenanthrene (PHE) given to Atlantic salmon (Salmo salar) acclimatized to a fish oil or vegetable oil based diet. Both BaP and PHE were absorbed along the intestine. Fish oil based feed increased BaP concentration in the pyloric caeca and that of PHE in the proximal intestine. In contrast, vegetable oil increased BaP concentrations in the distal intestine. Extraction of whole body autoradiograms removed PHE-associated radiolabeling almost completely from the intestinal mucosa, but not BaP-associated radiolabeling, indicating the presence of BaP metabolites bound to cellular macromolecules. This observation correlates with the increased cyp1a expression in the proximal intestine, distal intestine and liver in the BaP exposed group. Furthermore, BaP-induced cyp1a expression was higher in the distal intestine of salmon fed fish oil compared to the vegetable oil fed group. PHE had no significant effect on cyp1a expression in any of these tissues. We conclude that dietary lipid composition affects intestinal PAH uptake. Fish oil based feed increased intestinal PAH concentrations probably due to an enhanced solubility in micelles composed of fish oil fatty acids. Increased BaP accumulation in the distal intestine of vegetable oil fed fish seems to be associated with a reduced Cyp1a-mediated BaP metabolism.

Lipid Classes and Fatty Acids in Ophryotrocha cyclops, a Dorvilleid from Newfoundland Aquaculture Sites

A new opportunistic annelid (Ophryotrocha cyclops) discovered on benthic substrates underneath finfish aquaculture sites in Newfoundland (NL) may be involved in the remediation of organic wastes. At those aquaculture sites, bacterial mats and O. cyclops often coexist and are used as indicators of organic enrichment. Little is known on the trophic strategies used by these annelids, including whether they might consume bacteria or other aquaculture-derived wastes. We studied the lipid and fatty acid composition of the annelids and their potential food sources (degraded flocculent organic matter, fresh fish pellets and bacterial mats) to investigate feeding relationships in these habitats and compared the lipid and fatty acid composition of annelids before and after starvation. Fish pellets were rich in lipids, mainly terrestrially derived C18 fatty acids (18:1ω9, 18:2ω6, 18:3ω3), while bacterial samples were mainly composed of ω7 fatty acids, and flocculent matter appeared to be a mixture of fresh and degrading fish pellets, feces and bacteria. Ophryotrocha cyclops did not appear to store excessive amounts of lipids (13%) but showed a high concentration of ω3 and ω6 fatty acids, as well as a high proportion of the main fatty acids contained in fresh fish pellets and bacterial mats. The dorvilleids and all potential food sources differed significantly in their lipid and fatty acid composition. Interestingly, while all food sources contained low proportions of 20:5ω3 and 20:2ω6, the annelids showed high concentrations of these two fatty acids, along with 20:4ω6. A starvation period of 13 days did not result in a major decrease in total lipid content; however, microscopic observations revealed that very few visible lipid droplets remained in the gut epithelium after three months of starvation. Ophryotrocha cyclops appears well adapted to extreme environments and may rely on lipid-rich organic matter for survival and dispersal in cold environments.

Evaluation of a high-EPA oil from transgenic Camelina sativa in feeds for Atlantic salmon (Salmo salar L.): Effects on tissue fatty acid composition, histology and gene expression

Currently, one alternative for dietary fish oil (FO) in aquafeeds is vegetable oils (VO) that are devoid of omega-3 (n-3) long-chain polyunsaturated fatty acids (LC-PUFAs). Entirely new sources of n-3 LC-PUFA such as eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids through de novo production are a potential solution to fill the gap between supply and demand of these important nutrients. Camelina sativa was metabolically engineered to produce a seed oil (ECO) with > 20% EPA and its potential to substitute for FO in Atlantic salmon feeds was tested. Fish were fed with one of the three experimental diets containing FO, wild-type camelina oil (WCO) or ECO as the sole lipid sources for 7 weeks. Inclusion of ECO did not affect any of the performance parameters studied and enhanced apparent digestibility of individual n-6 and n-3 PUFA compared to dietary WCO. High levels of EPA were maintained in brain, liver and intestine (pyloric caeca), and levels of DPA and DHA were increased in liver and intestine of fish fed ECO compared to fish fed WCO likely due to increased LC-PUFA biosynthesis based on up-regulation of the genes. Fish fed ECO showed slight lipid accumulation within hepatocytes similar to that with WCO, although not significantly different to fish fed FO. The regulation of a small number of genes could be attributed to the specific effect of ECO (311 features) with metabolism being the most affected category. The EPA oil from transgenic Camelina (ECO) could be used as a substitute for FO, however it is a hybrid oil containing both FO (EPA) and VO (18:2n-6) fatty acid signatures that resulted in similarly mixed metabolic and physiological responses.

Lipids in Marine Ecosystems

Lipids provide the densest form of energy in marine ecosystems. They are also a solvent and absorption carrier for organic contaminants and thus can be drivers of pollutant bioaccumulation. Among the lipids, certain essential fatty acids and sterols are considered to be important determinants of ecosystem health and stability. Fatty acids and sterols are also susceptible to oxidative damage leading to cytotoxicity and a decrease in membrane fluidity. The physical characteristics of biological membranes can be defended from the influence of changing temperature, pressure, or lipid peroxidation by altering the fatty acid and sterol composition of the lipid bilayer. Marine lipids are also a valuable tool to measure inputs, cycling, and loss of materials. Their heterogeneous nature makes them versatile biomarkers that are widely used in marine trophic studies, often with the help of multivariate statistics, to delineate carbon cycling and transfer of materials. Principal components analysis has a strong following as it permits data reduction and an objective interpretation of results, but several more sophisticated multivariate analyses which are more quantitative are emerging too. Integrating stable isotope and lipid data can facilitate the interpretation of both data sets and can provide a quantitative estimate of transfer across trophic levels.

Medium-chain and long-chain fatty acids have different postabsorptive fates in Atlantic salmon

An increasingly larger proportion of the oils used in diets for farmed fish are plant derived and rapeseed oil is most commonly used. Despite high dietary lipid levels and a marked change in lipid composition, the transport and metabolic fate of absorbed fatty acids is not fully understood in teleost fish. The main purpose of this study was to trace the postabsorptive metabolic fate of 2 fatty acids of different chain length: oleic acid [(3)H-18:1(n-9)], constituting 70% of fatty acids in rapeseed oil, and the medium-chain decanoic acid [(14)C-10:0], which does not require carrier molecules for membrane passage. The fatty acids and their metabolites were traced in portal and peripheral blood, liver, heart, skeletal muscle, and visceral adipose tissue at time intervals from 3 to 48 h after feeding. The portal vein was the primary transport route for both 10:0 and 18:1(n-9) from the intestine to the liver the first 6 h after feed intake. From 12 to 48 h, the peripheral route became increasingly more important. The study also indicates a possible direct transport route of fatty acids from the intestine to the surrounding viscera. Our data demonstrate that whereas 18:1(n-9) is primarily deposited as TG in skeletal muscle and visceral adipose tissue, 10:0 is used by the heart and skeletal muscle as a source for rapid energy production.

Effects of dietary α-linolenic acid (18:3n-3)/linoleic acid (18:2n-6) ratio on fatty acid metabolism in Murray cod (Maccullochella peelii peelii)

Global shortages in fish oil are forcing the aquaculture feed industry to use alternative oil sources, the use of which negatively affects the final fatty acid makeup of cultured fish. Thus, the modulation of fatty acid metabolism in cultured fish is the core of an intensive global research effort. The present study aimed to evaluate the effects of various dietary α-linolenic acid (ALA, 18:3n-3)/linoleic acid (LA, 18:2n-6) ratios in cultured fish. A feeding trial was implemented on the freshwater finfish Murray cod, in which fish were fed either a fish oil-based control diet or one of five fish oil-deprived experimental diets formulated to contain an ALA/LA ratio ranging from 0.3 to 2.9, but with a constant total C₁₈ PUFA (ALA+LA) content. The whole-body fatty acid balance method was used to evaluate fish in vivo fatty acid metabolism. The results indicate that dietary ALA was more actively β-oxidized and bioconverted, whereas LA appears to be more efficiently deposited. LA was β-oxidized at a constant level (~36% of net intake) independent of dietary availability, whereas ALA was oxidized proportionally to dietary supply. The in vivo apparent Δ-6 desaturase activity on n-3 and n-6 PUFA exhibited an increasing and decreasing trend, respectively, in conjunction with the increasing dietary ALA/LA ratio, clearly indicating that this enzymatic activity is substrate dependent. However, the maximum Δ-6 desaturase activity acting on ALA peaked at the substrate level of 3.2186 (μmol g fish⁻¹ day⁻¹), suggesting that additional inclusion of ALA is not only wasteful but counterproductive in terms of n-3 LC-PUFA production. Despite a constant total supply of ALA+LA, the recorded total in vivo apparent Δ-6 desaturase activity on both substrates (ALA and LA) increased in synchrony with the ALA/LA ratio, peaking at 1.54, and a 3.2-fold greater Δ-6 desaturase affinity toward ALA over LA was recorded.

Egg fatty acid composition from lake trout fed two Lake Michigan prey fish species

We previously demonstrated that there were significant differences in the egg thiamine content in lake trout Salvelinus namaycush fed two Lake Michigan prey fish (alewife Alosa pseudoharengus and bloater Coregonus hoyi). Lake trout fed alewives produced eggs low in thiamine, but it was unknown whether the consumption of alewives affected other nutritionally important components. In this study we investigated the fatty acid composition of lake trout eggs when females were fed diets that resulted in different egg thiamine concentrations. For 2 years, adult lake trout were fed diets consisting of four combinations of captured alewives and bloaters (100% alewives; 65% alewives, 35% bloaters; 35% alewives, 65% bloaters; and 100% bloaters). The alewife fatty acid profile had higher concentrations of arachidonic acid and total omega-6 fatty acids than the bloater profile. The concentrations of four fatty acids (cis-13, 16-docosadienoic, eicosapentaenoic, docosapentaenoic, and docosahexaenoic acids) were higher in bloaters than in alewives. Although six fatty acid components were higher in lake trout eggs in 2001 than in 2000 and eight fatty acids were lower, diet had no effect on any fatty acid concentration measured in lake trout eggs in this study. Based on these results, it appears that egg fatty acid concentrations differ between years but that the egg fatty acid profile does not reflect the alewife-bloater mix in the diet of adults. The essential fatty acid content of lake trout eggs from females fed alewives and bloaters appears to be physiologically regulated and adequate to meet the requirements of developing embryos.

Bioaccumulation of anthropogenic contaminants by detritivorous fish in the Río de la Plata estuary: 1-aliphatic hydrocarbons

The temporal variability and bioaccumulation dynamics of C(12-25)n-alkanes, isoprenoids and unresolved aliphatic hydrocarbons (UCM) were studied in a detritivorous fish (Sábalo: Prochilodus lineatus) collected from 1999 to 2005 in the sewage impacted Buenos Aires coastal area. Fish muscles contain huge amounts of n-C(12-25) (165+/-93, 70+/-48 or 280+/-134 microg g(-1), dry, fresh and lipid weight, respectively) and UCM (931+/-560, 399+/-288 and 1,567+/-802 microg g(-1)) reflecting the chronic bioaccumulation of fossil fuels from sewage particulates. On a temporal basis, lipid normalized aliphatic concentrations peaked by the end of 2001-2002 during the rainiest period over the last four decades (1,750 vs. 1,083+/-4.6mm in 1999, 2004 and 2005), reflecting an enhanced exposition due to massive anthropogenic fluxes from Metropolitan Buenos Aires in wet years. The hydrocarbon composition in fish muscles is enriched in n-C(15-17) and isoprenoids relative to a fresh crude oil and settling particulates, with fresher signatures during the 2001-2002 maxima. Fish/settling material bioaccumulation factors (BAFs: 0.4-6.4 dry weight or 0.07-0.94 lipid-organic carbon) plotted against K(ow) showed a parabolic pattern maximizing at n-C(14-18) and isoprenoids. The optimal bioaccumulation window corresponds to highly hydrophobic (log K(ow): 7.2-9.9), intermediate-size C(14-18)n-alkanes and C(15-20) isoprenoids (MW: 198-282; length: 17.9 to 25.4A) with melting points ranging from -19.8 to 28 degrees C. The uptake efficiency is inversely correlated to melting points and increased from 75% for n-C(25) to above 90% for n-C(14-15) and isoprenoids.

Tailoring of Atlantic salmon (Salmo salar L.) flesh lipid composition and sensory quality by replacing fish oil with a vegetable oil blend

Atlantic salmon (Salmo salar L.) juveniles were fed either 100% fish oil (FO), 75% vegetable oil (VO), or 100% VO throughout their life cycle to harvest weight followed by a finishing diet period when all groups were fed 100% FO. The two experimental VO diets were tested at two different locations (Scotland and Norway) against the same control diet (100% FO). The VO blend was composed of rapeseed oil, palm oil, and linseed oil using capelin oil as a control for fatty acid class compositions. Flesh fatty acid profiles were measured regularly throughout the experiment, with the times of sampling determined by changes in pellet size/lipid content and fish life stage. Growth and mortality rates were not significantly affected by dietary fatty acid compositions throughout the life cycle, except during the seawater winter period in Norway when both growth and protein utilization were increased in salmon fed 100% VO compared to 100% FO. Flesh fatty acid composition was highly influenced by that of the diet, and after the finishing diet period the weekly intake recommendations of very long chain n-3 polyunsaturated fatty acid (VLCn-3 PUFA) for human health were 80 and 56% satisfied by a 200 g meal of 75% VO and 100% VO flesh, respectively. No effect on flesh astaxanthin levels was observed in relation to changing dietary oil sources. Sensory evaluation showed only minor differences between salmon flesh from the dietary groups, although prior to the finishing diet period, flesh from 100% VO had less rancid and marine characteristics and was preferred over flesh from the other dietary groups by a trained taste panel. After the finishing diet period, the levels of typical vegetable oil fatty acids in flesh were reduced, whereas those of VLCn-3 PUFA increased to levels comparable with a 100% FO fed salmon. No differences in any of the sensory characteristics were observed between dietary groups. By blending VOs to provide balanced levels of dietary fatty acids, up to 100% of the fish oil can be replaced by the VO blend without compromising growth or flesh quality. At the same time, 75% of the dietary fish oil can be replaced without compromising flesh VLCn-3 PUFA content, thereby providing a beneficial nutritional profile for human consumption.

Dietary protein:lipid ratio and lipid nature affects fatty acid absorption and metabolism in a teleost larva

Studies with teleost larvae have reported poor performance associated with quantitative lipid imbalances in the diet. The present study examined the effect of dietary protein:neutral lipid ratio on fatty acid (FA) absorption efficiency and metabolism in larval Senegalese sole. In addition, the effect of lipid class (triolein (TRI) and l-3-phosphatidylcholine-1,2-di-oleoyl (PC)), carbon number and degree of saturation of the labelled NEFA, stearic acid (SA), oleic acid (OA) and DHA) was tested. FA absorption was determined by tube feeding [1-14C]-labelled lipids and NEFA after a single meal of either non-enriched Artemia (NEA) or Artemia enriched on a soyabean oil emulsion (EA), or after feeding these diets over an extended period of time (18 d). The tested dietary protein:lipid ratios had no short-term influence but long-term feeding of a diet higher in neutral lipid (EA) increased lipid accumulation within the gut epithelium and resulted in lower FA absorption (higher label evacuation and lower retention of dietary FA), which may partially explain the trend for lower growth observed with this diet. The lipids and NEFA, showed different digestive and metabolic properties, independent of feeding regime. FA absorption increased with unsaturation, being lowest for SA, followed by OA, and highest for DHA. In addition, sole larvae had a lower capacity to digest and absorb FA esterified to TRI, compared with PC, with the order of decreasing absorption being NEFA>PC>>TRI. Moreover, larvae appeared to discriminate between the source of OA, as this FA in the free form or esterified to PC was catabolised less than TRI.

Interactive effects of dietary palm oil concentration and water temperature on lipid digestibility in rainbow trout, Oncorhynchus mykiss

An experiment was conducted to evaluate the interactive effects of dietary crude palm oil (CPO) concentration and water temperature on lipid and FA digestibility in rainbow trout. Four isolipidic diets with 0, 5, 10, or 20% (w/w) CPO, at the expense of fish oil, were formulated and fed to groups of trout maintained at water temperatures of 7, 10, or 15 degrees C. The apparent digestibility (AD) of the FA, measured using yttrium oxide as an inert marker, decreased with increasing chain length and increased with increasing unsaturation within each temperature regimen irrespective of CPO level fed to the fish. PUFA of the n-3 series were preferentially absorbed compared to n-6 PUFA in all diet and temperature treatments. Except for a few minor FA, a significant (P < 0.05) interaction between diet and temperature effects on FA digestibility was found. Increasing dietary levels of CPO lead to significant reductions in the AD of saturates and, to a lesser extent, also of the other FA. Lowering water temperature reduced total saturated FA digestibility in trout regardless of CPO level. Based on the lipid class composition of trout feces, this reduction in AD of saturates was due in part to the increasing resistance of dietary TAG to digestion. Increasing CPO level and decreasing water temperature significantly increased TAG content in trout fecal lipids, with saturates constituting more than 60% of the FA composition. Total monoene and PUFA digestibilities were not significantly affected by water temperature in fish fed up to 10% CPO in their diet. The potential impact of reduced lipid and FA digestibility in cold-water fish fed diets supplemented with high levels of CPO on fish growth performance requires further research.

Replacement of fish oil with sunflower oil in feeds for Atlantic salmon (Salmo salar L.): effect on growth performance, tissue fatty acid composition and disease resistance

Dietary sunflower oil (SFO) was used to gradually replace fish oil (FO) in six diets (which also contained fish meal) for Atlantic salmon parr (initial mass: 21.7 g). The effect on growth performance, tissue fatty acid profiles and disease resistance was monitored after 63 days. At the conclusion of the trial, no significant differences were detected in growth between any of the feeds. Fatty acid composition of whole carcass, dorsal muscle and liver generally reflected that of the diets. Forty percent of the FO could be replaced by SFO before tissue 22:6n-3 was significantly reduced, although other essential and non-essential fatty acids were more susceptible to change. Significant differences were detected in cumulative mortality of Atlantic salmon challenged with Vibrio anguillarum at the trials conclusion, although this was not correlated to the inclusion level of SFO. Despite the changes observed to the tissue fatty acid profile, there was no significant effect on growth suggesting that SFO is a suitable alternative to FO in diets for Atlantic salmon parr when fish meal is also included.

Pyloric ceca are significant sites of newly synthesized 22:6n-3 in rainbow trout (Oncorhynchus mykiss)

In this pulse-chase study, rainbow trout fed a diet containing deuterated (D5) (17,17,18,18,18)-18:3n-3 ethyl ester accumulated D5-22:6n-3 in pyloric ceca to a greater extent than in liver 2 d post-dose. The ratio of newly synthesized D5-22:6n-3 in ceca to that in liver 2 d after feeding D5-18:3n-3 was 4.7 +/- 1.2 when expressed as per mg tissue and 5.2 +/- 2.4 when expressed as per mg protein. The amount of D5-22:6n-3 in ceca then declined whereas that in liver and blood increased, with the ratio of ceca to liver falling to 1.7 and 1.4, respectively, by day 5 and approaching unity by day 9. A crude cecal mucosa fraction contained 123 +/- 50 ng D5-22:6n-3/mg protein/mg D5-18:3n-3 eaten 2 d after feeding the tracer, compared with 35 +/- 21 ng D5-22:6n-3/mg protein/mg D5-18:3n-3 eaten in liver. Three days later the amount in cecal mucosa had fallen by one-third and that in liver had increased threefold. Most of the D5-18:3n-3 was catabolized very rapidly. The ratio of D5-18:3n-3 to 21:4n-6 (a relatively inert FA marker) in the diet was 4.0, but this fell to 0.30 in ceca and ca. 0.8 in liver, blood, and whole carcass one day after feeding. These results indicate that ceca are active in the synthesis of 22:6n-3 and the oxidation of 18:3n-3.

Lipid metabolism and tissue composition in Atlantic salmon (Salmo salar L.)--effects of capelin oil, palm oil, and oleic acid-enriched sunflower oil as dietary lipid sources

Triplicate groups of Atlantic salmon (Salmo salar L.) were fed four diets containing different oils as the sole lipid source, i.e., capelin oil, oleic acid-enriched sunflower oil, a 1:1 (w/w) mixture of capelin oil and oleic acid-enriched sunflower oil, and palm oil (PO). The beta-oxidation capacity, protein utilization, digestibility of dietary fatty acids and fatty acid composition of lipoproteins, plasma, liver, belly flap, red and white muscle were measured. Further, the lipid class and protein levels in the lipoproteins were analyzed. The different dietary fatty acid compositions did not significantly affect protein utilization or beta-oxidation capacity in red muscle. The levels of total cholesterol, triacylglycerols, and protein in very low density lipoprotein (VLDL), low density lipoprotein (LDL), high density lipoprotein (HDL), and plasma were not significantly affected by the dietary fatty acids. VLDL, LDL, and HDL fatty acid compositions were decreasingly affected by dietary fatty acid composition. Dietary fatty acid composition significantly affected both the relative fatty acid composition and the amount of fatty acids (mg fatty acid per g tissue, wet weight) in belly flap, liver, red and white muscle. Apparent digestibility of the fatty acids, measured by adding yttrium oxide as inert marker, was significantly lower in fish fed the PO diet compared to the other three diets.

Digestion of the 1-O-alkyl diacylglycerol ethers of Atlantic dogfish liver oils by Atlantic salmon Salmo salar

Dogfish (Squalus acanthias) liver poses a waste disposal problem in Canada because it is not utilized for any commercial purpose. The liver of Atlantic dogfish, which is often up to 20% of the weight of the fish, contains 40-70% oil. The oil contains about 30-40% 1-O-alkyl diacylglycerol ethers (DAGE) which render it unacceptable for human use, and it has also not been considered satisfactory for animal feed use. Polyunsaturated fatty acids (20:5n-3 and 22:6n-3) are present in dogfish liver oils at levels comparable to those in herring oil. Dogfish liver oil could be a source of essential fatty acids for Atlantic salmon (Salmo salar), but their ability to hydrolyze DAGE from dogfish oil has not been examined. Experiments were designed to measure the digestibility of fatty acids of DAGE in salmon. The fatty acid moieties were liberated by the digestive enzymes of the fish and made readily available as a source of energy. The 1-O-alkylglycerol ether moiety was absorbed to a small extent but should not constitute a health problem in either the fish or the human fish consumer. The long-chain polyunsaturated fatty acids were particularly well absorbed, with an apparent digestibility in salmon of 87-95% when feeding on dogfish liver oil. The total fatty acids and other lipids were in fact both absorbed to the extent of approximately 85%.

Lipid digestion in turbot (Scophthalmus maximus). I: Lipid class and fatty acid composition of digesta from different segments of the digestive tract

The lipid content and lipid composition of digesta from the stomach, foregut, hindgut and rectum of juvenile turbot fed a commercial diet were determined in order to examine the process of lipid digestion in this species. The moisture content of the digesta increased along the digestive tract from 71.5% in the stomach to 89.6% in the rectum. The lipid content of the digesta increased initially from 15.7% of the dry weight in the stomach to 36.1% in the foregut but thereafter decreased through 23.2% in the hindgut to 9.1% in the rectum. The proportion of triacylglycerols (TAG) in the total lipid of the digesta decreased from 63% in the stomach to 17.4% in the rectum whereas that of free fatty acids (FFA) increased from 10016 to 48.9%. The highest proportions of monoacylglycerols (MAG), diacylglycerols (DAG) and most phospholipids were observed in the lipid of the hindgut digesta. In addition, a fall in levels of neutral and phospholipid classes as digesta moved from hindgut to rectum signified absorption.Analysis of the fatty acid composition of the lipid classes TAG, DAG and MAG suggest a polyunsaturated fatty acid specificity for hydrolysis may exist. Saturated, monounsaturated and polyunsaturated fatty acids (PUFA) accounted for 17.9%, 45.4% and 37.0%, respectively of the FFA present in the foregut whereas the corresponding values for the rectum were 32.6%, 51.9% and 16.3%. Overall, the results suggest a PUFA specifity for hydrolysis may exist alongside the positional non-specific lipolytic activity associated with the hindgut regions of the digestive tract of turbot and that PUFA, released by lipolysis are more effectively absorbed from the digesta than monounsaturated and saturated fatty acids.