Utilization Of Dietary Lipids Research Articles

Fatty acid translocase (FAT/CD36) in silver pomfret (Pampus argenteus): Molecular cloning and functional characterization

Understanding the mechanisms of lipid transport and metabolism in fish is crucial to enhance dietary lipid utilization. Here, fatty acid translocase (CD36) gene was characterized in silver pomfret (Pampus argenteus). The open reading frame of silver pomfret cd36 gene was 1395 bp, encoding 464 amino acids. The silver pomfret CD36 protein contained typical transmembrane regions and N-glycosylation modification sites, and was localized to the cytomembrane. The cd36 gene was ubiquitously expressed in all tested tissues, with the highest expression observed in brain tissue. In vivo, both fasting and short-term high-fat feeding could increase cd36 expression in intestinal tissue. In vitro, cd36 expression was induced by palmitic acid, oleic acid, linolenic acid, eicosapentaenoic acid (EPA), and docosahexaenoic acid treatment in intestinal tissue. Furthermore, dual-luciferase reporter assay results indicated that peroxisome proliferator-activated receptor gamma (PPARγ) could enhance cd36 promoter activity, and the co-expression of cd36 and pparγ was observed in EPA-incubated intestine, suggesting that EPA may regulate the expression of cd36 via PPARγ to maintain the homeostasis of intestinal lipid metabolism in silver pomfret. These results highlighted the crucial role of CD36 in silver pomfret, and suggested that the cd36 expression may be regulated by PPARγ. This study could contribute to a greater understanding of lipid metabolism and the development of effective strategies for nutrient requirements in fish.

Non-classical digestive lipase BmTGL selected by gene amplification reduces the effects of mulberry inhibitor during silkworm domestication

Efficient utilization of dietary lipids is crucial for Bombyx mori, also known as domesticated silkworms. However, the effects of domestication on the genes encoding lipases remain unknown. In this study, we investigated the expression difference of one triacylglycerol lipase (BmTGL) between B.mori and wild (ancestor) silkworm strains (Bombyx mandarina). An immunofluorescence localization analysis showed that BmTGL was present in all parts of the gut and was released into the intestinal lumen. BmTGL expression was significantly enhanced in different domesticated silkworm strains compared to that in the B. mandarina strains. The BmTGL copy numbers in the genomes of the domesticated silkworm strains were 2-to-3 folds that of the B. mandarina strains and accounted for the enhanced expression of BmTGL in the domesticated silkworm strains. The Ser144Asn substitution in the Ser-Asp-His catalytic triads of BmTGL resulted in relatively lower lipase activity and reduced sensitivity to the lipase inhibitor morachalcone A. Moreover, BmTGL overexpression significantly increased the weights of the B. mori silkworms compared to those of the non-transgenic controls. Thus, the selection of BmTGL by gene amplification may be a trade-off between maintaining high enzymatic activity and reducing the effects of mulberry inhibitors during silkworm domestication.

Enhancing Reproductive Performance of Freshwater Finfish Species through Dietary Lipids.

Dietary lipid manipulation in the feed of commercially cultured finfish is used not only to improve production and culture but also to enhance their reproductive performances. The inclusion of lipid in broodstock diet positively affects growth, immunological responses, gonadogenesis, and larval survival. In this review, existing literature on the importance of freshwater finfish species to aquaculture and the inclusion of dietary lipid compounds in freshwater fish feed to accelerate the reproduction rate is being summarized and discussed. Although lipid compounds have been confirmed to improve reproductive performance, only a few members of the most economically important species have reaped benefits from quantitative and qualitative lipid studies. There is a knowledge gap on the effective inclusion and utilization of dietary lipids on gonad maturation, fecundity, fertilization, egg morphology, hatching rate, and consequently, larval quality contributing to the survival and good performance of freshwater fish culture. This review provides a baseline for potential future research for optimizing dietary lipid inclusion in freshwater broodstock diets.

Tracing the Trophic Fate of Aquafeed Macronutrients With Carbon Isotope Ratios of Amino Acids

To meet future seafood demands, ingredients derived from algae and other novel and sustainable sources are increasingly being tested and used as replacers to traditional aquafeed ingredients. Algal ingredients in particular are being promoted for their sustainability and their additional functional attributes in farmed aquatic animals. Test on algal supplemented aquafeeds typically focus on a suite of immunological and physiological indicators along with fish growth performance or muscle quality. However, to optimize the replacement of fish meal with algal derived ingredients, it is crucial to understand the metabolic fate in the algal macronutrients (carbohydrates, fats, and proteins), and their nutritional interactions with other ingredients after ingestion. Here, we assess the potential of using the emerging technology- stable carbon isotope (δ13C) analysis of single amino acids (AAs) as a nutritional biomarker in aquaculture. Applications of δ13CAA-based approaches in feeding trials show promise in closing the knowledge gap in terms of understanding how fish and other aquaculture taxa assimilate and metabolize algal derived macronutrients. Source diagnostic δ13C fingerprints among the essential AAs can trace the protein origins to broad phylogenetic groups such as red macroalgae, brown macroalgae, bacteria, and terrestrial plants. Among the non-essential AAs, δ13C patterns have the potential to inform about metabolic routing and utilization of dietary lipids and carbohydrates. Despite the potential of δ13CAA as a nutritional biomarker, the few applications to date in fish feeding trials warrant further development and implementation of δ13CAA-based approaches to improve understanding of protein origins and macronutrient metabolic routing.

Diacylglycerol oil reduces fat accumulation and increases protein content by inducing lipid catabolism and protein metabolism in Nile tilapia (Oreochromis niloticus)

The increase of dietary lipid utilization leads a supply of more energy to reduce protein breakdown and promote protein deposition in fish. Therefore, a search for feed additives to stimulate lipid metabolism interests fish nutritionists. Diacylglycerol oil (DGO), as a safe food additive in human, can increase lipid metabolism and prevent obesity in mammals, but it has not been studied in fish feed. The present study evaluated the role of DGO on lipid utilization and protein deposition in Nile tilapia (Oreochromis niloticus) by feeding fish with the diets containing three levels of dietary DGO (0%, 0.5% or 2.5%) for 8 weeks. The 0.5% dietary DGO increased weight gain and significantly decreased the hepatosomatic and mesenteric fat mass. The total lipid and triacylglycerol (TG) contents of the whole fish, liver and muscle tissues, as well as the serum free fatty acid content were significantly lower in the fish fed with both doses of the DGO diet compare to the control (0%). The fish fed DGO diets also exhibited lower lipid droplets in liver tissues than in the control. Moreover, dietary DGO increased the protein content in the whole fish and muscle tissues. The fish fed with the 0.5% DG diet showed an increasing trend on the gene expression of lipid catabolism and protein metabolism in the liver and muscle tissues. However, the 2.5% dietary DGO tended to downregulate metabolism gene expression and upregulate inflammation and stress genes expressions in liver. This study indicates that proper dose of dietary DGO can improve lipid utilization and help to promote protein deposition, and could be a potential additive in aquaculture feeds.

Partial characterization, quantification and activity of pancreatic lipase in the gastrointestinal tract of Totoaba Macdonaldi

Lipids are one of the main macronutrients that constitute balanced feeds used in aquaculture. Adequate utilization of dietary lipid is influenced by the activity of pancreatic lipase, one of the enzymes that promotes digestion of dietary lipids in the gastrointestinal tract of fish. The culture of Totoaba macdonaldi is quite recent; its nutritional requirements have been partially established. Knowing the characteristics of pancreatic lipase for this species could help optimize the dietary lipids included in balanced feeds for its culture. Therefore, the aim of this work is to partially characterize and evaluate the enzymatic activity of pancreatic lipase for T. macdonaldi. Biological indices showed that experimental organisms had a good nutritional status. Pancreatic lipase molecular weight was determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and its activity was evaluated in crude enzymatic extracts from different gastrointestinal tract regions. The molecular weight of lipase was estimated to be 70.4 kDa; the highest lipolytic activity was observed at 45?C and at a pH optimum of 8.0 in the anterior intestine and pyloric caeca, where the concentration and activity of the enzyme was significantly higher (P=0.004) compared to the distal parts of the intestine. Biochemical characteristics observed for the pancreatic lipase of T. macdonaldi are quite similar to other lipases of fish cultured worldwide; results provided in this study will help understand the role this lipolytic enzyme plays in the digestive process of this species.

Influences of dietary lipid and temperature on growth, fat deposition and lipoprotein lipase expression in darkbarbel catfish (Pelteobagrus vachellii)

Darkbarbel catfish (Pelteobagrus vachellii) is an important freshwater fish in China. Water temperature greatly influences the absorption and utilization of dietary lipid by fish. Response values (including growth, hepatic fat deposition, and gene expression) for darkbarbel catfish mediated by two factors (water temperature 20–34°C; dietary lipid level 2–17%) were the focus of this study. The relationship between the two factors and the response values was evaluated by the response surface method using the central composite design. The experiment was conducted under laboratory conditions and lasted for seven weeks. A total of 975 experimental fish (average weight 11.75 ± 0.17g) were selected and placed in 39 plastic tanks. The results showed that the linear effects of lipid level on feed conversion rate (FCR), hepatopancreas somatic index (HSI), hepatic triglycerides (TG), cholesterol (TC), and lipoprotein lipase (LPL) gene expression were significant (P < 0.05). The linear effects of water temperature on specific growth rate (SGR), HSI, TC level, and LPL mRNA expression were significant (P < 0.05). The quadratic effects of water temperature and lipid level on SGR and FCR were significant (P < 0.05). Low water temperature and low lipid diets significantly inhibited growth, increased HSI, and reduced hepatic TG and TC levels, and LPL mRNA expression. The adjusted R2 values for the SGR, FCR, HSI, TC, TG, and LPL mRNA regression models were 0.77, 0.85, 0.62, 0.73, 0.85, and 0.91, respectively. The optimal combination of water temperature and dietary lipid level was 27.5°C and 9.2%, at which the greatest growth and FCR were 2.13%.d−1 and 1.31 respectively, with desirability of 0.904. These results indicated that water temperature may mediate the requirement and utilization of dietary lipid, and intervene in hepatic fat deposition. The results of this study can be used to help optimize the culture conditions of darkbarbel catfish.

Effects of dietary carbohydrate and lipid levels on growth and hepatic lipid deposition of juvenile tilapia, Oreochromis niloticus

As the major non-protein energy sources, high carbohydrate (CHO) and lipid (L) diets have been widely used in aquaculture to reduce cost, but they also caused excessive lipid accumulation in the fish liver. It is not yet clear which, lipid or carbohydrate, is a greater influence on hepatic lipid accumulation. To study the effects of dietary carbohydrate and lipid levels on hepatic lipid deposition in Nile tilapia (Oreochromis niloticus), six diets with different carbohydrate and lipid levels (carbohydrate level ranged from 11.2% to 54.24%, while lipid level ranged from 21.51% to 2.70%, namely, the dietary CHO:L ratios ranged from 0.52:1 to 20.09:1) were formulated and fed to tilapia for 8weeks. After the feeding trial, high specific growth rate (SGR) was observed in the groups with the CHO:L ratio of 1.95, 3.41 and 6.40. Hepatosomatic and viscerosomatic index increased as dietary CHO:L ratios increased. Low serum TG, CHL and HDL levels was observed in the groups with the CHO:L ratio of 6.40 and 20.09. Hepatic histology showed that the fish fed with dietary CHO:L ratios of 3.41 and 6.40 have more hepatic lipid droplets than fish fed with other diets. Hepatic gene expression data indicated that the cd36 transcript levels were significantly affected by dietary CHO:L ratios, with the highest expression in fish fed D4 and D5 with CHO:L ratio of 3.41 and 6.40. Higher transcript levels of lipogenic genes (fas, acc-α and dgat2) were observed in the liver of fish fed with high CHO:L ratio diets, whereas FA β-oxidation genes (cpt1 and acox1) expression were depressed in liver. Hepatic apoB100 expression was also down-regulated with the high dietary CHO:L ratios. These results suggested that dietary carbohydrates have a stronger effect on hepatic lipid accumulation than dietary lipids in tilapia. High dietary CHO:L ratios (>3.41) accelerated the hepatic lipid deposition by increasing de novo lipogenesis and reducing FA β-oxidation and lipoprotein clearance in the liver, and diet with around 1.95 CHO:L ratio is suitable for tilapia culture concerning the growth performance and health. The present results will be of great significance in improving the utilization of dietary lipid and carbohydrate to achieve better nutrition efficiency in tilapia.

Hypermetabolic Conversion of Plant Oil into Water: Endothermic Biochemical Process Stimulated by Juvenile Hormone in the European Firebug, Pyrrhocoris apterus L.

The physiological and biochemical mechanisms that enable insects to feed on dry food to secure enough water for larval growth were investigated. The study was carried out with a plethora of physiological methods, ranging from the simple volumetric determination of O2 consumption and water intake to more advanced methods such as scanning microrespirography and thermovision imaging of insect’s body temperature. The experiments were done on the European firebug, Pyrrhocoris apterus, which feeds exclusively on dry linden seeds. In order to survive, it needs to drink water or suck a sap from plants occasionally. It was found that the young larval instars compensate the occasional water deficiency by the increased production of metabolic water. The juvenile hormone (JH)-dependent production of metabolic water, which was previously found in other species consuming dry food, was achieved in P. apterus by total metabolic combustion of the dietary lipid (neutral seed oil). The water-producing, hypermetabolic larvae were heated from inside by endothermic energy released from the uncoupling of oxidation from oxidative phosphorylation. The “warm”, hypermetabolic larvae burning the dietary oil into CO2 and water showed the increased rates of respiratory metabolism. Microrespirographic recording of these larvae revealed the ratio of the respiratory quotient (RQ, CO2/O2) of 0.7, which indicated the breakdown of a pure triglyceride. The warm hypermetabolic larvae could be easily spotted and distinguished from the “cold” larvae on the screen of a thermovision camera. The last instar larvae lacking the JH were always only cold. They metabolized a carbohydrate substrate exclusively (RQ = 1.0), while the dietary lipid was stored in the fat body. In comparison with the hypermetabolic larvae of some other species fed on dry food, which exhibited the highest rates of O2 consumption ever recorded in a living organism (10–20 mL O2/g per hour), the metabolic difference between the warm and cold larvae of P. apterus was only some 30% (not a reported 10-fold difference), which was presumably due to their ability to drink. We conclude that a very important, though still largely neglected, epigenetic biochemical role of insect JH depends on switchover between the utilization of dietary lipid (+JH; production of metabolic water) and carbohydrate (−JH; lipid storage in the fat body). The hypermetabolic water supply in insects fed on dry food, which is associated with enormous rates of O2 consumption, liberates endothermic energy that heats the body and potentially influences the insect thermoregulation. A possibility that the JH-dependent lipolytic hormone stimulates the total metabolic breakdown of nutritional lipids may be absolutely different from the currently known adipokinetic peptides that have been emphasized.

Lipids in infant formulas: Current and future innovations

AbstractLipids in infant formulas are designed to mimic the composition of human milk and/or approximate the performance of the breastfed infant. Human milk lipids exhibit a complex, highly variable nature, varying by population, dietary intake, time of day, length of feeding and others. Continued understanding and characterization of human milk lipids has led to infant formula innovations aimed at a better comparison to human milk and/or improved dietary lipid utilization in the formula‐fed infant. The underlying aim of such innovation is the generation of outcomes as comparable to human milk feeding as possible. The present paper briefly reviews the current understanding of human milk lipid composition, with a focus on how this knowledge drives current and future innovations in the area of infant formula lipids.

Short Communication Genetic polymorphisms of LPL and HL and their association with the performance of Chinese sturgeons fed a formulated diet

It is very important to investigate the reasons for the large individual differences in individual performance of food acceptance when using formulated diets for the successful culture of larvae and juveniles of the Chinese sturgeon Acipenser sinensis. Genetic differences of the mitochondrial control region were investigated by direct sequencing in two groups of Chinese sturgeon, which were apt to accept or refuse formulated diets. Among 968-bp sequences, 111 variable sites were identified. One variable site showed close association with the individual performance of specimens fed with formulated diets. The commercial diet for Chinese sturgeons usually contains high levels of lipids. Lipoprotein lipase (LPL) and hepatic lipase (HL) are two members of the lipase gene family, which are essential for the utilization of dietary lipid. Single nucleotide polymorphisms (SNPs) in intron 7 were detected in the two experimental groups of Chinese sturgeons. We were able to demonstrate that one SNP in the LPL gene and one SNP in the HL gene showed close association with the performance of sturgeons on the formulated diet.

Soybean meal as a source of protein in formulated diets for tiger grouper, &amp;lt;i&amp;gt;Epinephelus fuscoguttatus&amp;lt;/i&amp;gt; juvenile. Part II: Improving diet performances

The present study was conducted as a continuation of our previous study on the effects of fish meal replacement with soy bean meal, SBM in the diets of tiger grouper, Epinephelus fuscoguttatus which revealed the possible level of fish meal protein replacement of 30% with positive effect of phytase supplementation in one of the test diet. In the present study, all experimental diets with SBM inclusion (10%, 20%, 30%, 40% replacement levels) were supplemented with phytase and fed to juvenile tiger grouper with initial body weight of 44.57 ± 0.28 g for eight weeks. Apart from the effects on growth performance, diet utilization and fish whole-body composition, apparent digestibility coefficient of diets was also measured. Similar findings to our previous experiment were observed in the present study. Diet SM40P (40% replacement level) had produced the poorest growth performance and feed conversion ratio (FCR). However, it was observed that FCR of SM40P was improved when compared to SM40 (without phytase) in our previous experiment. Other than that, SBM-based diets were performed as good as the control diet in terms of growth, feed utilization and survival rate. Replacement of fish meal did not significantly influence body composition, except for whole body lipid content in SM40P. In general, dry matter and protein apparent digestibility coefficients (ADC) of the test diets were influenced by SBM inclusion in the diets. However, crude lipid ADC was very high in all dietary treatments indicating efficient utilization of dietary lipid by juvenile tiger grouper. The findings of the present study confirmed that SBM can be used to replace FM at a level of up to 30% and supplementation of phytase in SBM-based diets is recommended to improve the diet performance.

Dietary non-protein energy sources: growth,physiology and biochemisty by the juvenile Australian redclaw crayfish, Cherax quadricarinatus(Von Martens)

A growth experiment was conducted to determine the optimal carbohydrate-to-lipid(CHO∶ L)ratio for juvenile Australian redclaw crayfish[initial weight(1.72±0.01) g(mean±SD)]cultured in indoor recirculating aquaculture system.Five isonitrogenous[(31.130±0.004) g/kg]and around isoenergetic[(17.490±0.396) MJ/kg]diets with dietary CHO∶ L ratios are 10.75∶ 1,4.81∶ 1,2.66∶ 1,1.52∶ 1 and 0.87∶ 1,were fed twice a day to apparent satiation.Over 8-week growth trial,the best final weight,weight gain,specific growth rate and feed conversion ratio value(P0.05)were observed in redclaw crayfish fed diets with a CHO∶ L ratio of 2.66∶ 1.Redclaw crayfish fed either the lowest(0.87∶ 1)or highest(10.75∶ 1)CHO∶ L ratio tended to produce lower growth and poorer feed conversion ratio.Dietary lipid levels was 40-145 g/kg,the lipase and alkaline phosphatase activities were stimulated by elevated levels of dietary lipid.However,the activities of hexokinase and pyruvate kinase showed opposite trend.The pepsin and intestine amylase activities were significantly(P0.01)affected by CHO∶ L ratios.The higher activity of pepsin were observed when the CHO∶ L were 2.66∶ 1 and 1.52∶ 1(P0.05).The intestine amylase activity was significantly increased(P0.01)as dietary CHO levels(156.3-360.4 g/kg)increased.Based on a second-order polynomial regression analysis of WG against dietary carbohydrate and lipid levels,growth maximum was observed when the dietary carbohydrate and lipid levels were 268.82 g/kg and 122.20 g/kg,corresponding to a CHO∶ L ratio of 2.20∶ 1.These results indicated that the utilization of dietary lipid and carbohydrate was moderate in redclaw crayfish and the preferential utilization of carbohydrate was higher than that of lipid.

Efficient utilization of dietary lipids inOctopus vulgaris(Cuvier 1797) fed fresh and agglutinated moist diets based on aquaculture by-products and low price trash species

The aim of this study was to evaluate growth, biochemical composition and dietary nutrients utilization in Octopus vulgaris fed on four diets based on bogue Boops boops, from different origin and in two presentations: fresh discarded bogue (aquaculture by-product) (DB-f), fresh wild bogue (low price trash species) (WB-f), discarded bogue agglutinated moist diet (DB-m) and wild bogue agglutinated moist diet (WB-m). Diets based on DB showed higher lipid content (19–26% dw) than those based on WB (5–6% dw). Octopuses fed on DB-based diets showed higher growth (1.5–1.9% day−1) and higher protein efficiency ratio (0.64–0.69) than those fed on WB-based diet (1.1–1.5% day−1 and 0.36–0.37 respectively), which suggests good utilization of dietary lipids and also a possible protein sparing effect by lipids in O. vulgaris. Octopuses fed on diets presented fresh showed a higher growth (1.9–1.5% day−1) and a higher feed efficiency (62–65%) than those fed on agglutinated diets (1.1–1.5% and 52–60% day−1 respectively). Regarding fatty acids, the digestive gland clearly reflected dietary lipid and fatty acid profile, while muscle showed a more stable composition. Low dietary ARA content reflected in octopus tissues, especially in specimens fed on DB-based diets, which did not seem to affect growth during the experimental period.

Potential of three new krill products for seabream larval production

The objective of this study was to evaluate three products derived from krill as sources of essential fatty acids, protein and, particularly, phospholipids in microdiets for larval gilthead seabream (Sparus aurata). Their effect on larval performance, biochemical composition and histological development was investigated. The addition of krill phospholipids, rich in highly unsaturated fatty acids, improved larval sea bream growth in terms of weight and length, enhanced hepatic utilization of dietary lipids and reduced the incidence of enterocyte injuries. These results confirm the higher nutritional value of marine phospholipids for the early development of marine fish larvae in comparison with soybean phospholipids.

Effect of EPA/DHA ratios on the growth and survival of Galaxias maculatus (Jenyns, 1842) larvae reared under different salinity regimes

Despite the importance of certain highly unsaturated fatty acids in osmotic regulation, few studies have been addressed to determine the essential fatty acid requirements for a given species cultured under different salinities. As Galaxias maculatus is a diadromic species, the present study aimed to determine the effect of salinity on the optimum dietary EPA/docosahexaenoic (DHA) ratio for survival and growth during the larval stages. Larvae were fed for 20 days with rotifers containing two different EPA/DHA ratios (low: 0.64 and high: 2.18) at three different salinities (0, 10 and 15 g L−1). The results of this study showed a marked effect of water salinity on larval dietary lipid utilization in G. maculatus larvae. These results suggested that G. maculatus larvae reared at higher salinities may have a higher dietary requirement for DHA, whereas larvae reared at 0‰ showed higher requirements for EPA. The overall results of the present study indicate that even small changes in salinity can determine the optimum dietary EPA/DHA ratio and the quantitative essential fatty requirements of fish. This may have important repercussions and affect the rearing performance of G. maculatus cultured under different salinities.

Effect of dietary carbohydrate-to-lipid ratios on growth performance, body composition, nutrient utilization and hepatic enzymes activities of herbivorous grass carp (Ctenopharyngodon idella)

Six isonitrogenous (390 g kg⁻¹) and isoenergetic (16.2 kJ g⁻¹) diets with varying carbohydrate : lipid (CHO : L) ratios (202.5-1.74), were fed to triplicate groups of 25 fish in indoor recirculation system. Over 8-week-growth trial, best weight gain (WG), specific growth rate, feed conversion ratio, protein efficiency ratio and protein production value (P < 0.05) were observed in fish-fed diets with CHO : L ratio of 7.5. Fish fed either the lowest (1.7) or highest (202.5) CHO : L ratio tended to produce lower (P < 0.05) growth and feed conversion efficiencies. The values of viscerosomatic index, hepatosomatic index and intraperitoneal fat ratio increased as dietary CHO : L ratios decreased. There were no significant differences in whole body and liver crude protein among dietary treatments. Whole body and liver lipid increased as CHO : L ratios decreased. Plasma cholesterol and triacylglyceride levels increased linearly as dietary CHO : L ratios decreased. Activities of glucokinase and pyruvate kinase were stimulated by elevated levels of dietary carbohydrate; however, activities of lipase (LPS) and alkaline phosphatase were stimulated by elevated levels of dietary lipid. Based on a second-order polynomial regression analysis of WG against dietary carbohydrate and lipid levels, 275 g kg⁻¹ of carbohydrate and 59 g kg⁻¹ of lipid, corresponding to a CHO : L ratio of 4.7, in a diet holding 390 g kg⁻¹ of crude protein and 16.3 kJ g⁻¹ of gross energy, proved to be optimal for grass carp. These results indicated that utilization of dietary lipid and carbohydrate was moderate in grass carp, but the fish were a little more capable of utilizing lipid compared with carbohydrate.

Dietary Lipid Utilization by White Sea Bream (Diplodus sargus) Juveniles

Abstract.— A 8‐wk trial was performed with white sea bream, Diplodus sargus, juveniles (17.3 g initial weight) to evaluate the effect of dietary lipid levels on growth performance and whole‐body composition. Six experimental diets were formulated to be isoproteic (45% protein) and to contain from 9 to 24% dietary lipid levels (dry matter basis). Fish meal and fish oil were used as the main protein and lipid sources, respectively. At the end of the trial, there were no significant differences (P &gt; 0.05) among groups in fish performance or in whole‐body composition. From the results of this trial, it is concluded that, within the range of values tested, increasing dietary lipid levels above 9% has no advantage as it does not promote growth or spare protein for growth purposes.

Lipid metabolism in Rhodnius prolixus (Hemiptera: Reduviidae): Role of a midgut triacylglycerol-lipase

The utilization of dietary lipids was studied in adult females of Rhodnius prolixus with the use of radiolabeled triacylglycerol (TAG). It was shown that 3H-triolein, when added to blood meal, was hydrolyzed to free fatty acids in the posterior midgut lumen. Subsequently, free fatty acids were absorbed by posterior midgut epithelium and used in the synthesis of phospholipids, diacylglycerol (DAG) and TAG. Phospholipids, DAG and free fatty acids were then found in hemolymph, from where they were rapidly cleared, and label was found in the fat body, mainly associated with TAG. Radioactive lipids, especially TAG and phospholipids, also accumulated in the ovaries. The TAG-lipase activities of posterior midgut luminal content and tissue were characterized by incubation of these samples with 3H-triolein in the presence of the detergent Triton X-100 and determination of the amounts of released radioactive free fatty acids. Under the conditions employed here, the release of free fatty acids was proportional to the incubation time and to the amount of sample obtained from insect midgut (enzyme source) that was added. TAG-lipase activities were affected by pH and posterior midgut tissue showed optimum activity around pH 7.0–7.5, but the luminal content had the highest activities as pH decreased. Differences in activities were observed according to calcium concentration in the medium. TAG-lipase activities were also affected by the concentration of NaCl and were activated in the presence of increasing salt concentrations. These activities were inhibited by phenylmethylsulphonyl fluoride (PMSF). On the second day after blood meal, when digestion is very intense, TAG-lipase activities were maximal and then gradually decreased.

Dietary lipid sources for seabream and seabass: growth performance, tissue composition and flesh quality

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