High dietary lipid levels enhance digestive tract maturation and improve dicentrarchus labrax larval development

Optimization of inclusion level of lipid in larval diet of Labeo rohita (Hamilton, 1822)

Formulation and preparation of larval feed according to the requirement of Indian major carp is a prerequisite for improving the survival (%) and growth during early developmental stages. A feeding trial of 50 days in a replicate of five was conducted to determine the optimal inclusion levels of fish oil (lipid) in the larval diet of Labeo rohita. Four isonitrogenous (50% CP) nanoparticulate diets with four lipid inclusion levels, L5 (5%), L7 (7%), L9 (9%), and L11 (11%) were prepared and fed to four groups of rohu (Labeo rohita) larvae. At the end of feeding trial, survival (%), growth performance, digestive enzyme activity, gut morphology, and expression of growth and feed intake genes were evaluated. All pairwise comparisons among groups indicated higher growth performance (weight gain, specific growth rate, and daily weight gain), survival (%), and IGF-1 gene expression of the L9 group followed by the L7 while the L11 showed poor performance even less than L5. All studied intestinal enzymes except amylase showed a similar trend. Amylase showed comparable results among L7, L9, and L5, while L11 showed the lowest value. The intestinal villi length also showed higher values in L9 followed by L7, and lowest in the L11 group. Feed intake regulating genes, leptin showed lipid inclusion level upregulation, while ghrelin showed the highest expression in the L9 group. Based on growth performance, gut morphology, intestinal enzyme activity, and gene expression analysis, 9% dietary lipid could be recommended to ensure the optimum growth and survival of L. rohita larvae.

Absorption of protein in teleosts: a review

Teleost is a widely diverse group of fishes and so do their feeding habits. From aquaculture points of view, there have been un-interrupted efforts to optimize feeding rates with protein as the chief ingredients in the supplementary diet. However, knowledge on its protein absorption is incomplete so far, to acquire absolute feeding design to mobilize enhanced production of animal-source protein as fish biomass. In this review, the variable protein absorption across digestive tract (DT) in this group of fish has been highlighted. Emphasis is given to outline how DT components, like enterocyte specific absorptive mechanisms, are different in anterior and posterior regions of DT or from the absorptive transporter system. The existence of a transporter-based absorption mechanism brings more variability in the protein absorption in teleosts. At least two such transport systems (Na⁺-dependent and Na⁺-independent) with within-system differences impart more variability to protein absorption. Further, shifting from one stage to another stage of development involves considerable modification of the protein absorptive mechanism in teleosts. Gut microbes may also indirectly facilitate protein absorption in teleosts. Overall, the present review projects a comprehensive understanding of the protein absorption in teleosts that will help to strategize the modulation of feeding technology in fish culture.

Protein and lipid requirements of three-spot cichlid Cichlasoma trimaculatum larvae

Determination of the main nutritional requirements at different developmental stages is a prerequisite in the formulation of feeds for newly cultured fish species. In the present study, the lipid and protein requirements of larvae of a native Mexican fish, the three-spot cichlid Cichlasoma trimaculatum, were assessed using a two-factor experimental design that considered four protein (35, 40, 45, and 50%) and two lipid levels (16 and 22%) on growth, survival, and digestive enzyme activities. The best growth and feed efficiency results were obtained when larvae were fed diets including 45% protein and 22% lipids. Comprehensive evaluation of the profile of digestive enzymes using multivariate analysis also demonstrated significant differences in nutritional condition generated by varying inclusion of nutrients. Thus, an increase in protein led to an increase in alkaline protease activity and a reduction in leucine aminopeptidase activity, and the reduction of dietary lipid content led to a significant increase in lipase and trypsin enzymatic activities. Based on our results, C. trimaculatum larvae have a high capacity to hydrolyze both nutrients (protein and lipids) for the high digestive enzyme activities and increase their growth, particularly with a diet containing 45% protein and 22% lipids.

Lipid digestion capacity in gilthead seabream (Sparus aurata) from first feeding to commercial size

To characterise the progression of lipid digestion capacity in gilthead seabream across life cycle, the activities of bile salt-activated lipase (BAL) and phospholipase A₂ (PLA₂) were determined in the digestive tracts of cultured gilthead seabream from first feeding to marketable size (49 μg to 300 g). Four trials were undertaken with gilthead seabream of different ages, fed on diets with fishmeal and fish oil as the main dietary protein and lipid sources and 21-25% lipid contents. Larvae of 4 days after hatching (dah) to 9 dah were fed rotifers with different fatty acid profiles: control (2.8% eicosapentaenoic acid, EPA; 1.6% docosahexaenoic acid, DHA; 5.4% n-3 long-chain polyunsaturated fatty acids, n-3 LC-PUFAs; and 0.2% arachidonic acid, ARA), low EPA (1.38% EPA, 1.6% DHA, 3.9% n-3 LC-PUFA and 0.4% ARA) or low LC-PUFA (0.7% EPA, 1.0% DHA, 1.8% n-3 LC-PUFA and 0.0% ARA) (% dry weight). Larvae fed the low-LC-PUFA diet showed a significantly lower growth at 10 dah. BAL activities were significantly higher in larvae fed the control diet than in those fed low-EPA and low-LC-PUFA diets at 9 dah. BAL activity increased with age across life cycle (49 μg to 300 g). PLA₂ activity could not be detected in larvae but increased with age in juvenile and adult gilthead seabream (86 g to 295 g), similar to BAL. Results suggested a correspondence between the stimulation of lipid digestion capacity and growth performance in gilthead seabream by dietary essential fatty acids, particularly by EPA when DHA requirements are met in the diet especially in the very early stages of life cycle, when the progression of BAL and PLA₂ activities could be used as indicators of the nutritional status of cultured gilthead seabream larvae. Finally, regarded that PLA₂ activity was not detected in 4-dah to 44-dah gilthead seabream larvae, future works are suggested to assess the dietary effect on PLA₂ activity and the PLA₂ activity pattern along the larval stage of this species using a more sensitive detection method.

Weaning European glass eels (Anguilla anguilla) with plant protein-based diets and its effects on intestinal maturation

Weaning glass eels with compound diets (36% proteins, 16% lipids) differing in their fishmeal (FM) level (50, 75 and 100% FM replaced by a blend of plant proteins, PP) was compared to a group fed cod roe. Weaning lasted for 20 days and then, eels were fed compound diets for 70 days, whereas the other group was only fed cod roe (90 days). Diets were tested with four replicates and evaluated in terms of growth, survival, glass eels metamorphosis into elvers, oxidative stress status and activity of digestive enzymes. Although glass eels are traditionally fed with fish roe and progressively weaned onto compound diets, results revealed that this strategy should not be prolonged for a long time, since feeding glass eels with cod roe for 90 days negatively affected their growth (2 times lower than fish fed compound diets), delayed their metamorphosis, as well as the maturation of their digestive function as the ratio of alkaline phosphatase and leucine-alanine peptidase indicated. Weaning glass eels onto compound diets differing in their FM levels did not affect their growth, metamorphic stage nor the activity of pancreatic enzymes (total alkaline proteases, trypsin, bile salt-activated lipase and α-amylase), although 75% FM replacement by PP sources delayed the level of intestinal maturation in eels. In comparison to glass eels fed the 100% FM diet, survival was negatively affected in groups fed diets with 50 and 75% FM replacement by PP ingredients, which indicated that further improvement is needed in diet formulation for this stage of development.

Red drum Sciaenops ocellatus growth and expression of bile salt-dependent lipase in response to increasing dietary lipid supplementation

Sciaenops ocellatus has a long history in aquaculture and many difficulties associated with its commercial culture have been addressed and successfully resolved; nevertheless, further research in lipid nutrition could address more comprehensive questions on the way these nutrients are utilized. The purpose of this study was to evaluate S. ocellatus growth and lipase gene expression in response to increasing dietary lipid supplementation. Four experimental diets were formulated to provide 3, 10, 16, or 23% lipid using menhaden fish oil. Twenty juveniles (mean initial weight 2.3 ± 0.1 g) were stocked per aquaria in a recirculating system; each diet was assigned to three aquaria and fed to fish for 6 weeks. At the end of the study, fish fed 3% of dietary lipid were significantly (P < 0.0001) smaller and showed significantly lower feed efficiency, condition factor, hepatosomatic index, and intraperitoneal fat than fish fed the other diets, but no differences were observed among fish fed 10, 16, or 23% lipid. A straight broken-line regression model for thermal growth coefficient provided an estimated value of 9.4% of dietary lipid as the optimal inclusion level. The bile salt-dependent lipase (BSDL) of red drum was 80.3 kDa. Relative gene expression of BSDL was significantly higher (P = 0.0007) in fish fed 10% lipid, with no differences among the other dietary treatments. Results provided could help monitor the metabolic status of farmed fish and contribute to optimize diet formulations based on maximum gene expression of BSDL for supplementation of dietary lipid.

Optimizing protein and lipid levels in practical diet for juvenile northern snakehead fish (Channa argus)

A 3 × 3 factorial feeding trial was conducted to evaluate the production response of juvenile northern snakehead fish (Channa argus). Nine diets containing 3 protein levels (45%, 48% and 51%) and 3 lipid levels (9%, 12% and 15%) were formulated and fed to triplicate groups of juvenile northern snakehead (15.78 ± 0.09 g/fish) for 8 weeks. The formulated diets were named as P45L9, P45L12, P45L15, P48L9, P48L12, P48L15, P51L9, P51L12 and P51L15 (P-Protein, L-Lipid), respectively. Fish fed diets with the lowest protein and lipid combination (P45L9) had the lowest growth performance. Weight gains (WG) of fish fed the 4 diets P48L12, P48L15, P51L9, and P51L12 were not significantly different (P > 0.05), but significantly higher (P < 0.05) than those of fish fed the other diets. Fish fed diets P48L12 and P48L15 had significantly lower (P < 0.05) feed conversion ratios (FCR) than the rest of the treatments. Protein retentions (PR) among fish fed the diets P45L12, P45L15, P48L12, P48L15, P51L9, and P51L12 were similar and significantly higher (P < 0.05) than those of fish fed the remaining diets. Protein sparing effect was observed in the treatments when fish was fed diets containing 45% or 48% dietary protein levels with dietary lipid increased from 9% to 12%. Fish fed diets with 9% lipid tended to have lower viscerosomatic index (VSI), hepatosomatic index (HSI), and whole-body lipid. Increasing dietary protein level significantly increased (P < 0.05) liver moisture and lipid while dietary lipid level increased liver lipid. Intestinal lipase activity increased significantly (P < 0.05) with increasing dietary lipid and protein levels while intestinal α-amylase and protease activities were not significantly influenced (P > 0.05) by dietary treatments. Based on these results, the diet containing 48% protein with either 12% or 15% lipid is the optimal for supporting growth and feed utilization of juvenile northern snakehead under the current testing conditions.

The transcriptome of metamorphosing flatfish

BACKGROUND

Flatfish metamorphosis denotes the extraordinary transformation of a symmetric pelagic larva into an asymmetric benthic juvenile. Metamorphosis in vertebrates is driven by thyroid hormones (THs), but how they orchestrate the cellular, morphological and functional modifications associated with maturation to juvenile/adult states in flatfish is an enigma. Since THs act via thyroid receptors that are ligand activated transcription factors, we hypothesized that the maturation of tissues during metamorphosis should be preceded by significant modifications in the transcriptome. Targeting the unique metamorphosis of flatfish and taking advantage of the large size of Atlantic halibut (Hippoglossus hippoglossus) larvae, we determined the molecular basis of TH action using RNA sequencing.

RESULTS

De novo assembly of sequences for larval head, skin and gastrointestinal tract (GI-tract) yielded 90,676, 65,530 and 38,426 contigs, respectively. More than 57 % of the assembled sequences were successfully annotated using a multi-step Blast approach. A unique set of biological processes and candidate genes were identified specifically associated with changes in morphology and function of the head, skin and GI-tract. Transcriptome dynamics during metamorphosis were mapped with SOLiD sequencing of whole larvae and revealed greater than 8,000 differentially expressed (DE) genes significantly (p < 0.05) up- or down-regulated in comparison with the juvenile stage. Candidate transcripts quantified by SOLiD and qPCR analysis were significantly (r = 0.843; p < 0.05) correlated. The majority (98 %) of DE genes during metamorphosis were not TH-responsive. TH-responsive transcripts clustered into 6 groups based on their expression pattern during metamorphosis and the majority of the 145 DE TH-responsive genes were down-regulated.

CONCLUSIONS

A transcriptome resource has been generated for metamorphosing Atlantic halibut and over 8,000 DE transcripts per stage were identified. Unique sets of biological processes and candidate genes were associated with changes in the head, skin and GI-tract during metamorphosis. A small proportion of DE transcripts were TH-responsive, suggesting that they trigger gene networks, signalling cascades and transcription factors, leading to the overt changes in tissue occurring during metamorphosis.

Regional variation of gene regulation associated with storage lipid metabolism in American glass eels (Anguilla rostrata)

Variation in gene regulation may be involved in the differences observed for life history traits within species. American eel (Anguilla rostrata) is well known to harbor distinct ecotypes within a single panmictic population. We examined the expression of genes involved in the regulation of appetite as well as lipid and glycogen among glass eels migrating to different locations on the Canadian east coast and captured at two different periods of upstream migration. Gene expression levels of three reference and five candidate genes were analyzed by real-time PCR with Taqman probes in recently captured wild glass eels. All gene transcripts were detected in glass eels. Of the five candidate genes, bile salt activated and triacylglycerol lipases were respectively 7.65 and 3.25 times more expressed in glass eels from the St. Lawrence estuary than in those from Nova Scotia, and there was no effect related to the two-week difference in capture date. These two genes explained 82.41% of the dissimilarity between the two rivers. In contrast, glycogen phosphorylase, ghrelin, and leptin receptor genes showed no significant differences in gene transcription. These results confirmed at the molecular level an observation that was recently made at the phenotypic level that glass eels from the St. Lawrence estuary have a greater capacity to use lipid reserves to sustain their metabolic needs. These observations add to the body of evidence supporting the hypothesis that regional phenotypic variation observed in American eel is determined early in life and that part of this variation is likely under genetic control.

Digestive enzyme activities during early ontogeny in Common snook (Centropomus undecimalis)

Common snook (Centropomus undecimalis) is one of the most important marine species under commercial exploitation in the Gulf of Mexico; for this reason, interest in developing its culture is a priority. However, larviculture remains as the main bottleneck for massive production. In this sense, our objective was to determine the changes of digestive enzymes activities using biochemical and electrophoretic techniques during 36 days of Common snook larviculture fed with live preys (microalgae, rotifers, and Artemia). During larviculture, all digestive enzymatic activities were detected with low values since yolk absorption, 2 days after hatching (dah) onwards. However, the maximum values for alkaline protease (6,500 U mg protein(-1)), trypsin (0.053 mU × 10(-3) mg protein(-1)), and Leucine aminopeptidase (1.4 × 10(-3) mU mg protein(-1)) were detected at 12 dah; for chymotrypsin at 25 dah (3.8 × 10(-3) mU mg protein(-1)), for carboxypeptidase A (280 mU mg protein(-1)) and lipase at 36 dah (480 U mg protein(-1)), for α-amylase at 7 dah (1.5 U mg protein(-1)), for acid phosphatases at 34 dah (5.5 U mg protein(-1)), and finally for alkaline phosphatase at 25 dah (70 U mg protein(-1)). The alkaline protease zymogram showed two active bands, the first (26.3 kDa) at 25 dah onwards, and the second (51.6 kDa) at 36 dah. The acid protease zymogram showed two bands (RF = 0.32 and 0.51, respectively) at 34 dah. The digestive enzymatic ontogeny of C. undecimalis is very similar to other strictly marine carnivorous fish, and we suggest that weaning process should be started at 34 dah.

Regulation of somatic growth and gene expression of the GH-IGF system and PRP-PACAP by dietary lipid level in early juveniles of a teleost fish, the pejerrey (Odontesthes bonariensis)

Growth and mRNA levels of the pituitary adenylate cyclase-activating polypeptide (PACAP) and its related peptide (PRP), and the system controlled by the growth hormone (GH) and insulin-like growth factors (IGFs) were analyzed in pejerrey fry fed with graded levels of dietary lipids: 10% (L10), 13% (L13) and 21% (L21). First, the full sequence of pejerrey PRP-PACAP was obtained by RT-PCR, using primers based on conserved fragments of teleosts PACAP sequences. The growth of the fish at 83 days after hatching (dah) and the GH mRNA levels were not significantly affected by the dietary treatment. Conversely, PRP-PACAP expression significantly decreased with increasing dietary lipids (L10 > L21). While GH receptor (GHR)-I and IGF-I transcripts did not differ among groups, GHR-II transcripts decreased in group L21. IGF-II expression apparently followed the same trend. These results in combination with the lower expression of the anorexigenic PRP-PACAP in fish fed diet L21 and the correlation analysis evidencing a particularly fine tuning of the GH-IGF system in group L13, suggest that this diet may cover the energy demands for growing pejerrey from 27 dah onwards. Our results show for first time in fish a differential response of PRP-PACAP transcripts to dietary manipulations, and confirm the sensitivity of the pejerrey GH-IGF system to changes in diet composition despite the lack of (or in advance to) a clear response of somatic growth.

Ontogeny of gene expression of group IB phospholipase A₂ isoforms in the red sea bream, Pagrus (Chrysophrys) major

The red sea bream (Pagrus major) was previously found to express mRNAs for two group IB phospholipase A(2) (PLA(2)) isoforms, DE-1 and DE-2, in the digestive organs, including the hepatopancreas, pyloric caeca, and intestine. To characterize the ontogeny of the digestive function of these PLA(2)s, the present study investigated the localization and expression of DE-1 and DE-2 PLA(2) genes in red sea bream larvae/juveniles and immature adults, by in situ hybridization. In the adults, DE-1 PLA(2) mRNA was expressed in pancreatic acinar cells. By contrast, DE-2 PLA(2) mRNA was detected not only in digestive tissues, such as pancreatic acinar cells, gastric glands of the stomach, epithelial cells of the pyloric caeca, and intestinal epithelial cells, but also in non-digestive ones, including cardiac and lateral muscle fibers and the cytoplasm of the oocytes. In the larvae, both DE-1 and DE-2 PLA(2) mRNAs first appeared in pancreatic tissues at 3 days post-hatching (dph) and in intestinal tissue at 1 dph, and expression levels for both gradually increased after this point. In the juvenile stage at 32 dph, DE-1 PLA(2) mRNA was highly expressed in pancreatic tissue, and DE-2 PLA(2) mRNA was detected in almost all digestive tissues, including pancreatic tissue, gastric glands, pyloric caeca, and intestine, including the myomere of the lateral muscles. In conclusion, both DE-1 and DE-2 PLA(2) mRNAs are already expressed in the digestive organs of red sea bream larvae before first feeding, and larvae will synthesize both DE-1 and DE-2 PLA(2) proteins.

Proteolytic cleavage of stingray phospholipase A2: isolation and biochemical characterization of an active N-terminal form

Background

Mammalian GIB-PLA2 are well characterized. In contrast, much less is known about aquatic ones. The aquatic world contains a wide variety of living species and, hence represents a great potential for discovering new lipolytic enzymes. The aim of this study was to check some biochemical and structural properties of a marine stingray phospholipase A2 (SPLA2).

Results

The effect of some proteolytic enzymes on SPLA2 was checked. Chymotrypsin and trypsin were able to hydrolyze SPLA2 in different ways. In both cases, only N-terminal fragments were accumulated during the hydrolysis, whereas no C-terminal fragment was obtained in either case. Tryptic and chymotryptic attack generated 13 kDa and 12 kDa forms of SPLA2, respectively. Interestingly, the SPLA2 13 kDa form was inactive, whereas the SPLA2 12 kDa form conserved almost its full phospholipase activity. In the absence of bile slats both native and 12kDa SPLA2 failed to catalyse the hydrolysis of PC emulsion. When bile salts were pre-incubated with the substrate, the native kinetic protein remained linear for more than 25 min, whereas the 12 kDa form activity was found to decrease rapidly. Furthermore, The SPLA2 activity was dependent on Ca²⁺; other cations (Mg²⁺, Mn²⁺, Cd²⁺ and Zn²⁺) reduced the enzymatic activity notably, suggesting that the arrangement of the catalytic site presents an exclusive structure for Ca²⁺.

Conclusions

Although marine and mammal pancreatic PLA2 share a high amino acid sequence homology, polyclonal antibodies directed against SPLA2 failed to recognize mammal PLA2 like the dromedary pancreatic one. Further investigations are needed to identify key residues involved in substrate recognition responsible for biochemical differences between the 2 classes of phospholipases.

Growth and body composition of zebrafish (Danio rerio) larvae fed a compound feed from first feeding onward: toward implications on nutrient requirements

Although zebrafish is used as a major model species for understanding a number of biological functions and mechanisms involved, there is practically no information on the nutritional requirements of this cyprinid. The rearing practices, especially with regard to feeds and feeding, also vary considerably. To obtain base line information on the nutrient requirements and to develop a standard diet, we initiated the present work of feeding zebrafish larvae with a formulated feed right from first feeding onward. Growth of zebrafish fed the compound feed was very good, reaching a total length of 23 ± 4 mm in 9 weeks with a survival rate of 89% ± 4%. We present the first ever published data on whole-body composition in terms of essential amino acids (ideal protein profile), total, neutral and polar fatty acid profiles, minerals, and trace elements. Results obtained here show clearly that zebrafish can be reared with formulated feed right from mouth opening without resorting to any live prey.

Purification and biochemical characterization of pancreatic phospholipase A2 from the common stingray Dasyatis pastinaca

BACKGROUND

Mammalian sPLA2-IB are well characterized. In contrast, much less is known about aquatic ones. The aquatic world contains a wide variety of living species and, hence represents a great potential for discovering new lipolytic enzymes.

RESULTS

A marine stingray phospholipase A2 (SPLA2) was purified from delipidated pancreas. Purified SPLA2, which is not glycosylated protein, was found to be monomeric protein with a molecular mass of 14 kDa. A specific activity of 750 U/mg for purified SPLA2 was measured at optimal conditions (pH 8.5 and 40 °C) in the presence of 4 mM NaTDC and 8 mM CaCl2 using PC as substrate. The sequence of the first twenty first amino-acid residues at the N-terminal extremity of SPLA2 was determined and shows a close similarity with known mammal and bird pancreatic secreted phospholipases A2. SPLA2 stability in the presence of organic solvents, as well as in acidic and alkaline pH and at high temperature makes it a good candidate for its application in food industry.

CONCLUSIONS

SPLA2 has several advantageous features for industrial applications. Stability of SPLA2 in the presence of organic solvents, and its tolerance to high temperatures, basic and acidic pH, makes it a good candidate for application in food industry to treat phospholipid-rich industrial effluents, or to synthesize useful chemical compounds.

Characterisation and expression of secretory phospholipase A2 group IB during ontogeny of Atlantic cod ( Gadus morhua)

The pancreatic enzyme secretory phospholipase A2 group IB (sPLA2 IB) hydrolyses phospholipids at the sn-2 position, resulting in a NEFA and a lyso-phospholipid, which are then absorbed by the enterocytes. The sPLA2 IB is a member of a family of nineteen enzymes sharing the same catalytic ability, of which nine are cytosolic and ten are secretory. Presently, there are no pharmacological tools to separate between the different secretory enzymes when measuring the enzymatic activity. Thus, it is important to support activity data with more precise techniques when isolation of intestinal content is not possible for analysis, as in the case of small teleost larvae, where the whole animal is sometimes analysed. In the present study, we characterise the sPLA2 IB gene in Atlantic cod (Gadus morhua) and describe its ontogeny at the genetic and protein level and compare this to the total sPLA2 activity level. A positive correlation was found between the expression of sPLA2 IB mRNA and protein. Both remained stable and low during the larval stage followed by an increase from day 62 posthatch, coinciding with the development of the pyloric ceaca. Meanwhile, total sPLA2 enzyme activity in cod was stable and relatively high during the early stages when larvae were fed live prey, followed by a decrease in activity when the fish were weaned to a formulated diet. Thus, the expression of sPLA2 IB mRNA and protein did not correlate with total sPLA2 activity.

Novel methodologies in marine fish larval nutrition

Major gaps in knowledge on fish larval nutritional requirements still remain. Small larval size, and difficulties in acceptance of inert microdiets, makes progress slow and cumbersome. This lack of knowledge in fish larval nutritional requirements is one of the causes of high mortalities and quality problems commonly observed in marine larviculture. In recent years, several novel methodologies have contributed to significant progress in fish larval nutrition. Others are emerging and are likely to bring further insight into larval nutritional physiology and requirements. This paper reviews a range of new tools and some examples of their present use, as well as potential future applications in the study of fish larvae nutrition. Tube-feeding and incorporation into Artemia of (14)C-amino acids and lipids allowed studying Artemia intake, digestion and absorption and utilisation of these nutrients. Diet selection by fish larvae has been studied with diets containing different natural stable isotope signatures or diets where different rare metal oxides were added. Mechanistic modelling has been used as a tool to integrate existing knowledge and reveal gaps, and also to better understand results obtained in tracer studies. Population genomics may assist in assessing genotype effects on nutritional requirements, by using progeny testing in fish reared in the same tanks, and also in identifying QTLs for larval stages. Functional genomics and proteomics enable the study of gene and protein expression under various dietary conditions, and thereby identify the metabolic pathways which are affected by a given nutrient. Promising results were obtained using the metabolic programming concept in early life to facilitate utilisation of certain nutrients at later stages. All together, these methodologies have made decisive contributions, and are expected to do even more in the near future, to build a knowledge basis for development of optimised diets and feeding regimes for different species of larval fish.

Ontogenetic development of digestive enzymes and effect of starvation in miiuy croaker Miichthys miiuy larvae

The ontogenetic development of the digestive enzymes amylase, lipase, trypsin, and alkaline phosphatase and the effect of starvation in miiuy croaker Miichthys miiuy larvae were studied. The activities of these enzymes were detected prior to exogenous feeding, but their developmental patterns differed remarkably. Trypsin activity continuously increased from 2 days after hatching (dah), peaked on 20 dah, and decreased to 25 dah at weaning. Alkaline phosphatase activity oscillated at low levels within a small range after the first feeding on 3 dah. In contrast, amylase and lipase activities followed the general developmental pattern that has been characterized in fish larvae, with a succession of increases or decreases. Amylase, lipase, and trypsin activities generally started to increase or decrease at transitions from endogenous to exogenous feeding or diet changes, suggesting that these enzymatic activities can be modulated by feeding modes. The activities of all the enzymes remained stable from 25 dah onwards, coinciding with the formation of gastric glands and pyloric caecum. These results imply that specific activities of these enzymes underwent changes due to morphological and physiological modifications or diet shift during larval development but that they became stable after the development of the digestive organs and associated glands was fully completed and the organs/glands functioned. Trypsin and alkaline phosphatase were more sensitive to starvation than amylase and lipase because delayed feeding up to 2 days after mouth opening was able to adversely affect their activities. Enzyme activities did not significantly differ among feeding groups during endogenous feeding; however, all activities were remarkably reduced when delayed feeding was within 3 days after mouth opening. Initiation of larvae feeding should occur within 2 days after mouth opening so that good growth and survival can be obtained in the culture.

Dietary lipid level induced antioxidant response in Manchurian trout, Brachymystax lenok (Pallas) larvae

This study was designed to determine the nutritional lipid requirement of Manchurian trout and to investigate the effects of lipid concentrations on the antioxidant status in larvae with experimental diets with different lipid levels. Oxidative stress differences between different organs and tissues were also assessed. Manchurian trout larvae were fed for 35 days and, during that period, growth and survival, the activity of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX) and content of malondialdehyde (MDA) in viscera, muscle, gill and brain of four diets, lipid levels from 15 to 30%, and control treatment were measured. Growth rates were similar, but survival was low, between high and low dietary lipid levels. SOD activity was stimulated in viscera, muscle and brain in high lipid diets, but reduced in gills with increased lipid content. SOD was kept lower in the control group. GPX activity was inhibited in viscera and stimulated in gill, muscle and brain. CAT activities were enhanced by all treatments and showed the lowest values in the control. Lipid peroxidation of the diet was promoted in all organs, excluding the gill which showed no regular pattern. MDA content increased with increased dietary lipid levels in viscera, muscle and brain. Our results indicate that the most appropriate lipid requirement is probably 20-25% and a higher dietary level of lipids might induce oxidative stress in Manchurian trout larvae. The brain and gill were probably the most sensitive organs to oxidative damage.

Development of digestive enzyme activity in larvae of spotted sand bass Paralabrax maculatofasciatus. 1. Biochemical analysis

Spotted sand bass Paralabrax maculatofasciatus is a potential aquaculture species in Northwest Mexico. In the last few years it has been possible to close its life cycle and to develop larviculture technology at on pilot scale using live food, however survival values are low (11%) and improvements in growth and survival requires the study of the morpho-physiological development during the initial ontogeny. In this research digestive activity of several enzymes were evaluated in larvae, from hatching to 30 days after hatching (dah), and in live prey (rotifers and Artemia), by use of biochemical and electrophoretic techniques. This paper, is the first of two parts, and covers only the biochemical analysis. All digestive enzyme activities were detected from mouth opening; however the, maximum activities varied among different digestive enzymes. For alkaline protease and trypsin the maximum activities were detected from 12 to 18 dah. Acid protease activity was observed from day 12 onwards. The other digestive enzymes appear between days 4 and 18 after hatching, with marked fluctuations. These activities indicate the beginning of the juvenile stage and the maturation of the digestive system, in agreement with changes that occur during morpho-physiological development and food changes from rotifers to Artemia. All enzymatic activities were detected in rotifers and Artemia, and their contribution to enhancement the digestion capacity of the larvae appears to be low, but cannot be minimised. We concluded that the enzymatic equipment of P. maculatofasciatus larvae is similar to that of other marine fish species, that it becomes complete between days 12 and 18 after hatching, and that it is totally efficient up to 25 dah.

Ontogenic effects of early feeding of sea bass (Dicentrarchus labrax) larvae with a range of dietary n-3 highly unsaturated fatty acid levels on the functioning of polyunsaturated fatty acid desaturation pathways

Four replicated groups of sea bass (Dicentrarchus labrax) larvae were fed diets containing an extra-high level of highly unsaturated fatty acids (HUFA) (XH; 3.7 % EPA+DHA), a high level of HUFA (HH; 1.7 %), a low level of HUFA (LH; 0.7 %) or an extra-low level of HUFA (XLH; 0.5 %) from day 6 to day 45 (experiment 1; XH1, HH1, LH1, XLH1). After a subsequent 1-month period feeding a commercial diet (2.7 % EPA+DHA), the capacity of the four initial groups to adapt to an n-3 HUFA-restricted diet (0.3 % EPA+DHA; R-groups: XH2R, HH2R, LH2R, XLH2R) was tested for 35 d. Larval dietary treatments had no effect on larval and juvenile survival rates. The wet weight of day 45 larvae was higher in XH1 and HH1 (P < 0.001), but the R-juvenile mass gains were similar in all treatments. Delta-6-desaturase (Delta6D) mRNA level was higher in LH1 and XLH1 at day 45 (P < 0.001), and higher in LH2R and XLH2R, with a significant increase at day 118.Concomitantly, PPARalpha and PPARbeta mRNA levels were higher in XLH1 at day 45, and PPARbeta and gamma mRNA levels were higher in XLH2R at day 118, suggesting possible involvement of PPAR in stimulation of Delta6D expression, when drastic dietary larval conditioning occurred. The low DHA content in the polar lipids (PL) of LH1 and XLH1 revealed an n-3-HUFA deficiency in these groups. Larval conditioning did not affect DHA content in the PL of R-juveniles. The present study showed (i) a persistent Delta6D mRNA enhancement in juveniles pre-conditioned with an n-3 HUFA-deficient larval diet, over the 1-month intermediate period, and (ii) brought new findings suggesting the involvement of PPAR in the Delta6D mRNA level stimulation. However, such nutritional conditioning had no significant effect on juvenile growth and lipid composition.

Dietary phospholipids are more efficient than neutral lipids for long-chain polyunsaturated fatty acid supply in European sea bass Dicentrarchus labrax larval development

We evaluated the effects of dietary lipid class (phospholipid vs. neutral lipid) and level of n-3 long-chain PUFA (LC-PUFA) on the growth, digestive enzymatic activity, and histological organization of the intestine and liver in European sea bass larvae. Fish were fed from the onset of exogenous feeding at 7 to 37 d post-hatch with five isoproteic and isolipidic compound diets with different levels of EPA and DHA. Diet names indicated the percentage of EPA and DHA contained in the phospholipids (PL) and neutral lipids (NL), as follows: PL5, PL3, PL1, NL1, and NL3. Histological observations showed different patterns of lipid absorption and accumulation in the intestinal mucosa depending on the level and nature of the dietary lipid fraction. Fish fed high levels of neutral lipids (11%, NL3 diet: 2.6% of EPA + DHA in the NL fraction) showed large intracellular and intercellular lipid deposits in the anterior intestine, but no such lipid accumulation was detected when larvae were fed with low and moderate levels of EPA and DHA in the phospholipid and neutral lipid fractions of the diet (PL and NL1 diets). PL were preferentially absorbed in the postvalvular intestine, and the accumulation of marine PL was inversely correlated to their dietary level. The postvalvular intestinal mucosa and liver showed signs of steatosis; large lipid vacuoles were observed in this region of the intestine and in the liver and were inversely correlated with the level of dietary neutral lipids. The best results in terms of growth, survival, and development (maturation of the digestive system and histological organization of the liver and intestinal mucosa) were obtained in the group fed with 2.3% of EPA and DHA in the PL fraction of the diet (PL3 diet), revealing that European sea bass larvae use the LC-PUFA contained in the PL fraction more efficiently than those from the NL fraction of the diet.

Dietary levels of all-trans retinol affect retinoid nuclear receptor expression and skeletal development in European sea bass larvae

European sea bass larvae were fed different dietary vitamin A levels. Growth, skeletal development and the expression of genes involved in larval morphogenesis were evaluated. From 7 to 42 d post-hatching, larvae were fed five isoproteic and isolipidic compound diets with graded levels of retinyl acetate (RA; RA0, RA10, RA50, RA250 and RA1000, containing 0, 10, 50, 250 and 1000 mg RA/kg DM, respectively), resulting in an incorporation of 12, 13, 31, 62 and 196 mg all-trans retinol/kg DM. Larvae fed extreme levels of RA had weights 19 % and 27 % lower than those of the RA50 group. The RA1000 diet induced a fall in growth with an increase of circulating and storage retinol forms in larvae, revealing hypervitaminosis. High levels of RA affected maturation of the pancreas and intestine. These data indicated that the optimal RA level was close to 31 mg/kg DM. Inappropriate levels of dietary RA resulted in an alteration of head organisation characterised by the abnormal development of the splanchnocranium and neurocranium, and scoliotic fish. Of the larvae fed RA1000, 78.8 % exhibited skeletal abnormalities, whereas the RA50 group presented with 25 % malformations. A linear correlation between vitamin A level and malformation percentage was observed and mainly associated with an upregulation of retinoic acid receptor-gamma expression in the RA1000 group during the 2 first weeks after hatching. The expression of retinoid X receptor-alpha decreased during normal larval development when that of the retinoic acid receptors increased. This work highlights the involvement of retinoid pathways in the appearance of dietary-induced skeletal malformations during post-hatching development in sea bass.

Partial purification and characterization of pro-phospholipase A2 activating proteases from gill membranes of the red sea bream, Chrysophrys major

We previously reported that gill group IB secretory phospholipase A(2) (sPLA(2)) exists as an inactive pro-sPLA(2) with the dipeptide Ala-Arg, at the N-terminus of mature sPLA(2) in mucous cells. Pro-sPLA(2) should be activated after being secreted to the surface of gill epithelia by trypsin-like protease. To clarify the above hypothesis, we investigated the existence of pro-sPLA(2) activating protease (PAP) in the gills of the red sea bream, using gill pro-sPLA(2) as a substrate. PAP was solubilized from the membrane fraction of the gills with 2% sodium cholate and partially purified by benzamidine-Sepharose chromatography and reversed-phase HPLC. Partially purified proteases, PAP1 and PAP2 showed a high molecular mass of about 200 kDa by gelatin zymography. PAP1 and PAP2 had optimal pH from 7 to 9 and were inhibited by trypsin inhibitors. These properties of PAP1 and PAP2 suggest that both enzymes belong to the membrane-associated trypsin-like serine protease family, such as enteropeptidase and corin. This is the first report verifying the existence of the activating protease of group IB pro-sPLA(2) isoforms in a non-digestive tissue.

Dietary TAG source and level affect performance and lipase expression in larval sea bass (Dicentrarchus labrax)

The influence of dietary TAG source (fish oil, triolein, and coconut oil) and level (7.5 and 15% of the diet) on growth, lipase activity, and mRNA level was studied in sea bass larvae, from mouth opening until day 24 and from day 37 to 52. Fish oil and triolein induced better growth in both experiments, this being significant at a higher dietary level. Coconut oil significantly decreased growth at the higher level, possibly as the result of an excessive supply of medium-chain TAG. Growth was not related to lipase specific activity, suggesting a production in excess to dietary needs. Body lipid content was positively related to dietary lipid level and was affected by lipid quality. In addition, larval FA composition generally reflected that of the diet. The source of dietary lipid, but not the quantity, was shown to affect lipase activity significantly. Coconut oil diets induced the highest lipase activity, whereas the effect of fish oil was age dependent-it was similar to coconut oil at day 24 but induced the lowest lipase activity in 52-d-old larvae. The differential lipase response was probably caused by differences in the FA composition of the diet, related to the specificity of lipase toward FA differing in chain length and degree of saturation. No significant differences were found in lipase/glyceraldehyde-3-phosphate dehydrogenase mRNA, which suggests the existence of a posttranscriptional regulation mechanism.

Single-cell protein diet of a novel recombinant vitellogenin yeast enhances growth and survival of first-feeding tilapia (Oreochromis mossambicus) larvae

Yeast single-cell protein (SCP) is a high-nutrient feed substitute. This study evaluates the dual applications of a novel recombinant Pichia pastoris SMD1168H (SMD) yeast, expressing a tilapia vitellogenin protein (rVtg), as an SCP diet for Artemia and the first-feeding fish larvae. Instar II Artemia fed rVtg, rVtg precultured in 5% fish oil (rVtg-FO), Saccharomyces cerevisiae (SC), or native SMD had greater lipid contents (P < 0.05) than the freshly hatched. Lipid deposition in the Artemia fed rVtg or rVtg-FO was greater (P < 0.05) than in those fed SMD or SC. Diet-induced accumulation of low levels of docosahexaenoic acid [22:6(n-3)] was detected only in Artemia fed the rVtg-based diets. Tilapia (Oreochromis mossambicus) larvae were fed solely yeast diets singly or in combination (d 3-22), or a staggered regimen of yeast (d 3-12) followed by unenriched or yeast-enriched Artemia (d 13-22). The larvae fed rVtg for 22 d increased in length and weight (P < 0.05), whereas those fed SC or SMD suffered growth suppression and high mortality. Such adverse consequences were ameliorated when 50% of SC was substituted with rVtg. The larvae prefed rVtg followed by a dietary switch to Artemia preenriched for 48 h with rVtg or rVtg-FO were greatest in length, had the highest weight gain, and lived the longest. Besides delivering rVtg protein, essential fatty acids and amino acids, rVtg may have probiotic effects in enhancing larval survival. This study suggests the feasibility of using the rVtg yeast as an Artemia booster and an SCP first feed for larvae.

Eicosanoid generation in the intertidal barnacle,Balanus perforatus—effect of season and reproductive status

The nature and quantity of the principal lipoxygenase (LO) products generated by the intertidal barnacle Balanus perforatus were examined at monthly intervals and their potential involvement in reproductive events was investigated. The main mono-hydroxy products generated were found to be formed through the action of an 8-lipoxygenase (8-LO) activity and were the mono-hydroxy fatty acids, 8-hydroxyeicosapentaenoic acid (HEPE) and 8-hydroxyeicosatetraenoic acid. Generation of these products was found to be correlated with the environmental seawater temperature, although no change in either 8-LO activity or the precursor fatty acid levels in total phospholipids was found with the time of the year. Changes in fatty acid composition measured in animals collected from summer and winter conditions were found to follow the pattern expected by homeoviscous adaptation of a cold-acclimated animal. Oogenesis was found to occur in August and was linked to a significant reduction in 8-HEPE generation. Spermatozoa were found to be present year-round in the seminal vesicles although the testes became atrophic during the winter months.

Effect of dietary phospholipid level and phospholipid:neutral lipid value on the development of sea bass (Dicentrarchus labrax) larvae fed a compound diet

The aim of the study was to determine the influence of dietary phospholipid concentration on survival and development in sea bass (Dicentrarchus labrax) larvae. Larvae were fed from day 9 to day 40 post-hatch with an isoproteic and isolipidic formulated diet with graded phospholipid levels from 27 to 116 g/kg DM and different phospholipid:neutral lipid values. The best growth (32 mg at the end of the experiment) survival (73 %) and larval quality (only 2 % of malformed larvae) were obtained in the larvae fed the diet containing 116 g phospholipid/kg DM (P<0.05). These results were related to the amount of phosphatidylcholine and phosphatidylinositol included in this diet (35 and 16 g/kg respectively). Amylase, alkaline phosphatase and aminopeptidase N activities revealed a proper maturation of the digestive tract in the two groups fed the highest phospholipid levels. Regulation of lipase and phospholipase A2 by the relative amount of their substrate in the diet occurred mainly at the transcriptional level. The response of pancreatic lipase to dietary neutral lipid was not linear. As in mammals 200 g triacylglycerol/kg diet seems to represent a threshold level above which the response of pancreatic lipase is maximal. The response of phospholipase A2 to dietary phospholipid content was gradual and showed a great modulation range in expression. Sea bass larvae have more efficient capacity to utilize dietary phospholipid than neutral lipids. For the first time a compound diet sustaining good growth, survival and skeletal development has been formulated and can be used in total replacement of live prey in the feeding sequence of marine fish larvae.

Localization of group IB phospholipase A(2) isoform in the gills of the red sea bream, Pagrus (Chrysophrys) major

We previously reported that PLA(2) activity in the gills is higher than that in other tissues in red sea bream and purified PLA(2) from the gills belongs to the group IB PLA(2) as well as other red sea bream PLA(2)s. In this study, we reconfirmed that the level of PLA(2) activity is extremely high in the gills compared with other tissues, and gill PLA(2) was detected only in the gills by immunoblotting and inhibition test using anti-gill PLA(2) monoclonal antibody. The level of PLA(2) activity and protein expression in the gills are well correlated. Fish can be roughly divided into high and low groups based on the level of PLA(2) activity. Gill PLA(2) was detected in the gills of the high group, but not the low group by immunoblotting. In the gills of the high group, gill PLA(2) was detected in the mucous cells and pavement cells located on the surface of gill epithelia by immunohistochemistry. On the other hand, positive signals were observed only in the mucous cells by in situ hybridization. We also isolated inactive proPLA(2), having AR propeptide, preceding the mature enzyme from the gill extract. These results suggest that gill PLA(2) is synthesized as an inactive proPLA(2) in the mucous cells and is secreted to the surface of gill epithelia.

Ontogeny of the gastrointestinal tract of marine fish larvae

Marine fish larvae undergo major morphological and cellular changes during the first month of life. The ontogeny of the gastrointestinal tract combines these two aspects of the larval development and is very interesting in that the timing of functional changes appears genetically hard-wired. The goal of this paper is to give an overview of the gastrointestinal development process in marine fish larvae, with particular attention to three species: sea bass; red drum; and sole, since the description of gut maturation in fish larvae was initiated during the last decade with these species. During the early stages, marine fish larvae exhibit particular digestive features. Concerning the exocrine pancreas, amylase expression decreases with age from the third week post-hatching in sea bass and red drum (approximately 400 degree days), whereas expression of other enzymes (trypsin, lipase, phospholipase A2...) increases until the end of the larva period. Moreover, secretory function of the exocrine pancreas progressively develops and becomes efficient after the third week of life. Concerning the intestine, enzymes of the enterocyte cytosol (in particular peptidase) have higher activity in young larvae than in older. Approximately in the fourth week of post-hatching development in sea bass, red drum and sole larvae, the cytosolic activities dramatically decline concurrently with a sharp increase in membranous enzyme activities of the brush border, such as alkaline phosphatase, aminopeptidase N, maltase. This process characterises the normal maturation of enterocytes in developing fish larvae and also in other vertebrates' species. The establishment of an efficient brush border membrane digestion represents the adult mode of digestion of enterocytes. This paper also describes the role of diet on the development of the gastrointestinal tract. Indeed, the maturational process of digestive enzyme can be enhanced, stopped, or delayed depending on the composition of the diet.

Cloning and expression of group IB phospholipase A2 isoforms in the red sea bream, Pagrus major

Two cDNA encoding red sea bream DE-1 and DE-2 phospholipases A2 (PLA2) were cloned from the hepatopancreas of red sea bream, Pagrus (Chrysophrys) major. The cDNA of DE-1 PLA2 encoded a mature protein of 125 amino acid residues with an apparent signal peptide of 20 residues and propeptide of 5 residues, and that of DE-2 PLA2, a mature protein of 126 amino acid residues with an apparent signal peptide of 17 residues and propeptide of 6 residues. Comparison of the predicted amino acid sequences for mature DE-1 and DE-2 PLA2 showed that both proteins contain 14 cysteines including Cys 11 and 77 and a pancreatic loop, which are commonly conserved in group IB PLA2; however, the identity in amino acid sequence between DE-1 and DE-2 PLA2 was low (47%). A previous report concerning the cDNA cloning of red sea bream gill G-3 PLA2 and the present results represent the first cloning and sequencing of three distinct isoforms of group IB PLA2 in a single fish species, red sea bream. Reverse transcription-polymerase chain reaction analysis showed that DE-1 PLA2 mRNA was expressed in the hepatopancreas, pyloric ceca, intestine, spleen, gonad, stomach, and kidney, whereas gill G-3 PLA2 mRNA was expressed only in the gills and gonad. The expression of DE-2 PLA2 mRNA was detected in all of the tissues analyzed. These results indicate that three distinct isoforms of group IB PLA2, DE-1 and DE-2 PLA2 in hepatopanceas and gill G-3 PLA2, are expressed in a tissue-specific manner in red sea bream.

Purification, characterization, and molecular cloning of group I phospholipases A2 from the gills of the red sea bream, Pagrus major

Phospholipase A2 (PLA2) activity was investigated in various tissues of male and female red sea bream. In both male and female fishes, the specific activity of PLA2 in the gills was 70 times higher than that in other tissues, such as the adipose tissue, intestine, and hepatopancreas. Therefore, we tried to purify PLA2 from the gill filaments of red sea bream to near homogeneity by sequential chromatography on Q-Sepharose Fast Flow, Butyl-Cellulofine, and DEAE-Sepharose Fast Flow columns, and by reversed-phase high-performance liquid chromatography. Two minor and one major PLA2, tentatively named G-1, G-2 and G-3 PLA2, were purified, and all showed a single band with an apparent molecular mass of approximately 15 kDa by sodium dodecylsulfate-polyacrylamide gel electrophoresis. The exact molecular mass values of G-1, G-2, and G-3 PLA2 were 14,040, 14,040 and 14,005 Da, respectively. G-1, G-2, and G-3 PLA2 had a Cys 11 and were all identical in N-terminal amino acid sequences from Ala-1 to Glu-56. A full-length cDNA encoding G-3 PLA2 was cloned by reverse transcriptase-polymerase chain reaction and rapid amplification of cDNA ends methods, and G-3 PLA2 was found to be classified to group IB PLA2 from the deduced amino acid sequence. G-1, G-2, and G-3 PLA2 had a pH optimum in an alkaline region at around pH 9-10 and required Ca2+ essentially for enzyme activity, using a mixed-micellar phosphatidylcholine substrate with sodium cholate. These results demonstrate that three group I PLA2, G-1, G-2, and G-3 PLA2, are expressed in the gill filaments of red sea bream.

Tricaproin, tricaprin and trilaurin are utilized more efficiently than tricaprylin by carp (Cyprinus carpio L.) larvae

We investigated the effect of chain length of dietary medium-chain fatty acids (MCFA) on growth performance and fatty acid composition of first-feeding carp larvae. In a first trial, five semi-purified isolipidic (23-24 g/100 g of dry matter) diets were formulated to contain either 10 g/100 g triolein (control diet) or 5 g/100 g triolein and 5 g/100 g medium-chain triacylglycerols (MCT) supplied as tricaproin, tricaprylin, tricaprin or trilaurin. After 21 d, survival and growth rates were significantly greater in larvae fed diets containing triolein, tricaproin, tricaprin and trilaurin (final survival: 92 +/- 7% and mean larval weight: 42 +/- 15 mg) than in larvae fed tricaprylin (final survival: 56 +/- 12% and mean larval weight: 15 +/- 1 mg). The recovered levels of the fed MCFA in larval total lipids were respectively 0, 1.3, 7.3 and 8.1 g/100 g of total fatty acids. In a second trial, two isolipidic (18 g/100 g) diets containing 10 g/100 g triolein or tricaprylin were tested. High amounts of capric acid (up to 25 g/100 g of total fatty acids) were found in neutral lipids of carp larvae fed tricaprylin for 11 d, suggesting an unusual elongation of caprylic acid. This study underlines the peculiarity of tricaprylin among other MCT which seem well utilized up to 20-30 g/100 g of total dietary fatty acids. The exception of tricaprylin raises the question of the metabolic pathways followed by this MCT, especially for the suggested direct elongation of caprylic acid into capric acid.