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Methionine-choline-deficient ( MCD) mammals are known to accumulate liver TAG probably due to phosphatidylcholine ( PC) deficiency and thus assembly of VLDL and transport of lipids from liver to peripheral organs. To assess whether supplementation of choline could spare methionine and secure a healthy liver metabolism, by reducing the endogenous PC synthesis without interfering with lipid transport and distribution, Atlantic salmon with initial BW of 700 g were fed adequate (1.9 g Met/16 gN) or surplus methionine (2.5 g Met/16 gN) diets of which were supplemented with choline or not for a period of 19 weeks. Fish fed the low-methionine diets had reduced growth ( p = .013) due to reduced protein gain ( p = .007), while lipid gain slightly improved in fish fed the choline-supplemented diets ( p = .047). Also, feed conversion improved when fed surplus methionine ( p < .001), while choline supplementation had no impact on feed conversion. No interaction between choline and methionine on growth performance or retention existed. Phospholipid status in liver and muscle was not affected by treatments, and no liver TAG accumulation occurred at the methionine levels used. Gene expression of ApoB100 necessary for assembling VLDL or pemt necessary for endogenous PC synthesis was unaffected by treatments. Capacity of methylation ( MAT, BHMT) within the liver was not affected by treatment nor was the gene expression of enzymes in liver transsulfuration ( CBS or CDO). Methionine status within liver was unaffected by treatments, while free methionine reduced in those fish fed the low-methionine diets in muscle and plasma. Cystathionine and taurine were elevated when fed surplus methionine. Choline supplementation had no impact on sulphur amino acid metabolites in either tissue. Neither did choline supplementation improve TAG mobilization from liver to muscle. To conclude, choline does not improve endogenous phospholipid synthesis or transport of TAG from liver to muscle depot when added to diets containing 1.9 g Met/16 gN, while surplus methionine improved growth and protein retention, indicating that 1.9 g Met/16 gN is enough to support a healthy liver metabolism, but too low to support muscle protein deposition in adult salmon fed high plant protein diets for longer periods of time. [ABSTRACT FROM AUTHOR]

We previously reported that juvenile Atlantic salmon with mean initial BW 11.5 g offed a methionine deficient diet had lower weight gain due to a reduced protein accretion, while lipid gain was unaffected. Muscle of the fish fed the methionine deficient diet was depleted for sulphur amino acids, while in liver, the concentration of these metabolites was maintained within narrow limits. We speculated whether this could be due to an increased muscle proteolysis to support a prioritized liver metabolism in fish fed the low methionine diets. In this study, we assessed whether genes associated with muscle proteolysis increased under methionine deficiency. The composition of the diets was similar to those used previously containing 1.6 or 2.1 g Met/16 g N. We confirmed that the fish fed the low methionine diet gained less protein compared to fish fed the DLmethionine enriched diet (P = 0.014), but growth did not reduce significantly. Also the deficient fish maintained the concentrations of liver sulphur amino acids and reduced muscle free methionine. Several of the other free amino acids within muscle increased. Further, methylation capacity was maintained in liver but reduced in the muscle (P = 0.78 and 0.04, respectively). Gene expression of muscle IGF-1 was lower (P = 0.008) and myosin light chain 2 tended (MLC2, P = 0.06) to be reduced in fish fed low methionine diet, concurrently the activity of cathepsins B+L increased (P = 0.047) in muscle of fish fed the low methionine diet. Gene expression of the muscle-specific E3 ubiquitine ligases (Murf and MaFbx) was not affected by treatment. Thus, the lower protein gain observed in fish fed the low methionine diet may be caused by reduced protein synthesis in line with the reduced IGF-1 gene expression in the white trunk muscle. Thus, to support metabolism, the dietary protein needs to be balanced in amino acids to support metabolism in all compartments of the body and secure maximal protein gain. [ABSTRACT FROM AUTHOR]

Phosphatidylcholine is synthesized endogenously through the enzyme phosphatidylethanolamine-methyl transferase. As endogenous choline synthesis requires methyl groups from S-adenosylmethionine (SAM), the endogenous synthesis of choline may depend on SAM availability. SAM availability depends on methionine and ATP. SAM is also a precursor for cysteine and may affect taurine and glutathione concentrations. To investigate whether choline synthesis or transsulphuration is prioritized and the interactions between taurine and choline supplementation when methionine availability is low, juvenile Atlantic salmon were fed low methionine diets with and without taurine and choline supplementation. There were no differences in growth or protein accretion following treatments. Fish fed the low methionine diets did not develop a fatty liver, but choline supplementation increased the concentration of total phospholipids in liver and muscle. Taurine supplementation increased taurine concentrations in liver and muscle, but no interactions with choline were present. Liver SAM was unaffected by treatments. Two of three tanks fed the low methionine diet without choline and taurine supplementation had a higher gene expression of p38MAPK (mitogen activated phosphokinase). Choline supplementation to low methionine diets thus may have beneficial effect on the metabolic health and lipid transport to extra-hepatic tissues. Taurine supplementation had no effect on phospholipids status, but increased taurine concentration in tissues and as such may affect oxidation status when methionine availability is low. [ABSTRACT FROM AUTHOR]

The current study aimed to investigate the effect of surplus dietary arginine on polyamine and amino acid metabolism and accretion of proteins and lipids, as previous studies have demonstrated a lipid-reducing effect following surplus arginine supplementation in viscera as well as increased muscle growth. Four plant protein-based diets were given increasing concentrations of L-arginine, from 21.1 to 36.1 g kg-1 DM, and fed to quadruplicate tanks of adult Atlantic salmon (1.1 kg) for 12 weeks. No effects on growth or deposition of fat or protein were observed. Free amino acid concentrations and related metabolites were unaffected in the liver, except for urea, while concentrations in muscle and plasma reflected production of arginine metabolites. Polyamine concentrations were unaffected in liver, muscle and white adipose tissue ( WAT), as were the abundance and activity of spermidine/spermine N1-acetyltransferase ( SSAT), the rate-limiting enzyme in polyamine turnover. Gene expression demonstrated differential regulation of ornithine decarboxylase ( ODC) in liver and WAT, although overall little effects were observed on gene expression. Liver S-adenosylmethionine ( SAM) concentrations decreased with arginine supplementation. We suggest that adult Atlantic salmon have adapted to surplus arginine, and the main long-term effect appears to be increased concentrations of arginine metabolites. [ABSTRACT FROM AUTHOR]

Cobia (8.4 ± 0.1 g body weight) were fed to satiation with three test diets of high plant protein-based ingredients and different lysine to arginine ratios, and one commercial diet (currently used for cobia rearing in Vietnam as a control for growth) for 6 weeks. The test diets contained 206 g marine ingredients kg−1, including fishmeal, krill meal and fish protein concentrate (in order of high to low inclusion), while the rest of the dietary protein was a blend of soya and pea protein concentrate, wheat protein and sunflower meal. Crystalline lysine and arginine were added in the test diets to produce either a balanced lysine to arginine ratio ( BL/ A; 1.1) and a high or low lysine to arginine ratio ( HL/ A; 1.8 and LL/ A; 0.8, respectively). There were no significant differences in final body weight, weight gain, feed conversion ratio or protein gain between cobia fed BL/ A- and commercial control diet ( CCT). Cobia fed BL/ A diet performed better than fish fed either HL/ A- or LL/ A diet. This was partly due to a higher feed intake and protein and lipid gain in cobia fed BL/ A diet as compared to HL/ A- and LL/ A diet. [ABSTRACT FROM AUTHOR]

The appetite-stimulating effect of krill hydrolysate ( KH), free amino acids and specific water-soluble low molecular N-compounds was explored in a short feeding trial with Atlantic salmon. A 100 g kg−1 fish meal positive ( MFM), a 30 g kg−1 fish meal negative control ( LFM) and six more LFM diets were produced added known attractants for fish- KH at two levels: low ( LAK) or high ( HAK), AMP, choline chloride ( CC); an amino acid mix resembling the free amino acid composition of KH ( AA) or a mix of AMP, CC and AA ( ACA). HAK, ACA and AA showed highest feed intake and significantly higher plasma phospholipids and cholesterol. The lower performing treatments ( LFM, AMP) showed higher liver lipids and hepatosomatic index. CC induced reduced liver lipids and increased plasma phospholipids and cholesterol. Appetite regulating neuropeptide gene expression analysis (q PCR) was performed in fish fed LFM, HAK and AA. Pyy showed the highest postprandial expression in LFM, whereas the expression of the anorexigenic neuropeptides cart, pomca1, pomca2 and pomca2s was low. These apparently contradictory results may be explained by initial appetite stimulation by HAK and AA, resulting in higher feed intake, followed by satiation and appetite downregulation. [ABSTRACT FROM AUTHOR]

In order to investigate the effects of dietary protein hydrolysates (PH) on larval growth performance, skeleton quality and proteome expression, triplicate groups of white seabream ( Diplodus sargus) larvae were co-fed from first-feeding with live feed and three microencapsulated diets differing in the molecular weight of their PH fraction (Control - inclusion of CPSP-90; H - inclusion of a high amount in 0.5-30 kDa hydrolysates; L - inclusion of a high amount in <0.5 kDa hydrolysates). At 15 days after hatching (DAH), proteome expression changes were assessed in entire larvae by two-dimensional gel electrophoresis and the quality of larval skeleton was analysed at 28 DAH through double staining of cartilage and bone. Dietary PH fractions tested affected growth, the larvae fed diet L being significantly larger than those fed diet H, but it did not affect the incidence of deformed larvae, nor the number of deformities per fish. Two-dimensional analysis of larvae proteome allowed the detection and the comparative quantification of a total of 709 protein spots having a pI between 4 and 7, around half of which had an expression significantly affected by dietary treatment, the main difference being between proteome of Control larvae with those of both groups L and H. From these spots, 52 proteins involved in diverse processes such as cytoskeletal dynamics, energetic, lipoprotein, amino acid (AA), and nucleotide metabolisms, protein chaperoning and degradation, and signal transduction, were identified. This study revealed that the molecular weight of the dietary protein hydrolysate fraction had a minor impact on skeletal deformities in white seabream larvae, but affected growth performance and had a strong impact on larvae whole body proteome. [ABSTRACT FROM AUTHOR]

The hypothesis of the present study was that cod larvae have a limitation in lipid digestion, and that absorption of lipids would increase by pre-hydrolysation. The diets used were designed to contain 15 % lipid, of which 40 % was phosphatidylcholine (PC) and 60 % was TAG. Cod larvae (40 d post hatch (dph)) were fed a single meal where either PC or TAG was radioactively labelled, and the labelled PC or TAG was either intact or hydrolysed (pre-digested). The larvae were then incubated individually in chambers with collection of CO2 for 10 h. The following fractions were analysed for radioactivity: the incubation water (evacuated feed); the intestine; the body; the CO2 trap. The larvae ate a 16–29 μg diet, equivalent to 3·4–5·2 % of dry body weight. In the whole population, 0–16 % of the lipid was evacuated. The larvae that had eaten less than 1·9–2·7 μg lipid absorbed close to 100 % of the lipid, absorption being defined conservatively as the amount contained in the carcass and CO2, excluding the intestinal tissue. In these larvae, approximately 100 % of the absorbed lipid was also catabolised. In the larvae that ingested more than 1·9–2·7 μg lipid, there was a linear reduction in lipid absorption to a minimum of 55 % at the highest lipid intakes parallel to an increasing retention of lipids in the carcass. There were only minor differences in digestion, absorption, retention and metabolism of lipids between the larvae fed the different diets, and the larvae tended to retain lipid classes as they were present in the feed. The study shows that 40-dph Atlantic cod larvae have an efficient utilisation of dietary lipids supplied as intact PC and TAG. [ABSTRACT FROM PUBLISHER]

Zebrafish is one of the most used vertebrate model organisms in molecular and developmental biology, recently gaining popularity also in medical research. However, very little work has been done to assess zebrafish as a model species in nutritional studies in aquaculture in order to utilize the methodological toolbox that this species represents. As a starting point to acquire some baseline data for further nutritional studies, growth of a population of zebrafish was followed for 15 weeks. Furthermore, whole body proteome was screened during development by means of bi-dimensional gel electrophoresis and mass spectrometry. Fish were reared under best practice laboratory conditions from hatching until 103 days post-fertilization (dpf) and regularly fed ad libitum with Artemia nauplii from 12 dpf. A growth burst occurred within 9-51 dpf, reaching a plateau after 65 dpf. Fork length and body weight were significantly lower in males than in females from 58 dpf onwards. Proteomics analysis showed 28 spot proteins differently expressed through development and according to sex. Of these proteins, 20 were successfully identified revealing proteins involved in energy production, muscle development, eye lens differentiation, and sexual maturation. In summary, zebrafish exhibited a rapid growth until approximately 50 dpf, when most individuals started to allocate part of the dietary energy intake for sexual maturation. However, proteomic analysis revealed that some individuals reached sexual maturity earlier and already from 30 dpf onwards. Thus, in order to design nutritional studies with zebrafish fed Artemia nauplii, it is recommended to select a period between 20 and 40 dpf, when fish allocate most of the ingested energy for non-reproductive growth purposes. [ABSTRACT FROM AUTHOR]

One of the main gastrointestinal hormones, cholecystokinin (CCK), was studied in order to advance understanding of the control of the digestive process in Atlantic cod Gadus morhua larvae after onset of first feeding. Larvae were fed either natural zooplankton or enriched rotifers in similar rearing systems and sampled from hatching to 22 days post-hatch (dph). CCK was visualized by immunohistochemistry and the first CCK-immunoreactive (IR) cells were detected at 8 dph corresponding to 6 days after first feeding. The CCK-IR cells were mostly found in the anterior midgut, and the number of CCK-IR cells was lower in the posterior midgut. They were also present in the hindgut of some of the larvae, but not in the foregut. No clear differences were found in the ontogenetic appearance and the distribution pattern of CCK-IR cells between the two dietary treatments. This indicates that the onset of CCK production in the gut as well as the spatial distribution of the CCK-IR cells is not differentially affected by these diets. To what extent the hormone production itself is influenced by dietary factors needs to be studied by more sensitive methods. [ABSTRACT FROM AUTHOR]

Membrane potential depolarization due to electrogenic peptide transport activity was examined in eel ( Anguilla anguilla) intestinal brush-border membrane vesicles (BBMV) by monitoring the fluorescence quenching of the voltage-sensitive dye 3,3′-diethylthiadicarbocyanine iodide. Our experimental approach consisted of generating an internal negative membrane potential mimicking in vivo conditions and measuring membrane potential depolarization due to different extravesicular dipeptides. Peptide-dependent membrane potential depolarization was observed in both the presence and absence of extravesicular Na+ and was inhibited by diethylpyrocarbonate, which is consistent with the involvement of electrogenic, Na+-independent, H+-dependent peptide transport activity. Kinetic analysis indicated that peptide-dependent membrane potential depolarization is a saturable process ( Km,app ∼ 1.5 mmol L−1) and that within the 0.1–10 mmol L−1 peptide range a single carrier system is involved in the transport process. Our results suggest that a peptide transport activity, kinetically resembling the PepT1(Slc15A1)-type-mediated H+/peptide cotransport action, can be monitored in eel intestinal BBMV using an easy and inexpensive fluorescence assay. [ABSTRACT FROM AUTHOR]

The current best practice intensive culture of larval Atlantic cod includes feeding rotifers from onset of exogenous feeding until 25–30 days after hatching. These larvae grow considerably slower and develop higher frequencies of deformities than larvae reared in semi-extensive systems, using copepods as feed. The present study compares the micronutrient concentrations in rotifers with those of copepods, with the aim of identifying nutrients that may be limiting for normal growth and development of cod larvae. An additional criterion used is the nutrient requirements given for fish in general, by NRC (1993) , as nutrient requirements of cod remains to be determined. Rotifers were fed on four different diets, consisting of baker's yeast with cod liver oil (3.3 : 1 dry weight (DW)/v), baker's yeast with Algamac 2000TM (3.5 : 1 DW), baker's yeast with live algae Chlorella (4.1 : 1 DW), and Culture Selco 3000TM (CS). CS was a complete commercial diet for rotifers while the other diets are considered as based on raw ingredients. Compared with copepod nutrient levels, rotifers grown on yeast-based diets supplemented with either cod liver oil, Algamac 2000 or Chlorella were apparently sufficient for covering the requirements in cod larvae for all the B-vitamins, except thiamine. Rotifers cultured on the CS diet also had sufficient amounts of thiamine. Of the minerals, only calcium and magnesium were sufficient, using this criterion while iron was on the borderline. However, with reference to the requirements given for larger fish ( NRC 1993 ), only thiamine, vitamin A, manganese, selenium and perhaps copper, appear too low in the rotifers cultured without extra micronutrient supplementation. The other nutrients were present at levels intermediate between copepod and fish requirement levels. This study suggests that it is necessary to develop enrichment techniques to produce rotifers with sufficient amounts of all micronutrients. Such techniques will also be important tools for determining which nutrients are present at levels below the actual requirements in cod larvae. [ABSTRACT FROM AUTHOR]

The digestion, absorption and post absorptive metabolism of a radiolabelled triacylglycerol (TAG; triolein) and a free fatty acid (FFA; oleic acid), delivered by tube feeding, was studied in herring Clupea harengus larvae, using metabolic chambers and video analysis. In general, a large amount of the delivered lipid was evacuated. Most of the evacuation occurred between 2 and 6 h after tube feeding although a group of larvae responded by rapidly evacuating the lipid (>50% before 2 h). The volume of the tube-fed lipid affected its utilization. A small volume of triolein (9·2 nl, representing c. 6% of gut filling capacity) resulted in a lower proportion of fast evacuating larvae and improved utilization (lower evacuation and higher absorption: body incorporation and catabolism) compared with 50·6 nl ( c. 17% of gut filling capacity). Increases in the volume of tube fed triolein enhanced only marginally label absorption and led to a steep rise in evacuation. At a comparable high volume (50·6 nl), oleic acid, which does not require digestion, was better absorbed and less evacuated than triolein. The video observation of the lipid digestive process revealed a considerable gut contractile activity that appeared effective in processing the tube fed lipid. Also, the gut wall seemed very sensitive to physical pressure. Signs of chemical degradation during lipid digestion were also noted. The metabolic studies, together with video image analysis, suggested that the limiting step for the utilization of high dietary lipid levels may have been the lipid absorption into the enterocytes and transport into the body, rather than lipid digestion. The results support the notion that the rate of lipid digestion and absorption in fishes is slower than that of mammals. [ABSTRACT FROM AUTHOR]

Ontogenetic changes in the capacity of Senegalese sole (Solea senegalensis Kaup, 1858) larvae to digest and metabolise Artemia protein and amino acids (AA) were studied using 12, 22 and 35 days after hatching (DAH) larvae that were fed Artemia metanauplii radiolabelled with a [U-14C] protein hydrolysate. About 82% and 18% of the label was incorporated into the Artemia trichloroacetic acid (TCA) precipitate (mostly protein) and soluble (mainly free AA) fractions, respectively. The digestibility of Artemia was high at all tested ages, with label absorption varying between 77% and 83% at 24 h after feeding (HAF). A rapid digestion, absorption and catabolism of Artemia AA were noted, with most of the absorption into the body occurring during the first 3 HAF. Traces of label were already found in the metabolic-CO2 trap at 1 HAF. Furthermore, label was largely and almost immediately incorporated into the TCA precipitate fraction (mostly protein) of gut and body tissues. Slight differences were noted in diet utilization between larvae at different ages. At 12 DAH larvae had a lower catabolism and evacuation of the label, as well as the highest accumulation in the gut. However, except for the amount of catabolised label, the results were not significantly different from those for 35 DAH larvae. Moreover, no significant differences were found in the amount of label incorporated into the body, although it seemed to be higher in 12 DAH larvae. Taken together, these results reveal a higher absorption and a significantly higher retention of the absorbed label in 12 DAH larvae. In addition, 12 DAH larvae appeared to have a slower absorption of the label, which, in continuously feeding larvae, might result in overall lower food absorption efficiency. Therefore, it seems that young larvae have the ability to compensate for a possible lower digestive capacity with higher body retention of absorbed AA. This study confirms that sole larvae, even young stages, have a high capacity for digesting live preys. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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Abstract Folate mobilization from the yolk compartment during larval development was studied by analysing the folate concentration in whole body, embryo and yolk in a single batch of Atlantic halibut, Hippoglossus hippoglossus L., eggs and larvae that showed successful fertilization and development. There was a net loss of approx. 50% of folate from yolk during endogenous feeding. Further, only 23% of the decrease in yolk folate was retained in the larval body. The data suggest a need for folate for metabolic and growth purposes during embryogenesis of approximately 2 μ g g-1 weight gain. Relative to these data and published folate requirement for cold-water species, batches of egg from 16 Atlantic halibut brood fish contained variable and, for some batches, critically low levels of folate. This may constitute a potential problem for larval development until start feeding. [ABSTRACT FROM AUTHOR]

With the aim of improving the formulation of diets for early stages of marine fish, post-larval Hippoglossus hippoglossus (56 days after first feeding; 23 mg dry weight) were tube-fed liquid diets of radiolabelled L-(14C) free amino acids (FAA diet), peptides (PEPT diet) and protein (PROT diet), in order to compare the kinetics of transfer from gut into the liver and carcass. The test diets were prepared using equal concentrations of amino acids (AA) and fed as a single pulse (0.3 µl, 2.2 µg AA). The PROT diet consisted of methylated-14C-labelled (mainly lysine) bovine serum albumin (BSA), the PEPT diet was the PROT diet digested with trypsin and the FAA diet consisted of an amino acid mixture based on BSA composition with added 14C-lysine. The common labelling with 14C-lysine permitted a comparison of the three diets. Based on dissection and distribution of the tracer in each compartment, the FAA diet was almost completely absorbed 1 h after the tube-feeding; PEPT and PROT diets required more time before they were processed by the digestive tract. The FAA diet was absorbed about eight times as fast as protein and about six times as fast as peptides from the gut. A low retention of label in the liver for all diets at all sampling times suggests that the liver does not store the AA at these absorption rates. The FAA diet had a higher assimilation efficiency (about 90%) than the PEPT diet (about 12%) and PROT diet (about 32%). FAAs, thus, appear to be superior to protein and peptides as a dietary source of amino acids in post-larval Atlantic halibut. [ABSTRACT FROM AUTHOR]

At 7 days after first feeding (DAFF), the peptide hormone cholecystokinin (CCK) content (fmol individual−1) and the tryptic activity [μmol arginine-methyl-coumarinyl-7-amide (MCA) min−1 individual−1] per individual gut of Atlantic halibut Hippoglossus hippoglossus larvae were low: 0·2±0·1 and 0·14±0·10, respectively. Thereafter, both parameters increased with the increase in gut mass and reached 19·67±5·58 and 2·71±0·64 at 26 DAFF, respectively. Due to the small sample size, the dry mass (MG, mg) of the individual gut could not be determined accurately at 7 DAFF. At 13 DAFFMG represented 5·5% of whole body dry mass (MW, mg) while at 26 DAFF it had increased to 23%. The mass specific tryptic activity [μmol MCA min−1 per mg dry mass (M)] in the gut increased from 2·74±1·98 at 13 DAFF to 5·00±0·78 at 26 DAFF. There was more individual variation in the mass specific CCK content (fmol M−1) but no significant differences were found, although the data indicated an increase (from 23·38±11·26 at 13 DAFF to 36·27±8·96 fmol M−1 at 26 DAFF). At 7 DAFF the CCK content of the gut represented c. 2% of the whole body CCK content while it increased to c. 62% of the whole body CCK content at 26 DAFF. This demonstrates that it is necessary to separate neural and gastrointestinal sources of CCK in order to determine its alimentary role in fish larvae. Trypsin activity was only found in the gut compartment. In larvae aged 45 DAFF dietary proteins delivery into the gut by tube-feeding appeared to stimulate post-prandial secretion of CCK from the gut as well as stimulate pancreatic trypsin secretion, suggesting that both factors contribute to protein digestion. Copyright 2002 The Fisheries Society of the British Isles. Published by Elsevier Science Ltd. All rights reserved. [Copyright &y& Elsevier]

To specifically study the functional ontogeny of the digestive tract, larvae of Japanese flounder at various developmental stages were injected with liquid solutions using tube feeding in vivo. The survival in the stages tested was on average 93%. The injected solutions were almost completely transferred from the presumptive stomach, or stomach to the midgut within 10 min of injection. The passage to the hindgut in some cases started 10 min after injection and over 90% of the solution had passed from the midgut to the hindgut after 1 h. In most cases the hindgut seemed to be completely empty after 3 h. Two different mixtures of pH indicators with sensitivities in the alkaline (7.5 to 9) and acid (4 to 6) ranges respectively were used for assessment of pH in the various gut segments. The pH of the stomach remained alkaline during the larval period, but had fallen close to 4 during late metamorphosis, an indication of active HCl secretion and progressive stomach differentiation. In mid and late metamorphosing fish a rapid colour change in the pH indicator was observed once it had passed the pyloric sphincter. This demonstrates that there was also active secretion of alkaline fluid, most likely HCO3 −, from the pancreas into the pylorus lumen. A single injection of liquid solution of 14C-FAA showed that assimilation of FAA was high in all stages tested (79.5 ± 7.1%; SD; n=91). The presently reported data for Japanese flounder support earlier studies that FAA are absorbed with a high efficiency in the early stages of marine fish. [ABSTRACT FROM AUTHOR]

Free amino acids (FAA) and protein have been measured in whole laboratory-readed halibut larvae and on dissected individuals separated into yolk and body compartments. At hatching both FAA and protein are mainly located in the yolk compartment. During the first 12 d of the yolk-sac stage more than 70% of the FAA pool disappeared from the yolk without any significant changes in the yolk protein pool. This suggests different uptake mechanisms for FAA and protein from the yolk, and a sequential utilisation of the endogeneous reservoirs of free and protein amino acids in Atlantic halibut larvae. The data suggest that in the early yolk-sac stage FAA enter the embryo from the yolk and are utilised both for energy and protein synthesis. Later on when the free pool cannot fulfil the nutritional requirements, additional amino acids are recruited from yolk protein. Of the total amino acids (free + protein amino acids) present at hatching ca. 60% will be used as precursors for body protein synthesis while the remaining 40% are used as fuel in the larval energy metabolism. [ABSTRACT FROM AUTHOR]

Comments on the article "Assimilation of Dietary Free Amino Acids, Peptides and Protein in Post-Larval Atlantic Halibut," published in previous issue. Study conducted on methylated bovine serum albumin (BSA) using the protein and peptide test solutions. Demonstration of the study in vitro hydrolysis rates of methylated BSA by two mammalian cytosolic proteases; Verification of the results for assimilation of protein and peptides with the use of non-methylated compounds.