Amino acid absorption and protein synthesis responses of turbot Scophthalmus maximus to lysine and leucine in free,dipeptide and tripeptide forms

The study aimed to investigate the effects of crystalline Lys and Leu, Lys‐Leu dipeptide and Lys‐Leu‐Lys/Leu‐Lys‐Leu tripeptide, on growth, postprandial Lys and Leu concentrations, gene expression of peptide and amino acid (AA) transporters and related gene expression of protein synthesis pathway in turbot. Three diets (CAA, Di and Tri) contained Lys and Leu as free (Lys and Leu), dipeptide (Lys‐Leu) and tripeptide (Lys‐Leu‐Lys/Leu‐Lys‐Leu) forms, respectively. Improved growth was observed in the Di group compared with the CAA group. For peptide and AAs transporters, PepT1, B⁰AT1 and y⁺LAT2 mRNA levels were affected in proximal intestine by dietary treatments. Free Lys and Leu concentrations in the CAA group were significantly higher than that of the Di and Tri groups at 6 hr postfeeding in serum and at 2, 6 and 24 hr postfeeding in muscle. For protein synthesis pathway in muscle, Akt2, TOR and S6k1 gene expression were the highest in the Di group and the lowest in the CAA group, whereas MuRF1 relative expression was the highest in the Tri group. In conclusion, dietary Lys‐Leu dipeptide was utilized more efficiently than free Lys and Leu or Lys‐Leu‐Lys/Leu‐Lys‐Leu tripeptide for turbot by regulating AAs transport, postprandial AAs concentration and the synthesis of muscle proteins.     

Effect of fish meal replacement by plant protein blend on amino acid concentration,transportation and metabolism in juvenile turbot (Scophthalmus maximus L.)

The objective of the study was to evaluate the effects of incorporating plant protein blend in juvenile turbot (Scophthalmus maximus L.) diet on free amino acid (AA) concentration and the expression of genes related to peptide and AA transporters, key enzymes of AA metabolism and AA response (AAR) pathway. Fish were fed diets with fish meal (FM), or 400 g/kg FM replacement by plant protein blend for 9 weeks. Compared with the FM diet, PP40 diet did not affect plasma essential amino acid (EAA) concentration or AA metabolic enzymes gene in intestine, while it significantly upregulated all the detected peptide and neutral AA transporters gene. Results in muscle indicated that PP40 diet led to a great reduction of EAA concentrations and mRNA abundance of two kinds of AA transporters (SNAT2 and b^0,+AT), while it greatly increased the gene expression of L‐type and T‐type AA transporters (LAT2 and TAT1) and the enzymes of AA catabolism (BCKDH‐E2) and anabolism (asparagine synthetase). In addition, the expression of genes related to AAR pathway were all greatly stimulated by PP40 diet in muscle. Our results provide a molecular explanation for the change of tissues AA concentrations caused by plant protein in turbot, which maybe applicable for general carnivorous fish.     

Effect of low molecular weight fish protein hydrolysate on growth performance and IGF‐I expression in Japanese flounder (Paralichthys olivaceus) fed high plant protein diets

Seven isonitrogenous and isoenergetic experimental diets were formulated to investigate the effect of low molecular weight fish protein hydrolysate (FPH) in diets on growth performance, feed utilization and liver IGF‐I mRNA levels in Japanese flounder (38.80 ± 1.11 g) fed with high plant protein diets. Fish meal protein was, respectively, replaced by 6% (FPH6), 11% (FPH11), 16% (FPH16), 21% (FPH21), 26% (FPH26) FPH of total dietary protein. FPH diets contained a constant high level of plant protein (690 g kg^?1) from soybean meal. As a positive control diet, FM2 contained about 590 g kg^?1 plant protein and 410 g kg^?1 fish meal protein, while negative control diet FM1 contained about 690 g kg^?1 plant protein and 310 g kg^?1 fish meal protein. The expression levels of liver IGF‐I mRNA were evaluated using real‐time PCR normalized against the 18S rRNA gene. The results showed that moderate low molecular weight FPH (FPH11) improved growth performance and protein retention. Fish fed with FPH11 and control diet FM2 had similar growth and feed utilization, while high‐level low molecular weight FPH did not improve growth performance and protein retention, and depressed liver IGF‐I mRNA expression in Japanese flounder.     

1H NMR‐based metabolomics studies on the effect of size‐fractionated fish protein hydrolysate,fish meal and plant protein in diet for juvenile turbot (Scophthalmus maximus L.)

This study was designed to evaluate changes in the metabolic profile of liver and muscle of turbot (Scophthalmus maximus L.) fed fishmeal‐based diet, diets containing size‐fractionated fish protein hydrolysate and plant protein‐based diet using ¹H NMR‐based metabolomics approach combined with the growth. Fish protein hydrolysate (FPH) was obtained by enzymatic treatment, permeate fraction was obtained as UF by ultrafiltered step, and retentate fraction was retained as RF. FM diet contained fish meal used as a single protein source. Four other diets (PP, UF, FPH and RF) contained 180 g kg^?1 diet fish meal. 54, 55 and 55 g kg^?1 dry diet UF, FPH and RF were supplemented to UF, FPH and RF diets. All diets were formulated to be isolipidic and isonitrogenous fed to five triplicate groups of turbot (16.05 ± 0.03 g) for 68 days. O‐PLS‐DA in FM versus UF, FM versus FPH, FM versus RF and FM versus PP resulted in a reliable model for muscle and liver tissue, while O‐PLS‐DA in UF versus FPH and UF versus RF only showed metabolites changes in liver tissue. Results indicated that metabolite changes among the different treatments were consistent with the growth tendency.     

大菱鲆利用水解鱼蛋白和牛蛙蛋白的差异

为探究大菱鲆对不同来源水解蛋白的利用效率,实验选取太平洋狭鳕和牛蛙下脚料为蛋白来源,分别制备水解鱼蛋白和水解牛蛙蛋白,以初始体重为(8.00±0.01) g的大菱鲆为研究对象,进行为期56 d的养殖实验。实验设2个对照组,正对照组(PC)鱼粉含量为35.0%,负对照组(NC)鱼粉含量为26.5%;设2个实验组,水解鱼组(FPH)为26.5%的鱼粉和8.0%的水解鱼蛋白,水解牛蛙组(BPH)为26.5%的鱼粉和9.5%的水解牛蛙蛋白。结果显示,FPH组的终末体重、增重率和特定生长率显著高于BPH组和NC组,与PC组无显著差异。摄食6 h后,食糜必需氨基酸中赖氨酸、精氨酸、苏氨酸和缬氨酸在BPH组的含量显著高于PC组;多数非必需氨基酸在BPH组含量最高,但无显著差异。质子偶联氨基酸转运载体PAT1和小肽转运载体PepT1的mRNA表达量分别在FPH组和BPH组都显著高于PC组和NC组;碱性氨基酸转运载体CAT1和y⁺L型氨基酸转运载体y⁺LAT2的mRNA表达量在各处理组中无显著差异。研究表明,在饲料中添加鳕和牛蛙蛋白水解物均能提高大菱鲆的生长性...     

日粮中鱼蛋白水解物对黄颡鱼生长、体成分和血清生理指标的影响

为了探讨鱼蛋白水解物对黄颡鱼生产性能的影响,以日本鳀粉为对照,以实用型黄颡鱼饲料配方模式为基础开展实验:1以30.5%鱼粉为对照(FM),在相同配方模式下,以6%鱼蛋白水解物(MPH6)替代20%的鱼粉;2以30.5%鱼粉为对照(FM),在无鱼粉日粮中分别添加3%(FPH3)、6%(FPH6)、12%(FPH12)鱼蛋白水解物;共设计5组等氮等能实验日粮,在池塘网箱中养殖黄颡鱼[初始体质量(30.08±0.35)g]60 d。结果显示:与FM相比,FPH12在SGR、FCR、PRR和FRR方面均无显著差异,而MPH6、FPH3、FPH6组SGR降低了15.45%~24.39%,FCR升高了32.14%~42.86%,MPH6、FPH6差异显著,在PRR和FRR方面,MPH6、FPH3、FPH6组PRR降低了21.11%~27.78%,MPH6组FRR降低了41.51%;全鱼水分、粗蛋白、粗脂肪和灰分各组间差异不显著,FPH3、FPH6、FPH12肌肉多种游离氨基酸水平显著高于FM,其中Thr、Val、His与其在日粮中的水平显著相关;FPH6组HSI显著低于FM,鱼蛋白水解物对CP、VSI、肠体比的影响不显著;血清AST、ALT、HDL、LDL、TP、CHOL、TG无显著差异,FPH3组ALB显著低于FM。研究表明:黄颡鱼日粮中,12%鱼蛋白水解物(干物质)与30.5%鱼粉在生长速度、饲料效率、血清生理指标等方面具有一定的等效性;过高的植物蛋白日粮影响了黄颡鱼的生产性能;饲喂鱼蛋白水解物日粮使黄颡鱼肌肉游离氨基酸的含量升高,特别是呈味氨基酸的含量增加。     

Taurine alone or in combination with fish protein hydrolysate affects growth performance,taurine transport and metabolism in juvenile turbot (Scophthalmus maximus L.)

The study was conducted to investigate the effects of taurine (Tau) alone or in combination with fish protein hydrolysate (FPH) on growth performance, the expression of Tau transporter (TauT) and metabolic profile in juvenile turbot. FM, FPH0, FPH0+T, FPH10 and FPH10+T diets, respectively, contained 300, 150, 150, 80, and 80 g/kg fishmeal. FPH10 and FPH10+T diets contained 62 g/kg FPH. FPH0+T and FPH10+T diets were, respectively, prepared by supplementing the FPH0 and FPH10 diet formulations with 8 g/kg Tau. Specific growth rate was the highest in FM group and the lowest in FPH10 group. TauT mRNA levels in fish fed Tau supplemented diets were significantly lower than that in Tau unsupplemented diets. NMR‐based metabolomics analysis showed that Tau contents in liver of FPH0+T and FPH10+T were significantly higher than that of FM, FPH0 and FPH10. In muscle, Tau contents were significantly decreased in the FPH10+T versus FPH0 and the FPH10+T versus FPH10 comparisons. In conclusion, 62 g/kg FPH to replace fishmeal may not affect Tau synthesis, transport and metabolism. However, Tau supplemented alone or in combination with a certain level of FPH could reduce the requirement for Tau synthesis and transport and increased Tau levels in muscle and liver.     

Nutrient utilization in Atlantic salmon (Salmo salar L.) fed increased levels of fish protein hydrolysate during a period of fast growth

The present work was designed to study whether changes in dietary protein quality by means of partial inclusion of fish protein hydrolysate (FPH) would alter fish growth, feed utilization, protein retention and metabolism and fish health in general. FPH was produced after hydrolysing whole minced herring using the industrial enzyme Alcalase®. The dietary protein source, low‐temperature‐dried (LT) fishmeal nitrogen was exchanged with FPH nitrogen at six levels of inclusion ranging from 0 to 300 g kg^?1. The experimental diets were fed to post‐smolt (1+) Atlantic salmon (Salmo salar), with mean initial weight of 174 g for a period of 68 days. All diets were iso‐nitrogenous, iso‐energetic and contained the same amount of amino acids. Fish fed medium inclusion of FPH (180–240 g kg^?1) showed a tendency to have higher feed intake than fish fed lower and higher levels of FPH inclusions. Significant higher individual specific growth rates were present in fish fed diets with 180 and 240 g kg^?1 FPH when compared with those fed 300 g kg^?1. Feed conversion ratio increased significantly (R² = 0.61) and protein efficiency ratio decreased significantly (R² = 0.59) in fish fed increased levels of FPH. Further, apparent digestibility of crude protein and the amino acids arginine, lysine, methionine and phenylalanine increased significantly with increased dietary inclusion of FPH. Plasma free amino acids, ammonium and urea indicated that FPH amino acids was absorbed earlier and nonsynchronously, and may thus be more prone to be catabolized than in those fish fed the less solubilized protein. FPH inclusion did not have an impact on fish health, as evaluated by haematology and clinical parameters.     

Application of different types of protein hydrolysate in high plant protein diets for juvenile turbot (Scophthalmus maximus)

A 10‐week feeding experiment was conducted to investigate the effects of different types of dietary protein hydrolysate (PH) on growth performance, body composition, trypsin activity and serum transaminase of juvenile turbot. Four high plant protein diets contained different types of PH, fish PH (FPH), yeast PH (YPH), pig blood PH (PBPH) and soy PH (SPH), replacing 10% fishmeal of the basal diet. The basal diet with 30% fishmeal and no PH was used as the control diet (C). Each diet was assigned to triplicate groups of 30 fish. The specific growth rate (SGR) was not significantly different between groups C and FPH, but groups C and FPH showed significantly higher SGR than other groups. The feed efficiency ratio (FER) and protein efficiency ratio (PER) were not significantly different among groups C, FPH and YPH, but groups PBPH and SPH showed significantly lower FER and PER than groups C and FPH. Group PBPH showed significantly higher hepatosomatic index than other groups except YPH. Fish fed YPH showed significantly lower whole‐body protein content, but significantly higher whole‐body lipid content than fish fed diets C, FPH and PBPH. The activities of serum GOT and GPT in group PBPH were higher than those in groups C, FPH and YPH. These results suggested that when used at a low level in high plant protein diets for juvenile turbot, FPH is a good alternative protein source and YPH also has the application potential, but PBPH and SPH can cause negative impacts on fish growth and health.     

Dietary krill hydrolysates affect the expression of growth‐related genes in juvenile turbot (Scophthalmus maximus L.)

A 10‐week feeding experiment in indoor flow‐through seawater system was conducted to investigate the effects of dietary krill hydrolysate on the expression of growth‐related genes in juvenile turbot (Scophthalmus maximus L.; initial body weight 9.45 ± 0.01 g). Three isonitrogenous and isolipidic experimental diets containing high plant protein were formulated to contain 0 (control), 50 g/kg (LKH) and 100 g/kg (HKH) krill protein hydrolysate (KH) to replace fishmeal, respectively. Triplicate groups of 30 fish were fed for 10 weeks to apparent satiation twice daily. At the end of the feeding trial, the mRNA expressions of insulin‐like growth factor (IGF‐1) gene in liver, peptide transporters (PepT1) gene in pyloric caeca and proximal intestine and neuropeptide Y (NPY) gene in brain in all groups were determined. IGF‐1, PepT1 and NPY expression levels in HKH group were significantly increased compared with those of LKH and control (p < 0.05), which was consistent with the SGR, feed efficiency, PER and PPV. These results indicated that dietary 100 g/kg krill hydrolysate could improve growth performance and upregulate the mRNA expression of IGF‐1, PepT1 and NPY genes in juvenile turbot.     

Blue mussel meal as feed attractant in rapeseed protein‐based diets for turbot (Psetta maxima L.)

Antinutritional factors in rapeseed products have been identified to reduce feed palatability and growth performance of turbot. Therefore, we evaluated the potential of blue mussel (Mytilus edulis L.) meal as feed attractant in rapeseed protein‐based diets for turbot. Triplicate fish groups received isonitrogenous and isocaloric diets with fish meal (FM) protein replacements of 50% or 75% by rapeseed protein concentrate (RPC 50, RPC 75). These diets were supplemented with 0%, 2%, 4% or 8% of blue mussel meal. In contrast with RPC 50 diets, fish fed with RPC 75/0 showed significantly reduced daily feed intake (DFI) and specific growth rate (SGR). With increasing mussel meal inclusion, RPC 75 diets resulted in increased DFI and SGR, suggesting mussel meal as attractant in rapeseed protein‐based diets for turbot. Feed conversion was unaffected by any treatment. Protein productive value and apparent digestibility coefficients were unaffected by either RPC or mussel meal inclusion. With regard to the whole body composition, no differences in crude protein, crude lipid and ash content could be determined. Haematological characteristics were unaffected among the treatments indicating good nourished and unstressed fish. In conclusion, we demonstrated that the utilization of blue mussel meal improved the palatability of rapeseed protein‐based diets for turbot.     

The effect of ultrafiltered fish protein hydrolysate level on growth performance,protein digestibility and mRNA expression of PepT1 in juvenile turbot (Scophthalmus maximus L.)

The intention of the study was to investigate the effect of ultrafiltered fish protein hydrolysate (UF) level on growth, feed utilization, apparent digestibility coefficients and proximal intestine peptide transporter 1 (PepT1) mRNA level for juvenile turbot (Scophthalmus maximus L.). Experimental diets (UF‐0, UF‐5, UF‐10, UF‐15 and UF‐20) were prepared containing about 68% plant protein, and fish meal protein was, respectively, replaced by 0%, 5%, 10%, 15% and 20% UF of dietary protein. Diet PP contained about 78% plant protein, and diet CAA contained about 10% crystalline amino acid mixture. All diets were fed to seven triplicate groups of turbot (initial weight 16.05 ± 0.03 g) for 68 days. Fish fed diet UF‐10 had an increasing tendency in growth compared with diets contained UF, while dietary UF level was not significantly correlated with specific growth rate and feed intake. Feed efficiency, protein efficiency ratio and protein productive value significantly correlated with dietary UF level, and fish fed diets contained low‐level UF had higher digestibility than that diets UF‐0, PP and CAA. There was a decreasing tendency in PepT1 expression level with dietary UF level. The results indicated that low‐level UF showed a positive effect on growth and feed utilization in juvenile turbot.     

The effect of dietary protein replacement by crystalline amino acid on growth and nitrogen utilization of turbot Scophthalmus maximus juveniles

A study was conducted to evaluate the effect of partial replacement of dietary fish meal by crystalline amino acids on growth performance, feed utilization, body composition and nitrogen utilization of turbot juveniles.

Four diets were formulated to be isolipidic (12% DM) and isonitrogenous (8% DM). A fish meal based diet was used as control. In the experimental diets, a crystalline amino acid (AA) mixture was used to partially replace fish meal, corresponding to a non-protein nitrogen content of 19, 37 and 56%, respectively (diets 19AA, 37AA and 56AA, respectively). The overall amino acid profile of the experimental diets resembled that of the whole-body protein of turbot. Each experimental diet was fed to triplicate groups of 20 fish (initial body weight of 31.8 g) twice daily to apparent satiation for 42 days. During the trial water temperature averaged 18 °C.

Final body weight, weight gain (g kg ABW^− 1 day^− 1) and specific growth rate were not different between the control and 19AA diet but significantly decreased with the increase of crystalline-AA inclusion from 19 to 56%. Feed intake and feed efficiency of fish fed the control and diet 19AA were similar and significantly higher than those of fish fed the 56AA diet. At the end of the growth trial, there were no significant differences in whole-body composition among groups. Hepatosomatic index was also unaffected by dietary treatments.

Nitrogen retention (g kg ABW^− 1 day^− 1) of fish fed the control and the 19AA diets were similar and significantly higher than that of fish fed the other diets. Expressed as a percentage of the nitrogen intake, N retention was significantly higher with the control than with the 37AA and 56AA diets.

Daily ammonia excretion (mg kg ABW^− 1 day^− 1) of fish fed the control diet was significantly higher than that of fish fed the 37AA and 56AA diets, while daily urea excretion (mg kg ABW^− 1 day^− 1) did not significantly differ among treatments. Non-fecal nitrogen (ammonia + urea) excretion (mg kg ABW^− 1 day^− 1) was significantly higher for fish fed the control diet than in those fed the 37AA and 56AA diets. However, as percent of N intake, ammonia excretion and non-fecal N excretion were significantly higher in fish fed the 56AA diet than in those fed the control and 19AA diets.

Specific activity of glutamate dehydrogenase, alanine and aspartate aminotransferases did not significantly differ among experimental groups.

In conclusion, in diets with an overall amino acid profile resembling that of the whole-body protein of turbot, crystalline-AA may replace 19% of dietary protein without negatively affecting growth performances or feed utilization efficiency. However, higher protein replacement levels of protein-bound-AA by crystalline-AA severely depressed growth performance.     

Modelling the effects of dietary methionine level and form on postprandial plasma essential amino acid profiles in rainbow trout (Oncorhynchus mykiss)

Aquafeed formulation is susceptible to affect amino acid (AA) availability for metabolic functions. Statistical models were applied to quantify the effect of dietary methionine level (from 6.01 to 16.17 g kg^?1 dry matter) and form (free, coated or bound) on postprandial concentrations of plasma essential amino acid (EAA) in rainbow trout. Twelve diets were formulated with pea and soya protein concentrate or fish meal as the main protein ingredients and were supplemented or not with increasing amount of either crystalline or agar‐coated methionine. Fish were acclimatized to one of the 12 diets for 6 weeks before postprandial plasma sampling (six sampling points up to 36 h, seven fish each time), further analysed for EAA content. Using generalized additive models, we show that (i) dietary methionine level and form explained 74% postprandial methionine plasma variations and that (ii) the methionine dietary form and plasma concentrations significantly affected the plasma concentrations of the other EAAs. Finally, linear model revealed a positive relationship (R² > 0.9) between plasma concentrations of the three branched‐chain AAs under the present experimental conditions. The results obtained add new information on the dietary effects on EAAs in the plasma availability and the interactions between them.     

The role of dietary methionine concentrations on growth,metabolism and N‐retention in cobia (Rachycentron canadum) at elevated water temperatures

This study determined impacts of dietary methionine concentrations at two temperatures on growth, feeding efficiency and N‐metabolites in juvenile cobia. Methionine concentrations of the experimental diets were deficient (M9; 9 g/kg), sufficient (M12; 12 g/kg) and surplus (M16, 16 g/kg). Water temperature was normal (30°C) or elevated (34°C). Twenty cobia in triplicate tanks were fed the experimental diets for 6 weeks. Both methionine and temperature affected cobia's growth and feeding efficiency. Cobia fed M9 performed lower than the fish fed M12 and M16 diets. Additionally, cobia reared at 34°C performed poorer than at 30°C, probably due to lower voluntary feed intake in the fish reared at 34°C. Protein efficiency ratio and protein productive value in cobia fed M9 diet were less than M12 or M16 diets. This was confirmed with the improved retentions of indispensable amino acids (AAs). No interactions between methionine and temperature were observed in growth and protein accretion. At 30°C, CF improved, while HSI and VSI declined upon methionine supplementation levels. Of which an interaction between temperature and methionine was present. Plasma, muscle and liver free AA and N‐metabolites were affected by methionine and temperature. Furthermore, temperature affected cobia's lipid class composition, resulting in increased phospholipids and cholesterol at 34°C.     

Fish protein hydrolysate in diets of turbot affects muscle fibre morphometry,and the expression of muscle growth‐related genes

The study was conducted to investigate the effects of fish protein hydrolysate (FPH) in diets for turbot on growth performance, muscle fibre morphometry, and the expression of muscle growth‐related genes. A control diet (FPH0) contained 0 g/kg FPH, and four experimental diets were formulated replacing fishmeal with FPH at levels of 45 (FPH4.5), 120 (FPH12), 180 (FPH18) and 300 (FPH30) g/kg. Fish fed the FPH12 and FPH18 diets had higher specific growth rate (SGR) than fish fed the FPH0 diet (p < .05), and a quadratic regression was found between SGR and dietary FPH level (p = .001, R² = .677). Cross‐section area (CSA) and the length of sarcomere in the FPH12 group increased compared with the control group (p < .05), and a quadratic regression was observed between CSA and dietary FPH level (p = .006, R² = .574) and between sarcomere length and dietary FPH level (p = .018, R² = .788). An appropriate level of FPH down‐regulated myostatin 2 gene expression and up‐regulated proliferating cell nuclear antigen gene expression, while the expression of myogenic regulatory factors was not affected by dietary treatments (p > .05). To conclude, an appropriate level of FPH may improve muscle growth by regulating the expression of muscle growth‐related genes, and muscle microstructure and ultrastructure.     

Effect of dietary fish protein hydrolysate on growth,feed utilization and IGF‐I levels of Japanese flounder (Paralichthys olivaceus)

This study was conducted to investigate the effect of fish protein hydrolysate on growth performance, insulin‐like growth factor I (IGF‐I) levels and the expression levels of liver IGF‐I mRNA in juvenile Japanese flounder (Paralichthys olivaceus). Fish hydrolysate was produced by enzymatic (alcalase and flavourzyme) treatment and size‐fractionated by ultrafiltration. The permeate after ultrafiltration (UF) and the non‐ultrafiltered fish hydrolysate were tested as feed ingredients using high plant protein diets. Fish meal was used in the control diet (FM). The feeding trial lasted for 60 days, and fish fed with 37 g kg^?1 UF showed the best growth, feed efficiency, digestibility and protein utilization. Plasma IGF‐I level was examined with radioimmunoassay, and the expression levels of liver IGF‐I mRNA were evaluated using real‐time PCR normalized against the 18S rRNA gene. Plasma IGF‐I levels were significantly increased by inclusion of fish protein hydrolysate. Liver IGF‐I mRNA expression was significantly higher in fish fed with 37 g kg^?1 UF diet than fish fed with control diet. The results indicated that small molecular weight compounds from fish protein hydrolysate showed a positive effect on growth and feed utilization in juvenile Japanese flounder. Dietary fish protein hydrolysate could improve plasma IGF‐I levels and liver IGF‐I mRNA expression in Japanese flounder.     

The effect of ultrafiltered fish protein hydrolysate levels on the liver and muscle metabolic profile of juvenile turbot (Scophthalmus maximus L.) by 1H NMR‐based metabolomics studies

A ¹H NMR‐based metabolomics approach was to explore the effect of ultrafiltered fish protein hydrolysate (UF) levels on the liver and muscle metabolic profile of juvenile turbot (Scophthalmus maximus L.). Fish protein hydrolysate (FPH) was produced from by‐products by enzymatic treatment, and UF was obtained by diluting FPH followed filtration. Fish were fed diets containing fish meal protein, which was, respectively, replaced by UF protein 0, 50, 100, 150 and 200 g kg^?1 of dietary total protein (UF‐0, UF‐5, UF‐10, UF‐15 and UF‐20) for 68 days. OPLS‐DA of liver and muscle showed that high levels of UF in diets may lead to corresponding tissue metabolites changes. In liver tissue, changing metabolites included dimethylamine, N,N‐dimethylglycine, valine, isoleucine, leucine, arginine and alanine and were mainly involved in choline metabolism and amino acid metabolism. For muscle tissue, changing metabolites included lactate, alanine, proline, fumarate, tyrosine, histidine, cystathionine and taurine. And the metabolites were mainly involved in glycolysis and gluconeogenesis, proline metabolism and taurine metabolism. ¹H NMR‐based metabolomics is a useful approach to investigate different levels of UF on metabolic profile in liver and muscle tissues combined with the growth.     

The differences in postprandial free amino acid concentrations and the gene expression of PepT1 and amino acid transporters after fishmeal partial replacement by meat and bone meal in juvenile turbot (Scophthalmus maximus L.)

Meat and bone meal (MBM) is a high‐quality alternative protein source used to replace fishmeal (FM). However, the molecular mechanisms of over‐substituted FM by MBM resulted in growth reduction are still not clear. The objective of the study was to evaluate the effect of FM replacement by MBM on the concentration of postprandial free amino acid (FAA) and mRNA abundance of peptide and amino acid transporters in juvenile turbot (Scophthalmus maximus L.). Fish were fed with FM diet (60% FM), MBM diet (33% FM + 34.2% MBM) and MBM + AA diet (MBM diet with essential amino acid (EAA) added to match the AA profile of FM) for 30 days. Results showed that compared with the FM diet, MBM diet led to a reduction in FAA concentration peak values in plasma and muscle. MBM + AA diet significantly elevated the peak values of FAA concentrations to FM diet level in plasma, but not in muscle. Furthermore, compared with FM diet, MBM diet significantly increased gene expression of PepT1 and major amino acid transporters in intestine, whereas MBM diet greatly downregulated gene expression of T‐type amino acid transporter‐1, system ASC amino acid transporter‐2 and cationic amino acid transporter‐2 in muscle. Supplemented EAA did not ameliorate these different effects in intestine and muscle. Overall, this study provided a comprehensive explanation for the relationship between diet, FAA concentrations and AA transportations, which provides a molecular basis for further using MBM to replace FM in aquafeeds.