Search

The study was primarily designed to analyze the effect of exogenous protease K on growth performance, amino acid metabolism, digestion and absorption capacities, expression of amino acid transporters related genes and proteins in intestine of sub-adult grass carp (Ctenopharyngodon idella). Six experimental diets with protease K (0, 3000, 6000, 9000, 12,000 and 15,000 U/kg) were fed to 450 grass carp (619.51 ± 0.54 g) for 60 days. The results indicated that the highest value of final body weight, percent weight gain (PWG), specific growth rate, protein efficiency ratio, activity of hepatopancreas glutamate-oxaloacetate transaminase and glutamate-pyruvate transaminase, and the lowest concentration of plasma ammonia were observed in groups with protease K of 6000 and 9000 U/kg. Meanwhile, the groups with 6000 and 9000 U/kg protease K exhibited the highest activities of digestive and brush border membrane enzymes in the three intestinal segments, as well as the highest value of intestinal somatic index and intestinal length index. The highest concentration of free amino acid in the serum and the lowest in intestine were observed in groups with supplementation of protease K 6000 and 9000 U/kg, which might be related to the up-regulated mRNA level and protein expression of intestinal amino acid transporters (SLC1A5, SLC7A6, SLC1A3 et al) in these groups. Furthermore, optimal levels of protease K up-regulated the mRNA levels of target of rapamycin (TOR), S6 kinase 1 (S6K1), and protein expression of TOR and phosphorylation TORSer2448, but reduced the mRNA level of 4E binding protein 1 (4EBP1). In summary, optimal levels of exogenous protease K was found to be conducive to facilitate the improvement of growth performance probably via enhancing digestion and absorption capacity, and utilization of amino acid in sub-adult grass carp. In addition, using quadratic regression analysis of PWG and alkaline phosphatase in the midgut, the optimum addition of protease K for the sub-adult grass carp were noted to be 7380.82 and 7406.44 U/kg, respectively. Graphic summary: The possible process of exogenous protease K improving the growth performance of grass carp. FAA: free amino acid; AAT: amino acid transporter; CK: creatine kinase; AKP; alkaline phosphatase; γ-GT: γ-glutamyl transpeptidase. [Display omitted] • Protease K enhanced the growth performance and amino acid utilization of fish. • Appropriate protease K improved digestion and absorption capacity of fish. • Appropriate protease K upregulatd amino acid transporters expression probably via the TOR signaling pathway. [ABSTRACT FROM AUTHOR]

An 82 days' feeding trial was conducted to investigate the potentiality of fishmeal replacement with the composite mixture of shrimp hydrolysate and plant proteins in diets for largemouth bass. Triplicate groups of fish were fed the experimental diets with 45 (FM45, the control), 40 (FM40), 35 (FM35), 30 (FM30) and 25% (FM25) fishmeal twice daily. Results showed that the mixture of protein sources can reduce the use of fishmeal to 30% with obvious improvement of growth performance, whereas higher substitution level (FM25 group) inhibited growth slightly compared to the control group. The fishmeal replacement supported significantly higher apparent digestibility coefficients (ADC) of protein and amino acids compared to the control, which may be partly involved in the activation of amino acid-sensing target of rapamycin (TOR) pathway. Consistently, the replacement of fishmeal elevated the expression of TOR and ribosomal protein S6, but significantly decreased the expression of eukaryotic translation initiation factor 4E (eIF4E)-binding protein 1 (4E-BP1), and this confirmed the activation of TOR pathway induced by the fishmeal replacement in the present study. In summary, appropriate fishmeal replacement with composite mixture of shrimp hydrolysate and plant proteins can activate the TOR pathway and improve the growth performance of largemouth bass, and fishmeal content in the diets for largemouth bass can be reduced to 30% with the compound proteins. • Shrimp hydrolysate was used to substitute the use of fishmeal in diets for largemouth bass. • The composite proteins containing shrimp hydrolysate can reduce the fishmeal content to 30% in diets for largemouth bass. • The fishmeal replacement with mixed protein affected the TOR pathway at the transcriptional level. [ABSTRACT FROM AUTHOR]

Our previous study showed that dietary soybean saponin (SA) consumption reduced growth performance and damaged the morphology of the intestinal mucosa in zebrafish (Danio rerio). Glutamine (Gln) plays an important role in ameliorating intestinal atrophy. Therefore, the present study tested the hypothesis that dietary alanine-glutamine (Ala-Gln) supplementation ameliorates the growth suppression and intestinal injury induced by dietary SA in zebrafish. Five experimental diets were prepared by supplementing the basal diet with either SA at 0, 5 or 10 g/kg, and Ala-Gln at 0 or 10 g/kg, with adjustment of Ala-Ala to maintain equal nitrogen levels among all diets. Fish with average initial body weight of (9.00 ± 0.13) mg were fed five diets for 4 weeks. The growth performance increased significantly and intestinal morphology was improved by supplementation of Ala-Gln at 10 g/kg. Ala-Gln supplementation improved growth via regulation of the growth hormone (GH)–insulin like growth factor I (IGF I) axis. The experimental diets significantly affected the mRNA expression levels of amino acid and peptide transporters. Dietary Ala-Gln upregulated the mRNA expression levels of glycolysis and fat synthesis-related factors, significantly reduced the activity of AMP-activated protein kinase (AMPK), but stimulated the activity of target of rapamycin (TOR). Overall, Ala-Gln might be broken down into free amino acids, with Gln being absorbed by the intestinal mucosa cells. Dietary Ala-Gln supplementation ameliorated the intestinal injury induced by SA, and promoted the breakdown of carbohydrates and fats for energy, thereby improving the growth performance of zebrafish. • Dietary Ala-Gln ameliorated the intestinal injury induced by SA. • Ala-Gln improved growth via regulation of the GH–IGF-I axis. • Dietary Ala-Gln promoted the breakdown of carbohydrates and fats for energy. [ABSTRACT FROM AUTHOR]