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

Effects of weaning American glass eels (Anguilla rostrata) with the formula diet on intestinal microbiota and inflammatory cytokines genes expression

This study aimed to investigate the effects of weaning American glass eels (Anguilla rostrata) with the formula diet on intestinal microbiota and the expression of inflammatory cytokines genes. During the feeding trial, the control group (termed IF group) was fed with initial feed for 34 days, and the experimental group (termed FF group) was fed with initial feed for 30 days, and then weaned with the formula diet for 4 days. After feeding trial, intestines were subjected to microbiota analysis using 16S rDNA high-throughput sequencing, and expression of three inflammatory cytokines genes in gut were examined by qPCR. The results indicated that the species richness and diversity of intestinal microbiota exhibited significantly higher in FF group than that in IF group (P < 0.05). At the phylum level, the core intestinal microflora was the same for two groups. The most abundant phylum was Firmicutes in IF group, while it was Proteobacteria in FF group. Five genera were significantly higher in the IF group compared with the FF group, and Bacillus was the most major enriched biomarker at genus level. Nine genera were significantly higher in the FF group compared with the IF group, and Acidovorax was the most major enriched biomarker. Weaning from initial feeding diet to formula feeding diet enhanced the expression levels of TNF-α and IL-8, and there was no significant change in IL-1β expression between the two groups. These findings would be very useful to improve the diet formulation for weaning stage of American glass eels.

Transcriptome Reveals the Effects of Early Weaning on Lipid Metabolism and Liver Health of Yangtze Sturgeon (Acipenser dabryanus)

The Yangtze sturgeon (Acipenser dabryanus) has recently been declared extinct in the wild, and artificial breeding is the only means to protect its germplasm resources, but it has difficulty in weaning (from live prey to artificial food). In this study, we first performed a histological observation, enzyme-activity determination, and transcriptome sequencing on the livers of juvenile Yangtze sturgeons, and we then cloned five critical genes of lipid metabolism according to the transcriptome-sequencing results. We designed a weaning experiment to analyze their expression levels during weaning. The results showed that the density of hepatocytes and the transaminase activity of the juveniles failed to wean. The differentially expressed genes were enriched significantly in the pathways involving steroid synthesis, amino acid metabolism, and pancreatic secretion. It was found that the mRNA level of the fatty acid-synthesis gene decreased, and the mRNA level of the lipolysis gene increased significantly during weaning. The results of this research indicated that weaning could affect the liver health of Yangtze sturgeon, and it could affect the liver lipid metabolism by inhibiting fatty acid synthesis and promoting lipolysis. This study enhances our understanding of the impact of weaning on the lipid metabolism in fish.

Co-modulation of Liver Genes and Intestinal Microbiome of Largemouth Bass Larvae (Micropterus salmoides) During Weaning

In recent years, largemouth bass have become one of the most commonly aquacultured species in China, however, its low survival rate during larval weaning has always been a bottleneck that has restricted industrial development. Understanding the changes in liver metabolism and intestinal microflora during the weaning of largemouth bass larvae can help to design better weaning strategies and improve survival. In this study, liver mRNA and intestinal microflora 16S rRNA genes were analyzed using high-throughput sequencing at the pre, mid, and post weaning stages [15, 30, 45 days post hatching; total length (cm) were 2.21 ± 0.12, 3.45 ± 0.21, 5.29 ± 0.33, respectively]. The transcriptome results revealed that the genes with increased expression were related to amino acid metabolism in the pre-weaning stage, but they were related to fatty acid metabolism in the post-weaning stage. A similar phenomenon was observed in the intestinal microflora where the dominant microbe Proteobacteria (relative abundance 56.32%) in the pre-weaning stage was gradually replaced by Firmicutes (relative abundance 62.81%) by the post-weaning stage. In addition, the three most important digestive enzymes (trypsin, lipase, and amylase) in the intestine were significantly decreased during the mid-weaning stage (P < 0.05), which was also true for some genes crucial to immune pathways in the liver. Overall, these findings showed that weaning in largemouth bass can cause changes in liver metabolism and intestinal microbial communities, which has improved our understanding of fish adaptation to changes in food sources during weaning.

An evaluation of mixed plant protein in the diet of Yellow River carp (Cyprinus carpio): growth, body composition, biochemical parameters, and growth hormone/insulin-like growth factor 1

The aim of this work is to evaluate the effects of dietary inclusion of mixed plant protein (MP) (rapeseed meal:cottonseed meal:peanut meal = 1:1:1) on growth, body composition, blood biochemical parameters, growth hormone/insulin-like growth factor 1, and relative non-specific immune response in Yellow River carp Cyprinus carpio. Five isonitrogenous and isoenergetic trial diets were formulated to replace fish meal at 0 (MP0, control), 25% (MP25), 50% (MP50), 75% (MP75), and 100% (MP100) mixed plant protein, respectively. The 25% mixed plant protein did not affect the weight gain, specific growth rate, and protein efficiency ratio, whereas these parameters were depressed by 50% and above mixed plant protein. The whole body protein content gradually decreased with increasing dietary MP; meanwhile, the whole body lipid content is the opposite. The MP75 and MP100 diets adversely affected the glucose level, total cholesterol value, alanine transaminase, and aspartate transaminase activity of serum. Fish fed MP75 and MP100 diets showed higher growth hormone level than that of MP0 diet; however, the insulin-like growth factor 1 level got the opposite result. The 50% and above inclusion of MP decreased lysozyme activity and increased malondialdehyde content. In conclusion, no more than 50% of fish meal could be replaced by mixed plant protein in diet. However, 50% and above inclusion of mixed plant protein in diet could depress the growth, insulin-like growth factor 1 level, and non-specific immune response, and significantly affect the whole body composition and serum biochemical parameters in Yellow River carp.