Research
| Title： | Effects of dietary chrysophyte (Poterioochromonas malhamensis) rich in beta-glucan on the growth performance, intestinal health, lipid metabolism, immune gene expression, and disease resistance against Aeromonas salmonicida in juvenile rainbow trout (Oncorhynchus mykiss) |
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| First author： | Liu, Yang; Chang, Hongmiao; Han, Danxiang; Lu, Shaoxia; Lv, Weihua; Guo, Kun; Wang, Changan; Li, Shaowu; Han, Shicheng; Liu, Hongbai |
| Journal： | AQUACULTURE |
| Years： | 2022 |
| DOI： | 10.1016/j.aquaculture.2022.738589 |
| Abstract： | An eight-week growth trial was conducted to investigate the effects of different dietary levels (0%, 2%, 4%, and 8%) of chrysophyte (Poterioochromonas malhamensis) rich in water-soluble beta-glucan on the growth performance, intestinal health, lipid metabolism, immune responses, and disease resistance of juvenile rainbow trout (Oncorhynchus mykiss). At the end of the feeding trial, no significant difference in weight gain was observed between the non-supplemented control and moderate doses (2% and 4%), but decreased weight gain was found at the highest dose (8%) of P. malhamensis compared with the control group. The survival rate in each group was above 97%, with no significant differences between groups. P. malhamensis supplementation in diets changed bacterial diversity and altered the composition of intestinal microbes. In particular, the abundance of the beneficial bacteria Lactobacillus was increased with moderate doses, and the abundance of the pathogenic bacteria Acinetobacter was enhanced with the highest dose (8%) of P. malhamensis. The mRNA expression levels of tight junction protein genes (e.g., claudin-1, occludin, and tricellulin) were also increased after P. malhamensis supplementation. Meanwhile, P. malhamensis supplementation altered lipid metabolism, including reduced crude lipid content in whole fish and decreased CHO, TG, HDL, and LDL in the serum of the highest dose group. Several free fatty acids, including C14:0, C16:1, and C18:3n3, were also reduced in the liver in the highest dose group. In contrast, P. malhamensis induced mRNA expression of the immune-related genes c3, c4, and c5 and the upregulation of mRNA expression in pro-inflammatory cytokines (IL1 beta and IL8) in the highest dose group. After the 8-week feeding trial, fish were intraperitoneally injected with a bacterial pathogen, Aeromonas salmonicida. The survival rate increased by 14% in the moderate dose groups and decreased by 11% in the highest dose group compared with the control. In addition, the mRNA expression levels of cytokines and complement system genes were differentially influenced by the challenge test, with an increase of c7 in the moderate dose groups, a decrease of c3 in the highest dose group, a reduction of IL1 beta in the moderate dose groups, and an upregulation of the anti-inflammatory cytokine IL10 in the moderate dose groups. In conclusion, the dietary inclusion of P. malhamensis at optimum levels (2-4%) efficiently regulated lipid metabolism, improved intestinal health, heightened immune responses, and increased resistance to A. salmonicida in juvenile rainbow trout. P. malhamensis could be a good source of beta-glucan for fish. |
