Effects of Dietary Bio-Fermented Selenium Supplementation on Growth, Immune Performance, and Intestinal Microflora of Chinese Mitten Crabs, Eriocheir sinensis

Abstract

Selenium is a vital trace mineral that is crucial for maintaining regular biological processes in aquatic animals. In this study, a four-week dietary trial was carried out to assess the impact of bio-fermented selenium (Bio-Se) on the growth and immune response of Chinese mitten crabs, Eriocheir sinensis. The crabs were randomly allocated to five dietary treatment groups, each receiving a different dose of Bio-Se. The doses included 0, 0.3, 0.6, 1.5, and 3.0 mg/kg and were accurately measured in basal diet formulations. The results showed the weight gain rate (WGR), specific growth rate (SGR), and survival rate (SR) in the 1.5 mg/kg Bio-Se group were the highest, and 3.0 mg/kg of Bio-Se has an inhibitory effect on the WGR, SGR, and SR. The activities of the immune enzymes, including glutathione peroxidase (GPX), superoxide dismutase (SOD), and acid phosphatase (ACP), of the hepatopancreas were significantly (p < 0.05) increased in the 1.5 mg/kg Bio-Se group, while they decreased (p < 0.05) in the 3.0 mg/kg feeding group compared to the 0 mg/kg feeding group. The concentration of maleic dialdehyde (MDA) exhibited the opposite pattern. Similarly, the mRNA expression levels of antimicrobial peptides (ALF-1, Crus-1, and LYS), ERK, and Relish genes were also observed to be the highest in the 1.5 mg/kg Bio-Se group compared with the other groups. Furthermore, the administration of 1.5 mg/kg of Bio-Se resulted in an increase in the thickness of the intestinal plica and mucosal layer, as well as in alterations in the intestinal microbial profile and bacterial diversity compared to the dose of 0 mg/kg of Bio-Se. Notably, the population of the beneficial bacterial phylum Fusobacteria was increased after crabs were fed the 1.5 mg/kg Bio-Se diet. In conclusion, the oral administration of 1.5 mg/kg of Bio-Se improved the growth efficiency, antioxidant capabilities, immunity, and intestinal health of E. sinensis. Through a broken-line analysis of the WGR against dietary Bio-Se levels, optimal dietary Bio-Se levels were determined to be 1.1 mg/kg. These findings contribute valuable insights to the understanding of crab cultivation and nutrition.

Keywords: Bio−Se; Eriocheir sinensis; growth performance; immune response; intestinal microflora.

Figure 1

Relationship between weight gain rate (WGR) and dietary Bio−Se levels based on a broken-line regression analysis.

Figure 2

Effects of different levels of dietary Bio−Se on activities of (A) acid phosphatase (ACP), (B) superoxide dismutase (SOD), (C) glutathione peroxidase (GPX), and (D) maleic dialdehyde (MDA) in hepatopancreas. The data are shown as mean ± standard deviation (n = 3). Different letters indicate significant differences at p < 0.05 and no significant differences with the same letters (p > 0.05).

Figure 3

The mRNA expression levels of (A) EsALF-1, (B) EsCrus-1, (C) EsLYS, (D) EsERK, and (E) EsRelish in hepatopancreas at different levels of dietary Bio−Se determined by qRT-PCR. Data are shown as mean ± standard deviation (n = 3). EsALF-1, anti-lipopolysaccharide factors-1; EsCrus-1, Crustin-1; EsLYS, Lysozymes; EsERK, extracellular signal-regulated kinase. Different letters are significantly different at p < 0.05.

Figure 4

The intestinal morphology of E. sinensis in the control group and Bio−Se group. The intestinal morphology determined by HE staining in control group (A) and Bio−Se group (B). The statistical analysis of the thickness of intestine (C) and thickness of intestine mucosal layer (D). P, the thickness of intestinal plica; ML, the thickness of intestinal mucosal layer; CG, control group (0 mg/kg of Bio−Se); Bio−Se, Bio−Se group (1.5 mg/kg of Bio−Se); data are shown as mean ± standard deviation (n = 3); * p < 0.05; ns, no significant difference.

Figure 5

The Venn diagram comparing the OTUs in E. sinensis between the control group and the Bio−Se group. CG, control group (0 mg/kg of Bio−Se); Bio−Se, Bio−Se group (1.5 mg/kg of Bio−Se).

Figure 6

Alpha diversity analysis of the intestinal microbial communities of E. sinensis in the control group (CG) and Bio−Se group (Bio−Se) according to the (A) Chao-1 and (B) Shannon indexes. Chao-1 and Shannon show the total number of species and classifications in the community sample, respectively. CG, control group (0 mg/kg of Bio−Se); Bio−Se, Bio−Se group (1.5 mg/kg of Bio−Se).

Figure 7

The beta diversity of intestinal microbiota of E. sinensis in the control group (CG) and Bio−Se group (Bio−Se) was evaluated via (A) PCoA, (B) UPGMA clustering of samples, and (C) NMDS. PCoA, principal coordinates analysis; UPGMA, unweighted pair-group method with arithmetic means; NMDS, non-metric multidimensional scaling; CG, control group (0 mg/kg of Bio−Se); Bio−Se, Bio−Se group (1.5 mg/kg of Bio−Se).

Figure 8

Effects of dietary Bio−Se on the relative abundance of intestine microbiota in E. sinensis at the phylum level (n = 3). CG, control group (0 mg/kg of Bio−Se); Bio−Se, Bio−Se group (1.5 mg/kg of Bio−Se).

Figure 9

LefSe analysis of intestinal microbes in control group (CG) and Bio−Se group (Bio−Se) of E. sinensis. (A) Linear discriminate analysis (LDA) value distribution histogram; (B) cladogram from linear discriminant analysis effect size (LefSe) analysis. CG, control group (0 mg/kg of Bio−Se); Bio−Se, Bio−Se group (1.5 mg/kg of Bio−Se).