Effect of Fly Maggot Protein as Dietary on Growth and Intestinal Microbial Community of Pacific White Shrimp Litopenaeus vannamei

Abstract

As the intensive development of aquaculture persists, the demand for fishmeal continues to grow; however, since fishery resources are limited, the price of fishmeal remains high. Therefore, there is an urgent need to develop new sources of protein. They are rich in proteins, fatty acids, amino acids, chitin, vitamins, minerals, and antibacterial substances. Maggot meal-based diet is an ideal source of high-quality animal protein and a new type of protein-based immune enhancer with good application prospects in animal husbandry and aquaculture. In the present study, we investigated the effects of three different diets containing maggot protein on the growth and intestinal microflora of Litopenaeus vannamei. The shrimp were fed either a control feed (no fly maggot protein added), FM feed (compound feed with 30% fresh fly maggot protein added), FF feed (fermented fly maggot protein), or HT feed (high-temperature pelleted fly maggot protein) for eight weeks. The results showed that fresh fly maggot protein in the feed was detrimental to shrimp growth, whereas fermented and high-temperature-pelleted fly maggot protein improved shrimp growth and survival. The effects of different fly maggot protein treatments on the intestinal microbiota of L. vannamei also varied. Fermented fly maggot protein feed and high-temperature-pelleted fly maggot protein feed increased the relative abundance of Ruegeria and Pseudomonas, which increased the abundance of beneficial bacteria and thus inhibited the growth of harmful bacteria. In contrast, fresh fly maggot proteins alter the intestinal microbiome, disrupting symbiotic relationships between bacteria, and causing invasion by Vibrio and antibiotic-resistant bacteria. These results suggest that fresh fly maggot proteins affect the composition of intestinal microorganisms, which is detrimental to the intestinal tract of L. vannamei, whereas fermented fly maggot protein feed affected the growth of L. vannamei positively by improving the composition of intestinal microorganisms.

Keywords: Litopenaeus vannamei; fly maggot protein; growth performance; intestinal microorganisms; survival rate.

Figure 1

Diversity and richness of intestinal microbial variability in Litopenaeus vannamei. (A) Venn diagram; (B) PCoA analysis on the basis of Bray-Curtis distance.

Figure 2

Changes in the composition of the intestinal microbial community of Litopenaeus vannamei. (A) relative bacterial abundance at the phylum level; (B) relative bacterial abundance at the class level; (C) relative bacterial abundance at the genus level.

Figure 3

Between-group variability of intestinal microorganisms of Litopenaeus vannamei. (A) In the LEfSe cladogram, the diameter of each circle is proportional to the bacterial taxon abundance. (B) LDA scores of LEfSe-PICRUSt, only the taxon with LDA values > 3.5 are shown. The lowercase letters in front of the strain name represent the taxonomic level at which the strain is located: k for kingdom, p for phylum, c for class, o for order, f for family, g for genus, and s for species.

Figure 4

Correlation network analyses of intestinal microbial of Litopenaeus vannamei. (A) The correlation network based on bacterial phyla. (B) The correlation network of bacteria genera. Circles indicate the species, size indicates its relative abundance, different colours indicate different species phylum classifications, the lines connecting the circles denote the significant correlation between the two species (p < 0.05), red lines represent positive correlations, and blue lines represent negative correlations. The thicker the line, the greater the absolute value of the correlation coefficient.

Figure 5

Analysis of bacterial metabolism in the intestinal KEGG pathway of Litopenaeus vannamei based on fermented feed and fly maggot protein: (A) results of KEGG level 2 analysis; (B) results of KEGG level 3 analysis; (C) results of the predicted variability of the pathway groups under KEGG level 3. Different letters are used to show significant differences (p < 0.05).

Figure 5

Analysis of bacterial metabolism in the intestinal KEGG pathway of Litopenaeus vannamei based on fermented feed and fly maggot protein: (A) results of KEGG level 2 analysis; (B) results of KEGG level 3 analysis; (C) results of the predicted variability of the pathway groups under KEGG level 3. Different letters are used to show significant differences (p < 0.05).

Figure 6

Heat map of the interrelationship between microbial species and environmental factors (SR and WG) at the genus level. * Denotes significant correlation (*p < 0.05; **p < 0.01).