Improvement of hybrid grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂) by enzyme-digested poultry by-product: Growth performance, amino acid and peptide transport capacity, and intestinal morphology

Abstract

Background: At present, fish meal (FM) resources are in short supply, and competition for food between humans and animals is becoming increasingly critical. Finding non-grain protein sources that can replace FM is the key to solving the rapid development of aquaculture.

Methods: Seven trial diets were prepared with 0 g/kg (EP0), 30 g/kg (EP3), 60 g/kg (EP6), 90 g/kg (EP9), 120 g/kg (EP12), 150 g/kg (EP15), and 180 g/kg (EP18) of enzyme-digested poultry by-product meal (EPBM) by replacing of FM. A total of 630 hybrid groupers (Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂) were equally portioned into 21 tanks. At 8:00 and 16:00 each day, groupers were fed until they were full for a cumulative period of 8 weeks.

Results: The results showed that 30 g/kg of EPBM significantly increased the rates of weight gain and special growth (P < 0.05). Significantly higher activities of serum glutamic pyruvic transaminase, glutamic oxaloacetic transaminase, catalase, and superoxide dismutase were observed in the EP3 group (P < 0.05). The categories and numbers of the top 10 dominant bacteria in the phylum and genus levels were not significantly influenced by feed (P > 0.05). In the proximal intestine and distal intestine, there were significantly higher expressions of SNAT3, LAAT1, CAT2, and CAT1 in the EP3 group compared with the EP0 group (P < 0.05). In the EP3 group, the expressions of PepT1, LAAT1, B^{0, +}AT, and CAT2 were significantly increased in MI than those in all other groups (except the EP0 group, P < 0.05).

Conclusion: When FM was replaced by 30 g/kg of EPBM, growth performance, antioxidant capacity, and the ability to transport amino acids and peptides of hybrid grouper were significantly improved.

Keywords: amino acid and peptide transporters; enzyme-digested poultry by-product meal; growth performance; hybrid grouper; intestinal microbiota; non-specific immunity.

FIGURE 1

Peptide molecular weight distribution of enzyme-digested poultry by-product meal. Da, Dalton.

FIGURE 2

Light microscopy (20×) of the proximal intestine (PI), mid-intestine (MI), and distal intestine (DI) morphology of hybrid groupers fed with diets. Scale bar: 200 μm.

FIGURE 3

Rarefaction curve of the intestinal microbiota in hybrid groupers fed with diets.

FIGURE 4

Principal coordinates analysis, PCoA (A); and analysis of similarities, ANOSIM (B) of the intestinal microbiota in hybrid groupers fed with diets.

FIGURE 5

Venn diagram of unique and shared OTUs.

FIGURE 6

Taxonomy classification of reads at the phylum (A) and genus (B) taxonomic levels of the intestinal microbiota in hybrid groupers fed with diets.

FIGURE 7

LEfSe analysis of the intestinal bacteria microbiota in hybrid groupers fed with diets. The circles radiating from the inside to the outside of the evolutionary branch diagram represent the classification levels of phylum (p), class (c), order (o), family (f), genus (g), and species (s).

FIGURE 8

Relative mRNA expression of amino acid and small peptide-related transport in the (A) proximal intestine (PI), (B) mid-intestine (MI), and (C) distal intestine (DI) of hybrid groupers fed with diets, respectively. The β-actin gene was used as a housekeeping gene, and the control group was used as the reference group. Columns represented the mean values ± S. E. M. of each group. Different letters in each figure indicate significant differences among groups (a > b > c > d; P < 0.05).