Succession of the Intestinal Microflora Structure of Haliotis discus hannai During the Weaning Period

Pacific abalone Haliotis discus hannai is an economically important aquaculture species in China, whose production accounts for approximately 93% of world abalone aquaculture production. Its weaning phase is a vulnerable life stage associated with high mortality, which has seriously impeded the sustainable development of Chinese abalone aquaculture. Previous research has shown that the intestinal microflora in farmed abalone is affected by numerous abiotic and biotic factors. The weaning post-settlement of diatom-fed abalone on artificial feed may alter the natural succession of microflora in their guts. To study the succession of the intestinal microbiota in the weaning of Pacific abalone, we collected Pacific abalone at the weaning period days 0 (T0), 4 (T4), 10 (T10), 35 (T35), and 40 (T40) by 16S rRNA high-throughput sequencing. Results showed no significant differences in alpha diversity (Shannon, Simpson, ACE, and Chao1) between T0, T4, and T10 and between T35 and T40. The ACE and Chao1 indices tended to decrease with sampling time. Both Good's coverage values exceeded 99.50%, indicating that the sequence libraries covered most of the microbial community in these samples. A total of 3609 OTUs were identified across all samples after pre-processing, and the unique OTUs tended to decline in the weaning phase, varying from 419 OTUs in T4 to 169 OTUs in T40. The beta diversity of intestinal microbiota showed that the T0/T4 and T35/T40 samples were clustered separately in principal coordinate analysis, with overlaps between T0 and T4, T35 and T40; T10 was in the transitional stage of intestinal microflora succession during the weaning period. In terms of the composition and structure at the phylum level, the dominant bacterial groups in diatom-fed abalone and weaning abalone were relatively consistent, including Proteobacteria, Bacteroidetes, and Firmicutes. The ratio of Proteobacteria decreased, while that of Bacteroidetes increased with the time of weaning. The composition of the dominant genera during the diatom feeding and weaning stages differed significantly at the genus level. The dominant genera of the diatom-feeding stage (T0) included Lentilitoribacter (14.18%), Dinoroseobacter (9.90%), and Neptuniibacter (9.86%). During the weaning stage, Lentilitoribacter (19.70%), Pseudoalteromonas (9.86%), and Arcobacter (5.52%) were the dominant genera in the T4 group; Lentilitoribacter (6.95%), Arcobacter (8.15%), and Vibrio (7.50%) were the dominant gener