The composition and structure of the intestinal microflora of Anguilla marmorata at different growth rates: a deep sequencing study

The aim of this study was to determine the intestinal microflora of Anguilla marmorata at different growth rates and to identify potential probiotic/pernicious bacteria. Bacterial communities from eight different eels' intestinal sites (including the intestinal contents and the intestinal mucosa) from three fish groups (three fast‐, two medium‐, and three stunted‐growth samples), two water samples, and one diet sample were characterized by Illumina next‐generation sequencing. The data revealed that the predominant genera (relative abundance of bacteria genera >1%) in the intestine of fast‐ and medium‐growth groups were Cetobacterium, Edwardsiella, Clostridium, Lactococcus, Bacteroides, Plesiomonas and Akkermansia. The dominant genus in the stunted‐growth group was Spiroplasma. Moreover, culture‐associated (water and feed) environmental microbes were distinct from those present in fish intestines, and included Flavobacterium (the dominant bacteria in water) and Corynebacterium (the dominant bacteria in feed). Only minor differences in gut microbial communities were observed between the fast‐growth group and the medium‐growth group; however, significant differences were observed between the normal‐growth group (including the fast‐growth group and medium‐growth group, which showed uninhibited growth during the rearing stage) and the stunted‐growth group. Together, these data suggested that intestinal microbes were significantly associated with marbled eels' growth rate. In this study, we demonstrated for the first time, the intestinal bacterial communities of A. marmorata at different growth rates. Moreover, we found that the genus Spiroplasma was abundant in the guts of stunted‐growth eels, which had never been noticed. Such a finding indicates that the genus Spiroplasma plays a key role associated with retardation in growth and should be controlled to recover the growth of stunted eels, which is meaningful to farmers.