Effects of Dietary Agavin on the Gut Microbiota of the Nile Tilapia (Oreochromis niloticus) Reared at High Densities.

High-density stress can lead to dysbiotic microbiota, affecting the organism's metabolic, and protective functions. Agavin is a fructan with prebiotic properties that regulate the gut microbiota by promoting the growth of beneficial bacteria. This study evaluated the effect of agavin on the gut microbiota using Next-Generation Sequencing (NGS) and its correlation with the growth parameters. Four groups of fish were fed different diets: a control diet (negative and positive control), without agavin supplementation, and two experimental diets supplemented with agavin at 20 g kg^-1 and 40 g kg^-1. Nile tilapias (1.04 g ± 0.01 g) were fed for 110 days. After 90 days of feeding, fish were subjected to high-density stress (63 kg m^-3) for 20 days, except for the negative control. NGS detected 1579 different operational taxonomic units in the samples. In the correlation analysis of growth parameters, the families Vibrionaceae and Methyloligillaceae showed a positive correlation with fish growth parameters, these results may serve to know the relation of agavin and microbiota on the growth performance, as well as the metabolic activities of families in tilapia. Furthermore, high-density stress and agavin supplementation modify the gut microbiota in tilapia. At a low-density, supplementation with 20 g kg^-1 agavin promoted the growth of the potentially beneficial families Sphingomonadaceae, Oxalobacteriaceae, and Chitinophagaceae; at high densities, reduced the abundance of pathogenic families (Vibrionaceae and Aeromonadaceae). These results suggest that, under stress conditions, agavin can stimulate the growth of potentially beneficial bacteria and reduce the growth of potentially pathogenic bacteria, suggesting its potential use as a prebiotic in aquaculture.