Effects of commercial dietary prebiotic and probiotic supplements on growth, innate immune responses, and intestinal microbiota and histology of Totoaba macdonaldi

Prebiotics and probiotics constitute a different approach to prevent diseases in cultured fish and shellfish and have shown a number of beneficial impacts, including improved growth, survival, immunological responses, increased area of intestinal absorption, and enhanced general well-being of the host. The dietary supplementation of prebiotics and/or probiotics has not been evaluated in Tototaba macdonaldi, thus, the objective of this study was to evaluate its growth, innate immune responses, and transient intestinal microbiota and histology after being fed commercial prebiotic and probiotic supplements singularly and in combination. Four iso-nitrogenous (43% crude protein) and iso-lipidic (13% crude fat) diets were formulated to contain either 0 (basal diet) or 2% of the yeast-based prebiotic GroBiotic®-A or the Bacillus-containing probiotic Aquablend® at 11 × 109 cell forming units (CFU)/kg, or both supplements, in a 2 × 2 factorial arrangement, feeding fish with an initial mean weight of 215.6 g for 109 days. No statistically significant differences were observed by supplementing either the probiotic, the prebiotic, or both for survival or any of the growth parameters evaluated at the end of the experiment. Lysozyme activity in plasma of fish fed the basal diet was significantly higher (P = 0.0031) than that of fish fed the prebiotic. Histometric analysis of the gastrointestinal tract revealed that fold length in the proximal section was significantly larger (P = 0.0045) in fish fed the diet containing the probiotic (435.6 μm), compared to those of fish fed the basal diet (382.3 μm). No differences were detected for the composition of the transient microbial populations from the gastrointestinal tract (GIT) contents of T. macdonaldi, as evaluated by denaturing gradient gel electrophoresis analysis. However, significant shifts in the overall transient microbial community and diversity were found using massive sequencing of the V3-V4 16S rRNA GENE. Our results showed different bacterial clustering patterns between the basal diet and the diets with additives (prebiotic, probiotic, pre + pro). Furthermore, the genus Bacillus appeared enriched only in the diet combining both supplements. To our knowledge, this is the first report of transient microbial community analysis from intestinal contents of totoaba using the 16S microbiome sequencing. Initial weight of totoaba, or the length of the trial, could partly explain the absence of growth differences among treatments. From these results, it was evident that studies with probiotics and prebiotics fed to sturdy fish like totoaba will benefit from including a challenge experiment in order to assess their potential role in preventing infections.