Supplementation of flavonoids and inulin in Totoaba macdonaldi: Microbiota, liver gene expression and growth performance responses

Totoaba macdonaldi is an endemic, vulnerable, carnivorous fish of the Gulf of California that is currently being cultivated in northwestern Mexico for commercial and conservation purposes. The challenge for aquaculture of Totoaba is finding a diet that meets the protein requirements at an acceptable price and does not compromise its overall performance. Current diets in aquaculture are either prejudicial for the environment or have caused adverse effects on the digestive system and liver of Totoaba. To counteract those negative effects, this study evaluates quercetin and epicatechin supplementation in two doses (0.25% and 0.5%), with and without inulin, as functional additives. A total of 360 juveniles were divided into 18 tanks and fed with six experimental diets in triplicate. Growth performance, intestinal microbiota, blood biochemistry, and liver transcriptomics were evaluated. The liver's transcriptome de novo assembly had an N50 of 2599 bp and 76.38% BUSCO completeness. Experimental diets showed higher growth performance than the control diet (p < 0.05). The lowest concentrations of triglycerides and cholesterol were observed in fish fed with Inulin (I), Flavonoids at 0.5% (FH), and Flavonoids at 0.5% + Inulin (IFH). In the liver, Flavonoids at 0.25% (FL) and IFH diets presented down regulated genes related to metabolic and biosynthetic processes, whereas FH and Inulin diets presented upregulated genes related to cellular and growth processes. Additionally, the FH diet presented a greater abundance of Lactobacillaceae and a reduction of Enterococcus faecalis and Vibrio anguillarum in the intestinal microbiome. The present results found that flavonoids and inulin improve metagenomic diversity at the intestinal level by increasing the abundance of beneficial bacteria. This leads to a reciprocal interaction improving the absorption of flavonoids, reducing fat absorption in the gastrointestinal tract, enhancing gene modulation of metabolic processes involved in lipid oxidation.