Cottonseed protein concentrate as fishmeal alternative for largemouth bass (Micropterus salmoides) supplemented a yeast-based paraprobiotic: Effects on growth performance, gut health and microbiome

Cottonseed protein concentrate (CPC) is a potential fishmeal alternative but may negatively influence the gut health of fish. A specific paraprobiotic consisting of multi-strain yeast fractions (MsYF) was recently shown to improve gut health via immune modulation. This study aimed to evaluate the effects of MsYF on the growth performance, gut health and microbiome of largemouth bass fed a diet using CPC as 40% fishmeal alternative. Juvenile largemouth bass (body-weight = 31 g) were fed for 65 days with three iso‑nitrogen and isoenergetic experimental diets: 1/ one Control diet (50% fishmeal), 2/ one low fishmeal diet (LFM; 30% fishmeal, 23.5% CPC) and 3/ one LFM diet + MsYF at 800 mg/kg (LFMY). The highest growth performance, estimated as specific growth rate and protein efficiency ratio, was observed in the LFMY followed by the LFM. Histopathology identified some specimens with distal intestinal lesions in the Control and LFM groups but not of the LFMY group. The gene expression level of il-10 (anti-inflammatory) was up-regulated in the LFM and LFMY groups but only LFMY down-regulated il-1β (pro-inflammatory) and hypoxia-inducible factor 1-alpha (hif1α) protein expression level compared to the Control group. Further, LFM and LFMY up-regulated occ-1b (tight-junction) and slc15a2 (peptide transporter) suggesting enhanced intestinal permeability and peptide transport compared to the Control group. Moreover, dietary CPC increased the abundance of genus Clostridium_sensu_stricto_12 and decreased the abundance of genus Escherichia-Shigella compared to the Control group, while the inclusion of MsYF increased the abundance of the potentially beneficial genus Cetobacterium compared to the LFM group. Our results showed 40% substitution of fishmeal protein by CPC could enhance growth performance and regulate the intestinal barrier and peptide transport relevant functions in largemouth bass. Moreover, in a low fishmeal basal diet, MsYF supplementation could increase growth performance and support intestinal health, which may be associated with the modulation of the intestinal permeability, inflammatory environment and microbiota.