Comparative effects of bile salts and free bile acids on intestinal health of grouper (<i>Epinephelus</i> spp.) fed a high cottonseed protein concentrate diet.

The physiological impacts of bile acids (BA) conjugation states remain underexplored in aquatic species. This study investigated the effects of supplementing conjugated BA (bile salts [BS]) or non-conjugated BA (free bile acids [FBA]) on the intestinal health of pearl gentian grouper ( Epinephelus fuscoguttatus ♂ × Epinephelus lanceolatus ♀) fed a high plant-protein diet for 8 weeks. A total of 300 healthy juveniles (approximately 90-d-old; initial body weight 15.21 ± 0.04 g) were randomly distributed into four dietary groups in triplicate (25 fish per tank): CD group (a fishmeal-based control diet [CD]), PD group (a plant protein-based diet [PD], with 50% fishmeal replaced by cottonseed protein concentrate), BS group (PD supplemented with 0.09% BS), and FBA group (PD supplemented with 0.09% FBA). Compared to the CD group, the PD group significantly impaired growth performance (final body weight and weight gain rate), gut morphology (muscle thickness, plica height, and width), and induced inflammatory response, oxidative stress, endoplasmic reticulum stress, cell apoptosis, and dysregulated amino acid metabolism ( P P P < 0.05). In conclusion, BS, but not FBA, effectively attenuates intestinal damage and promotes health in groupers fed high plant-protein diets, highlighting the critical importance of BA conjugation in nutritional interventions.