Enhanced intestinal health, immune responses and ammonia resistance in Pacific white shrimp (Litopenaeus vannamei) fed dietary hydrolyzed yeast (Rhodotorula mucilaginosa) and Bacillus licheniformis

•The growth and feed utilization could not be improved by dietary hydrolyzed yeast and/ or Bacillus licheniformis.•Dietary hydrolyzed yeast and/ or Bacillus licheniformis could positively altered intestinal morphology.•Dietary hydrolyzed yeast and/ or Bacillus licheniformis could enhance shrimp’s immune responses during the feeding period.•Dietary synbiotic could have more benefits than hydrolyzed yeast and Bacillus licheniformis alone. To explore the impacts of dietary hydrolyzed yeast (Rhodotorula mucilaginosa) and Bacillus licheniformis (B. licheniformis) on the growth, intestinal histology, innate immune response and ammonia resistance of Litopenaeus vannamei, four experimental diets (basal diet (Control); 0.5 % hydrolyzed yeast (HY); 0.1 % B. lincheniformis (BL) and 0.5 % hydrolyzed yeast + 0.1 % B. licheniformis (SYN)) were fed shrimps for 8 weeks. Results showed no significant differences on growth and body composition among all treatments, while a significantly higher feed efficiency (FE) in shrimp fed BL diet and a significantly higher protein efficiency ratio (PER) in shrimp fed BL and SYN diets were found compared to those in shrimp fed the Control diet (P