Effect of protein sources in formulated diets on the growth, immune response, and intestinal microflora of pearl oyster Pinctada fucata martensii

•This work is the first to analyze alterations in the intestinal bacterial profiles of pearl oyster fed with formulated diets.•Diet with corn gluten as the main protein source led to a low biodiversity level.•A suitable protein source must be selected to ensure the intestinal health of P. f. martensii. Diets affect the intestinal microflora, which in turn affects the growth performance and immune response on host. To study the effect of protein sources in formulated diets on the growth, immune response, and intestinal microflora of pearl oyster Pinctada fucata martensii, two major protein sources (yeast powder-D1 and corn gluten-D2) were used in the preparation of two isonitrogenous and isolipidic diets. The pearl oysters were divided into two groups, namely, ED1 and ED2, which were fed with D1 and D2 indoors respectively. After 45-day culturing, ED1 had significantly higher growth performance and protease and amylase activities than ED2. ED1 also had significantly higher alkaline phosphatase, catalase, superoxide dismutase, glutathione peroxidase activities and total antioxidant capacity. A 16S rRNA-based sequencing revealed that the main bacterial phyla in ED1 were Proteobacteria, Firmicutes, Tenericutes, and Bacteroidetes, which accounted for 97.70 % of the microbial population. Firmicutes were the main phylum in ED2 and accounted for 97.98 %. ED1 got significantly higher Sobs, Chao, ACE, and Shannon indices than ED2. ED1 achieved significantly lower Simpson index than ED2. Results suggested that diet with yeast powder as the major protein source promoted the growth, digestive activity, immune- and antioxidant activity, and intestinal bacterial diversity in pearl oysters. This study provides basic data with regard to the mechanism through which formulated diets enhance digestive tract health of shellfish under controlled conditions.