Effect of fresh and spray-dried microalgal diets on the growth, digestive enzymatic activity, and gut microbiota of juvenile winged pearl oyster Pteria penguin

Abstract

The effects of fresh and spray-dried microalgal diets on the growth, digestive enzymatic activity, and gut microbial community were investigated in juveniles of the winged pearl oyster Pteria penguin. A total of 240 pearl oysters were fed either live or spray-dried unialgal diets of the species Isochrysis zhanjiangensis and Platymonas subcordiformis at a final concentration of 150,000 cells/mL. The experiment was performed over 28 days in triplicate feeding trials under laboratory conditions. At the end of the feeding trials, the hepatopancreas and gut tissue were dissected to quantify the digestive enzymatic activity and analyze the gut bacterial community. The survival rate of the oyster juveniles in all trials was > 90 %. Moreover, the animals fed a spray-dried P. subcordiformis diet exhibited slightly higher shell growth rates. However, the mean shell height and the total wet weight were not significantly different among all experimental groups (P > 0.05). The digestive enzymes amylase, pepsin, and lipase exhibited significantly higher activity levels in oysters fed spray-dried diets than in those provided live microalgae. The different diets also provoked changes in the gut microbiota of the pearl oysters. A total of 27 phyla and 482 genera were detected within all groups examined; the Proteobacteria, Cyanobacteria, Bacteroidetes, and Spirochaetes were the dominant phyla. In general, spray-dried diets exhibited a higher number of operational taxonomic units (OTUs), Chao1, and Simpson and Shannon indices, implying the ability of these diets to promote high microbial biodiversity. Thus, these diets benefitted the maintenance of the intestinal micro-ecological balance and health. The study findings will help optimize intermediate culture technology and management of P. penguin juveniles.