Gut microbiome composition likely affects the growth of razor clam Sinonovacula constricta

Accumulating evidence has revealed that gut microbiota contributes crucial roles in the nutrient absorption, pathogen defense and growth of aquatic animals. The razor clam (Sinonovacula constricta) is one of the most important bivalve products among fishery trading commodities, and its intestine harbors a diverse microbial community, yet its relationship with the clam growth remains unclear. To address this gap, using 16S rRNA gene amplicon sequencing, we compared the gut bacterial community structures among cohabitating retarded, overgrown and normal clams collected from identically managed ponds. A significant difference in gut bacterial communities was observed between retarded and overgrown clams and between retarded and normal ones. Specifically, compared to retarded clams, overgrown clams had significantly higher proportion of Vibrionaceae and Oceanospirillaceae family and Vibrio genus, while normal clams had remarkably higher proportions of Mycoplasmataceae family and Lysobacter and Mycoplasma genera. Further, a structural equation modeling uncovered that variations in the gut bacterial community were positively correlated to digestive enzyme activities, which subsequently influenced clam growth traits (lambda = 0.78, P < 0.001). The retarded and overgrown clams exhibited a more cooperative and better connected gut bacterial interspecies interaction than normal clams. Notably, the distribution and shifts of gut keystone species were closely concordant with clam growth traits. Additionally, the relative abundances of gut bacterial-mediated functional pathways involved in amino acid, carbohydrate, energy, glycan biosynthesis, and lipid metabolism decreased dramatically in retarded clams compared to overgrown and normal cohorts. Based on above findings, we speculated that an altered gut microbiota could be a factor in determining the retardation or overgrowth of S. constricta.