Moderately elevated salinity rapidly promotes oyster meat yield by rewiring ammonia transport and metabolic networks.

Oysters are rich in high-quality proteins, and their aquaculture is experiencing rapid expansion driven by the increasing demand for premium aquatic products. Yet, the continuous expansion of aquaculture has resulted in a rapid decline in oyster fattening, posing a serious threat to global food security. Here, we demonstrated that moderately high salinity boosted oyster fattening by stimulating ammonia transport processes that drove oyster metabolic acceleration. Non-destructive micro-test technology revealed that different salinity conditions significantly altered the fluxes rates of NH4+ and H+ in oyster. Specifically, oysters temporally reared at low salinity of 18 exhibited ion efflux to resist cellular swelling, at moderately high salinity of 30 displayed optimal ion fluxes (the most favorable physiological status), and at extremely high salinity of 42 defended against dehydration through ion influx. Enzymatic activities of GLS and NKA increased significantly at 30, accelerating NH4+ transport. CA content together with T-ATPase and GDH activities increased significantly with rising salinity, indicating that oysters rely on salinity gradients to regulate H+ excretion. Expressions of genes underpinning ATPase, CA, and ammonium transporter at 30 were significantly upregulated, thus facilitating synergistic energy metabolism for NH4+ and H+ transports. Metabolic pathways (e.g., fatty acid metabolism, starch and sucrose metabolism, the TCA cycle, and glycolysis), likewise, synergistically regulated ammonia metabolism at 30. These findings indicate that oysters can leverage their physiological plasticity to enhance NH4+ transport under moderately high salinity conditions, stimulating metabolism and eventually facilitate increased oyster fattening.