Effects of a Plant Protein‐Based Diet on the Somatic Growth and Transcriptional Response of Oysters

Food scarcity often leads to emaciation in offshore‐farmed oysters, thereby diminishing their marketability. Land‐based intensive fattening is an emerging strategy to improve oyster somatic growth, yet its broad implementation is constrained by the scarcity of effective and stable feed sources. In this study, the fattening performance of a formulated diet based on fermented plant proteins (soybean and peanut meal) with minimal microalgae supplementation (diet group) was evaluated against a microalgae‐only control (control group) during a 10‐day intensive trial in Pacific oysters ( Magallana gigas ). In parallel, transcriptomic analysis was conducted to elucidate the underlying mechanisms of plant protein utilization. Relative to the initial state (Day 0), the diet group showed significant improvements in meat yield, condition index, dry flesh weight, and the contents of protein, glycogen, and lipid. By Day 10, the diet group exhibited significantly higher condition index, dry flesh weight, and protein content compared with the control group, whereas the glycogen content was significantly lower, indicating a distinct nutrient accumulation pattern. Enzyme activity assays revealed high protease but low amylase and lipase activities in the diet group, confirming preferential protein assimilation. Principal component analysis (PCA) of the transcriptomic profiles revealed a distinct separation between the diet and control groups. Functional enrichment and gene expression analysis indicated an enhancement of aminoacyl‐tRNA (aa‐tRNA) biosynthesis and mTOR‐mediated protein synthesis in the diet group, accompanied by a significant reduction of carbohydrate metabolism, including glycolysis, the TCA cycle, and oxidative phosphorylation. These results illustrated that plant protein improved oyster biomass accumulation via mTOR‐mediated protein synthesis, while underscoring the need for balanced carbohydrate and lipid supplementation to optimize nutritional outcomes. This study provides a practical framework for land‐based oyster fattening and informs future nutritional strategies for bivalve aquaculture.