<p>Optimizing protein utilization is critical for the sustainable aquaculture of the sea cucumber <i>Apostichopus japonicus</i>, because protein represents a costly yet indispensable component of aqua-feeds. The present study compared the behavioral and physiological differences among sea cucumbers that were fed a high-protein diet and had different growth performances. Here, sea cucumbers, which were fed a high-protein diet and subsequently exhibited higher growth rates, showed significantly higher food consumption and spent significantly less time in the food zone, indicating enhanced foraging efficiency. The tentacle activity of these individuals was significantly higher than that of those with lower growth rates. Thus, sea cucumbers that were fed a high-protein diet and showed better growth performance had more efficient feeding strategies. High-growth individuals exhibited significantly lower phosphofructokinase activity. This indicates a reduced reliance on glycolysis and a greater capacity for endogenous energy production or utilization in <i>A. japonicus</i>. In addition, the intestinal microbiota of high-growth individuals was characterized by a higher abundance of the family Erysipelotrichaceae. Furthermore, gut mass/body mass of high-growth individuals was significantly lower than that of those with lower growth rates. This indicates that these high-growth individuals responded better to the high-protein diet. The present findings are valuable to elucidate the effects of high-protein diets on sea cucumber behavior and physiology, and to offer useful insights into sea cucumber aquaculture.</p>