Dietary Protein and Lipid Levels Affect Growth Performance, Antioxidant Capacity, and Metabolism in Postlarval <i>Macrobrachium rosenbergii</i>

The protein‐to‐energy ratio is crucial for the overall performance of Macrobrachium rosenbergii postlarvae, yet the optimal range remains undetermined. We formulated nine experimental diets in a 3 × 3 factorial design, encompassing three graded protein levels (45.83%, P46; 49.03%, P49; 52.23%, P52) and three graded lipid levels (6.07%, L6; 8.03%, L8; 10.03%, L10). After an 8‐week feeding trial, the weight gain rate (WGR) was influenced by both protein and lipid levels, with a peak in the P49/L8 group ( p &lt; 0.05). Their interaction significantly affected hemolymph superoxide dismutase (SOD) and malondialdehyde (MDA) levels ( p &lt; 0.05). SOD initially increased and then decreased with increasing protein level, peaking in the P49/L8 group ( p &lt; 0.05). Total antioxidant capacity (T‐AOC) decreased with increasing lipid level but showed an initial increase followed by a decrease at the P52 level, reaching its highest value in the P52/L8 group ( p &lt; 0.05). At low lipid levels, trypsin increased with increasing protein, whereas it decreased at high lipid levels. Lipase initially increased and then decreased with increasing levels of both protein and lipid, reaching its peak in the P52/L8 group ( p &lt; 0.05). The relative lipid droplet area increased with increasing protein and lipid levels, reaching a maximum in the P52/L10 group ( p &lt; 0.05). Appropriate protein level significantly activated the TOR / S6K1 pathway, while elevated lipid levels upregulated genes related to lipid synthesis ( FAS and ACC ) and transport (fatty acid‐binding protein [ FABP ]), while downregulating genes associated with lipid breakdown. In conclusion, the optimal dietary protein and lipid levels for postlarval M. rosenbergii are 49% and 8%, respectively, corresponding to a P/E ratio of 29.34 mg protein·kJ −1 .