Effects of Dietary Protein Levels on <i>Macrobrachium rosenbergii</i> Reared Under a High‐Density Culture Model: Growth, Immune Response, Hepatopancreatic Health, and Antistress Capacity

Study of precision nutrition provides essential and accurate information on the nutrient requirements for animal growth under various farming modes, to offer guidance for the efficient utilization of compound feed. To evaluate the effects of dietary protein levels on the growth performance, immune response, and health of <i>Macrobrachium rosenbergii</i> reared under high-density conditions, prawns in five groups were cultured with a density at 70 prawns/m³, and fed diets with varying protein levels (40%, 42.5%, 45%, 47.5%, and 50%) and designated as CP40, CP42.5, CP45, CP47.5, and CP50, respectively. Our findings revealed that the prawns in the CP42.5 and CP45 groups exhibited significantly higher weight gain rates and specific growth rates, whereas the feed conversion ratio (FCR) was significantly lower in these groups (<i>p</i> < 0.05). The hepatosomatic index (HSI) of prawns in the CP45 group was significantly higher than the other treatments (<i>p</i> < 0.05). The <i>trypsin</i> activity in the CP45 group was the highest (<i>p</i> < 0.05). Additionally, prawns fed 42.5%-45% protein levels exhibited stronger antioxidant capacity (AOC), with higher total antioxidant capacity (T-AOC), and the activities of catalase (CAT), total superoxide dismutase (T-SOD), and glutathione S-transferase (GST) (<i>p</i> < 0.05), along with a substantial reduction in protein carbonyl (PC) levels (<i>p</i> < 0.05). Analysis of the expression of apoptosis-related genes and hematoxylin-eosin staining revealed that both insufficient and excessive dietary protein levels significantly led to autophagy in the hepatopancreas. The environmental stress tests demonstrated that the survival rate (SR) of prawns in the CP45 group was significantly higher compared to the other treatments (<i>p</i> < 0.05). From a growth and health perspective, our findings revealed that a 42.5%-45% protein level is appropriate for <i>M. rosenbergii</i> cultured under high-density (70 prawns/m³) conditions.