Metabolic biochemistry of the fighting limbs and muscles of the freshwater prawn, Macrobrachium rosenbergii, reflects agonistic behavior

This study investigated the behavioral and physiological responses of the freshwater prawn Macrobrachium rosenbergii in relation to fighting activity, aiming to elucidate how energy metabolism varies across locomotory organs under different combat durations. Based on observed fighting times, individuals were divided into control (no fighting), short-duration (16.67 ± 8.22 min), and long-duration (38.33 ± 9.65 min) groups. The movement frequency of the second pereiopods, pleopods, and uropods, along with energy substrates and metabolic enzyme activities in these appendages and abdominal muscles, was analyzed. Results showed that the second pereiopods exhibited the most pronounced increase in beating frequency during prolonged fighting, followed by pleopods and uropods, reflecting their hierarchical involvement in locomotion and aggression. Glycogen content decreased significantly with fighting duration, with the greatest depletion observed in the second pereiopods (up to 36.78 %), compared to moderate decreases in pleopods and abdominal muscles. This indicates a dominant metabolic burden on primary combat appendages. Long-duration fighting induced significant increases in lactate levels, as well as hexokinase (HK) and lactate dehydrogenase (LDH) activities in the second pereiopods and abdominal muscles, suggesting a shift toward anaerobic metabolism. In contrast, short-duration fighting was characterized by elevated malate dehydrogenase (MDH) and cytochrome c oxidase (COX) activities in the second pereiopods and pleopods, reflecting reliance on aerobic pathways. These results demonstrate that M. rosenbergii adopts organ-specific metabolic strategies during aggression. This mechanistic insight lays the groundwork for future aquaculture applications involving behavioral conditioning, dietary interventions, and selective breeding to reduce energy loss and improve animal welfare in intensive farming systems.