Behavioural and physiological responses to low- and high-intensity locomotion in Chinese shrimp Fenneropenaeus chinensis.

We explored stroke behaviour, energy sources, and their related metabolic enzymes during multi-intensity swimming and tail-flipping at low- and high-intensity modes in Chinese shrimp Fenneropenaeus chinensis. In swimming, shrimp were encouraged to swim at velocities of 3, 6, 9 cm s-1 for 200 min (low-intensity), and at 12, 15, 18 cm s-1 until fatigue (high-intensity). In tail-flipping, shrimp were encouraged to tail-flip by tapping cephalothorax at frequencies of 0.020, 0.040, 0.063 Hz (one tap every 50, 25, 16 s) for 5 min (low-intensity), and at 0.083, 0,100, 0.125 Hz (one tap every 12, 10, 8 s) until no response (high-intensity). Results showed that shrimp increased stroke rates of pleopods and uropods to elevate swimming and tail-flipping ability. For low-intensity locomotion, glycogen was burned in aerobic pathway due to low pleopods beat frequency in swimming; however, glycogen was anaerobically burned due to high uropods beat amplitude in tail-flipping. Anaerobic metabolism occurred in high-intensity locomotion in either swimming or tail-flipping. Critical contents of muscle lactate causing locomotion fatigue might be around threefold of rest condition. Shrimp reduced locomotive time to avoid glycogen exhaustion and lactate accumulation during high-intensity locomotion. These findings highlight our understanding of physiological mechanisms of locomotion activities in shrimp.