Critical swimming speed, tail-flip speed and physiological response to exercise fatigue in kuruma shrimp, Marsupenaeus japonicus.

Critical swimming speed (U(crit)) and tail-flip speed of kuruma shrimp, Marsupenaeus japonicus (9.92+/-0.60 cm, 10.18+/-1.89 g) were determined at 25-26 degrees C. Metabolite concentrations in hemolymph, pleopods and abdominal muscles, and hepatopancreas were measured before exercise and immediately after exercise fatigue to evaluate physiological effect of exercise in M. japonicus. U(crit) and tail-flip speed of M. japonicus were found to be 32.87+/-0.53 cm s(-1) (3.30+/-0.08 BL s(-1)) and 151.49+/-6.92 cm s(-1) (15.38+/-0.65 BL s(-1)), respectively. Pleopods beat frequency of M. japonicus increased as swimming speed increased from 23.0 to 38.6 cm s(-1). The relationship between pleopods beat frequency (f, Hz) and swimming speed (v, cm s(-1)) could be described by linear model as: f=0.0773v+2.608, R(2)=0.94 (P<0.01). Exercise to fatigue led to severe loss of glycogen concentrations of hepatopancreas and muscle in M. japonicus, whereas the plasma lactate concentration increased significantly. The plasma glucose and lactate concentrations of M. japonicus after tail-flip fatigue were significantly higher than that after swimming fatigue. The results in the present study indicated that exercise fatigue of M. japonicus might be due to the accumulation of lactate in the hemolymph.