Short Communication Lactate Dynamics during Locomotor Activity in the Blue Crab, Calljnectes

In recent years there has been considerable interest in the effects of locomotor activity on respiratory gas exchange and acid-base balance in the Crustacea (reviewed by Herreid, 1981; McMahon, 1981; McMahon & Wilkens, 1983). However, the partitioning of energy metabolism between aerobic and anaerobic pathways during crustacean locomotion is still poorly understood (Herreid, 1981; Full & Herreid, 1984). Booth, McMahon & Pinder (1982) recently reported that the highly active swimming crab, Callinectes sapidus, elevates oxygen uptake rate to a steady state level within 2 min after the onset of enforced swimming activity. In contrast, several terrestrial crabs studied by Herreid and co-workers (Herreid, 1981) showed sluggish aerobic responses to exercise, and did not attain steady state levels of oxygen uptake during 10—20 min of treadmill running at various speeds. The short 'oxygen deficit' period displayed by C. sapidus at the start of exercise resembles the oxygen uptake kinetics of highly aerobic mammals (cf. Cerretelli, Pendergast, Paganelli & Rennie, 1979) and suggests that C. sapidus might be less dependent on anaerobic metabolism to fuel locomotion than some of the terrestrial crabs studied thus far. Nevertheless, in C. sapidus haemolymph lactate concentrations rose to lOmequivP during 25 min of continuous swimming (Booth et al. 1982), indicating that anaerobic glycolysis was utilized to some extent. Because the temporal relationship between lactate formation in the tissues and its appearance in the haemolymph was not known, Booth et al. (1982) were unable to determine if lactate was produced only during the 'oxygen deficit' period of early exercise, or if lactate production continued while aerobic metabolism was at steady state. In the present study we report measurements of lactate concentration in haemolymph, locomotor muscle and in the whole animal for C. sapidus at rest and at various times during and after enforced swimming activity. These data allow us to examine for the first time in an exercising crustacean the time courses for net lactate formation