Metabolic characteristics of the Japanese clam Ruditapes philippinarum (Adams & Reeve) during aerial exposure

Some metabolic end-products in tissues and physiological parameters of haemolymph of the Japanese clam Ruditapes philippinarum (Adams & Reeve) were investigated under aerial exposure at 15 degrees C with low relative humidity (RH) (22%) or high RH (91%). Acclimated clams in water at 15 degrees C were used as a control and to supply the low or high RH experiment. The low RH experiment was conducted at air exposure for 50h (LHS50), and the high RH experiment for 50h (HH50) and 100h (HH100) Accumulation of succinate and alanine in the tissues proved that the clam shifted its metabolism to anaerobiosis. Lactate accumulation did not occur. Glucose concentrations in tissues increased slightly during exposure except for HH50. The total free amino acid contents (363-410 mu mol g(-1)) were higher than those of glucose (530-804 mu mol 100 g(-1)), suggesting that the free amino acids might play a more dominant role in the metabolism. Increase in the haemolymph pCO(2) did not influence the acid-base balance in the haemolymph during exposure at both humidity conditions. Increase in the haemolymph ammonia from 48.2 to 57.1 mu mol 100 g(-1) and to 131.0 mu mol 100 g(-1) at LH50 and HH100, respectively, suggested that ammonia might function as an important buffering factor during aerial exposure. Retention values of the haemolymph pot even at the longest exposure time (16.30 mmHg at LH50 and 14.69 mmHg at HH100) indicated that the clams depend partially on some aerobic manner.