Integrated physiological responses to feeding in the blue crab Callinectes sapidus.

The passage of a barium meal (15 % by mass) was followed through the digestive system of the blue crab Callinectes sapidus by flash-freezing crabs at set intervals, followed by radiography of specimens. Food moved from the oesophagus into the stomach region within 15 min. After 1-2 h, food was visible in the midgut, at 6 h it had reached the hindgut, and material was still present in the stomach at this time. The stomach was emptied between 8 and 10 h after feeding, and the entire digestive system was cleared of material after 18 h. A pulsed-Doppler flowmeter was used to monitor cardiac variables and arterial haemolymph flows during a 4 h control and 24 h postprandial period. Heart rate increased immediately upon food detection and remained elevated for 16-18 h after food ingestion. There was no significant change in stroke volume of the heart, and total cardiac output increased significantly and remained elevated above pre-feeding levels for 24 h after feeding. There was no change in haemolymph flow through the anterior or posterior aorta, but flow increased in the sternal, anterolateral and hepatic arteries. These changes in haemolymph flow reflected the use of the chelae and mouthparts in feeding, contraction of the visceral muscle surrounding the gut system and mobilisation of enzymes from the hepatopancreas. There was also a postprandial increase in the rate of oxygen uptake (apparent specific dynamic action). The rate of oxygen consumption (M(dot)(O2)) reached maximal levels 4 h after feeding and decreased slowly thereafter, reflecting the increased use of oxygen in digestion and absorption.