MEASUREMENTS OF OXYGEN-UPTAKE, HEART AND GILL BAILER RATES OF THE CALLIANASSID BURROWING SHRIMP TRYPAEA-AUSTRALIENSIS DANA AND ITS RESPONSES TO LOW-OXYGEN TENSIONS

Burrowing shrimps are likely to encounter temporal and spatial changes in oxygen tension as they move about in their burrows. Callianassid s hrimps apparently tolerate a wide range of oxygen tensions so the phys iological nature of this tolerance is of interest. The oxygen uptake, heart and gill bailer rates of the burrow-dwelling shrimp, Trypaea aus traliensis Dana were studied in the laboratory, particularly during fa lling oxygen tension. Trypaea australiensis had a critical point (P-c) of oxygen uptake of about 5 kPa and showed a very low ''settled'' or routine respiration rate (25.6 +/- 6.31 mu mol O-2 kg(-1). min(-1), me an +/-SD) for a decapod crustacean of this size (2 to 6 g wet weight). Some of the variation in oxygen uptake rate was explained by body siz e and the weight exponent (b) increased significantly when shrimp reco vered from handling. The heart and bailers of T. australiensis showed the same general responses to a gradual fall in oxygen tension as do o ther crustaceans that are strong ''oxy-regulators'' and the heart beat decreased but persisted during anoxic conditions, and responded rapid ly to re-oxygenation, An acute fall in oxygen tension (<1.5 kPa) did n ot lead to bradycardia. These results are consistent with an animal th at attempts to prolong aerobiosis for as long as possible but which ne vertheless curtails heart rate and presumably metabolic rate in respon se to long-term anoxia.