Influence of hypoxia on cardiac functions in the grass shrimp (Palaemonetes pugio Holthuis)

Crustaceans frequently encounter hypoxic water and have evolved a variety o f compensatory mechanisms to deal with low O-2 conditions. Typically, large decapod crustaceans attempt to maintain cardiac output by increasing strok e volume to compensate for the hypoxia-induced bradycardia. Grass shrimp (P alaemonetes pugio), small hypoxic tolerant decapod crustaceans, were used t o investigate cardiac responses to hypoxia in a smaller crustacean using vi deomicroscopy and dimensional analysis techniques. In addition, these techn iques were compared to the more established dye dilution technique for calc ulation of cardiac output. No significant difference was found between the two methods for determining cardiac output in grass shrimp. Cardiac paramet ers (heart rate f(H), stroke volume V-S, and cardiac output V-b) were monit ored in grass shrimp exposed to progressive hypoxia (P(O2)s = 20, 13.3, 10, 5.3, and 2 KPa O-2). Shrimp exhibit a cardiac response to hypoxia that is atypical when compared to larger crustaceans. Cardiac output was maintained until water P-O2 fell below 10 KPa O-2. This maintenance of V-b is consist ent in both large and small decapods, however the mechanism differs. In gra ss shrimp, V-S was P-O2 dependent and, declined significantly while f(H) in creased significantly when P-O2 was reduced to 13.3 KPa O-2. (C) 1999 Elsev ier Science Inc. All rights reserved.