REIBER, C.L.*; HARPER, S.L.; NEWELL, C; LAUNDRIE, N: Cardiac regulation in the grass shrimp (Palaemonetes pugio): larvae to adult.
Grass shrimp exhibit an anamorphic developmental pattern where successive larval stages show only minor anatomical changes. Larval shrimp exposed to stepwise reductions in water oxygen (150, 100, 75, 50 and 25 mmHg O2)were monitored for cardiac functions. Both heart rate and stroke volume of larval shrimp (stages 6 – 10) remained unchanged when exposed to moderate hypoxia (75 mmHg O2; below this a bradycardia was observed. Stroke volume remained at normoxic levels which resulted in a decrease in cardiac output. Juvenile and adult shrimp increased heart rate and decreased stroke volume when exposed to hypoxic water. This compensatory response maintained cardiac output down to 75 mmHg O2 below this cardiac output declined sugnificantly. This is in direct contrast to hypoxic responses observed in many other decapod crustaceans. Adult grass shrimp hearts also show only limited sensitivity to the cardioactive substances, GABA and 5-Ht. These results may suggest that cardiac regulatory mechanisms in decapods maybe more diverse than previously thought.
