Fever and antipyresis in the crayfish Cambarus bartoni.

1. Normothermic Cambarus bartoni crayfish thermoregulating behaviourally in an electronic shuttlebox prefer a mean temperature of 22.1 degrees C +/- 0.5 S.E. of mean. 2. Injection of 1% saline, or addition of paracetamol to the ambient water, caused a statistically insignificant decrease in preferred temperature of 0.4 degrees C. 3. Injection of killed Aeromonas hydrophila bacteria into the abdomen caused a significant mean increase in preferred temperature of 1.8 degrees C (defined as a behavioural fever). 4. Injection of A. hydrophila, with paracetamol in the water, resulted in an insignificant increase of 0.1 degrees C above the normothermic temperature; thus paracetamol is antipyretic in crayfish, preventing fever but not altering afebrile thermoregulation. 5. These results suggest that similar mechanisms may be operating in the neuropharmacological mediation of fever in vertebrates and invertebrates.