Photokinesis and behavioral thermoregulation in adult sea lampreys (Petromyzon marinus)

Photokinetic responses of adult sea lampreys were used to facilitate study of their thermoregulatory behavior in a laboratory thermal gradient. Lampreys swam about actively when room lights were switched on, but attached themselves to the side walls at temperature‐dependent sites in the gradient when lights were turned off. Attachment sites were significantly correlated with temperature (correlation coefficient = 0.73, p < 0.01). Acete mean preferred temperature of five lampreys, previously acclimated at 10°C, was 14.3 ± 3.0 (S.D.) °C. This is the first experimental demonstration of behavioral thermoregulation in this ancient class of jawless vertebrates (Agnatha).