Behavioral Response of Pacific Lamprey (Entosphenus tridentatus) to Predator Odors

Identifying odors that repel lamprey may aid in efforts to guide these fish past navigational hazards during spawning migrations. Using two-choice maze experiments, we tested responses of migratory-phase, adult Pacific lamprey (Entosphenus tridentatus) to four candidate repellent odors (white sturgeon Acipenser transmontanus, human saliva, dead Pacific lamprey, and river otter  Lontra canadensis). Fish were tagged with passive integrated transponders and monitored with antennas integrated into each maze. We counted the number of entries and duration of time spent in each arm of the maze during a 12 h control period (no odor) and a 12 h experimental night when repellent odor was introduced into one arm at a metered rate. Lamprey showed regular searching behavior at night and individual fish exhibited consistent movement between test nights. Unlike sea lamprey (Petromyzon marinus), Pacific lamprey did not appear to be repelled by the scent of dead conspecifics or human saliva (P>0.05). They also did not avoid the arm with sturgeon odor (an aquatic predator). However, contrary to our prediction, odor from river otters (a terrestrial predator) appeared to attract Pacific Lamprey: adults made significantly (P<0.01) more entries and spent more time in arms that received otter odor than those that did not.