There is very little known about the life history of lamprey species and the
data that is available is patchy and incomplete. Larval lampreys are referred
to as ammocoetes. They are pale brown, have a fleshy toothless oral hood
instead of sucker-like disc, and undeveloped eyes. They spend up to six
years burrowed in the sediment, feeding on diatoms and detritus by filtering
the water column. Physical cues initiate transformation and the river and
Pacific lamprey enter a juvenile stage termed macropthalmia. At this stage
the lampreys are silver in color, develop teeth and a sucker-like disc,
and form true eyes. Physiological transformations occur that initiate migratory
behaviors and enable them to tolerate sea water. They spend up to two years
as adults in the ocean, feeding on fishes and mammals. Conversely, the western
brook lamprey undergoes transformation directly into a non-feeding adult.
All three species of lamprey are highly prolific, they spawn in freshwater
during the spring, and die after spawning.
Species differentiation is difficult at the larval stage for these three species
of lamprey and is based largely on pigmentation. Transformers are identified
by dentition, with Pacific lamprey having three sharp cusps, the river lamprey
having two sharp cusps, and the western brook having two dull cusps. Adults are
much easier to differentiate. Pacific lamprey attend maximum lengths of 70 cm,
are bluish gray in the sea or during upstream migration and are dark brown on
the spawning grounds. River lamprey have similar color patterns as the Pacific
lamprey, but only attain a maximum size of 30 cm. Western brook lamprey attain
a maximum length of 15 cm and are dark brown.