Least brook lamprey do not have a juvenile period (see life cycle), and maturation continues directly into the adult stage, at which point the body swells as the gonads are developed.

The males (aided by females) construct small nests by picking up pebbles with their oral disks and moving them to form the rims of shallow depressions.

Ammocoetes leave the nest and seek out slow-flowing water in sandy areas, where they burrow and begin feeding.

Ammocoetes live burrowed for 3–7 yr, feeding on microscopic plant and animal life and detritus (decaying matter).

Mature ammocoetes will begin metamorphosis in the late summer through the fall in preparation for spawning the following year.