How do brook lampreys differ from parasitic lampreys?

The primary difference between brook lampreys and parasitic lampreys lies in their feeding behavior after metamorphosis.

While many lamprey species, such as the sea lamprey, are parasitic as adults—attaching themselves to bony fishes to feed on their blood and tissues—brook lampreys (such as Lampetra planeri) do not feed at all after they complete their metamorphosis. Instead, upon reaching adulthood, brook lampreys focus entirely on maturing sexually, reproducing, and then dying.12

Both types begin their lives as filter-feeding ammocoete larvae that burrow in silt for several years before undergoing a radical transformation into their adult forms. However, unlike their parasitic counterparts that migrate to seek hosts, the nonparasitic brook lamprey spends its entire life cycle in fresh water.312