Abstract
The brook lamprey (Lampetra reissneri) was collected at the Hosshoji River, Tottori Prefecture, Japan, once a month for a year.Metamorphosing individuals were collected in autumn and immature adults in winter.Ammocoetes larvae were collected throughout the year.From size-frequency histograms, the larval period was estimated to be more than three and one-half years.Ammocoetes larger than 160mm in total length were always female.Metamorphosing and adult females were larger than corresponding males.This may mean that at least some females metamorphose one year later than males.In ammocoetes, the relative prebranchial and branchial length decreased, and the relative tail length increased during growth.Egg diameter increased rapidly during metamorphosis.
