Maturation characteristics and life-history strategies of the Pacific lamprey, Entosphenus tridentatus

Abstract: Lampreys (Petromyzontiformes) have persisted over millennia and now suffer a recent decline in abundance. Complex life histories may have factored in their persistence; anthropogenic perturbations in their demise. The complexity of life histories of lampreys is not understood, particularly for the anadromous Pacific lamprey, Entosphenus tridentatus Gairdner, 1836. Our goals were to describe the maturation timing and associated characteristics of adult Pacific lamprey, and to test the null hypothesis that different life histories do not exist. Females exhibited early vitellogenesis – early maturation stages; males exhibited spermatogonia – spermatozoa. Cluster analyses revealed an “immature” group and a...

Incidence of male intersex in adult Pacific lamprey (Entosphenus tridentatus), with a brief discussion of intersex vs. hermaphroditism in lampreys (Petromyzontiformes)

Abstract: We report the incidence of male intersex in adult Pacific lamprey (Entosphenus tridentatus (Richardson, 1836)) during their pre-spawning migration in fresh water. Although “hermaphrodites” have been suggested in other adult lampreys, this is the first detailed description and discussion of this phenomenon. A total of 0.5% of our adult Pacific lamprey from Willamette Falls (2 out of 427 adults) were intersex, with oocytes in the testes. This phenomenon was identifiable only by histological examination. The testes of the intersex males were immature, in the beginning stages of meiosis. One intersex male possessed primary growth or perinucleolar stage oocytes loosely interspersed throughout the testes, and...