Aspects of life history characteristics and physiological processes in smolting Pacific Lamprey, Lampetra tridentata, in a central Oregon coast stream

Rotary screw traps were used to estimate Pacific lamprey smolt yield, outmigration timing, age structure and sex ratio for Tenmile Creek basin, Lane County, Oregon. Traps were fished March to June and August to December 1994 and March to June and October to December 1995. Lamprey smolts caught in the traps were marked and released upstream. Recaptured fish were used to calculate trap efficiencies and daily and weekly estimates of outmigrating smolts. Little movement of smolts occurred before November. Outmigration peaked in late November and was complete both years by 2 December. Ages of smolts were determined using length-frequency analysis and by reading statoliths. Tenmile Creek Pacific lamprey smolts have an extended freshwater residency. Male to female ratios were approximately 1:1 both years. Larval, metamorphosing and smolting Pacific lamprey were examined for changes in skin guanine concentrations, gill (Na+K)-ATPase activities and plasma thyroid hormone levels during a 14 mo period. Seasonal peaks were observed in gill (Na+K)-ATPase activities and plasma thyroid hormone levels in larvae. Metamorphosing and smolting lamprey showed increases in skin guanine concentrations and gill (Na+K)-ATPase activities along with decreases in plasma thyroid hormone levels. Smolting lamprey challenged with artificial seawater showed no significant changes in the parameters observed

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

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 “maturing–mature” group for each sex. We found statistically significant differences between these groups in the relationships between (i) body mass and total length in males; (ii) Fulton’s condition factor and liver lipids in males; (iii) the gonadosomatic index (GSI) and liver lipids in females; (iv) GSI and total length in females; (v) mean oocyte diameter and liver lipids; and (vi) mean oocyte diameter and GSI. We found no significant difference between the groups in the relationship of muscle lipids and body mass. Our analyses support rejection of the hypothesis of a single life history. We found evidence for an “ocean-maturing” life history that would likely spawn within several weeks of entering fresh water, in addition to the formerly recognized life history of spending 1 year in fresh water prior to spawning—the “stream-maturing” life history. Late maturity, semelparity, and high fecundity suggest that Pacific lamprey capitalize on infrequent opportunities for reproduction in highly variable environments.Keywords: Primitive, Petromyzontiformes, Life histor

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

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 the other possessed at least 6 mid-vitellogenic oocytes (0.6 mm, mean long diameter) separate from the testes. Because premetamorphic lamprey can possess both female and male gonial cells, we hypothesize that intersex is a remnant larval trait and that these fish failed to fully develop into males during metamorphosis.Keywords: intersex, maturation, primitive fish, reproduction, cyclostomes., gonochoristicKeywords: intersex, maturation, primitive fish, reproduction, cyclostomes., gonochoristi

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

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 the other possessed at least 6 mid-vitellogenic oocytes (0.6 mm, mean long diameter) separate from the testes. Because premetamorphic lamprey can possess both female and male gonial cells, we hypothesize that intersex is a remnant larval trait and that these fish failed to fully develop into males during metamorphosis