Changes in steroid hormone profiles and ovarian histology during salmon pituitary-induced vitellogenesis and ovulation in female New Zealand longfinned eels, Anguilla dieffenbachii gray.
To assess whether induced vitellogenesis in longfinned eels mimics that in naturally maturing conspecifics, female eels were artificially matured and steroid hormone status and oocyte cytology during oogenesis were evaluated. Successful induction of vitellogenesis was evident from the presence of yolk granules in the ooplasm of salmon pituitary homogenate (SPH)-injected, but not saline-, 17-hydroxyprogesterone-, and/or gonadotropin-releasing hormone-treated fish. In SPH-treated females, the migratory nucleus stage was reached after 33-53 days, followed by ovulation around 30 hours after induction of final maturation and ovulation. Only a portion of the germ cells matured, although resumption of vitellogenesis was seen in the majority of oocytes. In contrast, in ovaries of saline-injected controls, the most advanced oocytes were early vitellogenic. Atretic follicles were observed in ovaries of all eels, but abundance was greater in controls than in SPH-treated fish. SPH injections elevated plasma levels of estradiol-17beta and androgens, but not pregnenes, from within three days of treatment. Our results indicate that sex steroid levels in midvitellogenic hormone-treated females are similar to those in wild midvitellogenic females. In contrast, differences in yolk morphology of midvitellogenic follicles were seen between SPH-treated and wild females, especially in the second crop of midvitellogenic-sized oocytes measuring 300-400 microm in diameter. We discuss whether the observed differences affect egg quality, and perhaps explain the short life span of captive-bred eel larvae. J. Exp. Zool. 289:119-129, 2001.
Lokman
P M
PM
Department of Zoology, University of Otago, 316 Great King Street, P.O. Box 56, Dunedin, New Zealand. mark.lokman@stonebow.otago.ac.nz
Wass
R T
RT
Suter
H C
HC
Scott
S G
SG
Judge
K F
KF
Young
G
G
D019326:17-alpha-Hydroxyprogesterone / Q000494:pharmacology; D000818:Animals; D000835:Animals, Wild; D004524:Eels; D005260:Female; D012739:Gonadal Steroid Hormones / Q000378:metabolism*; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology; D008136:Longevity; D009866:Oogenesis / Q000502:physiology; D010053:Ovary / Q000033:anatomy & histology / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D010062:Ovulation Induction; D013256:Steroids / Q000378:metabolism*; D014818:Vitellogenesis / Q000502:physiology*
D012739:Gonadal Steroid Hormones; D013256:Steroids; D007987:Gonadotropin-Releasing Hormone; D019326:17-alpha-Hydroxyprogesterone