Changes in steroid hormone profiles and ovarian histology during salmon pituitary-induced vitellogenesis and ovulation in female New Zealand longfinned eels,Anguilla dieffenbachiigray

Abstract

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‐17β 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 μm 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. © 2001 Wiley‐Liss, Inc.

Changes in Sex Steroids and Ovarian Steroidogenic Enzyme mRNA Levels in Artificially Maturing Japanese Eel (Anguilla japonica) and Naturally Maturing New Zealand Longfin Eel (Anguilla dieffenbachii) during Vitellogenesis

“…These findings prompted Ijiri et al [41] to query whether artificial maturation of Japanese eels leads to abnormal steroidogenesis and aberrant oocyte development. Other freshwater eel species also display a rapid increase in blood E2 levels toward completion of oocyte growth [37,[42][43][44][45].…”

“…To provide insights on the rise and fall of measured endpoints during a weekly injection regime, subsets of the eels were anesthetized after 2-4 weeks (early vitellogenic, EV; n = 8) and after 5-7 weeks of treatment with SPH (midvitellogenic; MV; n = 10) or Ringer (PV; n = 3). Blood was sampled by syringe from the caudal vasculature, and ovarian biopsies were obtained as described previously [42]. These eels were killed by anesthetic overdose after 2-4 weeks (EV; n = 8) and after 5-7 weeks of treatment with SPH (MV; n = 10) or Ringer (PV; n = 3); samples from remaining eels were collected two days later.…”

Anguillid Eels as a Model Species for Understanding Endocrinological Influences on the Onset of Spawning Migration of Fishes

“…The gonadosomatic index (GSI, the % gonad weight of body weight) of female eels increases progressively during the silvering process. Gonad development is directly correlated to the other morphological changes that occur during silvering, such as skin color modifications and eye-size enlargement [ 10 , 11 , 12 , 13 , 21 , 22 ]. The GSI increase can be used as a good criterion for estimating the advancement stage of the European eel silvering process [ 12 ].…”

Identification of molecular markers in pectoral fin to predict artificial maturation of female European eels (Anguilla anguilla)

“…Hitherto unknown factors trigger the transition of immature yellow eels to pre-pubertal silver eels, a process called silvering, and subsequent migration from fresh water habitats in Europe and North-Africa to the presumed spawning area in the Sargasso Sea (Tesch, 2003). The silvering process is characterized by multiple external and internal changes, such as skin coloration, enlargement of the eyes, increased pectoral fin length, darkening of the pectoral fins, degeneration of the gastrointestinal system, increased plasma sex steroid and vitellogenin levels and increased oocyte diameter (Acou et al, 2005;Durif et al, 2005;Palstra et al, 2011;Pankhurst, 1982;Pérez et al, 2011;Sbaihi et al, 2001;van Ginneken et al, 2007; also reviewed by Aoyama and Miller, 2003;Lokman et al, 2001). Nonetheless, at the onset of their migration silver eels are still far from sexually mature.…”