Effects of unilateral ovariectomy on recruitment and growth of follicles in the rainbow trout, Oncorhynchus mykiss

Abstract

Virgin female rainbow trout, Oncorhynchus mykiss, were unilaterally ovariectomised at various stages of ovarian development to investigate the effect of the removal of one ovary on subsequent recruitment and growth of follicles in the remaining ovary. The right ovary was removed from groups of 12-15 fish, 12, 7 and 4 months before they were due to ovulate, and the gonadosomatic index and follicle number and size determined just prior to ovulation. There were no differences in fecundity or follicle size in fish unilaterally ovariectomised at 12 and 7 months prior to ovulation compared to the controls. However, in the females unilaterally ovariectomised 4 months prior to ovulation, the remaining ovary either had the normal number of follicles for a single ovary but of a significantly larger size than follicles in the controls, or alternatively had almost 70% more than the normal number of vitellogenic follicles but comprising two distinctly different size populations. Differences in plasma oestradiol-17β concentrations at the final sample were seen only in females unilaterally ovariectomised 4 months prior to ovulation, where the levels were significantly lower than both the sham operated and control fish (p < 0.05).These data show that in the rainbow trout, complete compensatory ovarian hypertrophy following unilateral ovariectomy can occur throughout a major part of ovarian development, but that follicle recruitment is limited to stages up to (and therefore fecundity is determined by) mid-vitellogenesis.

Mechanisms of oocyte development in European sea bass (Dicentrarchus labrax L.): investigations via application of unilateral ovariectomy

“…Macroscopically, the response of European sea bass to ULO was similar to those previously reported for other fish species (Goswami & Sundaraj 1968a, Dadzie & Hyder 1976, Tyler et al 1994, 1996, 1997, Luckenbach et al 2008, i.e. the ovarian lobe remaining after surgery underwent a compensatory growth ultimately reaching a total mass equivalent to that of intact paired gonads.…”

“…Therefore, and unlike that reported for rainbow trout hemi-castrated at pre-or early vitellogenesis (Tyler et al 1994(Tyler et al , 1996(Tyler et al , 1997, the compensatory ovarian growth observed in European sea bass after ULO was not associated with recruitment of a complete new batch of primary oocytes into the secondary growth phase. Rather, such compensation was based on an extra recruitment of follicles at mid and late vitellogenesis, probably derived from the pool of early vitellogenic oocytes already existing in the ovary.…”

“…In teleost fish, as for other vertebrate taxa, the surgical removal of one of the ovarian lobes, referred to as unilateral ovariectomy (ULO) or hemi-castration, induces a compensatory growth in the remaining ovarian lobe ultimately generating a single lobe equivalent in mass to the intact paired ovary of control individuals (Goswami & Sundaraj 1968a, Dadzie & Hyder 1976, Tyler et al 1994, 1996, 1997, Luckenbach et al 2008. The mechanisms involved in such compensatory growth, which may vary across species and with the reproductive status of the animal, include increased mitotic activity of oogonia, new recruitment of primary follicles into the secondary growth phase, increased size of pre-existing follicles, and/or reduced follicular atresia (see references above).…”

Croissance ovocytaire et régulation stéroïdienne chez les poissons à pontes unique et multiples : une revue

“…Il s'avérerait maintenant intéressant d'étudier les facteurs qui initient les processus de là croissance ovocytaire ainsi que ceux qui contrôlent le recrutement ovocytaire, surtout chez les poissons à pontes multiples qui divisent leur potentiel reproductif. La technique d'ovariectomie unilatérale, récemment développée (Tyler et al 1994), constitue un outil valable pour ce genre d'étude. D'autre part, l'étude des stéroïdes dits non classiques (Kime 1993) chez les poissons pourraient permettre une meilleure compréhension des mé-canismes contrôlant la régulation de l'ovogenèse.…”

Cloning and Characterization of a Novel Oocyte-Specific Gene Encoding an F-Box Protein in Rainbow Trout (Oncorhynchus mykiss).

“…The stages of ovarian development in fish were determined based on morphological characteristics and the size of the oocytes as described previously [15]. The five stages of ovarian development include: early pre-vitellogenesis (≤ 0.5 mm), late pre-vitellogenesis (≤ 0.65 mm), early-vitellogenesis (0.65-1.1 mm), med-vitellogenesis (1.1-2.1 mm) and latevitellogenesis (2.1-4.0 mm).…”