Reef Fish Reproductive Phases and Key Histological Indicators

Standardized terminology for describing reproductive development and histological indicators promotes better communication and comparison of research.

As the use of histology to evaluate reproductive condition in fishes has grown, so too have the number of histological classification schemes and the terminology used with them. Although there are several terms which are frequently used, the same term can often mean different things to different scientists. In addition, developmental stages are often referred to by number, but these numbers signify different classes depending on the classification scheme being used. In an effort to allow better communication and comparison of different species' reproductive strategies, a group of international scientists worked to develop a standardized terminology for describing reproductive development (Brown-Peterson et al. 2011). The table below demonstrates the use of this terminology and key histological indicators for red snapper. More examples are available in the Reef Fish Reproduction and Histology Flickr set.

 

Ovarian cross section Phase characteristics Most advanced oocyte or key histological indicator
 immature ovarian phase

Immature phase

Only oogonia and primary growth oocytes.

No muscle bundles.

Thin ovarian wall.

Well-organized lamellae.

 perinucleolar development

Perinucleolar

 early development ovarian subphase

Early developing subphase

Primary growth and cortical alveolar oocytes only.

Zona pellucida formed.

Can be some atresia.

 cortical alveolar development

Cortical alveolar

 developing ovarian phase

Developing phase

Primary growth, cortical alveolar, vitellogenic oocytes stages 1 (Vtg1) and/or 2 (Vtg2).

Atresia can be present.

 Vitelogenic oocytes stage 2 development

Vitellogenic 2

 Spawning capable ovarian phase

Spawning capable phase

Completed vitellogenesis (Vtg3).

Can have postovulatory follicles present.

 Completed vitelogenesis stage 3

Vitellogenic 3

 Actively spawning ovarian phase

Actively spawning subphase

Late oocyte maturation – germinal vesicle migration (GVM), germinal vesicle breakdown (GVBD), and hydration – or ovulation.

Fresh postovulatory follicles.

germinal vesicle migration

GVM


hydrating oocyte

fully hydrated oocyte

Hydration

 regressing ovarian phase

Regressing phase

Most vitellogenic oocytes are atretic.

First indicator of alpha atresia is a discontinuous zona pellucida.

Primary growth and cortical alveolar oocytes present.

 

 alpha atresia

Alpha atresia

 regenerating ovarian phase

Regenerating phase

Oogonia and primary growth oocytes present.

Muscle bundles common.

Thick ovarian wall.

May have late stage atresia. 

 

 thick ovarian wall

Thick ovarian wall



FWC Facts:
The bowfin, or mudfish, is a ‘living fossil’ and is the only freshwater fish with a gular bone, a bony plate on the exterior of the lower jaw between the two jawbones.

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