Reef Fish Reproductive Phases and Key Histological Indicators

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.

Immature phase

Phase characteristics

Only oogonia and primary growth oocytes.
No muscle bundles.
Thin ovarian wall.
Well-organized lamellae.

Most advanced oocyte or key histological indicator:
Perinucleolar

Early developing subphase

Phase characteristics

Primary growth and cortical alveolar oocytes only.
Zona pellucida formed.
Can be some atresia.

Most advanced oocyte or key histological indicator:
Cortical alveolar

Developing phase

Phase characteristics

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

Most advanced oocyte or key histological indicator:
Vitellogenic 2

Spawning capable phase

Phase characteristics

Completed vitellogenesis (Vtg3).
Can have postovulatory follicles present.

Most advanced oocyte or key histological indicator:
Vitellogenic 3

Actively spawning subphase

Phase characteristics

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