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| Stage | Development | Histological descriptions |
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F1
| Immature | Chromatin nucleolar stage dominant (large nucleus surrounded by a thin layer of cytoplasm; the nucleus contains a single and large nucleolus). Lamellae highly organised and well packed with previtellogenic oocytes, no signs of prior spawning in the form of brown bodies, postovulatory follicles or atretic oocytes. Thin gonadal wall and no spermatogenic materials present. |
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| F2 | Late immature | Perinucleolar oocytes present |
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| F3 | Early ripening | Chromatin nucleolar, perinucleolar, and cortical alveolar (appearance of York vesicles in the cytoplasm) oocytes present, with migrating nucleus |
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| F4 | Late ripening | Cortical alveolar and yolk granule oocytes abundant |
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| F5 | Ripe | Yolk plate formation is complete; oocytes are amoeboid in shape, and yolk granule oocytes (vitellogenic stages) are dominant. |
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| F6 | Mature running ripe | Oocytes in all stages of development may be present, although those in the early and late maturation stages are dominant. Hydrated oocytes or postovulatory follicles are present indicating that spawning had started. |
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| F7 | Mature resting | Lamellae not compact and often vacuolated, filled with previtellogenic oocytes; presence of brown bodies or atretic vitellogenic oocytes and intralamellae muscle bundles as the evidence of prior spawning and thick gonadal wall. |
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| F8 | Spent | Over 50% of the large yolk granule oocytes are atretic, brown bodies and postovulatory follicles are generally present. Lamellae disrupted and disorganised, with empty spaces previously occupied by oocytes. |
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| Transitional | Female tissue is degenerating; male tissue proliferating. Dorsal sperm sinus not fully formed; gonads consist of ovarian tissues but sperm crypts are present. |
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| M1 | Maturing | Post-transitional, newly transformed testes. Lobules containing spermatogenic cysts in all developmental stages. No sperm within the sperm sinuses; seminiferous lobules may be evident with previtellogenic oocytes in varying amounts that may fill the gonads. |
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| M2 | Mature ripening | Lobules containing cysts of male sperm cells in all developmental stages (spermatocytes and spermatids). Spermatozoa (tailed sperm) are free in the lumen. Little or no sperm in the sperm sinuses. |
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| M3 | Resting | Little spermatogenic activity, some free residual of spermatozoa within lobule, lumen, and sperm sinuses. Abundant cysts of spermatogonia inside the lobules. Vascularised and well developed stromal tissues. |
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| M4 | Mature ripe | Large pools of spermatids and spermatozoa in the large lumen of lobules and in the spermatic sinuses (dorsal and central). |
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| M5 | Spent | Testes disorganised and vacularised, with numerous brown bodies and well developed stroma tissues. |
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