Comparative Oogenesis in Annual and Non-annual African Killifishes: Oocyte Staging in the Fastest-Aging Vertebrate, Nothobranchius furzeri

Nothobranchius furzeri and Aphyosemion australe show a highly conserved oocyte development sequence across PG, SG, maturation, and ovulation, while N. furzeri develops a significantly thicker zona pellucida.

• Why it matters: Annual killifish must survive seasonal desiccation, but it is unclear how reproductive traits emerge during oogenesis and which ovarian structures evolve to support embryo-environment interactions.
• What they did: The authors compared oogenesis morphology and morphometrics in both species from early development through Primary Growth, Secondary Growth, maturation, and ovulation, tracking follicular epithelium, cortical alveoli, oil droplets, and zona pellucida thickness and ornamentation.
• The result: Oocyte diameter and follicular epithelial development were not significantly different between species at any stage, whereas zona pellucida thickness increased significantly in N. furzeri from early SG through maturation with distinct chorionic ornamentation patterns, suggesting egg-envelope divergence alongside conserved oogenesis.

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