Oogenesis, Oocyte Atresia, Ovarian Development and Reproductive Senescence in the Dusky Flathead Platycephalus fuscus (Teleostei)

The aim of the present study is to examine developmental changes of oocytes and ovaries of a wild population of dusky flathead Platycephalus fuscus (Cuvier, 1829). This fish is endemic to the east coast of Australia where it inhabits estuaries and coastal waters. It is extensively fished throughout its range. It is a serial spawning teleost, capable of producing vast numbers of externally fertilised eggs in batches over a protracted annual spawning period. Successful egg production, as indicated by the presence of hydrated oocytes and post ovulatory follicles, is commonly observed in small and mid-size females (35cm–65cm Total Length; 2-6 years old) which numerically dominate the female component of the spawning aggregation. Oocyte atresia, at various levels, commences at the vitellogenic oocyte stage, and occurs in all mature fish during the spawning period. Mass oocyte atresia and degenerate ovaries were commonly observed in large fish (>70 cm Total Length and 7 years old), indicating that reproductive senescence occurs after females reach this size.