Reproductive biology and early life history of the marine teleost Platycephalus speculator Klunzinger (Platycephalidae) in a temperate Australian estuary

A description is given of the seasonal trends exhibited by gonadosomatic indices, gonadal maturation and oocyte diameters of different age classes of the flathead, Platycephalus speculator , in Wilson Inlet, a seasonally closed estuary on the south coast of Western Australia. These data indicate that, although sexual maturity is attained by the vast majority of males at the end of the first year, it is delayed for a further year in females. Breeding occurs predominantly during the summer and early autumn (December to March). The presence of late stage eggs and preflexion larvae between January and March of 1988, when a sand bar was present across the mouth of the inlet channel, demonstrates that this marine species spawns in the estuary. Spawning also occurred within the estuary in the following year, even though the estuary mouth was open during the breeding period. Although P. speculator typically spawns at sea, spawning in Wilson Inlet takes place at salinities less than 30%, i.e. below full strength sea water. The distribution of oocyte diameters and the presence of mature eggs and post‐ovulatory follicles in the ovaries of many fish indicate that P. speculator spawns more than once in a breeding season. Late stage eggs of P. speculator are pelagic, ca 0.8 mm in diameter and possess embryos with an unpigmented yolk sac containing a single, pigmented oil globule. The larvae are pelagic and characterized by a relatively large and wide head bearing a series of spines, a moderately long gut, an elongated and compressed tail, large fan‐shaped pectoral fins and 25 or 26 myomeres. Flexion of the notochord occurs between 5 and 7 mm and settlement takes place at approximately 13 mm.