Fish demonstrate a variety of reproductive strategies. Wrasses are usually protogynous hermaphrodites, which means that they change sex from a functional female to a functional male. Males may develop either from larvae/juveniles or from adult females. The eastern blue groper, a species distributed throughout south-eastern Australia but with greatest numbers in New South Wales were investigated to describe their reproductive biology. This is an iconic species in New South Wales and information was first reported in old paper (published in 1995) originally forming part of my PhD research (Gillanders 1995).
Fish were sampled from two populations near Sydney. As they were caught the colour of the fish was recorded. Colour was then linked to the gender of the fish by examining their gonads. For both populations, the majority of females were brown and most males were blue suggesting that the species is sexually dichromatic. These results confirm that they change colour about the time of sex change.
Population structure (age and size frequency; sex ratios) showed that males dominated the larger sizes and ages, whereas females predominated the smaller size and age classes. The sex ratio was heavily biased towards females. These factors suggest that blue groper start life as females and change sex to males at larger sizes and ages. Histological examination of male gonads also suggested that they had all previously been females.
Fish reproduced during the winter months (between July and October). This is similar to the western blue groper which spawn between early winter and mid-spring (Coulson et al. 2009).
Fish appeared to change sex at a critical size, but further work is required to ascertain factors initiating sex change. For example, does removal of a large male cause the largest female to change sex? Or are the number of males determined by the ratio of females: males?
While the eastern blue groper is not subject to extensive fishing pressure, species that change sex require extra considerations in terms of management. Most stock assessments of sex changing fish ignore that fact that the species changes sex and rarely is it modelled.
Title by William Coutts (3rd year Marine Ecology student, 2016)
Graphics by Sean Vial (top) and Laura Male (bottom) (3rd year Marine Ecology students, 2016)
Coulson PG, SA Hesp, NG Hall, IC Potter (2008) The western blue groper (Achoerodus gouldii), a protogynous hermaphroditic labrid with exceptional longevity, late maturity, slow growth, and both late maturation and sex change. Fishery Bulletin 107: 57-75
Gillanders BM (1995) Reproductive biology of the protogynous hermaphrodite Achoerodus viridis (Labridae) from southeastern Australia. Marine and Freshwater Research 46: 999-1008