Otolith check formation and accelerated growth associated with sex change in an annual protogynous tropical fish

Stefan Walker and Mark I McCormick

James Cook University, DOUGLAS, AUSTRALIA

THEME: ASFB

There is a strong link between gender and growth trajectories in fishes. Many tropical fishes are protogynous, maturing first as females and later changing sex to male. Sex change has ramifications for lifetime growth trajectories, however few studies examine the link between growth and sex change. We examine the growth of a haremic sandperch, Parapercis cylindrica (Family Pinguipedidae), in relation to sex change using otolith microstructure. We also explore whether previous growth history influences either the timing of sex change or sex change candidature. Examination of otolith increments and gonad histology show that P. cylindrica has a maximum longevity of 450 days, which is reduced in lower latitude populations, and that the species is monandric with males being larger that females at any given age. An abrupt optical discontinuity or 'check' on the sagittal otolith cross-sections was found to be associated with sex change. This check appears to be formed at the initiation of sex change. At sex change the growth rate, inferred from otolith increment widths, increased markedly, and more than doubled in some individuals. This accelerated growth was evident for a period of up to 30 days, after which time growth declined. Larval growth rate and relative size at metamorphosis, determined from otolith microstructure, did not influence which individuals changed sex, or the timing of their sex change. Evidence suggests that sex change, and subsequent growth acceleration in this haremic fish is socially governed.