Age-based demography and sexual pattern of the white-streaked grouper, Epinephelus ongus in Okinawa

Abstract

The demography and sexual pattern of the white-streaked grouper, Epinephelus ongus (Serranidae), in the Yaeyama Islands, Okinawa, were examined based on age assessment using otoliths and gonadal histology. The von Bertalanffy growth parameters were estimated as follows: L∞ = 34.35 cm total length (TL); K = 0.187 yr. −1; and t0 = − 0.975 yr. The maximum age was 20 yrs. The smallest mature female was 18.9 cm TL, and the age of females at 50 % maturity was estimated to be 3.3 yrs. There were significant differences between sexes in size and age, with males (mean ± SD: 29.2 ± 3.3 cm TL, 9.0 ± 2.7 yr) being larger- and older than females (23.5 ± 3.4 cm TL, 5.9 ± 1.8 yr) Inactive bisexuals appeared in intermediate size and age between both sexes, suggesting that bisexuals were essentially recognized as being in a transitional phase from functional female to male. These facts indicated a monandric protogynous hermaphrodite of the species. Furthermore, transitionals were found only in the non-reproductive period that precedes the spawning aggregation period, indicating that the timing of the sex change has seasonality.