Age, growth, and reproductive traits of two large emperor fishes, Lethrinus olivaceus and L. xanthochilus, around Yaeyama Islands, Okinawa, southern Japan

Abstract

Age, growth, and reproductive traits of two large emperor fishes Lethrinus olivaceus (n = 144, 26.9–76.8 cm fork length) and L. xanthochilus (n = 127, 24.2–64.8 cm) were investigated in the Yaeyama Islands (24°N, 124°E), Okinawa, southern Japan. Spawning was confirmed from April to June for L. olivaceus and April to May for L. xanthochilus. Otolith opaque zones in both species were found to be formed during spawning season and to be annual marks. Maximum observed ages were 22 years old for L. olivaceus and 17 years old for L. xanthochilus. Estimated von Bertalanffy growth parameters were L∞ = 71.9 cm, k = 0.258 year− 1, t0 = − 0.613 years for L. olivaceus and L∞ = 62.5 cm, k = 0.175 year− 1, t0 = − 2.157 years for L. xanthochilus. Hermaphrodite gonads were observed in adult size of L. olivaceus and immature size of L. xanthochilus. However, dominance of females in young age classes (L. olivaceus: 1–8 years old; L. xanthochilus: 1–4 years) and of males in older age classes (L. olivaceus: >9 years old; L. xanthochilus: >5 years) implied that both species are basically functional protogynous hermaphrodite. Relatively long lives and functional protogyny, which leads to low abundance of males, indicate that both species are vulnerable to fishing pressure.