Age, growth and maturation of the brown surgeonfish Acanthurus nigrofuscus at Okinawa-jima Island, Japan

Acanthurus nigrofuscus (Acanthuridae), a common fish on the coral reefs of the Ryukyu Islands, southern Japan, is considered to be important for maintaining the health of coral reef ecosystems. However, the life history of the species in Japan is largely unknown. In this study, age, growth and maturation of A. nigrofuscus was determined from 395 specimens [44.7-174.5 mm fork length (FL)] collected between September 2020 and March 2022 on the Miyagi coast, located on the west coast of Okinawa-jima Island, central Ryukyu Islands. Mean gonadosomatic indices were high in September 2020 and from May to August 2021 for both sexes, with histological observations of the gonads revealing that individuals with developed oocytes (migratory nucleus and hydrated stages) occurred from May to September. Postovulatory follicles were observed in individuals collected in September 2020 and from May to August 2021. The length (age) at 50% maturity was 104.1 mm FL (1.0 yr) for females and 93.9 mm FL (0.5 yr) for males, the age range being 0-25 yr (n = 193) for females and 0-20 yr (n = 170) for males, with von Bertalanffy growth functions of Lt = 148.6 {1 - exp [-0.51 (t + 1.55)]} for females, Lt = 156.0 {1 - exp [-0.38 (t + 2.01)]} for males, and Lt = 151.8 {1 - exp [-0.40 (t + 2.11)]} for both sexes combined. Similar to other species of Acanthridae, A. nigrofuscus has a long-lived biphasic growth trajectory, with rapid initial growth and a long lifespan after reaching asymptotic size.

Automated summary

This study examined the age, growth, and maturation of Acanthurus nigrofuscus on the Miyagi coast. Results showed that both male and female individuals had higher maturation levels in September 2020 and from May to August 2021. The species exhibited a long-lived biphasic growth trajectory after reaching asymptotic size.