Investigation on the interrelation between total length, age,sex maturation and sex reversal in <italic>Epinephelus fasciatus</italic>

Abstract

The growth, development and maturation are comprehensively affected by age, total length, sex hormone and so on in teleosts. The blacktip grouper <italic>Epinephelus fasciatus</italic> is an important and valuable marine economic species widely distributed in the coastline of east Asian countries. Recently, with the global warming and increase of sea water temperature in the coastline of Japan, the time of growth, development and maturation of this species has become shorter than before while the size of growth and maturation has become smaller than before. Therefore, the access to information and research work on the growth, development and maturation of this species becomes very important and indispensable in the coastline. To understand the interrelation between total length(TL), age, sex maturation, and sex reversal, <italic>Epinephelus fasciatus</italic> was captured in the coastline of Nagasaki city in Japan from July 2015 to June 2018. The TL, body weight, age, sex, gonadal developmental maturity, and gonadosomatic index (GSI) were measured and calculated. In addition, the changes of 17β-Estradiol (E₂) content in the serum were analyzed. The results indicated that the mature proportion and GSI of female <italic>Epinephelus fasciatus</italic> individuals reached the peak in July, suggesting that the sexual mature timing of this species might be in July. The mature female <italic>Epinephelus fasciatus</italic> individuals were firstly detected at 3 years old, and the TL was about 24.5 cm. Accompanied with the increase of TL, the quantities of the mature individuals gradually increased, which indicated that the age of the first sex maturation was at 3 years old in this species. In addition, at 3 and 4 years old in female <italic>Epinephelus fasciatus</italic>, the E₂ content in the mature individuals was significantly higher than that in the immature individuals (<italic>P</italic><0.05), suggesting that E₂ played an important role in inducing oocyte maturation in this species. The intersex individuals were detected at about 35.7 cm and 9 years old, and the male individuals were detected at about 36.7 cm and 7 to 12 years old. In summary, the sexual mature timing of the <italic>Epinephelus fasciatus</italic> in the coastline of Nagasaki city in Japan was in July, which was closely related to the increase of E₂ content. The first sex maturation and sex reversal were at 3 years old or 7 to 12 years old, respectively. Based on the investigation of <italic>Epinephelus fasciatus</italic> in the coastline of Nagasaki city, the interrelation between total length, age, sex maturation and sex reversal was studied to provide the basic biological data and theoretical basis for resource conservation and artificial propagation.