Reproductive Biology of Red Tilefish Branchiostegus japonicus in the East China Sea

The red tilefish Branchiostegus japonicus is an economically important demersal fish species with high-quality. However, research on its reproductive biology and population structure characteristics is limited. To better understand the reproductive biological features of B. japonicus, a study was conducted on 461 individuals collected from the East China Sea (27˚00΄ – 31˚00΄N, 122˚30΄– 127˚30΄E) from March to December in 2021. This study analyzed the relationship between standard length and the body weight, and detected the sex ratio, length at first sexual maturity, reproductive period, fecundity, and spawning type of this species. The results revealed a power function relationship between body weight (W) and standard length (L) in the samples as the following regression equation: W = 0.000014 L^3.16 (R² = 0.956). The sex ratio was close to 1:1 (χ² = 1.11, P > 0.05), and the sex ratio exhibited significant differences according to different standard lengths. Using the logistic equation, we estimated that 50% of B. japonicus individuals had a standard length at sexual maturity of L₅₀ = 210 mm. By analyzing the monthly variation in the gonadal index and the proportion of each stage of ovarian development in each month, we assumed that the spawning period of B. japonicus occurred from May to November, and the peak spawning period occurred from June to October. The absolute fecundity was 51441 ± 33232 eggs, the relative fecundity at the standard length was (210 ± 117) eggs mm^–1, and the relative fecundity relative to body weight was (184 ± 89) eggs g^–1. The distribution of the egg diameter of B. japonicus had only one obvious peak, indicating the spawning pattern of B. japonicus was once a year. This study updated and enriched the basic biological data of B. japonicus, which is beneficial for obtaining a better understanding of its population dynamics, and promoting the conservation and sustainable utilization of B. japonicus in East China Sea.