Growth and reproduction of Japanese seabass, Lateolabrax japonicus, in the southern waters off the Korean Peninsula.

Japanese seabass (Lateolabrax japonicus) is a commercially and ecologically important species found in Korean waters, which functions as a top predator in coastal marine ecosystems. However, research on the reproduction and growth of L. japonicus in Korean waters remains limited; furthermore, comprehensive investigations integrating both reproductive and growth characteristics are lacking. Therefore, we examined the growth parameters and reproductive characteristics of L. japonicus inhabiting the southern waters of Korea. A total of 639 specimens (250 females and 389 males), ranging from 20.2 to 97.6 cm in total length (TL), were collected monthly between January and December 2020. The overall sex ratio (female: male) was 1:1.56, indicating male dominance; however, the proportion of females increased among individuals larger than 60 cm TL. Analysis of otolith marginal increments revealed that annuli formed once annually between March and April, following the spawning period. Growth parameters estimated using the von Bertalanffy growth function yielded an asymptotic TL of 117.36 cm for females and 109.58 cm for males, with a maximum estimated age of 11 years in both sexes. Based on monthly variation in the gonadosomatic index (GSI) and histological observations, spawning occurred from January to March. Males matured earlier and exhibited a longer spawning duration than females. Oocyte developmental patterns indicated that L. japonicus is a multiple spawner, releasing batches of eggs at least twice within the spawning season, and displayed group-synchronous oocyte development. The TLs at 50% maturity were estimated to be 34.2 cm for females and 27.3 cm for males. These findings provide essential information for the sustainable management of L. japonicus stocks, and support the establishment of effective conservation measures-including the designation of spawning protection areas, implementation of minimum size limits and preservation of critical habitats.