Maturation process and reproductive biology of female Arabesque greenling Pleurogrammus azonus in the Sea of Japan, off the west coast of Hokkaido

Abstract

The sexual maturation process and reproductive biology of female Arabesque greenling Pleurogrammusazonus in the Sea of Japan, off the west coast of Hokkaido, was examined using histological observations of ovaries. Maturation of P. azonus was classified into seven phases based on the presence of nine oocyte stages, post ovulatory follicles, and residual unspawned ova. Although vitellogenesis of P. azonus begins annually in August, hydrated oocytes were present in September and likely occurred several times during the spawning season until November. However, few oocytes at the intermediate stages of development were found during the premature and spawning phases. Based on these observations, the maturation pattern of female P. azonus can be classified as “group-synchronous, spawning several batches in a single spawning season,” as in other hexagrammid fish. The probability of maturation of female P. azonus depended on body size rather than age. The estimated length at 50 % maturity was approximately 240 mm in standard length (SL). The mean SL of age-1 females just before the spawning season varied yearly around the 50 % maturity length. Overall, these findings suggest that the growth of female P. azonus before the spawning season at age 1 year can markedly affect spawning biomass.