Gonad Maturity Stages of the Pacific Ocean Perch Sebastes alutus (Sebastidae)

The results of a study of the ovaries and testes of the Pacific ocean perch Sebastesalutus are presented based on the materials collected in the spring of 2019 and 2021 in the Bering Sea. Histological methods were used to accurately determine the phases of maturity and to visually identify the scale of gonad maturity. The maturity scale includes IX maturity phases for ovaries, and VI phases for testes. Females are characterized by synchronous development of larvae and their hatching; males have multiple-batch spawning. After larvae hatching, the gonads of females are transformed to the developing phase IX-III. According to the physiological state of the gonads, three groups of individuals were identified which differ in size: immature, maturing and mature, taking part in the current year spawning. The maturation of the gonads in the Pacific ocean perch begins at a fork length of 25 cm (FL), 50% of individuals became mature at a fork length of ∼30 cm, and the maturation of all fish occurs at 35 cm or more.