マサバの卵巣成熟と産卵〔英文〕

概要

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The ovarian maturation and spawning process of Japanese common (chub) mackerel Scomber japonicus was studied on the basis of three years samples. The degree of maturity of ovaries was judged by the external appearance, gonad maturation index and frequency distribution patterns of egg diameters. Frequency distributions of egg diameter of ovaries were classified into 10 profiles. Ovarian maturation begins with enlarging of the egg diameter and increasing of the amount of yolked eggs. When the mean size of the most advanced egg group reaches about 0.6 mm, its increasing seems to stop and only the number of yolked eggs continues to increase. When the mean KG value exceeds 4-5, hydration occurs in a fraction of yolked eggs and these are rapidly released as a batch. It is difficult to find clear relationship between the distribution profiles of egg size and the mean KG of mature ovaries owing to the multispawning trait. The minimum sizes at the first maturity was estimated to be approximately 30 cm.
日本水産學會の論文