On the Life-history of Acetes japonicus K_ISHINOUYE, in Ariake Sea

Abstract

The small shrimp. Acetes japonicus is most abundant in Ariake Sea, excepting shell fishes. The results of its bionomic studies are as follows:
1) There are two types of generation of the shrimp during a year. One that passed the winter dies after spawning between May and July. The other than hatched early in summer grows rapidly in warmer season, and spawning takes place early in August (First summer generation). The shrimps born from the first summer generation lay eggs in late September (Second summer generation) (Fig. 4), whole individuals of spent shrimps die after spawning.
2) Thus the duration of the life of this shrimp is 9-10 months in former generation and 2.5-3months in latter.
3) The number of ovarian eggs increares with linear correlation to the body length. The female shrimp of l8-30mm in body length bears 2, 000-7, 000 eggs (Fig. 6).
4) The growth of body length is inferior during winter, December to March, although it grows rapidly from middle of April. In the warmer seasons it increases 4mm in female, 2mm in male at a month. Finally it reaches the body length of about 30mm in female, 24mm in male. The summer generation grows more rapidly than that of the 2years shvimp, resultly it reaches about 20mm in female, 16mm in male during three months (Figs. 7, 8).