Development of Female Reproductive Organs During Sexual Maturation in the Japanese Common Squid Todarodes pacificus.

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Abstract
Development of female reproductive organs during sexual maturation was studied for Japanese common squid caught from feeding and spawning grounds. The female maturity was divided into six stages based on the histological observation of ovary. The maturity was compared with the ovary somatic index (OSI: ovary weight as a percentage of body weight), oviduct somatic index (ODSI: oviduct weight as a percentage of body weight), gonad somatic index (ovary and oviduct weight as a percentage of body weight) and nidamental gland index (m: a ratio of nidamental gland length to mantle length). Results showed that the female maturational process consists of two phases and ovary and oviducts development are correlative with the nidamental gland development. In the first phase, ripe eggs are produced in the ovary with the rapid development of the nidamental gland and in the next phase, ripe eggs are transferred into the oviducts and stored there until spawning. The nidamental gland development is slower in the next phase, which suggests that the production of jelly material is started in this organ. It is possible to express the female maturity condition by GSI and m. These numerical values are GSI>1.0 and m>0.208 in yolk formation stage; GSI>2.6 and m>0.290 in the mature stage

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