Comparative Studies on the Maturation Process of Two Types of Cottus nozawae-I.The Annual Cycle of Ovarian Development

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Monthly changes in the ovaries of the small-egg type (SE) and the large-egg type (LE) of Cottus nozawae were compared biometorically and histologically.The relative weight of ovaries (GSI) scarcely differed between two types for six months after spawning in May to November.The GSI values were slightly higher in the SE than in the LE during the period of December to January.In the spawning period (April), however, the relation was inverse, because of the rapid increase in the ovary weight of the LE since February.The diameter of ovarian eggs in the spawning period was significantly larger in LE than in SE.From a comparison of the monthly changes of egg sizes between the two types, it is definite that the difference was a result mainly of the rapid increase of egg sizes in the LE after March. Vitellogenesis in the LE became active in early August, and in mid September for SE.The beginning of formation of yolk globules also differed between LE and SE. Thus, there are two types of C.nozawae, each with unique modes of ovarian development.The mode in the LE is not simply an extention of development in the SE.
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