抄録
More than 104 live specimens reared in ponds were observed during the maturation and the differentiation of gonads under macroscopical anatomy derived the results as follows. A review on the subject was given firstly.
The main structure of ovary of rainbow trout is about the same as that of Oncorhynchus described by KENDALL, W. C. (1921). The ovary is nearly triangular in shape and its one side in each organ is not covered by the ovarian membrane, but open to the body cavity.
In immature stages, this uncovered side faces to inward of the body caivty on the right organ and to the ventral side of air bladder on the left organ (Stage I). As maturation advances, the uncovered part begins to turn round gradually outward and faces directly to the lateral peritoneal wall (Stage II). After this stage, ovarian membrane and lamellae which contain mature eggs shrink in a shorter period and turn into spent ovary positioned on the anterior ventral part of the air bladder, leaving mature eggs in pieces in the body cavity (Stage III).
The Stage I lasts from earlier part of the year to September when the organs develope into the structure as shown in Fig. 4, A; the Stage II from September up to full maturation immediately prior to spawning (Fig. 4, B), the growth of ovary taking place rapidly after September; the Stage III, lasting only 4 to 5 days, precedes spawning (Fig. 4, C).
Fatty tissue in the body cavity reduces in amount, and the intestine and stomach are moved upward during maturation process of ovary, Stages I to III.
The eggs, it was confirmed in the present study, cannot be collected in the trough formed by the extension of peritoneal membrane surrounding the ovary, without falling into the body cavity as described by KENDALL. The mature eggs “lie free in”, instead of “fall into” (as described hitherto), the body cavity by the contraction of ovarian membrane and lamellae (Pl. I); with slight pressure free eggs can be forced out through the oviducal channel to the genital pore.
