カサゴの研究―5 : 海産卵胎生硬骨魚類の卵巣の成熟及びその季節的循環に関する研究

1) The marine ovoviviparous teleost, Sebastiscus marmoratus and Sebastes inermis, were collected monthly all the year round at Sasebo Bay, and the author studied the maturation and the seasonal cycle of their ovaris. 2) The sex-ratio of Sebastiscus marmoratus was not change all the year round. In Sebastes inermis, this ratio was 1:1 untill the copulation, but the ratio of female in caught fishes increased suddenly after the copulation and it denote about the five times of the male. This tendency continued untill the end of spawing of larvae. 3) In both species, the maturity of ovary in external appearance was divieded in several stages. The ovaris hold the larvae observed between November and March in Sebastiscus marmoratus, and the heighest spawnig season of larvae is seemed from December to February. In Sebastes inermis the spawning season between the first half of January and the first half of February, and is not longer than in Sebastiscus marmoratus. It is due to the fact that Sebastes inermis is mono-spawning and Sebastiscus marmoratus is many poly-spawning. 4) Owing to know their spawning season and maturation and seasonal cycle of ovary, the weight of ovary was weigh and it was shown as the Gonad Index (G. I.) of maturity. In Sebastiscus marmoratus the value of G. I. is high from Nov. to Mar., and especially in Jan. and Feb. it shows a peak. In Sebastes inermis, this value is high between Dec. and Feb., and in Jan. it shows a peak. The period of the high value of G. I. continued during five monthes in Sebastiscus marmoratus but in the case of Sebastes inermis is shorter than the former and shows more acute angle. Sebastes inermis is mono-spawning, therefore oocytes of ovary mature all together and the weight of ovary is more heavy than that of Sebastiscus marmoratus. 5) The auther measured the ova-diameter to know the following facts that is, spawning season, process of maturity, number of times of spawning and number of egg in the case of spawning. Consequently, it is more clear that Sebastes inermis is mono-spawning and Sebastiscus marmoratus is poly-spawning. In the frequency distribution of ova-diameterof mature ovary, there are always three or four modes in Sebastiscus marmoratus, on the contrary two modes are seen in Sebastes inermis. And it seems that the former spawn at least four times at one spawning season, and the latter is one time. This is plain enough by the change of the modes according to the stage at the freqeuncy distribution of ova-diameter. The ova-number of mature Sebastiscus marmoratus increased to the advance of stage, namely, in stage I the number of oocytes was about 50,000 but it increased gradually untill 170,000 in maximum. In the case of Sebastes inermis the number of oocytes was about 50,000 and it was not changed even if the advanced stages. 6) Owing to know the state of maturity of ovary certainly enough, the sections of ovaries of Sebastiscus marmoratus, S. albofasiatus, Sebastes inermis and Sebastichthys pachcephalas were prepared and observed monthly. In these fishes the state of advancement of oocytes were all the same, therefore the author divided and described their advancement into the same nine stages, and according to the month in which these stages appear in ovary the cycle of ovary-maturation during a year was made clear. Zona-radiata come out clearly at the stage of yolkvesicle stage and primary yolk stage in normal oviparous fishes, but it was not evident in these ovoiviparous fishes, and the follicle cells were very thin. In oviparous fishes the fully matured oocyte become transparent and yolk globules dissolve, on the contrary in oocyte of the ovoviviparous fishes, the yolk globules is not dissolve even if before and after the fertilization. In spite of the earnest observation in numerous histological section of ovary, the author could not found entirely the stage between the fertilization and the molura stafe of egg, and the ovaries which included the eggs in molura stage and blastula stage were a few. In the marine ovoviviparous teleost, with the exception of Sebastichthys pachcephalus, at the late yolk stage the many oil globules in oocyte grow a large globe and it push out the nucleus to the animal pole, In these fishes, the ovulation were taken place at the molura stage. In the poly-spawning fishes such as Sebastiscus spp., the eggs in the same stage assembled together for the convenience of movement in ovary after the ovulation. The follicle cells after the spawning of larvae formed the ovarian tissue, and this tissue remained during three monthes after the spawning in ovary, and in this period the egg-number was not increased and the oocytes in ovaries were not developed from the chromatin-nucleous stage and peri-nucleolus stage. In the marine ovoviviparous teleost, the mono-spawning fishes were sebastes inermis and Sebastichthys pachcephalus, and the poly-spawning fishes were sebastiscus spp., the ova-diameters of these fishes in each stages were indicated at the Table. 8.

長崎大学水産学部研究報告, v.8, pp.84-110; 1959