Kazunori Takano

Increased calcitonin levels during ovarian development in the eel, Anguilla japonica

Abstract Female silver eels ( Anguilla japonica ) were matured with repeated injections of chum salmon pituitary homogenate. Blood samples and ovaries were taken at various stages of ovarian development for the analysis of serum immunoreactive calcitonin (CT), Ca content, and gonadosomatic index. Serum CT levels gradually increased in accordance with an increase in gonadosomatic index and the highest level was observed at the time of ovulation. An increase in serum Ca level was also observed during ovarian development. These results suggest an involvement of CT in sexual maturation in the eel.

Immunochemical identification and partial characterization of female-specific serum proteins in white-edged rockfish,Sebastes taczanowskii

SynopsisFemale-specific serum proteins (FSSPs) in white-edged rockfish,Sebastes taczanowskii, were identified and partially characterized by immunochemical procedures. Two FSSPs, which clearly reacted with antiserum against egg proteins, were confirmed in the serum of mature females, and estrogen treatment induced similar FSSPs in the serum of mature males. Hence, the FSSPs were considered to be vitellogenin. The vitellogenin concentration in female fish was high during the vitellogenic period and low during gestation, parturition and the recovery period, indicating that vitellogenin is used only for yolk formation in the oocytes and not as a direct nutritional source for developing embryos during gestation. On the other hand, an FSSP (FS3), which was considered not to be vitellogenin, was also identified in the sera of mature females and males after estradiol-17β administration by using an antiserum (a-FS3) that removed the components of the male serum and egg extracts from the anti-mature female serum antiserum. Moreover, immunohistochemical observation with a-FS3 illustrated that FS3 was a major constituent of the ovarian fluid but not of vitellogenic oocytes. The cross-reactivities of these FSSPs among seven viviparous rockfishes demonstrated that vitellogenin existed in the sera of all rockfishes studied belonging to the generaSebastes andSebastiscus, whereas FS3 was not present in several species ofSebastes.

Serum steroid hormone levels in relation to the reproductive cycle ofSebastes taczanowskii andS. schlegeli

SynopsisChanges in serum steroid hormones were studied during the reproductive cycle of two viviparous rockfishes of the genusSebastes. During the annual reproductive cycle of femaleS. taczanowskii, serum levels of estradiol-17β (E2) gradually increased from their lowest in August to maximal levels towards the end of vitellogenesis in February, and rapidly returned to low levels in pregnant females in April and May. Serum progesterone (prog) fluctuated at low levels throughout the annual reproductive cycle, while 17α, 20β-dihydroxy-4-pregnen-3-one (17α, 20β-diOHprog) levels were high during gestation in May. Serum levels of these steroids were also measured in femaleS. schlegeli at weekly intervals during late vitellogenesis, gestation and post-parturition. In pregnant females, E2 was high during vitellogenesis, then decreased and remained low throughout gestation. The 17α, 20β-diOHprog levels were low during vitellogenesis, then rapidly increased and remained high during gestation. On the other hand, prog values remained low, with temporal peaks coinciding with the peak of 17α, 20β-diOHprog during gestation. Based on these results and the literature, it is suggested that E2 is the most important steroid involved in vitellogenesis and that 17α, 20β-diOHprog may play an important role in final oocyte maturation and subsequent gestation.

Reproductive cycles ofSebastes taczanowskii, compared with those of other rockfishes of the genusSebastes

SynopsisSeasonal reproductive cycles were examined in both sexes ofSebastes taczanowskii, captured in southern Hokkaido, Japan. The reproductive cycle in females was divided into four periods: recovery (July–August), vitellogenesis (September–March), gestation (April–May) and parturition (June). Spermatozoa were first observed in November in the ovarian cavity, where no structural specialization was present for sperm storage. Fertilization of oocytes appeared to occur in April, when the oocytes underwent a rapid process of final maturation. Embryos developed in the ovary quite synchronously and were released in June; empty ovaries indicated the rockfish has a single parturition. The reproductive cycle in males comprised five periods: resting (December–July), early maturation (February–May), mid-maturation (June–August), late maturation (September–October) and functional maturation (November). In November when active spermatogenesis had been completed, a large amount of spermatozoa was preserved in the sperm duct, and the males were therefore ready for mating. A comparison was made of the reproductive cycles of four species of the genusSebastes inhabiting southern and northern waters of Japan. It suggests that the northern species tend to prolong gametogenesis in both sexes while the southern species have the opposite tendency. Sperm storage in the ovary also tends to be longer in the northern than in the southern species.

Immunochemical identification and purification of coelomic fluid-specific protein in chum salmon (Oncorhynchus keta)

Abstract 1. 1. A coelomic fluid-specific protein (CFSP) was identified and isolated from coelomic fluid of ovulated chum salmon ( Oncorhynchus keta ) by means of an immunological procedure. 2. 2. The purified CFSP had a mol. wt of 36,000 and was composed of two identical subunits each with a mol. wt of 16,000. 3. 3. As tissue homogenates of coelomic epithelium and mesovarium of the chum salmon reacted immunoelectrophoretically with anti-chum salmon CFSP serum, it is proposed that the CFSP originates from these tissues. 4. 4. The cross-reactivity of the antiserum to chum salmon CFSP with coelomic fluid of 10 other species was tested. Only related protein of the genus Oncorhynchus showed the cross-reactivity.

Annual reproductive and spawning cycles of femaleSebastiscus marmoratus

SynopsisChanges in serum steroid hormones were studied during the reproductive cycle of a viviparous rockfish,Sebastiscus marmoratus. Serum levels of estradiol-17β (E2) and testosterone (T) were moderately high throughout the spawning period from December until February (E2), and until post-spawning in April (T). Serum progesterone (prog) fluctuated but remained low throughout the annual reproductive cycle; 17α,20β-dihydroxy-4-pregnen-3-one (17α, 20β-diOHprog), on the other hand, was relatively high during the spawning period. During the spawning period, 7 of 12 females reared under laboratory conditions spawned twice at 10-to 16-day intervals. Histological observations indicated that oocytes developed gradually during gestation of the preceding brood and; after parturition, developed more quickly towards the end of vitellogenesis and subsequent fertilization. In repeat spawners, E2 and female-specific serum proteins remained high several days after the first parturition, then gradually decreased. Prog showed no significant changes over the period. The 17α, 20β-diOHprog, however, was low immediately after parturition, then rapidly increased, remained elevated during the middle of the period and then decreased. These results indicate that E2 is involved in vitellogenesis, and 17α, 20β-diOHprog may have some important roles in gestation in the multiple spawnerS. marmoratus.

Ontogeny of the sodium pump in embryos of rockfish of the genusSebastes

SynopsisThe purpose of the present investigation was to determine at what stages of embryonic development the sodium pump (Na+,K+-activated ATP phosphohydrolase, EC 3.6.1.3) appears and whether the ontogeny of the sodium pump plays a role in the matrotrophic viviparity ofSebastes. Early larval stages (stages 1–14) had embryonic tissues nearly devoid of Na, K-ATPase activity. After epiboly, tissues from embryos taken from both species,S. schlegeli andS. taczanowskii, had significant levels of enzymatic activity coincident with the appearance of neuronal tissue in the head fold (stages 15–20). Maximal levels of specific activities of the enzyme were reached with the onset of the vascular circulation and the opening of the buccal cavity together with maturation of the midgut and hindgut regions of the intestinal tract (stages 26 and 28). Ouabain, a specific inhibitor of Na, K-ATPase, was used to measure survival of embryos placed in different seawater concentrations under in vitro conditions. The most sensitive stages to external ouabain were 26–30. These findings support the hypothesis that the intestinal tract is functional prior to gestation and could be transporting important nutritive material found in maternal ovarian fluid.