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Hiratsuka S.,University of Shizuoka | Hiratsuka S.,Shizuoka Prefectural Research Institute of Fishery | Honma H.,University of Shizuoka | Saitoh Y.,University of Shizuoka | And 3 more authors.
Journal of Nutritional Science and Vitaminology | Year: 2013

The effects of dietary sialic acid in dams on the learning abilities of their pups after weaning were investigated using rats deficient in n-3 fatty acids. Nine-week-old female Wistar rats were fed an n-3 fatty acid-deficient diet for 3 wk and were mated at 12 wk of age. During pregnancy and lactation, the female rats were fed the n-3 fatty acid-deficient diet, and were given water or water containing 1% N-acetylneuraminic acid (NANA) ad libitum. After weaning, the learning abilities of the pups were evaluated using a novel object recognition test. The recognition index of pups nursed by dams fed on water containing 1% NANA (NANA-intake dams) was significantly higher than that of pups nursed by dams fed only on water (NANA non-intake dams). There were no significant differences in the total sialic acid or docosahexaenoic acid contents in the cerebral cortex or hippocampus of pups nursed by dams fed on either type of water. The total dimethylacetal (DMA, from plasmalogen) level in the cerebral cortex of pups nursed by NANA-intake dams was significantly higher than that of pups nursed by NANA non-intake dams. These results suggest that dietary sialic acid in dams during pregnancy and lactation might be beneficial for the learning abilities of pups after weaning, which may be related to the plasmalogen level in the brain of pups. Source


Yoshikawa M.,Shizuoka Prefectural Research Institute of Fishery
Journal of Fish Biology | Year: 2013

To assess the relationship between growth rate of body mass and sex in the Japanese eel Anguilla japonica in the early life stage; the growth rates of males and females were compared under experimental conditions. The mean growth rate of females was significantly slower than that of males. To assess the relative priority of growth rate and sex, growth was delayed by restricted feeding, resulting in a significantly higher proportion of females in the delayed than in the normal growth group. These findings indicate that the mean growth rate of A. japonica is slower in females than in males in the early life stage around sex determination and differentiation under experimental rearing conditions. Moreover, growth rate probably has priority over sex determination, with slow growth rate increasing the probability of being female. © 2013 The Fisheries Society of the British Isles. Source


Unuma T.,Hokkaido National Fisheries Research Institute | Hasegawa N.,Hokkaido National Fisheries Research Institute | Sawaguchi S.,Hokkaido National Fisheries Research Institute | Tanaka T.,Shizuoka Prefectural Research Institute of Fishery | And 3 more authors.
Aquaculture | Year: 2011

The quality of eggs obtained from maturation-induced Japanese eel, Anguilla japonica, is unstable. One of the causes for low quality eggs is that females are artificially induced to ovulate at an inappropriate maturational status. Here we investigated the feasibility to use the morphological changes of lipid droplets in oocytes as a biomarker to show the optimum timing for injections of salmon pituitary extract (SPE) for priming and maturation-inducing steroid (MIS) for final oocyte maturation and ovulation. Various sizes of oocytes (700 to 1000 μm) were collected by cannulation from maturation-induced female eels during five days until ovulation. Morphology of the lipid droplets in these oocytes were classified into 10 stages mainly on the basis of their diameter, which increased with the progress of maturation as the droplets fused together. To assess the maturational status of each female, the lipid droplet stage was determined for 10 oocytes randomly chosen among the most advanced mode of developing oocytes and the median value was defined as the stage for the individual. Relationship between the lipid droplet stage at induction of ovulation and hatchability of the ovulated eggs was examined in 23 females, in which the hatching rate markedly fluctuated. Stages of females from which good quality eggs were obtained converged around stage 4 (five largest droplets, 55 to 70 μm) at priming with SPE, stage 6 (90 to 110 μm) at injection with MIS, and stage 7 (110 to 130 μm) at ovulation, while those of females from which low quality eggs were obtained showed distributions over broader ranges. Furthermore, 466 females were induced to mature and the lipid droplet stage at induction of ovulation was examined in 13 females from which high quality eggs (hatching rate >80%) were obtained. Most of the 13 females were at stage 3 (40 to 55 μm) or 4 when primed with SPE, at stage 6 when injected with MIS, and at stage 7 when they ovulated. These results suggest that the optimum stages for SPE priming, MIS injection, and ovulation are stages 3 to 4, 6, and 7, respectively, though the optimum stage for priming will be variable if the temperature and/or the time between priming and MIS injection is varied. We conclude that the lipid droplet stage can be used as a sensitive biomarker to show the optimum timing for inducing ovulation by hormonal treatments. © 2011 Elsevier B.V. Source


Sano K.,Sophia University | Kawaguchi M.,University of Tokyo | Yoshikawa M.,Shizuoka Prefectural Research Institute of Fishery | Iuchi I.,Sophia University | Yasumasu S.,Sophia University
FEBS Journal | Year: 2010

A fish egg envelope is composed of several glycoproteins, called zona pellucida (ZP) proteins, which are conserved among vertebrate species. Euteleost fishes synthesize ZP proteins in the liver, while otocephalans synthesize them in the growing oocyte. We investigated ZP proteins of the Japanese eel, Anguilla japonica, belonging to Elopomorpha, which diverged earlier than Euteleostei and Otocephala. Five major components of the egg envelope were purified and their partial amino acid sequences were determined by sequencing. cDNA cloning revealed that the eel egg envelope was composed of four ZPC homologues and one ZPB homologue. Four of the five eel ZP (eZP) proteins possessed a transmembrane domain, which is not found in the ZP proteins of Euteleostei and Otocephala that diverged later, but is found in most other vertebrate ZP proteins. This result suggests that fish ZP proteins originally possessed a transmembrane domain and lost it during evolution. Northern blotting and RT-PCR revealed that all of the eZP transcripts were present in the ovary, but not in the liver. Phylogenetic analyses of fish zp genes showed that ezps formed a group with other fish zp genes that are expressed in the ovary, and which are distinct from the group of genes expressed in the liver. Our results support the hypothesis that fish ZP proteins were originally synthesized in the ovary, and then the site of synthesis was switched to the liver during the evolutionary pathway to Euteleostei. © 2010 The Authors Journal compilation © 2010 FEBS. Source


Okutsu T.,Japan International Research Center for Agricultural science | Shikina S.,National Taiwan Ocean University | Sakamoto T.,Tokyo University of Marine Science and Technology | Mochizuki M.,Shizuoka Prefectural Research Institute of Fishery | Yoshizaki G.,Tokyo University of Marine Science and Technology
Aquaculture | Year: 2015

Mono-sex culture provides economic advantages in aquaculture. In particular, YY supermales, which produce all-male progeny, are desirable in many fish species whose males have more economically desirable characteristics than females, such as faster growth. The production of YY supermales has been achieved by mating XY males with XY sex-reversed females in many fish species. However, the production of sex-reversed XY females requires long-term estrogen administration, which requires considerable time and labor. As an alternative technique, we attempted a spermatogonia transplantation technique to obtain Y eggs in the present study using rainbow trout, Oncorhynchus mykiss. Spermatogonia are the testicular male germ cells that are known to be able to be involved in oogenesis and subsequently differentiate into functional eggs when transplanted into female recipients (Okutsu et al., 2006a). However, whether Y eggs can be derived from transplanted spermatogonia remains unclear.First, we produced F1 progeny by insemination of donor spermatogonia-derived eggs and wild-type milt and then determined their sex. Out of 16 donor-derived fish examined, 3 and 13 were females and males, respectively (1.0:4.3 female:male ratio). Second, we used the milt from the sex-reversed males, which possessed XX sex chromosome sets, for artificial insemination with the donor spermatogonia-derived eggs produced by the female recipients. In the progeny, 8 out of 21 donor-derived fish examined were males, although no males were observed in the control group produced by sex-reversed XX males and intact XX females. Finally, we produced F2 progeny by insemination of the milt from F1 males, which were generated from spermatogonia-derived eggs and wild-type sperm, and the eggs from wild-type females. As a result of a progeny test, 3 out of 10 F1 males (30.0%) produced all-male progeny in the F2 generation. These findings clearly demonstrate that we successfully achieved the production of Y eggs and subsequent YY supermales via spermatogonia transplantation. The present study offers a unique system that enables us to produce YY supermales without administering exogenous sex steroids. This system can be applied to many valuable fish species targeted for aquaculture.Statement of relevance. In this manuscript, we show that a successful production of YY supermales in rainbow trout using spermatogonia transplantation system (for a spermatogonia transplantation system, detailed in Okutsu et al., 2006, PNAS, 103, 2725-2729). The present study offers a promising alternative method to produce YY supermales, which can be applied to a wide range of fish species. This technique is expected to contribute to the development of mono-sex cultures in important aquaculture species. © 2015 Elsevier B.V. Source

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