National Research Institute of Aquaculture

Tamaki, Japan

National Research Institute of Aquaculture

Tamaki, Japan
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Kamaishi T.,National Research Institute of Aquaculture | Miwa S.,Japan National Research Institute of Fisheries And Environment of Inland Sea | Goto E.,Shimane Prefectural Fisheries Technology Center | Matsuyama T.,National Research Institute of Aquaculture | And 2 more authors.
Diseases of Aquatic Organisms | Year: 2010

In February 2005, a mass mortality of giant abalone Haliotis (Nordotis) gigantea Gmelin, 1791 occurred on a private abalone farm in Shimane Prefecture, Japan. The cumulative mortality rate reached about 84%. In histological observations, bacteria-like spherical particles were found in affected animals, suggesting a bacterial infection. Many of the bacteria-like particles were found in the cells that were presumably host phagocytes. DNA was extracted from the hemolymph of a diseased abalone and a bacterial 16S rRNA gene was amplified by PCR. The bacterium was classified within the genus Francisella by gene sequence analysis. A bacterial isolate was obtained by spreading hemolymph of a diseased abalone on modified Eugon agar dissolved in 70% seawater containing 1% (w/v) hemoglobin. A gene fragment of the expected size was amplified from the bacterial isolate by PCR using specific primers for the 16S rRNA gene obtained from the diseased abalone. Experimental infections were carried out by intramuscular injection with the bacterial isolate or by immersion in the bacterial suspension using 2 species of abalone, the giant abalone and the Japanese black abalone Haliotis (Nordotis) discus discus Reeve, 1846. Most (98.6%) of the abalone challenged with the bacterial isolate died in experimental infections. These results suggest that the Francisella sp. isolate was the causative agent for the mass mortality of giant abalone. This is the first report of a pathogenic Francisella sp. isolate for mollusks. © Inter-Research 2010.

O'Rorke R.,University of Auckland | Jeffs A.G.,University of Auckland | Fitzgibbon Q.,University of Tasmania | Chow S.,National Research Institute of Aquaculture | Lavery S.,University of Auckland
Journal of Experimental Marine Biology and Ecology | Year: 2013

Better understanding the diet of small marine predators such as the planktonic larvae of spiny lobsters is important for our awareness of interactions within marine assemblages and for species commercialisation. In DNA-based diet studies of small organisms there is a risk that any DNA contaminating the outside of an organism will be detected and falsely assumed to originate from the gut. Experiments with terrestrial predators have overcome the problem of exogenous contamination by treating the exterior of the predator with bleach (sodium hypochlorite). However, the use of bleach is a risky strategy when treating either a rare predator or aquatic predators, which are generally more permeable than terrestrial animals. Many plankton studies have not reported how they dealt with exogenous contamination, or do not use a control during PCR to detect false positives due to exogenous contamination. One approach is to wash the predator with MilliQ filtered water or ethanol and to use the final wash as a PCR template to detect residual DNA. In the present study we report that washing has variable success at removing exogenous contaminants and that using the final wash as a control for exogenous contamination consistently fails. Based on our results we recommend using DNA extracted from a swab of the exterior of the predator as a control for exogenous contamination. We also report on the benefit of using a novel syringe technique to obtain gut content that minimises contact with the predator surface, and therefore the risk of exogenous contamination. © 2013 Elsevier B.V.

Kobayashi T.,University of Shizuoka | Kobayashi T.,Ehime University | Kobayashi T.,National Research Institute of Aquaculture
International Journal of Developmental Biology | Year: 2010

To clarify the sexually dimorphic mechanisms of gonadal sex differentiation, we established an in vitro culture system for gonadal sex differentiation using the teleost fish Oreochromis niloticus. In vivo, the entry of germ cells into meiosis occurs around 35 days after hatching (dah) in XX gonads, whereas in XY gonads, meiotic cells became differentiated around 85 dah. In our in vitro culture system using gonads from young fry at 23 dah, the meiotic cells in the XX gonads appeared after 21 days of culture. In contrast, in the XY gonads, no meiotic cells were detected after 21 days. These results indicate that germ cell differentiation in this culture system progresses in a manner similar to that in vivo. To identify the gene products that are involved in the entry of germ cells into meiosis or in the arrest of germ cells at the gonial stage of gonadal sex differentiation, we performed subtractive hybridization screening with this in vitro culture system. From the screening process, we identified the female-related gene, FR-3, which is a homolog of zebrafish nanos-related gene (nos). The nos gene was expressed after gonadal formation around 35 dah in XX gonads, but not in XY gonads. In situ hybridization indicated that nos is expressed in oogenic meiotic cells, but not in spermatogenic meiotic cells. Further examination revealed that nos was expressed in oogenic meiotic cells after gonadal formation, specifically in teleost fish. Together, nos may be also involved in oogenic meiosis, with the exception of primordial germ cell migration. © 2009 UBC Press.

Nomura K.,National Research Institute of Aquaculture | Takeda Y.,Kinki University | Unuma T.,National Research Institute of Aquaculture | Morishima K.,Hokkaido University | And 3 more authors.
Aquaculture | Year: 2013

Spontaneous polyploids and mosaics have often been observed in artificially propagated larvae of the Japanese eel, Anguilla japonica. However, the mechanisms responsible for such unusual cytotypes are unclear. In this study, we examined the relationship of such polyploidization and mosaicisms in larvae resulting from artificial propagation to egg quality (fertilization rate and hatching rate) and viability of larvae, and then clarified the inducing factors and the mechanism for occurrence of such phenomena. Eggs stripped from females after induced maturation were artificially inseminated with sperm pre-cultured with artificial seminal plasma. Ploidy was determined by measuring the relative DNA content of the nuclei with flow cytometry. Of 968 embryos from 32 full-sib families, 9.1% were determined to be abnormal, most of which were triploids (86.5% of abnormal embryos); others were haploids (1.1%), aneuploids (2.3%), and mosaics (10.1%). The percentage of normal diploids from each family varied between 56.3% and 100% (90.9. ±. 11.7%, n= 32). A significant positive correlation was found between the fertilization rate (P<. 0.001) or the hatching rate (P<. 0.001) and the percentage of diploids. Survival rate of triploid eels was similar to diploid eels at 10. days after fertilization whereas aneuploids were inviable. When eggs were left in the body cavity of the female for four hours after ovulation and subsequently fertilized, the percentage of diploids decreased. We tried to elucidate the cause for the occurrence of spontaneous triploids by genetic analysis using 26 microsatellite DNA markers, which have been developed and mapped in relation to the centromere. These results suggest that the occurrence of cytogenetically unusual progeny is associated with over-ripening or aging of ova caused by the lapse of time from ovulation until fertilization, and spontaneous triploid larvae are derived from the duplication of the maternal chromosome set by inhibition of the second polar body release after normal meiosis I (crossing over) in oocyte and fertilization with normal sperm. © 2013 The Authors.

Nakamura Y.,Kochi University | Hirota K.,Kochi University | Shibuno T.,National Research Institute of Aquaculture | Watanabe Y.,University of Tokyo
Marine Biology | Year: 2012

Seagrass beds are often considered to be important nurseries for coral reef fish, yet the effectiveness of these nursery functions (refuge and food availability) at different juvenile stages is poorly understood. To understand how the demands of juvenile fish on seagrass nursery functions determines the timing of ontogenetic habitat shifts from seagrass beds to coral reefs, we conducted visual transect survey and field tethering and caging experiments on three different sizes of the coral reef fish Pacific yellowtail emperor (Lethrinus atkinsoni) during its juvenile tenure in seagrass beds at Ishigaki Island, southern Japan. The study showed that although the number of individual L. atkinsoni juveniles decreased by >90 % during their stay in the seagrass nursery, the shelter and/or food availability functions of the nursery, at least for a juvenile size of approximately 5 cm total length (TL), provided the best survival and growth option. The timing of ontogenetic migration to coral reefs of larger fish (>8 cm TL) was attributed to foraging efficiency for larger food items in different habitats. Overall, the function of the seagrass bed nursery changed with juvenile body size, with marginally higher survival and significantly greater growth rates during early juvenile stages in seagrass beds compared to coral reefs. This would contribute to the enhancement in the number of individuals eventually recruited to adult populations. © 2012 Springer-Verlag.

Sudo R.,University of Tokyo | Tosaka R.,National Research Institute of Aquaculture | Ijiri S.,Hokkaido University | Adachi S.,Hokkaido University | And 2 more authors.
Zoological Science | Year: 2012

To evaluate the effects of sex steroids on silvering in the Japanese eel, Anguilla japonica, the development of oocytes, eye size, digestive tract, and swim bladder were studied in relation to observations of the profiles of plasma levels of sex steroids (estradiol 17β, E2; testosterone, T; 11-ketotestosterone; 11-KT) during silvering for each sex and by administrating 11-KT to yellow eels. All steroids examined in the study increased in female eels after silvering had begun, whereas in males, only 11-KT increased significantly, and no statistical differences were found in plasma levels of E2 and T between eels in both developmental stages. 11-KT appeared to induce the early stage of oocyte growth, enlargement of the eyes, degeneration of the digestive tract and the development of the swim bladder. This suggested that 11-KT synchronously accelerates early development of the ovaries and the morphological changes, possibly in adaption to oceanic migration, and that 11-KT is one of the most important factors in early stages of development in the Japanese eel, as it appears to be in other anguillid eels. © 2012 Zoological Society of Japan.

Soeparno,Gadjah Mada University | Soeparno,Kochi University | Nakamura Y.,Kochi University | Shibuno T.,National Research Institute of Aquaculture | Yamaoka K.,Kochi University
Journal of Fish Biology | Year: 2012

The influence of pelagic larval duration (PLD) and egg type dispersal capabilities of 35 demersal and pelagic-spawning tropical fish species is examined in relation to their abundance on the temperate coasts of Japan. The PLDs of pelagic spawners were significantly longer than those of demersal spawners, and a high occurrence of pelagic spawners on the temperate coasts suggests that these fishes are more easily transported to temperate coasts than demersal spawners. For demersal spawners, the common species on the temperate coasts had significantly longer PLDs than the rare species; this suggests that PLD is a major factor influencing the distribution patterns of tropical demersal spawners on temperate coasts. Moreover, a negative correlation between PLD and the abundance of some species of pelagic and demersal spawners suggests the presence of reproductively active fishes in northern subtropical and even in temperate waters. © 2012 The Authors. Journal of Fish Biology © 2012 The Fisheries Society of the British Isles.

Tosaka R.,Hokkaido University | Todo T.,Hokkaido University | Kazeto Y.,National Research Institute of Aquaculture | Mark Lokman P.,University of Otago | And 3 more authors.
General and Comparative Endocrinology | Year: 2010

In order to elucidate how androgens may mediate their effects on ovarian growth, we investigated the mRNA levels of two subtypes of androgen receptor (ara and arb) in the ovary of feminized Japanese eel (Anguilla japonica) during artificially induced ovarian development by quantitative real-time reverse transcriptase polymerase chain reaction and in situ hybridization. Ara mRNA levels were high from the late oil droplet stage to the late vitellogenic stage, whereas arb mRNA levels were high from the late oil droplet stage to the midvitellogenic stage. Both ar mRNAs were predominantly observed in the follicle cells and the epithelial cells of the ovigerous lamellae in all stages. In the oil droplet stage, oogonia exhibited intense signals for ar mRNAs. There was no obvious difference in localization pattern between ara and arb in all ovaries examined, irrespective of maturational stage. It was difficult to identify the follicle cell types that were positive for ar mRNA during ovarian development. Only in post-ovulatory follicles could theca and granulosa cells be clearly identified, and ar signals were observed in both layers. The predominant localization of ar mRNA in the follicle cells suggests that androgens play important roles in oocyte growth by acting on these cells in this species. We have shown the expression profile and localization of ar mRNA during ovarian development for the first time in an oviparous vertebrate. © 2010 Elsevier Inc.

Iguchi K.,National Research Institute of Aquaculture
Ichthyological Research | Year: 2012

The classic model of Smith and Fretwell predicts that the optimal egg size will vary according to the shape of the relationship between offspring size and offspring fitness, which may vary among environments. Adaptive significance of intrapopulation egg size variation was examined using Ayu (Plecoglossus altivelis). The species has an annual and migratory life history. Fish under controlled rearing conditions become sexually mature with a trend that smaller females produced larger eggs later in the season. Observed egg size variation was explained by the maternal specific growth rate, which was composed of maternal body size and growing period. Hatchlings from larger eggs had a larger notochord length, larger yolk-sac and grew faster. Such offspring traits provide general advantages of increased larval size, which confer competitive ability for assuring early survivorship. In conclusion, egg size plasticity in Ayu suggests higher offspring fitness through enhancement of their accessibility to food. © 2011 The Ichthyological Society of Japan.

Egg size is a critical life-history trait in which maternal investment is optimized to maximize maternal fitness. The adaptive significance of variable egg size among spawning groups of Ayu (Plecoglossus altivelis) landlocked in the Lake Biwa system was examined through field investigations and rearing experiments. Observed egg size variations were explained by the water temperature around spawning grounds established near the mouths of inlet streams. Two typical streams with different incubation temperatures showed similar maternal body sizes and hatchling sizes, but eggs attached to the stream bed were larger in the colder stream. An experiment that used eggs from a single clutch showed that a smaller hatchling size was obtained with a lower incubation temperature, indicating that the effect of differences in egg size on hatchling size can be canceled out by variations in incubation temperature. In general, larvae that are less than a certain threshold of effective body size are not expected to be assured of early success among conspecifics competing for foods. It is proposed that environments in which the incubation temperature varies favor variability in egg size to ensure that sufficient food is accessible to larvae. © 2011 The Ichthyological Society of Japan.

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