K. Mikimoto and Co.

Mie, Japan

K. Mikimoto and Co.

Mie, Japan
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Yamasaki Y.,Nagasaki University | Zou Y.,Nagasaki University | Go J.,K. Mikimoto and Co. | Shikata T.,Graduate University for Advanced Studies | And 7 more authors.
Journal of Sea Research | Year: 2011

We used bi-algal culture experiments to investigate and verify the roles of growth interaction between Heterocapsa circularisquama and Prorocentrum dentatum in monospecific bloom formation. Growth of H. circularisquama was slightly inhibited when inoculated at 102cellsmL-1 along with P. dentatum at 104cellsmL-1. In other combinations of inoculation densities, P. dentatum density rapidly decreased to extremely low levels in the presence of H. circularisquama. We used a mathematical model to simulate growth and interactions of H. circularisquama and P. dentatum in bi-algal cultures. The model indicates that one species will always inhibit the growth of the other and that the relative initial cell densities of the species are critical in determining the outcome. When cultured together under conditions without cell contact, growth of H. circularisquama and P. dentatum was not inhibited. As with P. dentatum, the growth of Heterosigma akashiwo and Skeletonema costatum was inhibited in intact cell suspensions with H. circularisquama, but a nontoxic species, Heterocapsa triquetra, did not affect the growth of P. dentatum or the other species. Similarly, cell suspensions of H. circularisquama showed hemolytic activity toward rabbit erythrocytes, but those of H. triquetra did not. In addition, the cell-free supernatant of H. circularisquama cultures showed no significant hemolytic activity. These results suggest that H. circularisquama causes lethality in P. dentatum by direct cell contact in which live-cell-mediated hemolytic activity might be a contributing factor. © 2010 Elsevier B.V.


Higuchi K.,K. Mikimoto and Co. | Nagai K.,K. Mikimoto and Co. | Hattori F.,Mikimoto Pharmaceutical Co. | Maeyama K.,Mikimoto Pharmaceutical Co. | And 3 more authors.
Nippon Suisan Gakkaishi (Japanese Edition) | Year: 2016

Waste from activities associated with pearl culturing has become a cause of environmental deterioration on pearl farms. As part of our researches on reducing the environmental burden of Akoya pearl culturing, we investigated methods of composting pearl culture waste and effectively using this compost. We conducted composting tests using the soft body of Pinctada fucata after pearl harvesting as the main material, supplemented with debris resulting from sessile organisms removed during shell cleaning, and plant materials. We found that it was possible to convert Akoya oyster meat to mature compost in approximately 45 days without desalinization, and it was observed that including the debris of removed sessile organisms improved the aeration of the composting materials and increased the fertilizer components of the mature compost. Moreover, a seedling test showed that the mature oyster meat compost, when used at a rate of 10 g compost/1000 cm3 soil, improved the fresh weight of komatsuna. These results indicated that compost made from discarded oyster meat and the debris of removed sessile organisms can be effectively utilized in agriculture. The compost is also expected to reduce the environmental burden on pearl farms. © 2016 The Japanese Society of Fisheries Science.


Go J.,K. MIKIMOTO and Co. | Nagai K.,K. MIKIMOTO and Co. | Segawa S.,Tokyo University of Agriculture | Honjo T.,Kagawa University
Nippon Suisan Gakkaishi (Japanese Edition) | Year: 2016

Recently, red tides caused by the dinoflagellate Karenia mikimotoi in pearl-culturing areas such as Ago Bay, Mie Prefecture have raised concerns about their effects on the Akoya pearl oyster Pinctada fucata. We assessed the mortality of juvenile oysters in red tide seawater and investigated the effect of the dinoflagellates on valve movement of mature oysters. Of juvenile oysters, 7.5percent,died after 36 h in seawater with a K. mikimotoi density of 1×104 cells/mL and all oysters died after 24 h with 6×104 cells/mL. Frequency of valve movement of mature oysters rose with increase of cell density, and became significantly higher than that of the control at 3×103 cells/ mL.


Basti L.,Japan National Research Institute of Fisheries Science | Nagai S.,Japan National Research Institute of Fisheries Science | Go J.,K Mikimoto and Co. | Okano S.,K Mikimoto and Co. | And 4 more authors.
Harmful Algae | Year: 2015

The effects of four harmful and potentially harmful dinoflagellates, Alexandrium affine, Alexandrium catenella, Karenia mikimotoi and Karenia papilionacea, on the early-life development of Japanese pearl oyster, Pinctada fucata martensii, were assessed. Density- and time-dependent, mild to severe effects on cleavage, hatching, D-larvae, and pre-settling larvae of pearl oysters were found. The non-PST-producer A. affine was highly toxic to both cleavage and hatching with potent lytic activity at a density of 2.5×102cellsml-1. The PST-producer A. catenella also affected cleavage and reduced hatching, but at 2-fold higher density with lytic activity only at the highest density tested (2×103cellsml-1). Cleavage was affected by K. mikimotoi and K. papilionacea at 1.5×104cellsml-1, but hatching was only affected by K. mikimotoi. Mortalities in both larval stages were not observed. D-larvae were not affected by K. papilionacea, but their activity decreased following exposure to A. affine, A. catenella, and mainly K. mikimotoi. Pre-settling larvae were more sensitive to all four harmful algae than were D-larvae. The dinoflagellate A. catenella had the highest effect on the activity of pre-settling larvae (10cellsml-1), followed by K. mikimotoi (5×102cellsml-1), A. affine (5×102cellsml-1), and K. papilionacea (1.5×104cellsml-1). The results of this study suggest that complex mechanisms, including paralytic shellfish toxins (PST), brevetoxins (PbTx) and a variety of lytic and membrane-disruptive toxins and/or other metabolites, could have been involved in such inimical stage-specific effects. It also highlight the threat posed by harmful algae on the recruitment of Japanese pearl oysters and potentially other bivalve species, and show that they could exert subchronic to chronic effects at realistically low cell densities, and impact bivalve populations through altered reproductive and recruitment processes, ultimately hampering both wild populations and aquaculture industries. © 2015 Elsevier B.V.


Hiramatsu J.,K. Mikimoto and Co. | Nagai K.,K. Mikimoto and Co.
Seibutsu-kogaku Kaishi | Year: 2010

Various factors such as heat and sunlight cause the quality of akoya pearls to deteriorate. We examined the influence of heat and sunlight treatments on the nacreous shell matrix proteins (NSMPs) of akoya pearl by detecting changes in the reflectance (i.e. the ratio of reflectance at a wavelength of 254 nm and 282 nm) and fluorescence peak intensity (fluorescence intensity at 340 nm). Heat treatment at 100°C for up to 768 h caused a small decrease in reflectance value and a large decrease in fluorescence peak intensity, whereas sunlight at 250 W/m 2 for up to 768 h caused large decreases in both reflectance value and fluorescence peak intensity. Quantitative analysis of amino acid composition revealed that the only aromatic amino acid that decreased in content with heat treatment was tyrosine (by 18 %). Sunlight treatment decreased the tryptophan content by 78 % and tyrosine by 33 %. These results implied that the degeneration mechanisms of NSMPs by heat and sunlight treatments were different. By assessing these different changes in reflectance value and fluorescence peak intensity it may be possible to judge the two types of quality deterioration without the need to destroy the pearl.


Nagai K.,K. Mikimoto and Co.
Zoological Science | Year: 2013

During the 18th and 19th centuries, studies of how pearls are formed were conducted mainly in Europe. The subsequent pearl culturing experiments conducted worldwide in the early 20th century, however, failed to develop into a pearl industry. In Japan, however, Kokichi Mikimoto succeeded in culturing blister pearls in 1893 under the guidance of Kakichi Mitsukuri, a professor at Tokyo Imperial University (now the University of Tokyo) and the first director of the Misaki Marine Biological Station, Graduate School of Science, University of Tokyo. This success and subsequent developments laid the foundation for the pearl farming industry, developed new demand for cultured pearls in the European jewelry market, and initiated the full-scale industrialization of pearl culturing. In addition, research at the Misaki Marine Biological Station resulted in noteworthy advances in the scientific study of pearl formation. Today, pearls are cultured worldwide, utilizing a variety of pearl oysters. The pearl farming industry, with its unique origins in Japan, has grown into a global industry. Recently, the introduction of genome analysis has allowed cultured pearl research to make rapid progress worldwide in such areas as the dynamics of mother-of-pearl layer formation and biomineralization. This signals another new era in the study of pearls. © 2013 Zoological Society of Japan.


Hiramatsu J.,K.Mikimoto and Co. | Iwahashi Y.,K.Mikimoto and Co. | Nagai K.,K.Mikimoto and Co.
Fisheries Science | Year: 2013

We exposed Akoya cultured pearls separately to heat (60-120 °C) and artificial light to investigate changes to fluorescence in the visible range and yellowing. We found that for both heat-treated and light-treated pearls, the fluorescence peak shifted from 480 to 430 nm with an increase in fluorescence intensity. This change in intensity was more prominent in heat-treated pearls, with the initial speed of increase rising with treatment temperature; treatment at 100 °C caused the greatest increase in fluorescence intensity. However, aminoguanidine suppressed the heat-induced change in the fluorescence of an ethylenediaminetetraacetic acid-soluble nacreous layer matrix. These results suggest that the heated-induced changes in the fluorescence of Akoya cultured pearls were caused largely by a buildup of fluorescent advanced glycation end products through the Maillard reaction. Although heat treatment led to a large increase in fluorescence intensity of the peak at approximately 430 nm in a deoxygenized environment, hardly any change in fluorescence intensity was observed after light treatment in this environment. Moreover, a new shoulder peak appeared at about 460 nm after light treatment. These results suggest that the Maillard reaction was not a major factor in the light-induced changes in the fluorescence of Akoya cultured pearls. © 2013 The Japanese Society of Fisheries Science.


Basti L.,Tokyo University of Marine Science and Technology | Go J.,K. Mikimoto and Co. | Higuchi K.,K. Mikimoto and Co. | Nagai K.,K. Mikimoto and Co. | Segawa S.,Tokyo University of Marine Science and Technology
Journal of Shellfish Research | Year: 2011

The effects of the toxic dinoflagellate Heterocapsa circularisquama on the activity rate, development rate, prevalence of damage, and survival rate of trochophore and D-shaped larvae of the pearl oyster Pinctada fucata martensii were studied in relation to H. circularisquama cell densities and exposure duration. In addition, larvae were regularly processed via scanning electron microscopy to investigate morphological damage. The activity rate of both larval stages was significantly decreased after 3-6 h of exposure to H. circularisquama at densities ranging from 100 to 2 × 104 cells/mL. The prevalence of damage was significantly high after 3-6 h of exposure to H. circularisquama at densities of 100 to 2 × 104 cells/mL and 5 × 103 to 2 × 104 cells/mL for trochophores and D-shaped larvae, respectively. Cytoplasmic discharge, mass mucus production, irregular shape, delayed or inhibited mineralization of the shell, mantle protrusion, the appearance of abnormal masses in the velum, and the exfoliation of the larvae cilia coupled with epithelial desquamation were frequently observed. The activity rate of D-larvae transformed from trochophores exposed to H. circularisquama for 12-48 h at densities ranging from 10 to 2 × 104 cells/mL was significantly reduced. The survival of D-shaped larvae plummeted to less than 0.013 for densities ≥ 5 × 103 cells/mL. The results indicate that H. circularisquama blooms have detrimental impacts on bivalves at early life stages. Blooms of H. circularisquama occurring during the spawning periods will influence the natural recruitment in P. fucata martensii and will have profound impacts on its population biology. Therefore, shellfish farms should not be built in coastal areas where H. circularisquama occurs, or genitors should be relocated during potential blooming periods.


Basti L.,Tokyo University of Marine Science and Technology | Nagai K.,K. Mikimoto and Co. | Tanaka Y.,Tokyo University of Marine Science and Technology | Segawa S.,Tokyo University of Marine Science and Technology
Marine Biology | Year: 2013

Blooms of the toxic dinoflagellate Heterocapsa circularisquama cause massive bivalve kills in Japan. Mariculture of the Japanese pearl oyster, Pinctada fucata martensii, is the industry most affected by these blooms, especially in Ago Bay, Mie Prefecture, where they are frequent, cause mass mortality of oysters, and overlap with their spawning season. The goal of this August 2009 study was to assess the effects of a toxic strain of H. circularisquama isolated from Ago Bay on gametes, fertilization, and embryo development of pearl oysters. Spermatozoa, eggs, spermatozoa and eggs, and fertilized eggs of pearl oysters from Ago Bay were exposed to H. circularisquama at cell densities reported during the bloom (10-104 cells mL-1) for different periods of time. The concentration of H. circularisquama, exposure duration, and their interactions all had significant effects on gamete quality, fertilization, and embryo development. The motility and swimming velocity of spermatozoa, egg viability, fertilization, and embryo development rate were significantly reduced in all concentrations, with a cell density of 10 cells mL-1 determined to be the critical density of H. circularisquama for deleterious effects. This is the first evidence of inimical effects of an HAB species on bivalve spermatozoa upon direct exposure. Further field and laboratory studies are required to investigate the potential effects of H. circularisquama blooms on the reproduction and recruitment of Japanese pearl oysters and other bivalves. © 2012 Springer-Verlag Berlin Heidelberg.


Awaji M.,Japan National Research Institute of Fisheries And Environment of Inland Sea | Yamamoto T.,K. MIKIMOTO and CO. | Kakinuma M.,Mie University | Nagai K.,K. MIKIMOTO and CO. | Watabe S.,Kitasato University
Nippon Suisan Gakkaishi (Japanese Edition) | Year: 2014

A method of forming pearls by transplanting outer epithelial cells (OEC) isolated from the mantle of pearl oyster Pinctada fucata was investigated. Two methods, 1) injection of OEC around the pearl nucleus inserted beforehand and 2) insertion of the pearl nucleus carrying a small pit inoculated with OEC, were compared in terms of performance. As a result, method 2 had a higher pearl formation rate than method 1.With method 2, about 70% of the inserted nuclei formed the nacreous layer when OEC were inoculated at 1×104cells/nucleus. Next, OEC isolated from two types of pearl oyster that significantly differed in color (yellowness) of the shell nacre were mixed at four different ratios, and the prepared OEC mixtures were transplanted by method 2 to investigate the effects of the blend on the yellowness of harvested pearls. The yellowness of harvested pearls differed significantly in accordance with the mixing ratio.

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