The University of Tokyo · Environmental Science
Professor Tomoyoshi Yoshinaga's research lab specializes in parasitology and aquatic animal health, with a primary focus on the biology, pathology, and in vitro culture of parasitic ciliates and monogeneans affecting economically important fish species such as the Japanese flounder. The lab investigates host-parasite interactions, disease mechanisms, and environmental factors influencing parasite development and transmission, aiming to support sustainable aquaculture. A key strength lies in establishing axenic and axenic-like cultures of parasites, enabling controlled studies on pathogenesis and chemotherapeutic interventions.
Figures are computed from collected data and may differ slightly.
The ciliate causing scuticociliatosis in Japanese flounder was isolated, and axenic cultures were established. Sterilization of the ciliate was accomplished by serial washing with capillary pipettes. Growth of the ciliate was compared in different dilutions of Millport S solution containing 2% proteose peptone and 1% yeast extract at different temperatures. Optimum growth was obtained at dilution of 1 : 2 (osmolarity : 438 mOsm) at 22.5-27.5°C with a maximum cell density of 1.0×104 cells/ml.
A method for the propagation of the parasitic ciliate Cryptocaryon irritans, with black mollies Poecilia latipinna as the host fish, is described. A stable infection has been maintained for 2 years in this system. Parasites remained on fish for at least 3 d before leaving and secreting cysts. Parasites divided within cysts to form infective theronts, which began exiting on day 4. All theronts left the cysts during the same time of day: 0200–0900 hours. When fish were exposed to theronts that had
[in Japanese]
Challenges of the Japanese flounder Paralichthys olivaceus with the monogenean Neoheterobothrium hirame were carried out to clarify the cause of the anemia, recently prevailing in the Japanese flounder in Japan. Hematological changes very similar to those previously reported in both wild and cultured anemic flounder were produced by the challenges with H. hirame. In the challenged flounder, the hemoglobin concentration decreased considerably and abnormal immature and mature erythrocytes having v
Abstract Ciliates are considered the most harmful parasites of fish, causing mass mortalities and thus substantial economic losses to the aquaculture and ornamental fish industries. To better elucidate their pathogenic mechanisms and facilitate the development of effective prevention and control strategies, it is essential to apply novel technologies to ensure the continuous and sufficient supply of parasite specimens. This review discusses the latest research progress in the artificial culture
A freshwater life cycle of Hysterothylacium aduncum was demonstrated experimentally for the first time. Third-stage larvae of H. aduncum from naturally infected Japanese smelt, Hypomesus transpacificus nipponensis, developed to the adult stage in experimentally infected rainbow trout, Salmo gairdneri, in fresh water. Larvae in eggs developed to the second stage and hatched even in fresh water. Although hatched larvae died quickly in fresh water, unhatched second-stage larvae remained alive there
Effects of temperature, salinity and chlorine treatment on egg hatching of the monogenean parasite, Neoheterobothrium hirame, of the Japanese flounder, Paralichthys olivaceus, were examined. More than 85%of the eggs developed and hatched between 10 and 25°C, but at 30°C hatching rates were lower than 5%. They hatched similarly in a wide range of salinities from 1/3-to full-strength seawater (salinity : 11-33‰). In distilled water and double-strength seawater, they did not hatch at all. In 1.5-st
A medium for the in vitro culture of Cryptocaryon irritans, which is an obligatorily parasitic ciliate of marine teleosts and causes 'white spot disease', was developed. The medium consisted of a layer of cultured fish cells (FHM), with an agarose gel layer covering the cell layer. The agarose gel contained 0.22% agarose, 10% fetal calf serum, 100 I.U. ml(-1) Penicillin G potassium and 100 microg ml(-1) streptomycin sulphate. Theronts of C. irritans transformed to trophonts and grew to 180 micro
近年ヒラメに頻発している原因不明の貧血症について, 血液学的, 寄生虫学的検査と造血器官の病理組織学的観察を行った。血液学的には, 幼若赤血球の増加と赤血球細胞質の空胞変性および染色性の低下が認められた。病魚の造血器官にヘモジデリンの沈着や組織壊死像はほとんど見られず, 貧血魚にはN.hirameが高率に寄生していた。このことから, 本貧血症は寄生虫による失血性貧血であることが強く示唆された。
The effects of high temperature on the parasitic stage (trophont) and encysted stage (tomont) ofCryptocaryon irritans were examined. The effects on trophonts were examined by rearing fish artificially infected withC. irritansat 25, 28, 31 or 34°C. The effects on tomonts were examined by incubating tomonts at the same temperatures. In these experiments, both the trophonts and tomonts showed normal developments below 31°C, whilst their development was badly damaged at 34°C. The effects of dissolve
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