Dr. Toki-o Yamamoto, Professor of Animal Physiology at the Biological Institute in the Faculty of Science of Nagoya University, has made many contributions during a span on 40 academic years. On the 16 of February in 1969, he reached the age of sixty three, and will retire from the university in march. On this occasion, we would like to take the opportunity of honoring his contributions to the biological sciences and to thank him for his years of devoted service to us, his students.

The Yamamoto family were noted land-owners in Yamamoto County, Akita Prefecture, and served as village headmen for generations. Dr. Yamamoto, who is known as "Dr. Medaka" or "Dr. Killifish", was born in 1906, as the first son of Tokiyoshi (father) and Tama (mother), who was the daughter of a Medical Doctor (Jun-an Hara). Growing up by the Yoneshiro (Noshiro) riverside, he early developed a fascination for the various animals, especially fishes, in his pastoral surroundings. This curiosity about animal life naturally led him to a career in Zoology. After graduation from Tomine primary and Akita middle (former) schools, he entered Hirosaki High school (former) in Aomori Prefecture. Upon finishing school, he was admitted to the Zoological Institute of the Faculty of science in the Imperial University of Tokyo in 1926. There he met and was influenced by Professor Seitaro Goto and Naohide Yatsu. The latter's lectures on Experimental Zoology were particularly influential on a receptive mind. Thus, his career in the biological sciences was molded by the tutelage and encouragement of Dr. Yatsu.

Upon graduation in 1929 he was appointed as an assistant in Zoology in the University and entered his doctoral work; "Studies on the rhythmical movements in early embryos of Oryzias latipes". These studies continued fruitfully over the subsequent ten years. During this period he was able to demonstrate the occurrence of rhythmical movements in eggs of other fishes such as the goldfish, the trout, and the ice-fish. In 1936 he was awarded the degree of Rigaku Hakushi (D.Sc.).

Later, at Tokyo Imperial University, his interest was drawn to the physiology of fertilization in fish eggs. Physiological research in fertilization of fresh-water fish had long been hampered by the fact that their ripe unfertilized eggs lose their capacity for fertilization and activation when placed in fresh water. His first contribution in this area then was the formulation of an isotonic balanced saline for the medaka (Oryzias latipes) based on osmotic pressure of the egg (1939). By the use of the isotonic saline, in which the unfertilized eggs retain their capacity for fertilization for several hours, Dr. Yamamoto was able to perform a series of beautiful experiments on fertilization and artificial activation.

When the Faculty of Science of Nagoya University was established in 1942, Dr. Yamamoto was first appointed as an instructor, and then was quickly made an Assistant Professor. The following year he was promoted to the professorship which he now holds. Along with his colleagues, Professors N. Takamine (Botanist), T. Sato (Embryologist), T. Shimamura (Cytogenetist) and assistant Professors J. Ishida (Physiochemist) H. Kubo (Plant Physiologist) and M. Sugiyama (Embryologist, Marine Biological Station), Dr. Yamamoto was responsible for the establishment of the biological Institute.

In earlier years he lectured on "Animal Physiology" and "Vertebrate Zoology", but more recently has concentrated on "Animal Physiology" and "Genetics". Throughout his teaching career, he has always maintained the principle of training students in the art of independent research. Approximately 20 students have completed their doctorate training under his guidance. Imbued with his vigorous and selfless dedication to research, and inculcated with the sound use of scientific methods, they reflect the influence of the master.

During his early years at Nagoya, he continued physiological studies on fertilization of the medaka, the goldfish, the brook lamprey as well as the pond smelt. on May 14, 1945, during World War II, the Biological Institute building was destroyed during a large-scaled bombing raid. nearly all his materials, books and reprints were lost. Along with his staff, he evacuated to a public house by Lake Kizaki, Nagano Prefecture. However, his love for the academic life forced him to emulate the phoenix which rebuilt itself out of the ashes.

Returning to Nagoya, his interest was focussed on the experimental induction of sex differentiation. He established the d-rR strain of the medaka in which white (r), XrXr is female and orange-red (R), XrXR is male. By using this stock, sex-genotypes, either XX or XY, could be discriminated by their body color. At present, the breed belongs to the 18th generation and proves to be a most suitable material for obtaining confident evidence for reversals in sex differentiation.

The first full paper reporting induction of XrYR females, by administration of estrogens to medaka fry, was published in 1953. A YY male was detected among offspring from estrogen-induced females, E (XY) females, mated with normal XY males (1955). Methyltestosterone-induced M (XX) males were obtained only after an intensive five year effort. Successful reversal of sex-differentiation in both directions by administration of heterologous sex-hormones, rendered it possible to mate E (XY) females with M (XX) males (1961). By administration of estrone in two consecutive generations, he succeeded in the production of E (YY) females (1963). A further study on mass production of E (YY) females and YY males was performed, which made the mating of E (YY) females with YY males possible (1967, 1968).

Concurrently with these experiments, Dr. Yamamoto, in collaboration with Dr. T. Kajishima, has been attempting to inverse sex differentiation in the goldfish. After working for nine years, induction of reversals in both directions have been accomplished. This demonstrates that the principle obtained in the medaka can be applied to other fishes. Test crosses of treated goldfish, used to determine their sex-genotype, has disclosed that the male is heterogametic (1968).

The prodigious energy and talent expressed by Dr. Yamamoto's scientific work are reflected in his bibliography of over 80 original publications, annexed herewith. In addition, he authored two monographs and two excellent and comprehensive reviews; one monograph in 1943, entitled Physiology of Development in Fishes (Japanese), early established him as an authoritative, but young, voice in reproductive Physiology of fish. His second book, Experiments in Animal Physiology (Japanese), an experimental guide book, was published in 1949 and has been well accepted by students in Physiology. The extensive review, Physiology of fertilization in fish eggs, (International Review of Cytology 12, 1961) summarized his work on fertilization in fish. Another review entitled Sex differentiation in fish, will be published in the near future as a chapter on Fish Physiology, edited by W.S. Hoar and D.J. Randalls, and represents a crowning achievement in the study of sex differentiation in the medaka which was first published in 1953.

The achievements of Dr. Yamamoto have brought him numerous prizes and tributes. Among these may be mentioned: The prize from the Zoological Society of japan (1950); Cultural Prize of the Chubu-nippon Press (1952); Prize from the Genetics Society of Japan (1957); and the Science-Technology Prize of the Toyo Rayon Science Foundation (1964). he is a member of many scientific societies and organizations including: councilor of the Zoological Society of Japan; the Genetics Society of Japan; the Ichthyological society of Japan; and is a member of the Zoological Communication Committee of the Japan science Council. His editorial skills found outlet through memberships on the editorial boards of Embryologia, Annotations Zoologicae Japonenses and Japanese Journal of Zoology. Dr, Yamamoto's activities clearly exemplify his belief in the internationalism of science. He has made many lecture trips abroad. In 1960, he made his first round-the world tour visiting the U.S.A., England, France, Italy and Turkey. he gave lectures on artificial control of sex differentiation in fish at the California Institute of Technology (Pasadena), the Zoological Station at naples, and the University of Palermo. In August and September of 1963, he again travelled to the U.S.A. to attend the 16th International Congress of Zoology representing the Japan science Council and then continued on to the 11th International Congress of Genetics, held in the Hague, Netherlands. in May of 1965, he was invited to attend the Conference on intersexuality in Fishes, held at Sarasota, Florida, U.S.A.. In October of that year he accepted a visiting Professorship at the Downstate Medical Center of the State University of New york (Brooklyn). He travelled to New York with his research associate Dr. H. Tomita, carrying three strains of medaka as well as YY males. During his stay he established a medaka colony and with the construction of a high temperature room, was able to obtain spawnings throughout the winter months.

Dr. Yamamoto's love of Nature was not entirely academic for it carried over into his hobbies as well; He collects stones, rocks and sea shells of all kinds. His interest in the beauty of the goldfish prompted him into acting as a consultant to the Association of Goldfish Culture.

Dr. Yamamoto's work over the past forty years is distinguished not only by his imagination, insight and ability to concentrate many experimental techniques on a problem, but also by his diligence and thoroughness. His conviction, expressed already in his earliest work, that the solutions of problems in Animal Physiology require the skillfully blending of the special expertise of the Physiologist, the Morphologist and the Genetist is still impressed upon all his students.

While we honor especially Dr. Yamamoto the scientist, we do not wish to ignore Dr. Yamamoto the fiend and citizen. This man of many talents who loves classical music as well as the drinking songs of the "Kuroda-bushi" and Chinese poems, truly manifests a personality as distinct as the ancient "Samurai". All of us, his students and colleagues, at the Biological Institute of Nagoya University sincerely hope that dr. Yamamoto will continue to enjoy excellent health, will continue to give us his expert counsel, and continue his contributions to the field of Zoology.

March, 1969

Tomi-o HISHIDA, D.Sc.