By H. Tomita
The medaka is an excellent material for general and comparative physiology, reproductive physiology, embryology and genetics. It has the following merits as unequaled material among fishes.
( l ) As they are small and hardy, they can be kept even in an aquarium of small size.
In 1957, he introduced the fused(fu), color interferer(ci) and x-type which have been kept by Aida at his Kyoto laboratory. The x-type is the strain in which the sex chromosomes of both sexes are XX. In Aida's breed rare exceptional XX males appeared. These exceptional males may be regarded as individuals in which autosomal M-genes are so overly accumulated that they differentiated into males in spite of XX constitution(see Chap. 15). By repeated crossings of normal females and exceptional XX males, the x -strain(XX females - XX males) has been established.
Following Yamamoto the writer also began to establish strains of the wild (B, R), orange-red (b, R) and white (b, r) in 1956. Since then the collection and maintenance of new mutant genes in various sources has been continued. One new gene(fm) was offered to our laboratory by courtesy of Takahashi in 1971. The all other new mutants have been found and established in our laboratory by the writer. To our regrect, these stocks of mutant genes are not yet established in isogenic strains.
At present the following 37 mutant genes pertaining to body colors and deformities are keeping in our laboratory: b (colorless melanophore), B' (black variegated), bd (dilute black), ci(color interferer), cm (concentrated melanophore), co (concentrated xanthophore), Da (double anal fins), de (decreased melanophores), di (dispersed xanthophore), dm (dispersed melanophore), dx-1 (dilute xanthophore-1), dx-2 (dilute xanthophore-2), fl (a few leucophores), fm (a few melanophores), fs (fused interhemal spins), fu(fused), fu-2 (fused-2), fu-3 (fused-3), fu-4 (fused-4), fu-5 (fused-5), fu-6 (fused-6), gl (guanineless), i (albino), il-1 (iridocyteless-1), il-2 (iridocyteless-2), lf (leucophore-free), ml-1 (many leucophores-1), ml-2 (many leucophores-2), mm (mixed melanophores), r (colorless xanthophore), rd (dilute orange-red), rf (reduced fins), rs (reduced scale), sm (slow response melanophore), vc (variegated chromatophores), wl (white leucophore), wy (wavy).
Facilities
Outdoor fish keeping farm (660 m exp2) is equipped with hundreds of concrete pools (75cm ´ 75cm ´ 18cm) and large-sized earthenware bowls. Indoor fish keeping room (36m exp2 constant temperature) is equipped with some dozens of glass vessels(24cm diameter and 15cm depth) and a number of metal-framed rectangular aquarium.
The collection and maintenance of mutant genes of the medaka in our laboratory are partially supported financially by the Ministry of Education.
A small number of certain types of the medaka can be supplied only to independent investigators who want to obtain fish for research purpose, providing the researcher himself or his representative visits our laboratory. Sending of living fish by mail is flatly refused on account of various matters.
Address of the laboratory
Biological Institute, Faculty of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464.
In: "MEDAKA(killifish) : Biology and Strains"
Yamamoto, T. (ed.) , Keigaku Pub. Co., Tokyo, 1975, pp. 273--275.
( 2 ) They reach adulthood within three to six months in adequate conditions.
( 3 ) As many genes are found and established, marker genes can be used in certain fields of biology.
( 4 ) The reproductive activity is easily controlled by the regulation of temperature and light conditions. A female usually spawns 30 to 50 eggs every day under the condition of 25 oC and over 13 hours of light per day.
( 5 ) As ripe unfertilized eggs are easily obtained, the process of fertilization can be observed.
( 6 ) As the chorion is transparent, the cleavage and later developmental stages are easily observed.
( 7 ) As the sexual dimorphism is distinct, the sexes are easily dis-tinguishable.
( 8 ) Artificial control of sex differentiation is possible.
The maintenance and collection of stocks of the medaka at Nagoya University was begun by Yamamoto in 1946. He first established homozygotes of the orange-red (yellow) (bbRR) and the white (bbrr). Further the variegated orange-red (B'R) and variegated white(B'r) types have also been reared by him. He established the d-rR strain in which genotype of white is bbXrXr and that of orange-red is bbXrYR. In this strain, phenotypes of white and orange-red can simply be symbolized as r and R respectively, since they have common bb. The sex-linked R and r genes can be used as markers to distinguish sex genotypes as XrYR and XrXr, respectively.
The following mutant genes concerning with body colors are added to the stock list mentioned above:
dl (dilute melanophore), Si (spotless iridocyte), lc (light color).