GENETIC AND DEVELOPMENTAL ANALYSIS OF SOME NEW
COLOR MUTANTS IN THE GOLDFISH, CARASSZUS AURATUS
TAKA0 KAJISHIMA
Biological Institute, Faculty of Science, Nagoya University,
Nagoya 464, Japan
Manuscript received August 31, 1976
Revised copy received January 4, 1977
ABSTRACT
The genotypes of three color mutants in goldfish: a depigmentation character
of larval melanophores, albinism and a recessive-transparent character,
were analyzed by crossing experiments. The depigmentation character in the
common goldfish is controlled by two dominant multiple genes, Dp, and Dpd,
and only fish with double recessive alleles dp,dp, dp,dp, can retain larval
melanophores throughout life. Albinism is also controlled by double autosomal
genes, p and c. The genotype of an albino fish is represented by pp cc; the
non-albino fish is PP CC. Fish with either a pp CC or pp Cc genotype are
albino when scored at the time of melanosome differentiation in the pigment
retina, but after the time of skin melanophore differentiation, they change to
the nonalbino type under the control of the C gene. The recessive-transparent
character is controlled by a single autosomal gene, g. The mechanisms of gene
expression of these characters were proposed as a result of observation and/or
experimental data on the differentiation processes of their phenotypes, and the
genotypes of these color mutant goldfish were considered in relation to the
"gene duplication hypothesis in the Cyprinidae."
HE goldfish is one ol the most popular animals used as an experimental
subject in many laboratories. Although it has many varieties of color and
form, only a few genetic analyses of these characters have been carried out. One
of the reasons €or this is that a great deal of time and space is required to raise a
sufficient number of off spring. Furthermore, as has been pointed out, many
characters of the goldfish are controlled by multiple factors, so that it is difficult
to get invariablc and regular ratios that fit Mendelian expectations (CHEN 1934).
The first report on the genetics of the goldfish was that of HANCE (1 924), who
reported the recessiveness of the telescope-eye to the normal-eye, although no
experimental data were shown. The first well-founded case of a Mendelian
character in the goldfish was reported by BERNDT (1925) and CHEN (1925,
1928) on the transparency and mottling character of the scales. A few years
later, MATSUI (1 934) reported his detailed results on the genetic analysis of the
goldfish varieties involving scale-transparency and telescopeeye. In the same
year, CHEN (1934) reported on the inheritance of blue and brown coloration in
the goldfish, and concluded that there are four pairs of independent factors controlling
the production of these characters, and only when all of these pairs were
in the homozygous recessive condition was the brown coloration produced.
Genetics 86: 161-174 May, 1977
162 T. KAJISHIMA
When rearcd at 21 “C, the common goldfish begins to differentiate the melanosomes
in its retinal pigment cells about 36 hours after spawning (Stage-21,
developmental stage from KAJISHIMA 1960d), and more than 14 hours later
three kinds of skin chromatophores begin to differentiate successively; at first
the melanophores (50 !iours after spawning, St-22) , then iridophores (80 hours
after spawning, St-24) and finally xanthophores (50 hours after hatching, 150
hours after spawning, St-26). Then the fry usually have black eyes and blackishbrown
coloration. However, as is well known, the larval melanophores of the
common goldfish begin to depigment about two to three months after hatching,
and within a month the fish becomes xanthic to deep orange in coloration. On
the other hmd, the black moor (black telescope-eyed goldfish) usually retains
its melanophores throughout life. In the present paper, the depigmentation and
nondepignien tation character of larval melanophores is analysed first.
Albinism is a common mutation, which has been reported in many animals,
including the fish. In the goldfish, however, it was not reported until 1956 in an
American hobbyists magazine, “The Aquarium”. According to the report, albino
goldfish were offspring of an albino fish found in Singapore, but unfortunately
all of the fish died without any genetic investigations. In 1967, YAMAMOTO and
his colleague, TOMITA, found albino goldfish in Favor’s Aquarium in New York,
and the following year they brought the live fish back to our laboratory. These
fish did not seem to be related to the 1956 strain, because the eye character of the
1956 fish secmed to be genetically dominant (normal-eye) in type, whereas the
present animals are all homozygous recessive (telescope-eye) in type.
The original fish and their progeny lack melanosomes not only in the skin,
but also in the retinal pigment cells from the earliest developmental stage; they
are orange in color and have pink eyes. The results of genetic analyses of albino
goldfish that were carried out by crossing albinos with various genetically
defined, color-mutant fish are described, and the processes of the phenotypic
expression of the albino genes, including the mechanisms of their functions, are
discussed.
From 1957 to 1960 we were engaged in experiments to clarify the mechanisms
of gene function of the dominant transparent-scaled character T (KAJISHIMA
1960a,b,c; MATSUMOTO, KAJISHIMA and HAMA 1960). During that time, a new
recessive transparent mntant was discovered. The results of the gene analysis of
this mutant are also reported here.
Recently, OHNO and his co-workers have proposed the hypothesis that some
of the teleosts of the family Cyprinidae duplicated their chromosome numbers
during the evolutionary process, and the genomes of these fish are tetraploid and
not diploid (OHNO 1970). The data obtained from the genetic analyses of color
mutants in the goldfish will be considered in relation to this hypothesis.
MATERIALS AND METHODS
The fish used in these experiments were of the following varieties:
The common goldfish, “wakin”: The wakin acquires its mature coloration following destruction
of the larval melanophores. The fish used in these experiments were inbred more than ten
COLOR MUTANTS IN GOLDFISH 163
generations by brother-sister matings in our laboratory, and all of the offspring had depigmented
melanophores within a year.
The red telescope-eyed goldfish: The red telescope fish also loses its skin melanophores during
its life, but the time of depigmentation varies extensively, usually occurring at an age of more
than two years. Until that time, it cannot be distinguished from the black moor. However, after
depigmentation it has a deep orange coloration and usually does not develop melanophores
again. The fish used in these experiments were progenies which were inbred more than five
generations.
The black telescope-eyed goldfish, “black moor”: The black moor usually does not show
depigmentation of its melanophores throughout its entire life and produces more of them during
development. The fish used in these expeiiments were also inbred in our laboratory more than
ten generations and during that period none of the individuals lost their melanophores.
The transparent-scaled goldfish: The adult homozygous transparent-scaled goldfish is pinkish
in coloration and has no pigment except in the retinal pigment cells. At the time of hatching,
however, it has the same three kinds of chromatophores as the common goldfish, i.e., melanophores,
iridophores and xanthophores. But when the fry reaches six to seven mm in length
(St-27+), about ten days after hatching, all three kinds of chromatophores begin to depigment
and within a month they acquire the final coloration.
The transparent-scaled character (TT) is incompletely dominant to the normal-scaled character
(It), and heterozygous F, fish show a characteristic “calico” pattern (CHEN 1928; MATSUI
1934) following partial depigmentation of the three kinds of chromatophores. The F, offspring
segregate into the homozygous transparent type, heterozygous transparent type (calico) and
normal type in the ratio of 1:2:1. The homozygous fish used in these experiments were also
inbred more than ten generations.
The albino goldfish: The albino goldfish used in these experiments were the inbred offspring
of the albino goldfish discovered in Favor’s Aquarium. Albino goldfish have no melanosomes
in the skin or the retinal pigment cells, and they have an orange body color and pink
eyes.
As mentioned above, in the nonalbino goldfish (wakin, black moor, transparent-scaled goldfish,
etc.) the retinal pigment granules become visible at St-21, and the skin melanophores begin
to appear at St-22. In the analysis of albino genes, the scoring of phenotype was carried out in
two different stages; first in St-21, soon after the differentiation of retinal pigment granules,
and then in St-27, when the skin melanophores are completely developed.
The recessiue transparent-scaled goldfish: Fish carrying this character were isolated in our
laboratory in 1960 from the F, offspring of homozygous transparent fish and wakin. In one of
these matings, six new mutant fish appeared, which almost completely lacked pigment granules
in their iridophores. These fish were apparently different from the ordinary transparent-scaled
fish, because they did not differentiate the pigment granules from the time of iridophore differentiation
(St-24), although some of the fish later synthesized them incompletely.
The melanophores and xanthophores differentiated as usual in the embryonic stage, and they
did not depigment at the time the pigment cells degenerate in the ordinary transparent-scaled
goldfish (St-27-k). Two of them, however, lost their melanophores two to three months after
hatching, at the time of depigmentation of larval melanophores in the common goldfish. The
remaining four have retained their melanophores throughout their lives. The former type was
designated “red recessive-transparent