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Marble angelfish have been very popular in the 19 years since
they were introduced (Ash, 1969). Later the even more attractive
gold marble angelfish became widely available. Apparently it
originated in the Far East. The gold marble is more striking in
appearance because of its jet black markings compared to the
less intensely-pigmented (gray and black) markings of the
original marble.
Original marbles have gray and black marbling in heterozygous
individuals, those having one dose of the dominant gene for
marble. Homozygous original marbles, those having two doses of
the gene for marble, are very extensively covered with black,
having only a small percent of white area (Norton, 1971, 1982a).
Homozygous original marbles grow much more slowly than
heterozygous ones, which grow at least as fast as silvers. Gold
marbles also are either heterozygous or homozygous for marble,
but heterozygous (for marble) and homozygous (for marble) gold
marbles grow about the same rate. Homozygous (for marble) gold
marbles are not as extensively covered with black pigment as are
homozygous original marbles. In the gold marbles that I tested
for genotype, individuals that are heterozygous for marble have
less black, as a general rule, than occurs in homozygous
individuals. I suspected that this might be true because I got
all sparsely-marked fish from a cross of a gold with an
extensively-marked gold marble.
Fig. 2: No. 6. Heterozygous for marble.
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| Fig. 2: No. 6. Heterozygous for marble. |
I had some gold marbles that I knew were heterozygous for
marble because they had one parent that was marble and one
parent that did not have marble. All of these heterozygous gold
marbles were sparsely-marked with black. Another sparsely-marked
fish, which had gold marble parents, was tested by crossing him
with a silver female. This cross produced both marbles (127) and
non-marbles (119), so I knew that the tested gold marble was
heterozygous for marble. If he were homozygous for marble, all
of his offspring would have been marble. All heterozygous (for
marble) gold marbles that I have tested (by crossing them with
gold), had marble on one chromosome and gold on the other
chromosome of the pair. The genes for marble (dominant to
wild-type) and gold (recessive to wild-type) behave as alleles
(Norton, 1982a,b). Such genes might be true alleles, which have
the same locus on a chromosome, or they might be closely linked,
having loci that are near each other.
Fig. 3: No. 12. Heterozygous for marble.
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| Fig. 3: No. 12. Heterozygous for marble. |
I tested five of the more extensively-marked gold marbles,
all of which had both parents that were gold marble. These
extensively-marked gold marbles were tested by crossing each of
them with an angelfish that did not have marble. All five
produced 100% offspring with the marble pattern. The spawn
counts were: 303, 109, 168, 85, and 376. So I was accurate in my
predictions that these five gold marbles were homozygous for
marble. However, the method is not foolproof. The black pattern
of some gold marbles is borderline as to whether the fish is
sparsely-marked or extensively-marked, making it difficult to
tell whether certain individuals are heterozygous or homozygous
for marble by their appearance. But I do think you can be
successful most of the time if you choose the extremes. To
attempt to select a heterozygous fish, pick one with the least
black; for a homozygous fish, choose a fish that has the most
extensive black pattern.
Fig. 4: No. 5. Homozygous for marble.
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| Fig. 4: No. 5. Homozygous for marble. |
Why does it matter whether a gold marble is heterozygous or
homozygous for marble? First, being able to select heterozygous
or homozygous individuals enables you to raise the type of gold
marble (sparsely-marked or extensively-marked) that you want.
Second, accurate selection enables you to pick breeders that
will produce 100% gold marbles, thus eliminating the production
of golds in the same spawn, and eliminating the time-consuming
job of sorting. If you want to raise 100% of the more
extensively-marked type, use breeders that are
extensively-marked. To obtain 100% sparsely-marked gold marbles,
cross an extensively-marked gold marble with a gold.
Heterozygous gold marble parents produce 75% gold marbles and
25% golds. Crossing a gold with a heterozygous gold marble
produces 50% gold marbles and 50% golds.
Fig. 5: No. 8. Homozygous for marble.
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| Fig. 5: No. 8. Homozygous for marble. |
Recently, an angelfish called "koi" was introduced (Jones,
1987a,b). From the appearance of the fish in the photos in these
articles and from the author's information on "koi" parentage, I
deduced that the "koi" angelfish is a blushing gold marble.
Jones stated that the "koi" strain produces 75% "koi" and 25%
gold blushing. The "koi" angelfish breeders that produce this
ratio must be homozygous for stripeless, resulting in blushing.
In addition, these fish have one marble-carrying chromosome like
that of a gold marble; the other chromosome of the pair has the
gene for gold. You can produce blushing gold marble ("koi")
angelfish in two generations by first crossing a gold blushing
with a gold marble. There should be some "koi" (blushing gold
marble) individuals in the F2, produced by crossing F1 gold
marbles brother to sister.
Fig. 6: Homozygous for marble.
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| Fig. 6: Homozygous for marble. |
It is not known yet exactly what a gold marble is
genetically. As I already stated above, a gold marble may be
either heterozygous or homozygous for marble, and a heterozygous
fish has marble on one chromosome and gold on the other
chromosome of the pair. The gold marble angelfish might have the
same gene for marble that occurs in original marble angelfish,
or the gold marble could have a different gene that also
produces a marble pattern. If the gold marble angelfish does
have the same gene for marble as in the original marble
angelfish, and if the genes for marble and gold are closely
linked instead of being alleles, then the gold marble angelfish
could have the genes for marble and gold on the same chromosome
as the result of a chromosome crossover. This happening would be
rare for genes that are closely linked, and the resulting
chromosome with both genes would be fairly stable. A homozygous
gold marble would have two such chromosomes. A heterozygous gold
marble would have one chromosome carrying genes for both gold
and marble: the other chromosome of the pair would have the gene
for gold. To test for linkage of the genes for gold and marble,
I obtained some heterozygous for marble fish from a cross of a
gold marble and a silver. So I had marble breeders in which the
chromosome carrying marble is the same as the marble-carrying
chromosome of a gold marble; the other chromosome of the pair
does not carry gold. When these special marble angelfish are
crossed with golds, they produce silvers and gold marbles. If
the genes for gold and marble are linked, and if a chromosome
crossover were to occur between these two genes, then a
chromosome having the gene for gold but not the gene for marble
could be produced in the ova or sperm of the marble parent. Then
a gold angelfish could appear in the offspring of these special
gold marbles crossed with gold. I raised 11 such spawns and have
not yet obtained a gold. If evidence of linkage of the genes for
marble and gold is obtained, it may take many such crosses
because the closer the gene linkage the lower the crossover rate
between those two genes. I counted 10 of the 11 spawns, which
totaled 1552 gold marbles and 1911 silvers. Only one of these
ten spawn had more gold marbles (204) than silvers (189). The
expected ratio is one silver to one gold marble. The lower than
expected percent of gold marbles might be due to higher fry
mortality rate in gold marbles than in silvers.
A fish that resembles a gold marble (because of its jet black
markings) is produced by crossing a marble (original type) with
a gold. The resulting marbles are heterozygous for marble and
have the gene for gold on the other chromosome of the pair
(Norton, 1982b). Although the markings are jet black, as in a
gold marble, the black pattern of this heterozygous marble is as
extensive as that of a gold marble that is homozygous for
marble. If you have an angelfish of unknown parentage that looks
like a homozygous (for marble) gold marble, how can you tell
whether it is a gold marble that is homozygous for marble or the
look-alike heterozygous marble that has marble on one chromosome
and gold on the other chromosome of the pair? You can test the
fish by crossing it with a gold. If the tested fish is a
homozygous (for marble) gold marble, you will get 100% gold
marbles. If the tested fish is the look-alike that is not a gold
marble, you will get 50% offspring like the marble being tested
and 50% golds.
In my opinion, the gold marble is one of the most attractive
of all angelfish types. By selecting the proper parents, the
fish breeder can produce spawns of 100% gold marbles.
Literature Cited
Ash, Charles A. The new marble angel. The
Aquarium 2 (No. 3):4. 1969
Jones, Phil. Ghianni's koi angel. Freshwater and
Marine Aquarium 10 (No. 12):40. 1987a.
-----.At last a new angelfish strain: introducing
Ghianni's koi angel. Tropical Fish Hobbyist 36
(No. 4):70-75. 1987b.
Norton, Joanne. Angelfish--breeding and genetics.
The Aquarium 6 (No. 10):34-41. 1971.
-----.Angelfish genetics. Part One. Freshwater and
Marine Aquarium 5 (No.4):15-18, 90-91. 1982a.
-----.Angelfish genetics. Part Three. Freshwater and
Marine Aquarium 5 (No. 7):8-10, 91-92. 1982b.
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