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Reprinted with permission
from:
Dr.
Joanne Norton
Freshwater And Marine
Aquarium magazine
Gold
Marble Angelfish
Photos and Text by Dr.
Joanne Norton
FAMA: September 1988, Vol.
11, #9
Figure 1: No.4.
Heterozygous for marble.
Gold
Marble Angelfish
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.
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.
Figure 2: No.6.
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.
Figure 3: No. 12
Heterozygous 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-comsuming
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.
Figure 4: No. 5.
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.
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.
Figure 5: No. 8.
Homozygous for marble.
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.
Figure 6: No. 9.
Homozygous for marble.
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 loi angel.
Tropical Fish Hobbyist 36
(No. 4):70-75. 1987b.
Norton, Joanne.
Angelfish--breeding and
genetics. The Aquarium 6
(No. 10):34-41. 1971.
Norton, Joanne. Angelfish
genetics.
Part One. Freshwater
and Marine Aquarium 5
(No.4):15-18, 90-91.
1982a.
Norton, Joanne. Angelfish
genetics.
Part Three. Freshwater
and Marine Aquarium 5 (No.
7):8-10, 91-92. 1982b.
Half-Black
Combinations In Angelfish
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