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Fig. 1: Black lace half-black.
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| Fig. 1: Black lace half-black. |
Fig. 2: Zebra half-black.
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| Fig. 2: Zebra half-black. |
The half-black angelfish is black on its tail and rear
one-third of the body. By combining the half-black pattern with
other patterns, we can see what these combinations look like and
also we can investigate the genetic relationships between the
genes in angelfish.
Fig. 3: Zebra lace half-black.
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| Fig. 3: Zebra lace half-black. |
Fig. 4: Blushing half-black.
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| Fig. 4: Blushing half-black. |
For several years angelfish having half-black along with
other patterns have been available from Singapore. Thus I
obtained, through a wholesaler, black lace half-black (Fig. 1),
zebra half-black (Fig. 2), zebra lace half-black (Fig. 3), and
blushing half-black (Fig. 4). By appropriate crosses, I obtained smokey half-black (Fig. 5) and marble half-black (Fig. 6).
Fig. 5: Smokey half-black.
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| Fig. 5: Smokey half-black. |
Fig. 6: Marble half-black.
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| Fig. 6: Marble half-black. |
To obtain smokey half-blacks, I crossed a half-black female
and smokey male. The offspring were some each of silver and
smokey. Next I crossed one of these smokey (a male), which
carried half-black, with a half-black female. Some of the smokey
offspring from this cross also had the half-black pattern,
looking like smokey except that it was solid black rather than
the mottled pattern that is characteristic of smokey (Fig. 7).
Fig. 7: Smokey
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| Fig. 7: Smokey |
Fig. 8: Ghost half-black.
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| Fig. 8: Ghost half-black. |
Marble half-blacks were produced by first crossing a
half-black female with a marble male, producing silvers and
marbles. Crossing one of these marble offspring with a
half-black produced some marble half-blacks.
Ghost half-blacks (Fig. 8), having one dose of the gene for stripeless, were obtained from a cross of blushing half-black
(having two doses of the gene for stripeless) with a half-black.
The ghost half-black never exhibits a vertical black bar on the
front of the body. This bar appears and disappears in a
half-black, depending on mood changes in the fish.
I have never seen a gold half-black and have not tried to
produce it. Also, gold half-blacks are not offered in wholesale
lists that I have seen. Evidence that the half-black pattern
cannot develop in a gold was obtained by Bill Lutz. He crossed a
half-black with gold, producing silver offspring, the expected
result because both half-black (as I shall discuss later in this
article) and gold are due to recessive genes. Then he crossed
these F1 brother to sister to produce some fish homozygous for
both gold and half-black. This genotype would be expected to
occur because the genes for gold and half-black are not alleles,
and inference that I made because gold acts as an allele of dark
and marble (Norton, 1982), and half-black is not an allele of
dark or marble (explained later in this article). Some
half-blacks and some golds were produced, but no gold
half-blacks. It appears, then, that gold is epistatic to
half-black, homozygous gold preventing expression of half-black.
Homozygous gold also prevents development of zebra and smokey
(Norton, 1982).
To understand the inheritance of half-black combinations,
first we need to know how half-black is inherited. Earlier
(Norton, 1985) I stated, "Therefore, I am concluding,
tentatively until more ratios are obtained, that half-black is
due to a single recessive gene." Now I can say, backed up by
further evidence, that the half-black pattern is due to a single
gene that is recessive to wild type.
Understanding of the inheritance of half-black was elusive
for many years because environmental factors influence whether
or not the pattern develops in a fish that is genetically a
half-black (homozygous for half-black). Unlike the other
angelfish pigment pattern genes (dark, marble, gold, stripeless,
zebra, and smokey), all of which are expressed in stunted fish,
the half-black pattern does not develop in stunted fish (Norton,
1985). Insufficient feeding or inadequate water changes can
result in genetic half-blacks that do not develop the half-black
pattern. Half-blacks must be raised under excellent conditions
to develop the half-black pattern.
Give the fry heavy feedings of live newly hatched brine shrimp.
I feed them twice a day every other day. On alternate days they
are fed once a day. The abdomens of the fish should bulge after
every feeding. On the days that I feed twice, I do not feed any
more to fish that are still full from the morning feeding.
Usually older fry can use two feedings per day.
Half-blacks should receive frequent large water changes in
their first few months of life, until their patterns are
established. From the time the fry are three weeks old, change
90% of their water two or three times a week. Later, frequency
of water changes may need to be increased to as often as every
day, depending on the tank size and, of course, on the number
and size of the fish.
From the time that genetic half-blacks become free swimming,
it takes over a month (in the ones that I have raised ) before
the half-black pattern appears in any of them. In spawns from
half-blacks, the first half-blacks became evident in the
following number of days after the fry became free swimming: 30,
31, 34, 34, 36, 42, 43, 44, and 45. A partial half-black
pattern, consisting of black only in part of the tail to black
in the tail and extending slightly onto the body (a partial
half-black pattern) is a frequent occurrence in fish that are
starting to get the half-black pattern or in fish that are
losing all or part of the pattern if environmental conditions
become unfavorable for development and maintenance of the
pattern. Adult genetic half-blacks do not change even if
environmental conditions become better or worse. If they did not
develop the pattern they will not get it. If they have a full
pattern or partial pattern, these remain.
Evidence that half-black is due to a recessive gene is that
crosses of smokey x half-black and marble x half-black produced
no offspring with the half-black pattern; but backcrosses to
half-black did produce some fish with and some without the
half-black pattern.
It is evident that the gene for half-black is not an allele
of the other pigment pattern genes that are present in today's
commercially produced angelfish types.
The cross that combined one dose of the gene for marble and
one dose of the gene for half-black did not produce any marble
half-blacks. It took a backcross to get marble half-blacks,
which have two doses of the gene for half-black. Only two genes
of a set of alleles occur in an individual. If marble and
half-black were alleles, then we would not be able to get a fish
with one dose of the gene for marble and two doses of the gene
for half-black. Therefore, marble and half-black obviously are
not alleles.
Because gold and dark act as alleles of marble, it is concluded
that half-black is not an allele of gold or dark.
My cross of smokey x half-black did not produce any smokey
half-blacks. It took a backcross to produce smokey half-black,
which has one dose of the gene for smokey and two doses of the
gene for half-black. My conclusion is that smokey is not an
allele of half-black.
Blushing angelfish are homozygous for stripeless (Norton,
1971). If the genes for stripeless and half-black were alleles,
then a blushing half-black would have one dose each of the genes
for stripeless and half-black; then blushing half-blacks would
produce three kinds of offspring: blushing, blushing half-black,
and half-black. But this does not happen; blushing half-blacks
breed true. I deduce that stripeless and half-black are not
alleles.
Stripeless and zebra behave as alleles (Norton, 1982).
Because stripeless is not an allele of half-black, I conclude
that zebra also is not an allele of half-black.
Of the described half-black combination, two are worthwhile
additions that are more attractive than half-blacks. The ghost
half-black, lacking the front body stripe, is more striking than
the half-black. The blushing half-black having pearly white
anterior body color contrasting sharply with its jet black rear
pattern, is the most beautiful of the half-blacks and one of the
most beautiful of all angelfish. As I mentioned, blushing
half-blacks breed true. You can get 100% ghost half-blacks by
crossing a half-black with a blushing half-black.
Literature Cited
Norton, J. Angelfish ---breeding and genetics. The
Aquarium 6(10): 34-41. 1971.
-----.Angelfish genetics. Part three. Freshwater and
Marine Aquarium 5(7): 8-10, 91-92. 1982
-----.Half-black angelfish. Freshwater and Marine
Aquarium 8(8): 18-21, 23. 1985
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