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Reprinted
with permission from:
Dr. Joanne Norton
Freshwater And Marine Aquarium
magazine
Half-Black
Angelfish
Photos and Text
by Dr. Joanne Norton
FAMA: August 1985, Vol.8, #8
Half-blacks. Body stripe faded.
Half-black. Body stipe evident.
Body stripe is faded but it is visible
as a
light-colored stripe. Black stripe
below eye is
present even when body stripe is
faded.
Of all the pigment
pattern variations in angelfish, the
half-black pattern has remained a
mystery the longest. I discussed the
inheritance of black lace, black,
marble, gold, zebra, blushing and
smokey in previous articles (Norton,
1982a-e). But an explanation of the
inheritance of half-black was omitted
because of lack of information at the
time.
The half-black
angelfish appeared about 30 years ago,
with no documentation on its origin (Axelrod,
1985). Numerous aquarists and fish
farmers have asked me questions like,
"How do you get a half-black
angelfish?" These people had
half-blacks, mostly Far East imports,
which produced only silver (wild-type)
offspring. It was a mystery that
half-blacks were common imports while
many people were unsuccessful in
producing them in this country. I
crossed the half-black with black
lace, marble, smokey and zebra
angelfish; the F1 were mated brother
to sister or backcrossed to
half-black. From all these crosses, I
got no half-blacks. I began to suspect
that the half-black pattern is not
inherited, so I raised silvers in a
short (4-hour) day. This did not
produce half-blacks, although it
produced a fish with only a single
rear stripe or spot (Norton, 1985). I
already knew that a silver angelfish
raised in countinuous light has no
stripes (Norton, 1982f).
Occasionally I would
hear of an exception, a report of
half-black offspring from half-black
parents. I did not have an opportunity
to follow up on any such rumors until
I met Paul Kirtley, of Tampa, Florida,
when I was one of the judges for the
Florida Tropical Fish Farmers
Association show in Tampa. Mr. Kirtley
had in the show a pair of half-blacks
that had been imported at dime size
and raised in a fish farm pond until
they were silver dollar size. He said
that these fish had produced several
spawns of 100% half-black offspring,
but that later spawns contained some
silvers. Later, Mr. Kirtley sent me
the pair and described in detail how
he had raised the fry. The fry hatched
in a 2-gal. tank, where they became
free swimming. Then they were moved to
a 10 gal. tank for 10 to 14 days.
During this time they were fed live
baby brine shrimp and flake food, as
much as they could eat. Now they were
transferred to a 125-135 gallon vat.
In two to three weeks, they were
changing from silver to half-black.
Young half-black 40 days from free
swimming.
Rear stripe is darkening.
But Mr. Kirtley
later raised a spawn of all silvers
from the same pair of half-blacks that
had produced previous spawns of 100%
half-blacks. He thought that he had
stunted the fry as they were three
months old (older than usual) before
they were large enough to sell to a
pet shop. Later, he heard reports that
some of these silvers changed to
half-blacks in customers' tanks. Mr.
Kirtley told me that he strongly
suspected that stunting the fry (from
half-black parents) can prevent the
half-black pattern from developing.
The results of a test that I did later
confirm this suspicion.
Young half-black 46 days from free
swimming.
Pigment is present in body behind the
rear stripe
and also in dorsal, anal, and caudal
fins.
I kept Mr. Kirtley's
pair by themselves for several months
but did not get a spawn. Then I put a
silver female with the half-black
male. These spawned, producing several
hundred offspring, all silvers. I
mated one of these silver females with
her half-black father. They spawned
Jan. 28, 1984, and the fry were free
swimming on Feb. 8. On March 15, the
half-black pattern was starting to be
evident in some of them. As
half-blacks developed, they were
removed from the tank to make more
room for their siblings. Half-blacks
were removed from April 11 to May 9.
On May 16, no more half-blacks had
appeared, and no more developed later.
The brood count was: 80 silver, 64
half-black. Using chi-square (a
statistical test), I found that these
numbers would occur about 20% of the
time by chance. Therefore, I am
concluding, tentatively until more
ratios are obtained, that half-black
is due to a single recessive gene. The
expected result of the back cross
(silver, from half-black, x
half-black) is a 1:1 ratio (72 silver
and 72 half-black) if half-black is
due to a single recessive. A dominant
that is not always expressed
(incomplete penetrance) could produce
similar results. Since the change from
silver to half-black is gradual,
showing first as an intensification of
the posterior body stripe, I
photographed several stages of the
pattern development.
Young half-black 50 days from free
swimming.
Half-black pattern is increasing,
compared with
46-day fish.
Young half-black, 70 days from free
swimming.
Young half-black, 57 days from free
swimming.
The next person who
told me that he had half-blacks
producing half-black offspring was
David Mueller of Minneapolis. He had
bought juvenile half-blacks (imports)
and raised them to breeding size. Mr.
Mueller brought me the pair to borrow.
He also brought about 30 of their fry,
which were being kept with the
parents. Mr. Mueller kept the rest of
the spawn, about 200. The interesting
thing was that all except one of the
fry that he gave me (about pea body
size when I got them) became
half-blacks a few weeks later; the one
that remained silver was a runt. But
all of his remained silver until he
sold them after mine had changed to
half-black. He said that he had not
given these fry as good care as he had
given previous spawns, in which the
fry turned to half-black.
The Mueller
half-black pair spawned while I had
them. There were 153 fry, and all
except one became half-black. An
interesting sidelight concerns some
juvenile (half-dollar size)
half-blacks that Mr. Mueller raised
from his pair and gave me when he
brought the pair. These juveniles had
a half-black pattern on the rear part
of the body but they lacked the
anterior body stripe that is present
in most half-blacks, especially when
they are disturbed or aggressive.
These fish had been raised in
continuous light, which is known to
prevent stripe development in silver
angelfish (Norton, 1982f).
Angelfish 108 days from spawning date.
The half-black was well-fed and
uncrowded. The
two small fish were crowded and
underfed.
To find out if
stunting the fry would produce silvers
instead of half-blacks, I split a
spawn; some were crowded and fed
sparingly while the rest were less
crowded and they were fed as much baby
brine shrimp as they would eat twice a
day. The spawn came from the pair that
had produced 80 silver and 64
half-black offspring previously. They
spawned June 27, 1984. The fry were
free swimming on July 5. These were
well-fed twice a day with live baby
brine shrimp. On August 1, 298 fry
were put into a 30-gallon tank and
underfed from then on. On the same
day, the rest (56) of the fry were put
into a 15-gallon tank and fed heavily.
Both groups received live baby brine
shrimp as their only food.
Of the well-fed fry,
one started to show the half-black
pattern 15 days later, on August 16.
From this tank, I removed the
following numbers of half-blacks on
the given dates:
| Aug.
24 |
3 |
| Aug.
26 |
1 |
|
Sept. 3 |
8 |
|
Sept. 6 |
1 |
|
Sept. 12 |
3 |
|
Sept. 16 |
2 |
|
Sept. 20 |
3 |
| Oct.
5 |
1 |
On Oct. 5, I
discarded the remainder (34) of the
well-fed fry. At this time, the fry
that had been underfed and crowded
were still all silvers, and they were
about half the size of the well-fed
fry.
On Sept. 16, I put
30 of the underfed fry into a
15-gallon tank and fed them heavily
from then on. It worked! Twelve days
later, on September 28, the half-black
pattern was starting to show on one of
these fish. During the next 27 days,
more half-blacks appeared. Half-blacks
were removed on the following dates:
| Oct.
3 |
4 |
| Oct.
5 |
3 |
| Oct.
7 |
1 |
| Oct.
14 |
1 |
| Oct.
20 |
3 |
| Oct.
25 |
1 |
Incomplete half-black pattern.
Incomplete half-black pattern.
The important
information obtained from this test is
that expression of the half-black
genetic makeup can be environmentally
inhibited, and this inhibition can be
reversed by "improving" the
environment. I do not have information
on the age limit for this
transformation, the upper limit of the
age at which a stunted genetic
half-black can still develop the
half-black pattern after it begins to
receive appropriate care.
In my test, there
was variation in the number of fish
per gallon of water and also the
amount of food. The temperature
probably was not exactly the same in
all the tanks used. Temperature is
known to affect the expression of
certain genes in other organisms, with
expression occurring only within a
certain temperature range. At other
temperatures, the trait will not
develop even though the genotype for
it is present. For example, the black
pattern of the Himalayan rabbit does
not develop if the animal is raised at
a temperature above 30C. If raised at
about 25C, the rabbit will be white
with black feet, ears, nose and tail.
If a white area is shaved, and the
rabbit kept cool, the hair will come
in black in that area. In an animal
raised at 25C or cooler, the
extremities are cool and the hair
comes in black in those areas. A
similar situation in half-black
angelfish would not exist because the
fish is close to the same temperature
throughout. I just want ot make the
point that the results of a test can
be misinterpreted if more than one
variable, including temperature, is
involved.
Incomplete half-black pattern, limited
to a wide
black band in the center of the tail.
The body
stripes in this fish are faded
temporarily due to
moving the fish to a photo tank.
Incomplete half-black pattern. Also,
this fish was
raised in continuous light. Result: no
body stripe,
but the stripe under the eye is
present.
The half-black
pattern can have variable expressivity
in the spawn from certain pairs. The
half-blacks that I raised from Mr.
Mueller's pair were mostly uniform,
with a complete half-black pattern.
But the half-blacks from the backcross
to Mr. Kirtley's male included a
number of individuals with an
incomplete pattern. In some, the black
on the body was less extensive and
formed a semicircle instead of a
straight vertical line on the rear
part of the body. Others had even less
black, with the black area being
confined to the tail, or part of the
tail.
The useful
information about half-black angelfish
is that the pattern is inherited,
probably as a single recessive gene,
and environmentally influenced. Slow
growth rate of the fry from half-black
parents can be correlated with
inhibition of half-black pattern
formation. Stunted fry that are still
silvers may develop the half-black
pattern later (assuming they are
genetically half-blacks) if they are
given excellent care.
To raise
half-blacks, obtain stock with the
full pattern, not ones having only a
partial half-black pattern.
Outcrossing a half-black can cause
problems other than that of losing the
pattern in the F1. Some of the F2
half-blacks may not have a complete
pattern. for example, crossing a
half-black with a silver may result in
loss of the "desirable" gene modifiers
or addition of "undesirable" modifiers
of the half-black gene. Then you might
get a higher incidence of incomplete
half-blacks in the F2 than you would
get from half-black breeders having
the incomplete half-black pattern.
I recommend a
shotgun approach for raising
half-black fry: pamper them. Raise no
more than 100 to 150 in a 30-gallon
tank. Keep them warm, about 80F, for
fast growth. Feed them all the newly
hatched brine shrimp they can eat
twice a day. Make large, frequent
water changes. By the time the young
are three or four weeks old, change
about 90% of their water once a week.
Good luck, and I hope that more
half-blacks will be produced in this
country.
Literature Cited
Axelrod, H.R. The angelfishes,
Pterophyllum. Trop. Fish Hobbyist
33(6): 34-53, 1985
Norton, J. Angelfish genetics.
Part one. Freshwater and Marine
Aquarium 5(4):15-18 et seq. 1982a.
Norton, J. Angelfish genetics.
Part two. Freshwater and Marine
Aquarium 5(5):22-23. 1982b.
Norton, J. Angelfish genetics.
Part three. Freshwater and Marine
Aquarium 5(7):8-10 et seq. 1982c
Norton, J. Angelfish genetics.
Part four. Freshwater and Marine
Aquarium 5(8):15-17. 1982d.
Norton, J. Angelfish genetics.
Part five. Freshwater and Marine
Aquarium 5(9):8-10. 1982e.
Norton, J. Angelfish genetics.
Part six. Freshwater and Marine
Aquarium 5(10):38-40. 1982f.
Norton, J.
Leopard angelfish. Freshwater and
Marine Aquarium 8(2):10-14. 1985.
Gold Marble Angelfish
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