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Domestic Angelfish
 

Gold Marble
Sept 1988: Vol.11, # 9

Published with permission from BowTie Inc., publisher of FishChannel.com.

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.

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.

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.

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.

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.

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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