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Dr. Norton's Articles - Part 17

Reprinted with permission from:

 Dr. Joanne Norton
 Freshwater And Marine Aquarium magazine

Blushing Half-Black Gold Marble Angelfish

Photos and Text by Dr. Joanne Norton
FAMA: December 1993, Vol. 16, #12

Fig. 1. Male #1
Fig. 1: Male #1: Blushing gold marble half-black.
Heterozygous for gold marble.

Fig. 2. Male #2
Fig. 2: Male #2: Blushing gold marble.
Homozygous for gold marble.

Blushing Half-Black Gold Marble Angelfish

Gold marble angelfish that are heterozygous (single dose) for marble are less extensively pigmented that gold marbles that are homozygous (double dose) for marble (Norton, 1988). That article contained photos of both types.

The half-black pattern is due to a single recessive gene (Norton, 1989). In that article there were photos of various half-blacks, including ghost half-black, blushing half-black, and marble half-black.

There are numerous genetic types of marble angelfish (Norton, 1990). It is not known whether or not an identical gene for marble is present in marbles and gold marbles. Another possibility is that the gold marble has either one or two chromosomes carrying closely-linked genes for gold and marble. This linkage could have arisen as the result of a chromosome crossover whereby the gene for gold and the gene for marble, which are known to be alleles or closely-linked (Norton, 1988), would end up on the same chromosome instead of separate chromosomes of the pair. In any case, a gold marble angelfish having only one marble-containing chromosome has the gene for gold on the other chromosome of that pair.

A distinctive marble phenotype results when one chromosome is gold marble and the other chromosome of that pair is wild-type. This fish has the marble pattern along with vertical body stripes like the stripes in a silver angelfish (Norton, 1990). However, these stripes are eliminated in such a fish that also has the gene for stripeless, which is an incomplete dominant (Norton, 1971).

 

Fig. 3. Male #3
Fig. 3. Male #3: Blushing gold marble.
Homozygous for gold marble.

 

Fig. 4. Male #4.
Fig. 4. Male #4: Blushing gold marble.
Homozygous for gold marble.

 

Fig. 5. Male #5.
Fig. 5. Male #5: Blushing gold marble.
Homozygous for gold marble.

Fig. 6. Female #6.
Fig. 6. Female #6: Blushing gold marble half-black.
Heterozygous for gold marble.

To find out whether blushing gold marble angelfish have more widely distributed black markings in homozygous (for marble) individuals than in heterozygous (for marble) fish, I first made a cross to obtain some of each. Both fish that I used for this cross had one gold marble chromosome paired with a wild-type chromosome. Also, both fish that had one dose of the gene for stripeless and two doses of the gene for half-black. Their phenotype was gold marble half-black. (Fig.8).

The offspring from the above pair included some blushing (double dose of the gene for stripeless) gold marbles. Some of these blushing gold marbles also had the half-black pattern and others did not, even though all of them were known to be homozygous for half-black because both of their parents were homozygous for half-black. Only the sparsely marbled ones (heterozygous for gold marble?) had the half-black pattern. The more heavily marbled ones (homozygous for gold marble?) fish did not have the half-black pattern. I then made crosses with seven of these blushing gold marbles to find out whether the darker individuals (also without half-black) were indeed homozygous for gold marble and the lighter ones (all with half-black pattern) were heterozygous for gold marble. This turned out to be the case in all seven fish. The three lightly marbled blushing gold marble half-blacks were found to be heterozygous for gold marble. The four darkly marbled blushing gold marbles (without half-black) were found to be homozygous for gold marble.

 

Fig. 7. Female #7
Fig. 7. Female #7: Blushing gold marble half-black.
Heterozygous for gold marble.

Fig. 8. Female produced the fish in Figs. 1-7.
Fig. 8. This female (also a male like her) has a
wild-type chromosome paired with a chromosome having
gold marble. Also, she is homozygous for half-black
(and has the half-black pattern) and heterozygous for
stripeless. They produced the fish in Figs. 1-7.

I then made crosses with seven of these blushing gold marbles to find out whether the darker individuals (also without half-black) were indeed homozygous for gold marble and the lighter ones (all with half-black pattern) were heterozygous for gold marble. This turned out to be the case in all seven fish. The three lightly marbled blushing fold marble half-blacks were found to be heterozygous for gold marble. The four darkly marbled blushing gold marbles (without half-black) were found to be homozygous for gold marble. The progeny counts were:

 

  • Male #1 (Fig. 1). Sparsely marbled, with half-black pattern. Mated to silver female.
    Progeny: 50 with marble pattern, 69 non-marble.
    Conclusion: this male has heterozygous for gold marble.
     

     

  • Male #2 (Fig. 2). Heavily marbled, without half-black pattern. Mated to a silver female.
    Progeny: 102 with marble pattern.
    Conclusion: this male was homozygous for gold marble.
     

     

  • Male #3 (Fig. 3). Heavily marbled, without half-black pattern. Mated to a silver female.
    Progeny: 315 with marble pattern.
    Conclusion: this male was homozygous for gold marble.
     

     

  • Male #4 (Fig. 4) Heavily marbled, without half-black pattern. Mated to a silver female.
    Progeny: 83 with marble pattern.
    Conclusion: this male was homozygous for gold marble.
     

     

  • Male #5 (Fig. 5). Heavily marbled, without half-black pattern. Mated to a silver female.
    Progeny: 129 with marble pattern.
    Conclusion: this male was homozygous for gold marble.
     

     

  • Female #6 (Fig. 6). Sparsely marbled, with half-black pattern. Mated to a ghost (heterozygous for stripeless) half-black male.
    Progeny: 72, including some with and some without the marble pattern.
    Conclusion: this female was heterozygous for gold marble.
     

  • Female #7 (Fig. 7). Sparsely marbled, with half-black pattern. Mated to a silver male.
    Progeny: 27 with marble pattern, 29 without marble pattern.
    Conclusion: this female was heterozygous for gold marble.

For a number of years the inheritance of half-black was not understood. Then it was discovered that the half-black pattern does not develop in genetic half-blacks that are raised in below-optimum conditions (Norton, 1985). Prior to this discovery, many aquarists and fish farmers were puzzled when no half-blacks were produced by half-black parents.

Unexpected results also could come from a cross involving one parent that is a genetic half-black (homozygous for half-black) in which expression of the half-black pattern is suppressed if the fish is also a homozygous gold marble. Then a cross in which only one parent has the half-black pattern might produce offspring in which 100% have the half-black pattern. This is an example of the advantage to the fish breeder of knowing how a certain gene can affect the expression of another gene.

References
Norton, Joanne. Angelfish --- breeding and genetics. The Aquarium 6(10):34-41. 1971.
Norton, Joanne. Half-black angelfish. Freshwater and Marine Aquarium 8(8):18-23. 1985.
Norton, Joanne. Gold marble angelfish. Freshwater and Marine Aquarium 11 (9):88-90. 1988
Norton, Joanne. Half-black combinations in angelfish. Freshwater and Marine Aquarium 12(5):26-28, 134. 1989.
Norton, Joanne. Seven kinds of marble angelfish. Freshwater and Marine Aquarium 13(5):127-135. 1990.

Notched - An Angelfish Deformity: Part Eighteen

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