Angelfish Genetics - part 2

Article Index

Angelfish Color Mutations:  There are hundreds of mutations of little importance by themselves, that occur in angelfish. The following are the new angelfish gene mutations that have had a major effect on the appearance of angelfish and whose inheritance characteristics have been discovered. The letter in parenthesis is the gene notation (shorthand used to track the genotype). These are the only mutations whose allelic inheritance characteristics are demonstrated with documented spawnings. 

  • Albino(a)  A recessive mutation that removes the pterin and melanin pigments leaving the carotenoid pigment layer exposed.
  • Dark(D)  A incomplete dominant that is present in our Blacks and many other dark angelfish. Commonly referred to as the Black gene, in error. An allele of Gold Marble, New Gold and Marble.
  • Gold Marble(Gm)  A lightly marked marble that act similar to the Gold allele in crosses. An allele of Dark, Marble and Gold.
  • Halfblack(h)  Recessive mutation whose penetrance  may be influenced by modifiers. Environment will influence the expression of this gene.
  • Marble(M)  An incomplete dominant that is an allele of Dark, New Gold and Gold Marble.
  • Gold(g)  A recessive mutation that can be hidden in many strains. Originally referred to as New Gold. It is only one of a few gold mutations. Naja Gold and Hong Kong Gold (which are probably both lost to the hobby) are the other two. New Gold is an allele of Dark, Gold Marble and Marble.
  • Pearl(p)  Not a color mutation, but a recessive scale mutation that reflects light in a sparkling manner. Expressivity is environmentally influenced. The phenotype is commonly referred to as pearlscale.
  • Blue(b)  This recessive mutation is a relatively new one that most likely arose in Thailand. When homozygous, it increases iridescence in all strains and it greatly inhibits the storage of carotenoid pigments in those that are normally orange or gold in color. For example, Golds become white. With strains like Wild-type, since there is no orange to remove, it simply adds iridescence to the adults. Iridescence in the juveniles is very subtle and increases as the fish ages. It also appears to be somewhat deleterious, causing lower fertility, weaker, smaller fry and more deformities to occur in many spawns.  Our opinion of this gene is somewhat tainted.
  • Smokey(Sm)  A dominant mutation. The phenotype of an angel that is homozygous for Smokey is known as a Chocolate.
  • Streaked(St)  A dominant mutation that acts as a modifier of the Dark gene. It causes white or clear streaks in the fins and iridescent patches on the body in Blacks and others varieties containing the Dark gene. It exhibits variable expression. The streaks can be one or two fine lines or a bold white stripe. An underlying mottling can also be seen in (DD) and (Dg) that contain the gene for Streaked. There is some evidence that it is now expressing in some fish without the Dark gene present.
  • Stripeless(S)  An incomplete dominant that exhibits variable expressivity. It is not a color mutation, but a modifier that effects the expression of other color genes. More complete explanation below.
  • Zebra(Z)  A dominant mutation that is an allele of Stripeless, therefore you cannot have a Blushing Zebra - Wild-type(+)The gene that occurs most frequently in a population at any given gene location. The one that is designated as normal, is called wild-type.
Symbols for Alleles: The initial letter of the name of the mutant trait is selected, if not already in use. If the trait is recessive to wild-type, the lowercase letter is used. If it is dominant, the uppercase is used. The contrasting wild-type gene is denoted by (+). If the first letter is in use, then we use the first two letters, the second one, always being lower case. This angelfish genetics notation standard was adopted by The Angelfish Society (with the exception of (b), and is the one we encourage everyone to use

For information purposes we will list Dr. Norton's angelfish gene notation. This is a more descriptive angelfish notation that is more useful once learned. Each gene is named by location. The location name is determined by the first mutation discovered there. If the gene being discussed is not the original, it is superscripted. The first letter is uppercase if the allele is dominant over wild-type and it is lowercase if it is recessive to wild-type.

Locus #1 - Hong Kong Gold (hg), recessive to wild-type. Probably lost to the hobby.

Locus #2 - Smokey (Sm), dominant to wild-type.

Locus #3 - Stripeless (S), dominant to wild-type; Zebra (Sze), dominant to wild-type.

Locus #4 - Dark (D), dominant to wild-type; Marble (Dm), dominant to wild-type; New Gold (dng), recessive to wild-type; Gold Marble (Dgm), dominant to wild-type.

Locus #5 - Halfblack (h), recessive to wild-type.

Locus #6 - Pearl (p), recessive to wild-type.

Locus #7 - Streaked (St), dominant modifier of Dark.

Locus #8 - Blue (b), recessive modifier of all tested color mutations.

Using the above notation, the genotypes for the following strains are:

  • Smokey - Sm/Sm +
  • Chocolate - Sm/Sm
  • Ghost - S/s+
  • Blushing -  S/S
  • DD Black - D/D
  • Black Lace - D/d+
  • Zebra (one dose) - Sze/s+
  • Zebra Lace  - Sze/s+ - D/d+

iridophores

Stripeless:  The most misunderstood angelfish gene, so it will be mentioned here. Many angelfish breeders do not even know of the existence of the gene Stripeless. In error, they commonly call this, Blushing. Stripeless is the gene, Blushing is the phenotype(trait). An angelfish that is homozygous for Stripeless will be a Blushing angelfish, but an angelfish that is heterozygous for Stripeless does not show the blushing trait. These are commonly referred to as Ghost angelfish. Fish with Stripeless in one dose exhibit intermediate inheritance resulting in an angelfish with incomplete bars and greater amounts of blue/green iridescence as an adult. It also appears to inhibit the expression of pigment on striped angelfish, such as Halfblack patterns and the orange coloration on any angelfish. Homozygous Stripeless also inhibits red eye color.

iridophores

At this point it appears that Koi angelfish are the only blushing angelfish capable of having red eye color. It took many generations of selective breeding to accomplish this. Stripeless also causes iridophores to form as the angelfish matures. The amount of iridophores is variable in expression and may be due to modifiers that accompany the Stripeless allele. Stripeless and Zebra act as alleles, therefore you can not have a double dose Stripeless Zebra angelfish (Zebra Blushing). All other angelfish strains can be homozygous for Stripeless and exhibit the blushing trait.

Environmental Influences:  Many people assume angelfish genetics control the look of our angelfish almost exclusively, however, the appearance of our angelfish (the expressivity of the genes) is very much influenced by environment. Most, if not all color types are influenced by environment, some more than others. Mutations like Dark and Marble are not affected much. Those such as Gold, Smokey, Albino and Gold Marble are intermediate in their susceptibility to environmental conditions, whereas, genes like Halfblack, wild- type, Zebra and Pearlscale are highly affected by environment. Fish containing the Stripeless gene appear to be on the highest end of the spectrum of variability due to environment. In other words, Stripeless and/or its modifiers appear to be very susceptible to the affects of environment, especially in angelfish that normally exhibit the orange pigment layer, like Koi or Sunset Blushing angelfish.

Orange Pigment Genetics:  There is quite a bit of confusion about the inheritance of orange pigment that appears on some angelfish, particularly Koi angelfish. First, some basics on pigments.  There are four main groups of pigments that affect the color of our fish. There are the melanins, which provide the darker colors, and the pteridines, which are water soluble pigments that result in bright colors. There doesn't appear to be many pteridines in freshwater angelfish. Then there are the purines, which consist largely of guanines. Guanines are not really pigments, but waste products that accumulate and are stored in skin cells. They produce the silvery iridescence that occurs on many of our angelfish, especially blushing types. Combine these compounds with proteins and the result are structures that refract light into the blue, violets, and greens we see. The final group are the carotenoids. Carotenoids are lipid soluble pigments ranging from yellow to red.

Carotenoids cannot be produced by angelfish and therefore must be added to their diet. Carotenoids have been shown to stimulate the immune system. They also assist in any detoxification processes. It has been demonstrated that fish that are exposed to more stress, diseases and parasites, use carotenoids to defend themselves. Fish that use fewer carotenoids, have the potential to retain the stored pigments, thus looking more orange. When a previously orange fish fades, it is an indication that the carotenoids were needed to help combat a stress situation. However, the genetics that produces the potential to store carotenoids remains the same.

Genetic factors - There are genes that enable the storage of carotenoids. There is strong evidence that these genes are activated by the lack of stress factors and a healthy immune system. Therefore, expression of carotenoids is environmentally influenced. The degree of expression appears to vary according to the degree of stress, combined with a complex gene interaction. The maximum expression appears to be genetically determined. If adults have the genes needed to store excess carotenoids, then it appears that most of their offspring will also have the genes. Assuming the proper genes were inherited, the degree of expression and retention will be both diet and stress related. It will be different in every situation. The one common denominator is the genetic makeup of the fish. Those which have the genes for the storage of carotenoids will pass them on to their young, regardless of whether they express the pigment or not. This is one reason why some Koi offspring will not express orange to the degree their parents do, or that they lose the pigment over time. We have shown time and time again, that very orange offspring can be produced by adults with little or no orange, if the genes needed to store carotenoids are present.

In Conclusion:  When studying the angelfish genetics, one must first eliminate the affects of environment before analyzing the allelic inheritance of the genes. Many people studying angelfish genetics are unable to provide a proper environment to prevent inhibiting the expression of all genes involved in the study. They also don't take into account that several environmental and genetic factors may be involved in combination, making analysis difficult if not impossible with some genes.

For those interested in mutation identification on the hobby level, the following guide as given by geneticist, Dr. Joanne Norton, should be used. "The studied trait should produce phenotypes that are statistically predictable and uniquely identifiable." If this holds true, then environmental influences were probably not much of a factor, and you should be able to determine the inheritance characteristics of the mutation.

© 2006 Angels Plus