Angelfish Genetics
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.
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.
Example of iridophores on a Koi angelfish
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 it's 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.
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