Kallman, K. D. and Brunetti, V. Genetic Basis of Three Mutant Color Varieties of Xiphophorus maculatus: The Gray, Gold, and Ghost Platyfish. Copeia, vol 1 pp. 170-181 (1983).
I have previously written about and given examples regarding hifin variability and discussed the likelihood that multiple genes affect hifin appearance ("Why It's So Difficult to Obtain Great Hi-Fins", Livebearers, #194, 2007). The fish shown below are siblings from a single mating between a store-bought female hifin maculatus platy and a store-bought male variatus platy. These fish likely express the same Simpson hifin gene (H), but each hifin has a distinct appearance. The extent of hifin variability is striking and likely reflects the fact that multiple genes and gene alleles regulate the number, length and extent of branching of the rays of the dorsal fin.
Nigra (N)- Fish expressing this dominant gene contain large black pigment cells (macromelanophores) and have black or partially black bodies.
Stippled (St)- A dominant gene that increases the production of small black pigment cells (micromelanophores) resulting in the grey background color found in wild platies. In fish expressing nigra, St also increases the number of macromelanophores and the extent of black body coloration. St may also negatively regulate the number of xanthophores (yellow pigment) and erythrophores (red/orange pigment) (see below).
Wild color (I)- A dominant gene that enables the development of black pigment. The I gene encodes the enzyme tyrosinase that is required for the production of melanin. A fish that is homozygous for the recessive allele (ii) generally lacks black pigment and has red eyes (albino).
Relevant Genes Affecting Black Body Pigmentation
Pigment patterns in wild and domesticated platies and swordtails have been studied for almost one hundred years. Several of the genes that affect black pigmentation and body color have been identified and are listed below. The crosses shown on this page illustrate how these genes can affect pigmentation patterns in swordtails and platies.
Cross 1 lyretail female
Predicted genotype: Nn Stst Ii
Cross 1 male
Mating Cross 1 Siblings
Cross 3
The brood includes the expected koi (K) and albino (A) (red eye) babies. A few tuxedo (Nn stst) babies are also visible.
Predicted genotype: nn Stst Ii
Cross 1
Cross 1
The fish shown in these videos represent a subset of the color varieties from Cross 1 and Cross 2.
Albino koi male
Predicted genotype: Nn Stst Ii
Black lyretail female
Cross 2
"Bronze" male
These fish express nigra and one copy of the dominant St gene. They have partially black bodies with orange coloration on the dorsal region of the body and orange fins. Two copies of the recessive st gene would decrease the amount of black pigment even further, resulting in the tuxedo phenotype.
These fish express nigra and two copies of the dominant St gene. They have all black bodies and significantly reduced orange coloring on the body and fins.
Cross 2
Predicted genotype: Nn StSt II
What is somewhat surprising is that the StSt fish expressing nigra (Cross 2, video on the right) have a significant reduction in orange coloration on the body and fins. In their 1983 Copeia article (see reference below), Kallman and Brunetti show that in addition to lacking melanin containing micromelanophores, gold (stst R-) platies have a large increase in the number of yellow pigment containing xanthophores in the scales and dermis. This suggests that the dominant St gene may act to decrease the number of xanthophores and possibly erythrophores (red/orange pigment). If this is correct, a StSt fish expressing nigra would have a large number of melanophores and a significantly reduced number of xanthophores and erythrophores. The body would be mostly black and the fins would be clear or lightly pigmented (Cross 2). In contrast, a Stst fish expressing nigra (Cross 1, left video) would potentially have a larger number of xanthophores and erythrophores because the number of melanin containing melanophores has been reduced. These fish would only have a partially black body and increased amounts of non-black pigment (in this case, orange) on the body and fins.
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