I have no desire to repeat too much of what is already established on this topic, as there are a number of absolutely fantastic resources available on the Web. However, I will use this post as a quick primer on angelfish genetics and chronicle my experience breeding angels as it happens (or does not, as the case may be).
With most species, you have no more than a handful of variants, resulting from one or two mutant genes, if any exist at all. However, angelfish genetics can get hella-complicated, as there are thirteen known gene mutations spread across nine different loci, which results in…a lot…of different possible genotypes. I’ll figure that number out when my brain comes back from vacation.
If you’re unfamiliar with angelfish, why not first jump on over to The Angelfish Society, where there are some really in-depth discussions of all things angelfish, especially a Phenotype Library and the late Dr. Joanne Norton’s work, which both contain lots of photos, as well as everything you need to know about angelfish genetics. After reading through these resources, you’ll have a pretty good handle on which of which of the genotypes will result in differing phenotypes and which will look identical.
Angelfish Genetics: A Super-Brief Primer
The nine loci are modernly known as: dark, stripes, smokey, Philippine blue, pearlscale, half-black, streaked, albino and veiled. Genes with symbols below that start with a capital letter are dominant over/co-dominant with the wild-type, while genes with symbols that start with a lowercase letter are recessive and are masked by wild-type genes. A couple different notations are out there, but I’m going to use my own slightly-modified variation for this post, which has all alleles use the same first letter as the locus at which they form, in order to minimise confusion.
First, it’s important to note that most of these genes tend to have a dominant/recessive relationship with the wild-type, and between all the alleles at a given locus. Genes that form alleles that are higher on the list will totally or partially mask genes lower on the list, yet each of these alleles has a co-dominant effect in relation to itself. This gives rise to the concept of gene doses (or copies of a gene present). Zero doses of a gene results in no expression, one dose results in partial-expression and two doses results in full-expression of the trait the particular gene mutation modifies. A double-dose of any given gene can result in slower growth or weakness of the fish, which can even be semi-lethal in certain cases.
Now, on to a description of what effect the gene mutations have on the wild-type or silver angelfish, which I probably should mention is your standard mutation-free “classic” angelfish – solid silver body with four vertical stripes spread evenly over the body (one through the bright red eye, one mid-body hitting the front of the anal fin, one through the middle of the anal & dorsal fins, and one just in front of the tail fin). Remember that at each locus there can be any combination of exactly two doses taken from the list of alleles including the wild-type.
The Nine Loci & Thirteen Mutations
Dark Locus Alleles:
D – “dark” darkens the fish all over resulting in partial or total melanism.
Dm – “marble” (aka ‘M’) clumps the black pigment in to large patches.
Dgm – “gold marble” (aka ‘Gm’) clumps black pigment into smaller and more sparse patches.
dng – “new gold” (aka ‘g’) is total xanthism, allowing the underlying gold colour to show.
Stripes Locus Alleles:
S – “stripeless” removes the four vertical stripes in a single-dose and causes (partial) leucism in a double-dose.
Sze – “zebra” (aka ‘Z’) adds a fifth stripe to the body in the middle of the existing four.
Note: Sze has the same effect on appearance in either one or two doses.
Sm – “smokey” partially or totally reduces the iridescence of the fish, resulting in a duller appearance.
Philippine Blue Locus:
pb – “Philippine blue” in a double-dose ramps up the iridescence of the fish, resulting in shiny blue hues, or platinum fish when it is combined with a double-dose of gold.
h – “half-black” in a double-dose causes melanism in the back half of the body, where scales from the third vertical stripe through to the end of the tail go black.
ps – “pearlscale” in a double-dose ripples the scales in a to give them a diamond or pearly appearance.
St – “streaked” is a subtle mutation that adds flashes of white to the unpaired fins.
a – “albino” in a double-dose reduces all pigment levels causing colourless scales and red eyes.
V – “veiled” is a co-dominant mutation that extends the length of the fins.
Wild-type: + (This is the default gene at all loci unless specified)
Don’t care: – (In the case where a paired gene is irrelevant or makes no difference to the phenotype of the fish, the “don’t care” symbol ‘-‘ will be used. For example, Sze/+ and Sze/Sze fish look identical, so they both can be represented by Sze/- instead.)
After growing out a number of specimens, pairs started to form and spawn. While no fry have been produced thus far, I at least know the possibility exists!
True black male (D/D) and silver pearlscale female (ps/ps). Should this pair spawn, the resulting offspring will likely be 100% black lace (D/+ +/ps), however, since either fish (dad in particular) may carry some other masked genes, the offspring would have to be observed closely.
Pair #2:Blushing male (S/S) and platinum female (dng/dng pb/pb). Should this pair spawn, the resulting offspring will likely be 100% ghost (+/dng S/+ +/pb). Boooooring! However, there are some interesting crossing possibilities for future spawns provided.
[The black male above with the lame dorsal fin has turned out to be quite the little grump, murdering the other 3 fish, so this project is “on hold” for the time being, until some new pairs develop. ]
Oh! Good news!
Brain is back from vacation! The total number of genetic possibilities is determined by multiplying together the total number of samples of two possible at each locus, without regard for order. In math language, this means calculating the nine combinations of two with replacement and then multiplying them all together. Combinations of k from n with replacement is calculated as follows:
= C(n + k – 1, k)
= (n + k – 1)! / ( k! (n – 1)! )
where n! = (1)(2)(3)…(n)
Since k is always two, representing the two genes inherited at each locus, one from each parent, we can collapse our formula a bit:
(n + k – 1)! / ( k! (n – 1)! )
= (n + 2 – 1)! / (2! (n – 1)! )
= (n + 1)! / 2(n – 1)!
And since we have values of n that are 5 for one locus, 3 for one locus and 2 for seven loci, we can determine the number of possible angelfish genotypes as follows:
= [ (5 + 1)! / 2(5 – 1)! ][ (3 + 1)! / 2(3 – 1)! ][(2 + 1)! / 2(2 – 1)!]7
= [ 6! / 2(4!) ][ 4! / 2(2!) ][ 3! / 2(1!) ]7
= [ 720 / 24 ][ 24 / 4 ][ 6 / 2 ]7
= [ 30 ][ 6 ][ 37 ]
= [ 30 ][ 6 ][ 2187 ]
There are 393,660 possible angelfish genotypes!
Of course, many of these will be visually undecipherable, representing the same phenotype. Actually, since there are four loci involved (with genes recessive to the wild-type) that act in a binary fashion, we can reduce this number considerably:
= [ (5 + 1)! / 2(5 – 1)! ][ (3 + 1)! / 2(3 – 1)! ][(2 + 1)! / 2(2 – 1)!]3[ 24 ]
= [ 30 ][ 6 ][ 33 ][ 24 ]
= [ 30 ][ 6 ][ 27 ][ 16 ]
= 77,760 …eh, may as well scratch the veiled options too…
Still, this is a mindbogglingly-large number of possibilities, wouldn’t you say? More than I’d like to breed in my lifetime! *gulp* I hope I did my math right!