Red eye red swords have been around for years first saw them over 10 years ago.
First problem.
Black fish get their colour from melatonin, this is similar to the pigment in our skin, As this is totally black in German Black Swords it's has far to much melatonin and this can cause cancer's in or on the fish very easy.
This is why their Testes in Labs all over the world using chemicals fighting cancer.
Seconed problem.
A Black fish has a gene that tell the body to produce to much black pigment, this gene was discovered in wild swords called,
Xiphophorus helleri guntheri
photo from
www.xiphophorus.org
These where then breed to develope the black gene.
But the gene for red eye's (albino) is the gene that removes all black pigment, so It's impossible to creat the fish your wanting to do.
Third Problem.
To develop a new strain you cant simply to it in a home aquaria. You should be looking for at least 20 tanks.
Each batch of fry need their tank, and then as they sex out the males have to be removed, to keep the females virgin.
Then u need to backcross dad with best daughter and or mother with son to try to fix the line your working towards.
If you start do with multiple breeding fish then you can easily fill 40-50 tanks.
Each batch has to be recorded and worked with and keeping the very best virgin to cross back is very important .
Course if u do devlop a new strain of livebearer that everyone wants it's easy to get money back, I buy line breed guppies now and then and pay £10 for standed fish, but new lins will sell for £30-50 a pair....
