If you mean starting your own strains or whatnot just get some colors that you like and put them together. From those, pick the ones that have the best of whatever color, pattern, shape,etc that you like and then segregate them to their own tank. Once those breed just keep doing the same thing until you get the desired traits. When line/selective breeding you will have to introduce some fresh blood in every 5 or 6 generations or so, but that's still a lot of time in between starting a line and having to introduce new blood.
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