On the subject if sexing guppy fry... i have several batches right now as im developing my own line of fancies from wild type feeders, i generally see the gonopodium start to develop on my males @ about 3.5-4 months old. Before then, around 2 months some females will show a small dark spot that will become the gravid spot when she matures. Also, if you keep young females with just older females some may switch their sex 2 male. This is not reversible and only possible when they are young. As for the inbreeding thing it takes a few generations for deformities 2 show. Good luck with ur guppies everyone!!