i have herd 4 inch for breeding, i was woundering about wether to add the female and male now at 2-3inch or wait to 4inch...hopefully someone will no more and give some feedback
about 3 inches, usually, some say 4 inches. But as soon as you can tell what sex they are a few weeks later pairs should form if you are keeping them an a big enough tank.
if you have alot of babies 4-8 of each jack then the pairs should form on their own, if you just have 1 male and female it may never form like what happened to me 10 years ago, the male got frustrated and killed the female.