It's VERY hard to tell them apart unless you have wild caught specimens. Yellow labs are one of the most inbred and commercialized of all the cichlids so the gender lines get blurred. Normally the ones with the most black are typically male but that doesn't always work nowadays. They can start breeding at about 3 inches but that's also debatable. The anal fin should be more pointed on the males and more rounded on the females but that isn't always surefire. The best way to get males and females is to put a bunch in the tank and just wait until some of them start spawning. Also be sure you get them from different mothers or you'll just add to the already overly inbred populations. JMHO, hope that helps.
