Well, after some further research it seems that they do not change sex later in life, but rather that the sex is set early in their development:
Bisexual Juvenile Gonad and Gonochorism in the Fairy Basslet, Gramma loreto
Still, the approach of getting a larger group of small individuals should generally result in pairs/harem groups.
From first hand experience, I beg to differ from the above article. Royal Gramma are dimorphic and they are protogynous hermaphrodites.
Males different than females, but just supple only. Unless we know what we are looking for, we will not notice it. The pelvic fins are longer in males than in females. Also males have more purple and less yellow than females.
Here is a picture to demonstrate this in my tank. Sorry I do not have close up pictures that demonstrate the length differences of the pelvic fins.
The female will change sex first, the color change and the elongation of the pectoral fins come a few weeks later.
I know first hand that Royal Gramma change from female to male. This happen in my tank. More than 10 years ago, I keep a harem of Royal Gramma in my 450 gal tank. I think there were 6 of them total. I had them in a stable harem for many years. At about 4 years or so, my Male become weak and old. He had some sort of scale disease where the scale raised and some fell off. Because he was weaken, the largest female change sex and promptly killed him. He was not able to hide from the new male in a 450 gal tank full of rock. A month or so later, the coloration change is complete. There was a full chromatically male in my tank again.
The best way to get a harem of Royal Gramma is have the LFS order them for you but put them together on arrival. If they keep the RG together as a group, there will be only one male. Singleton will change sex quickly. I have not tried, but from reports of many people who put two RG together and end up will only one due to fighting, I suspect that they change sex quickly, in the mater of days if not suppressed by a male. Royal Gramma are docile fish, have more of a bark than bite. They displayed a lot to other intruders to their space, but I have never actually observed the biting any fish. The only time where there is fighting is when we put to male together. Their fight is every bit as aggressive as two fighting beta fish. They circle each other torn at each others fins, lock jawed and everything. (As a child in Vietnam, I often observed Beta fighting fish matches). I have the unfortunate experience of seen my new male kill my old male and cannot do anything about it. Getting a rock dweller like RG out of a 450 gal in wall tank is close to impossible. Trapping is the only way, other than remove all the rock. Neither of my males have any inclination of doing anything other than killing each other. I expect this was the reason Royal Gramma have an undeserved reputation of being an aggressive fish, and that they should be keep as a singleton in a tank.
The authors of the article reference above does not even know that Royal Gramma are dimorphic, evidence that they are not too familiar with this species, despise mention in their report that they removed the male from the population and no evidence of a new male developed after 5 months. I am sure that this is an example of sloppy research that come up with wrong conclusion. Just because an article got published in a scientific journal doe snot guarantee that it is all proper research, and that the conclusion the authors come up with is accurate.
