Here's a photo of a day 45 larva changing into it's juvenile colors and sporting the extra black. Normally that posterior area of black would be white. I was very excited and intrigued by this. I sent this photo and the videos around hoping to get some information as to what could cause this. So far the main consensus is that possibly something different in the larval rearing environment may have caused it. I didn't change anything intentionally but there are always many variables at play through the larval period especially when using wild plankton.
Here is a video of that same fish at 49 days old. (It's the fish with the black caudal and black on the dorsal and anal fins.)
Here is a video at day 52 and you can see that the fish with the black caudal has lost the black on the dorsal and there is just a smudge on it's anal fin.
Today, at day 60, only the caudal remains black. That is a normal marking on a juvenile personatus however that black caudal doesn't normally show up until approximately 6 months of age (in my experience rearing this species). The other four fish that had extra black markings all currently look like normal G. personatus. I have the black caudal fish separated so that I can follow it's development and I'll keep you posted if anything changes.
I just love larval rearing surprises!!