Haven't kept them in awhile. Last set that I got weren't P. tuka but P. pascale instead. They came in with euronema and didn't clear quarantine.
I agree with Rich that you have to get them to eat and feed them often. The last P. tuka that I kept was back in 2012 and they were eating roe before I got them on pellets. They were then fed 8x a day via a couple of Eheim feeders. They got fat and were eventually given to Boun when I broke down that tank.
If you're looking at aggressiveness, from less to more:
dispars = purple queen, followed by ignitus, sunsets, bartletts, ventralis, bimacs
Here's the one of the dispar hanging out with one of the purple queen females in the background.