The two I have are both over the 24" mark and whilst they can be grumpy and quaralsome , I wouldn't call them aggressive ( although they are in with and compared to wykii, and sperata aor). Their mouths don't really allow for great aggression but they do give each other good suck/nibble and a swim around now and again. Whilst mine get fish bits they love nothing better than sitting through the gravel for sinking sturgeon pellets, although be warmed, feeding them to giraffes is a messy business and a good big filter is required.
great fish.