Very similar behaviour to the sort I see on a fairly frequent basis in the shoal of golds- very unusual to see any damage but lots of posturing before they calm right down and carry on swimming around together. Beautiful pair, though. Would be a really impressive sight to see a pair of 15"+ blacks together.
And snap on the vulture Cat. I've been looking to get a big one for ages but they only seem to come up in the most annoying places so getting them is usually a right PITA.