We don't have direct experience with the watanabe, but we do have a pair of bellus. Thorough and patient QT and introducing at the same time is a good plan. Watch carefully for swim bladder problems as all of these swallowtails are deep water. Our male bellus (love his awesome tail and colors!):
<a href="http://www.flickr.com/photos/terryl93/5796301650/" title="nt 1110 by terryl93, on Flickr"><img src="http://farm4.static.flickr.com/3337/5796301650_78bb803e85_z.jpg" width="640" height="425" alt="nt 1110"></a>
and the female:
<a href="http://www.flickr.com/photos/terryl93/5796301612/" title="nt 1108 by terryl93, on Flickr"><img src="http://farm3.static.flickr.com/2366/5796301612_588bf5e45f_z.jpg" width="640" height="425" alt="nt 1108"></a>
This pair was put in at the same time. The male, as he has grown, chases others in the tank (our regal, the anthias, the female bellus of course), but his aggression is definitely lessened by frequent feedings. They also do better when they have a cave to call their own; the male bellus actually dug out a cave under one of our rocks. I would expect to see the larger watanabe male show dominance and agression towards all the other swallowtails. But perhaps you'll find the same thing we did that by providing them with enough space to have their own caves and offering frequent feedings, they will sort it all out and be fantastic together.
We use an acrylic acclimation box for new additions into the DT. Copps told us to be very patient in this - days if not weeks can really help to reduce the harassment between these angels when introducing new members to the community.
Bellus are known for sex-changing so you may find that one of the two females might change over if conditions are right...wouldn't that be great! :thumbsup:
