Here is a pic of one of my male Threadfins showing off to a female. Sorry for the quality, they are still a little skittish as they have only recently moved up from q-tine.
Finatic - I have two pairs of them, they are now a lot more settled and happier in the tank. I found one in the bloodworm feeder cone yesterday morning, not trapped, just cleaning out the inside (I keep the top below water level to prevent the surface film and algae appearing). I love the way they present at each other and the two males have developed slightly different colouration with one having red highlights and the other black - not sure if this indicates one has become the dominant male but the redder one seems to be with the females more.....
Steve-O - the scientific name is Iriatherina werneri and they are in the Melanotaeniidae family along with most of the other Rainbows. I liked them as they were a bit different from the more usual rainbows. It took a while to get them as I hadn;t seen them at any of the LFS that I went to - Monty at Tri-Mar got hold of them for me - very reasonably priced as well. I believe he still has some in stock. About a week ago I saw some in a LFS in central London which were smaller and darker than these and they were almost double the price......