Heh, guppies....might as well as swordtails and the other FW livebearers.
I understand what you mean about the clowns. When I was helping out down in SD, Leslie, the aquarist in charge of the seahorses @ Birch mentioned how she would love to be breeding clowns instead of the ponies. Basically the same reason as the BC: clowns will eat the rots for sure, whereas you can only hope the baby BC/ponies are eating enough of the BBS with enough nutrition.
I was more questioning if there are any other mouthbrooders/livebearers of the BC type in SW (signanthids excepted). I think that's how you spell that at least.... :/
And I know some surf perch do the whole livebearing thing, but those are only good for eating, not reefkeeping
