I only wish I'd worked with these with a little dedication now, same with chili rasboras. I put a hundred of each in a 125 display and watched them breed/spray eggs every water change. Did manage to grow up chilies but don't recall if the threadfins didn't breed in my 20 gallon breeders or if I screwed up with the fry. AFAIK
any you get from a shop are coming in as WC imports. I never saw batches that were dramatically different from each other, but my eyesight is poor at best close up. Yeah I know, and now I'm into micro shrimp.
Threadins are the only species in the genus Iriatherina, but we all know taxonomy is as the French say, "crappe," and there might well be 8 distinct species when all is said and done. But little attention is given as far as non important food fish and minnows go. My gut feeling is that any you can get your hands on will color up and look amazing when settled in and fed properly. I don't know if it exists any longer but Piscine Energetics PE myiasis were THE BOMB for mine -and when of any species fry went from wrigglers to free swimming. Nothing compared and then it went unavailable. I let my contract with them lapse years ago but think I'd have heard if they had it again.
But this is an adult fish small enough to relish live baby brine shrimp, and feeding them pods and these may not be needed but I doubt my own would have stayed in breeding condition without. I just happened to culture it for other things at the time. If you can get CBB fishes (captive born/bred) that's nothing but a bonus. I hope someone at your closest club has them, but if not, talk to rainbow breeders -they WILL know someone. And just an aside but........ just pay what breeders at your auctions/meetings are asking. If you want a group that's one thing, obviously. "What would you take for the lot ?" is fine. Few things ever irked me more and made me remember a person more than them looking at my homebred and now sexable Apistos and saying... "$40 a pair... would you take $25?" But something tells me you would never be that guy and I'm a jerk for even saying it.