Gulpers! Gotta love gulpers, and the idea of comm'ing them with swordtails sounds like it would make an impressive display.
-Do gulpers accept Massivore?-I never got mine off of pellet stuffed shrimp but that's because I liked handfeeding. However every other woodcat I've had took to pellets so I can't see why Gulpers wouldn't. I'd recommend floating since they're very slow and might miss sinking and I've never seen them forage the bottom. My Trachy cats loved Aro sticks and found them easily compared to other pellets making me believe the smell of Aro Sticks is strong and desirable to them. Given Trachys close relation to Gulpers and similar feeding habits I believe they should work with Gulpers as well.
-Do Gulpers eat other Gulpers?-IME and in all I've seen no they don't cannibalize one another. Will they taste each other once in awhile? Sure but they immediately let go with minimal marks left on the other Gulper that heals extremely quickly. I don't know what it is that makes it so they can differentiate one another from other fish but they do. They also seem to ignore other woodcats as far as being a food source. At least when the woodcats and other Gulpers are of similar size IME. My Gulpers shared their PVC Pipes with Trachys and Jaguar Cats.
-Any reports on successful breeding?-None that I know of. Most woodcats have yet to be bred in captivity. My trachys have come close though. Fertilization is internal with the Gulper male having the leading rays of the anal fin fused to form a urinogenital organ. Making sexing easy. My guess is all you need is a well fed mature pair(my trachys didn't start entwining till they where about 6 years old.) and a pipe big enough for both but tight enough for them to feel secure.
-Be honest, how big do they really get? And while we're at it, how old?-Biggest I've seen are around 11 inches. As for age I'm guessing since my Trachy's are about 7 and still not full grown and Gulpers are fairly closely related I'd guess at least 20 years.
- I read about a sword tail colony in a gulper tank. Reminded me of my Endler colony with my pirayas. Any similar cohabs? How about Otocinclus?-No personal experience with that cohab and hard for me to guess what would happen. My Gulpers ate brine shrimp intended for other tankmates so I know they'll eat fairly small prey. How ever they're sit and wait ambush predators so small fish may know enough to stay far away while a similar sized fish wouldn't expect it and get too close. As for Otocinclus again no personal experience but since I've never seen my Gulpers forage the bottom I think a fish that remains close to the glass, ornaments and substrate should be safe.