I don't think you'll find much info.
Otos are difficult to breed, so there's few reports about breeding, and most there are, are either accidental breedings where the aquarist never noticed anything until there suddenly were small otos all over the place, or cases of mistaken identity.
Several of the breeding reports on the net don't really concern otos at all, but species of
Parotocinclus or
Hisonotus.
Notably
Otocinclus flexilis has a reputation for being easy to breed - because it is frequently confused with
Hisonotus leucofrenatus (even e.g.
http://www.scotcat.com gets them confused). To the best of my knowledge
O. flexilis has never been bred in captivity.
I've tried breeding
O. flexilis, and while I got plump females and some suspicious-looking behaviour, I never found the trigger to actually get them to spawn.
If I was to do another serious attempt at breeding otos, I'd probably try the small otos of the
Otocinclus vittatus group. All well-documented breeding reports I've seen have been with otos of this group (e.g. this one:
http://www.planetcatfish.com/shanesworld/s_r_256.php ).
Also, although
Parotocinclus and
Hisonotus probably are easier to breed, those genera
are closely related to
Otocinclus and checking their breeding reports may give useful hints on how to breed
Otocinclus. E.g. you might find these interesting:
http://www.scotcat.com/articles/article20.html
http://www.planetcatfish.com/cotm/2004_12.php