It is near impossible, if not impossible to sex these fish, regardless of what I published back in 1997, and 1999, even Vagelli (1999) agrees.
That said, it is still possible to generate breeding pairs without knowing the sexes of the fish. finding compatible mates takes time and careful attention, and several approaches have been tried with varying degrees of success are described below.
#1- A group of sub-adults (3 to 5 individuals) are placed together in a communal tank where they develop pair bonds as they mature. Once pairs are formed and move away from the group, the “outsider fish are removed. It is important to note that any BC seen with dark coloration and cowering in a corner must be removed immediately or it will soon die.
#2- Place a fish of unknown sex with a known “sexed†fish. Back in1995 I had a male Banggai who was 100% accurate in sexing. When a new BC was placed in his tank, he did one of two things. A) Try to beat the snot of out him (new fish=male) or mate with it (new fish=female). This technique often requires a bit of time as initially the established known sexed fish will display and present to either sex, but within 30mins the display are over and the fighting or mating starts. What I found useful was a small breeding net with thin mesh webbing, this way the established fish can view the new fish, but not get access to the new fish.
#3- purchase two BC’s from an LFS that has a tank full of multiple BC’s and choose the two fish that’s are “hanging out†together, frequently away from the other fish.
My personal choice when obtaining pairs or broodstock is to obtain many young (small) BC and allow them to separate and pair up as they mature. Frequently multiple pairs of BC can be obtained this way.
Freebie from an upcomming article
Marini 1996-
http://www.breedersregistry.org/Articles/v4_i4_marini/marini.htm
Marini 1999-
http://www.reefs.org/library/talklog/f_marini_020799.html
Vagelli, A. 1999. The reproductive biology and early ontogeny of the mouthbrooding Banggai cardinalfish Pterapogon kauderni (Perciformes, Apogonidae). Env. Biol. of Fish. 56:79-92.