Pairing Apistos

If possible, watch the tank at the lfs, and see if you can pick out a male and female hanging out together. If that's now possible, then you just have to pay your money and take your chances. What usually happens is the male will harrass the female for several days before things calm down. Once they do, they should be fine untill they spawn, at which point the female will become very aggressive toward the male, and in rare cases kill him if kept in too small a tank.

Nijsseni and thier close relatives panduro are, according to internet accounts and my own observations, highly monogamous. Once a pair start to get along, thier bond is fairly strong. I kept a pair of panduro in a 10g for nine months through numerous failed spawns with no friction. They spend alot of time interacting, and made a really nice pair of display fish.