[helene schoubye]

I am sure Bernd wanted to say more than just the smiley, so we will wait for it 🙂 …
but in my own experience, I would say, that yes, you can see them form pairs, – and if you can see a clearly preferred pairing up, its worth while to keep those two fish together.
However, I would also say, that if you have a mature male and a mature female, and you ‘bring’ them together, I have never seen it not work.
And I also often see that keeping more fish together – (though not always), bot sometimes it suppresses the natural tendency to breed.
Once you seperate a male and female and most importantly add a good cave, – spawning behaviour will most likely follow really quick.
I would try it if I were you.