Biggest Pair Of Fish I Could Keep In A 51L?

[Jessman]

I have an empty cycled 51L tank and want to fill it with a pair of fish, what is the biggest that could live in it? Would help if it was colourful too please

 

[the_lock_man]

A trio of platies?
A pair of honey gouramis?

 

[DerpPH]

breeding colony of Neolamprologus spp.
 
A breeding trio of scalet badis
 
Apisto macmasteri pair.