I only ordered two, I am taking a chance there...
These are from Oliver.
The danios were added as target fish, to give the pikes something to turn their attention/aggression towards and help build/strengthen a pair bond. I was quite surprised at how well they worked as dither fish, the pikes seemed instantly more comfortable with their new surroundings.
I had not thought of adding aggressive fish to 'force' a pair bond, but I think that would be a very reasonable option before trying to acquire more, thanks for the tip!