Out of 25, you may get 3 or 4 pairs that may simply divide the tank into territories.
Be ready to remove the others as pairs form.
And just to be safe, observe your 25 very closely, if you see any with defects, remove them right away so they don't fall into the pairing mix.
Defects often get more apparent with age, things such as an unnaturally curved spine, or jaws that don't line up.
In a group of 25 all may be perfect, or a few may may not.
Defects can be subtle or overt.
I picked up 20 Guianacara, all were perfect, I picked up 10 T. asfraci, half had deformities.
Here are a few overt defects.
