Im not sure as to how your tank is set up, or what size it is, but I have an identical situation with 4 blue azureus, I know one pair is sexed, the other two im not sure
, I have them in a 30 gallon breeder with heavy pythos for coverage, and I also have a couple of bark pieces to section off the areas a bit with no direct line of sight from one part of the tank to the other, kinda like a maze with one or two areas with one way in or out. I have seen them wrestle at times, but they break up and seem just fine
, as a matter of fact I just got 5 great
looking eggs out of the tank this morning. I keep them well fed and happy
. I hope you find him soon, I hate to say the worst
, but from my past experience with loses , they break down pretty fast with out a trace, so just in case you may never solve the missing part,I hope you find them, good luck!!!