Any body difference to show signs of breeding?

[wildaltum]

Hi all. I am new in keeping arowana. Have one HB for nearly two years bought from someone and recently bought one xb gold head from one bro. Both have been living peacefully for the past two months sometime I see them swimming together side by side. Suspected female is 19 inch and suspected male is 18inch.

Suspected female is because the fish is fatter and thicker and has been like that for many months. Few days ago the pair started to chase away my 6 giant Oscars to one side of the tank and even started to bite them at the fins. Then I noticed the female anus area got a bit swollen like going to pop out something.

All that happened in one day..now it is back to normal. Both fishes are doing well and eating very well on MP BF and feeders. Just wanna know if any bros encountered or noticed such swelling b4 the female lay eggs.