Jardini Tail split

So I have an Jardini arowana housed with a silver arowana and a clown knife... All seems to be fine, no fights or anything and issues. But i noticed today that my jardini's tail was split in 2. When i tried researching the reason why, the first thing was a post on this site saying that it was rumoured that is a sign of "growth". Is that true?

Yes i know jardini are bullies. I didnt see any fights and i know they can fight when im not there like children in daycamp. Water parameters seem fine. Ammonia 0, Nitrite 0, Nitrates 5-10.
jardini is 5+, silver is 6-7+, clown is 8-9+.. but clown knife is extremely skittish so i doubt its a fighter. Ideas? (instead of the fighting of course)

And is it really a sign of growth?

I am not too worried as all fish are eating fine. and im sure tail will heal in about a week as i put in some stress coat.

my tank is pretty much empty really.. All i have is a 4 inch pvc pipe about a foot long for my clown knife to hide in... I am planning on putting a potted plant there though to help with the water quality/decoration. mostly decoration though. Wisteria.