I don't think african aro grow more docile past 20". I'm only able to keep african arowana with other south american, asian and australian aro as I have more aros in the tank. I sold all my asian aros and other south american and australain and was left with 2 silver aros and 1 jardini. Jardini was killed in the 3rd day but 2 silver were kept alive as they were much bigger. African aro at 20" and even at 20" they still have a slender smaller body build compared to a 22" jardini. Still manage to overpower a much bigger jardini. Unless you have a bigger tank and with more aros you can keep both. But if only jardini and african aro, both fish have temper and don't usually back out from fights. However african aros don't get tired easily compare to asian and australian thus that make African aro able to take out other aros.