OP, curious, is this a "get-a-reaction" thread?
Ive gotten away from aggressive fish because I cant stand the constant bickering and ensuing injuries. It could be an easy thing for me to ask, "are Arowana really useful?" From where I sit, Arowana are stunning. But from a PREFERENCE perspective, I prefer calm, peaceable fish.
Like i said before, what fish is "useful"?
I got it! Horseshoe Crabs! They use their blood, which is blue, by the way, for testing purity in medications....cool.