any body know why a 18 inches silver arrowana is very agressive. I have one in a 135g tank by it self. It killed sevral fish that I was trying to put with it. last december 10 inches clown knife lasted only for 12 hrs, january large hand size red devil same died in 12hrs, 2 days ago 1 foot red tail catfish died in 12 hrs. It kills its tank mate at night while I am work. big bite marks on all of them. I feed my aro 3 3inches goldfish a day.