When i first got my arowana i had the same problem. The best thing to do is just let him settle in his new home first, in a few days it will start to develop an appetite and want to eat. I started my Aro with pellets and then went to blood worms. Just give it a few days it will work it self out. ps do your aro have any tank mates?
It is just stress. My jardini didn't eat for 2 weeks when I first brought her home. Just let him get settled and Im sure he will eat vigorously pretty soon.
so he ate today around 8 am =] pretty excited about that and yes he does have some tank mates a longnose gar thats about 4 inches and a black ghost knife and a sen. bichir
IMO, I wouldn't rush it. Give him some time to bulk up first, then train him to eat pellets. IME, silver's aren't really that hard to convert to pellets.