Arowana have not evolved in millions of years. Taking in this fact, they have a very strong immune system. If a "sick" feeder is consumed quickly, the odds of an aro developing a disease is unlikely. The nutritional value is the main concern(In my opinion). I would suggest some market shrimp, tilapia fillets, and pellets for your jar (or any other aro for that matter).... You can also feed insects for treats... All my aros love them..
Good luck,
Chris