Mine live on a whole prawn every other day, sometimes I put an Arowana pellet inside the prawn. And from time to time take a platy out of the pond and throw it in. My Jardini will eat koi pellets and indeed used to live off of them when he was smaller but I don;t think feeding any arowana over 5 inches in length pellets is fair. They have such gaping jaws for a reason, and that is surely to eat massively large prey. It would be more appropriate to feed it dog biscuits than koi pellets if it's of any size IMHO.
Off topic, I've found a truly massive silver arrowana for sale, at 80cms from tip to tail what would you say it's worth here?