Try live mealworms...good for small arowana, and he will beef up quickly...try to feed one right in front of its face....Its easy to get him to eat sticks once it starts eating mealworms. hikari food sticks look similar and it should start hitting the sticks pretty soon after.
Edit: This is not my opinion, this was told to me by my local LFS store owner when I bought my first Jardini three weeks ago. He was three inches when I got him and he ate the mealworms right away. The next week he was eating the food sticks. Now he is eating both for his diet.