jacks are shy, yours is almost a baby still, there fish can get 4-5ft in the wild or in well sized tanks once it hits 5-8 inch it will not hide once it hits 24 inch you will be scared to put ur hand in a tank. as for food, prawns are good but if your looking to save money u will have to starve him for a while even then he may not eat these fish can last months without food, if you want fast growth id stay with the prawns, I have noticed the new hikari food sticks to have great growth but from past history it sprouts them for a few months then they grow as normal which is why I would try to mix the diet up.
Hate to say but the price you paid is a bit high, down here 180-250 gets you a 8-20 inch mangrove jack, jardinis anywhere from 90-210 depending where u go.
But awesome fish none the less, my fav aussie native craps all over jardinis =D just make sure you have a big tank. honestly they should be kept in a 8x3 but a 6x2 will last many years.
