try small pieces of raw beefheart or chicken raw small meatballs of ground beef. dont feed the fish for at least 24 hours before so. my 5 inch male jack dempsey is spoiled and this and feeder minnows or goldfish is all he wants. he dont like pellets or flakes or crumbles too much.
my jag eats everything its not bad to faste him a lil its healthy but make sure he get a varied diet dont want no hole in head never keep a fish alone so mine always act like the havent ate in weeks attack the food he is smart he wont kill himself
I had the same problem with my Jag.
I got him last year at about 2.5inches and he would not eat any prepared foods.
The battle of wills began with me caving after about two weeks. He is now a self proclaimed beef heart lover, with the occassional prawn thrown in for good measure.
Attached are him as a babe and as the mid sized monster that he has become.
Starve it out. I drove to florida caught me some jags drove 1,500 miles home put them in a tank after 5 days of captivity from the wilds they took pellets. the ones i have now will take out pinky mice TOOOOOO!