Most healthy flowerhorn will let you pet them. The more aggressive ones will always try to attack you. The male in my profile picture was a gentle giant. I got him at 3.5 inches and he grew in to a giant at 11.0 inches. He would swim and put his head into my hand and then I could gently move my hand to his stomach and sides and he was always very relaxed as he swam and interacted with my hand. Now the Magma that I currently have at 7.5-8.0 inches is a total psycho path. He lets me touch his head and then pulls back to find a better angle to attack me. Each flowerhorn is different. If I were you I would start with a cube of frozen bloodworm and let him slowly pick apart the frozen cube. As he does this you can start to pet him. If he is a less aggressive individual this will allow him to associate you petting him with food and he will respond positively to your hand. Don't pet him at every meal as this can cause damage to their slime coat. Petting 2-4 times a week is what I always would do without any negative impact.
