I'm not so proud about it, but i tryed feeding my polypterus with just everything that had meat in it. I really don't know how it afflicts their health, because i've read a study wich shows the incredible resiliency of poly's digestive system.
By now, i can say, thath maybe cooked food could not afflict their healt, but it surely take away a lot from the food.
I give them fish(in italy they don't sell tilapias, and they don't eat pangasius fillets, so i give them, trout or marine fishes.), bottom feeders pellets, and avian meat. (they love it, but i don't know if it's the best for them. i give it, maily because i have to feed them like once or twice a week and it's a really fat and energetic food)
They just eat everithing at every size. just keep an eye to not overfed them