Get it on prepared foods asap. Only use live foods if nescesary really, my ornate eats algae tabs, bottom feeder disks, the cichlid pellets that get to the bottom and shrimp pellets no problem. Hes only about 4 inches himself.
I think Ive only used live food maybe once with my bichirs and thats just with my 2 sens. Cut up some tilapia fillets, they are cheap and the fish love em. Also mine love their carnivore pellets so you could try that. Better choice since both probably have better nutrition and no parasites.
You just keep trying and wait him out, he'll come around. Bichirs will not starve themselves, they get hungry, and they just let their strong olfactory sense guide them to the food, whether it's sinking or floating.
my polys have been eating omega-one shrimp pellets for months now and they are healthy, i'll also throw in a few veggie rounds(break'em up a bit), my lima shovelnose and plecos like them too. i rarely put in feeders but when i do they go nuts, polys are actually good hunters!!