In the wild these fish will travel on land to hunt for insects and what not and return by the morning. They are excelent hunters, but I believe they prefer to hunt at night. Try and get yourself a moon light and see if he will eat at night.
I have a trio all around 10 inches and ghost shrimp are one of their favorites. Actually they have alot of favorites live earthworms, tadpoles, insects, small fish and a baby senegal bichir once. Ive never actually seen them eat the fish but they disappear slowly over night.
We've had a 8" rope fish for about a month. He eats live earthworms (prepurged and GL) with gusto. However, he didn't' seem to like superworms (but he was already fed a worm so could have been full) and i'm going to try a variety of insects soon such as mealworms and dubia as well as molly/guppy fry and experiment. I'll let you guys know how it goes.