Considering it's that small, I'd guess smaller, meatier foods... as a side note, I always used to try and feed my GBTA reasonable pieces of silversides, etc., and it always seemed to reject it... my latest 'homemade' batch of food which includes raw blended salmon, mysis, cyclops, plankton, etc. is gobbled up by the GBTA...
I do have to say though, for about a year I really didn't spot feed it other than squirting some mysis it's way every so often... and it did nothing but grow and grow (was about your size when i got it, takes up 1/3 of my 29gal now).
I'm sure people will have suggestions, I say trial and error based on the size and other livestock that you have (since many will simply snatch food away from the anem).