they only eat that cuz thats what theyre acquainted to. my fish have been addicted to 3 pellet brands over the years (wardleys, then hikari gold, then kensfish). You can break the little buggers down to eat whatever you damn well feel like feeding them though, with a week or two of forced starvation. I had a female JD and senegal bichir that took 1 and a half months to switch from Hikari to Kensfish. It pretty much looked like they were going to be stubborn pricks to their very deaths (which would have been fine by me; I dont entertain spoiled fish
), but nay, they cracked 
3.5 years old 