i find that shrimp are kinda like humans in respect to appetite. i spent a few months in isolation once, in a swamp. i went in weighing about 145, came out weighing 96(damned dysentery drove me back to society eight days earlier than i planned). while i was there, my preference for food changed dramatically. meat just didnt taste good after a couple months of eating it. the eyeballs tasted fantastic. so did the cartilage between the bones, and wild onions were to die for(strangely enough, so were pine needles). i had plenty of food in the form of meats, but it was lacking something my body needed(i think?).
my shrimp seem to have been the same way. if i feed them the same type of food over and over again, they seem to lose interest in it if they have plenty of it laying around. change the food up and they will pounce on it.
the sludge that forms around CO2 diffusers seems to be a delicacy to my shrimp, but when i cultured it and fed it to them for three days straight, they started to ignore it and would instead shove each other out of the way just to get to the pellets i was feeding them before.
i think shrimp just like variety. they seem to get bored with just one type of food.