There are certain fish that will, such as the Aiptasia Eating Filefish (Acreichthys tomentosus), which is also called a Matted Filefish or a Bristletail Filefish.
Copperband Butterflyfish have also been known to eat aiptasia.
Here's the issue though, there is no guarantee that these fish will eat it, especially if there is other food (from feeding other fish) being offered. It's never a good idea to get a fish solely for one purpose, so you have to also consider the longevity and compatibility if the fish you're going to add.
I currently own two Aiptasia Eating Filefish. One eats aiptasia, majanos and frozen food. The other will only eat frozen and occasionally pucks at aiptasia, but never eats it. I did previously own one that would not touch aiptasia, but was nipping at my SPS polyps, which some have been known to do.
Copperband Butterflies are a finicky fish. Some never accept frozen. Some never eat aiptasia, some do. Some nip at corals. My Copperband doesn't touch coral or aiptasia or clams, and readily accepts frozen food and algae sheets, but prefers to eat from my hand.
I enjoy my fish. I knew they would be long term members of my tanks, and considered their possible help with aiptasia a plus. I also quarantined all of my fish and placed corals with them to make sure they wouldn't eat them. The one filefish that did eat corals was not tested with corals ahead of time, and it cost me dearly :-(
Have you tried Aiptasia X, Joe's Juice or a Kalkwasser paste?