I am currently keeping Esox americanus americanus and Esox americanus vermiculatus, Redfin and Grass pickerel. The Grass are 3-4", the Redfin just an inch! Right now they are eating live only. The Grass have just stepped up to rosies, from guppies. The Redfins came in eating daphnia. One is a little larger and was able to take down a small feeder guppy right away. I had to start the smaller one on free-swimming guppy fry.
I won't try to convert them until they're a bit thicker. I believe it is possible though. While I've never kept these two species of Esox before, I have kept Esox masquinongy, Muskie, and it accepted frozen pretty readily once about 7-8".
I'll be posting some pictures and videos soon.