Mine, which aren't morphed yet have been eating lots and lots of mosquitoes larva and water snails. I have a chemicals free garden, where I haver several seasonal tiny ponds. At this time of year the mosquitoes larva are abundant, and alive, and the salamanders seem to enjoy both eating and hunting them, and have been growing and seem quite content.
Before feeding, I net a bunch at a time, move them into water with identical chemical composition to that of the sallies (not sure if this is necessary but...) and after some hours feed them.
W