I don't think tender vittles would be a good option. They're fatty, and really more of a cat thing...
Protien wise-(and remember, any of these should be given only as an
occasional treat), many people give their turts feeder fish (guppies or minnows,
NOT goldfish), blood worms, freeze dried shrimp, or gut-loaded crickets.
I've also heard of people giving boiled white chicken meat or egg whites.
Also don't be afraid to start offering them veggies (if you're not already). The younger they get introduced to veggies, the better the chance you'll have getting them to eat them. They may not be interested in start, but leave a piece of some leafy green in there all the time, and they're likely to catch on
