Odd! My instinct would be that andersoni are more likely to morph on a pellet diet, as most pellets contain iodine which has been linked to axolotl morphing. That was my guess on all the andersoni morphs, as every one I've heard of having morphs have used pellets. I've always fed my andersoni Canadian nightcrawlers, since I got them at about 6 inches. No pellets at all. I tried and failed to feed tilapia, but their entire diet was earthworms, white cloud minnows, and maybe some snails that snuck in.
Ian
Thyroxin is levothyroxin - a thyroid hormone supplement used to treat hypothyroidism. It would make sense that a diet rich in levothyroxin would cause metamorphing. If I recall Stebbins amphibian book discusses levothyroxin inducing/ being needed to induce morphing.
Heather
to make thyroxin you need iodine, therefore either the diet needs high iodine(so it can be made) or thyroxin(which can be used directly). i would guess that feeding a diet high in thyroxin would increase the body's levels more as it is direct, wheras the body would only convert as much iodine into thyroxin as it thinks it needs- wheras we're trying to force the matter. that's only my thoughts though...i'm willing to be corrected!