I realise this is an old thread, but the question posed at the beginning, "Is there a way of keeping tiger salamanders from metamorphosing?"- deserves a better reply.
My emotional response is let them morph, but the scientific answer is yes there is.
If you knock out the ability of almost any amphibian to make thyroid hormone it will remain a neotenic larva. Most of the work was done on Xenopus, producing giant sexually mature tadpoles. This can be done surgically by cutting out the thyroid or with drugs called goitrogens. They are used in humans to treat hyperactive thyroids the drugs include carbimazole, perchlorate and aminotriazole.
Given in appropriate dosage and continued for life you would probably get axolotl like creatures. If you stopped treatment you would probably get an early death during or shortly after metamorphosis and you might kill them anyway.
You would have to be careful not to absorb any of the chemical yourself, if ingested by humans the hormone drive to the thyroid will lead to a goitre or promote the growth of any thyroid tumour present. (A small dose of radioiodine followed by aminotriazole produces multiple papillary thyroid cancers in guinea pigs).
The mode of action of the drugs is lethal to most plants (the main use of aminotriazole is as a weedkiller) so not only will you have a bare tank you have a problematic waste water disposal problem.
Since tiger salamanders seem to be often successful breeders as neotenic larvae there may be milage in research to attempt the captive breeding of endangered hard to breed species and varieties. It is not something to be undertaken as a one off on a few random animals.
