I notice you're keeping them on pine needles and wood from a pine tree. I would think that the oils (gives them the scent) from the pine needles as well as the acidity (that keeps plants from growing under pine trees) would be harmful to most salamanders. Take a look at the Caudata Culture safe wood article. So, if the salamanders are in fact bloated, it could be because of the acidity of the pine needles causing the salamanders to release ions and electrolytes.