  We address the degradation of continuous variable (CV) entanglement in a
noisy channel focusing on the set of photon-number entangled states. We exploit
several separability criteria and compare the resulting separation times with
the value of non-Gaussianity at any time, thus showing that in the
low-temperature regime: i) non-Gaussianity is a bound for the relative entropy
of entanglement and ii) Simon' criterion provides a reliable estimate of the
separation time also for nonGaussian states. We provide several evidences
supporting the conjecture that Gaussian entanglement is the most robust against
noise, i.e. it survives longer than nonGaussian one, and that this may be a
general feature for CV systems in Markovian channels.
