  The isotopic properties of the primary and secondary fragment yield
distribution in the multifragmentation of $^{58}$Fe + $^{58}$Ni and $^{58}$Fe +
$^{58}$Fe reactions are studied with respect to the $^{58}$Ni + $^{58}$Ni
reaction at 30, 40 and 47 MeV/nucleon. The reduced neutron and proton densities
from the observed fragment yield distribution show primary fragment yield
distribution to undergo strongly secondary de-excitations. The effect is small
at the lowest excitation energy and smallest neutron-to-proton ratio and
becomes large at higher excitation energies and higher neutron-to-proton ratio.
The symmetry energy of the primary fragments deduced from the reduced neutron
density is significantly lower than that for the normal nuclei at saturation
density, indicating that the fragments are highly excited and formed at a
reduced density. Furthermore, the symmetry energy is also observed to decrease
slowly with increasing excitation energy. The observed effect is explained
using the statistical multifragmentation model.
