  Several deep observations such as those carried out at the
Canada-France-Hawaii Telescope (CFHT) have revealed prominent Low Surface
Brightness (LSB) fine structures that change the apparent morphology of
galaxies. Previous photometry surveys have developed observational techniques
which exploit the diffuse light detected in the external regions of galaxies.
In these studies the outer perturbations have been identified and classified
like tidal tails, stellar streams, and shells. These structures are tracers of
interacting and merging events and they keep a memory of the mass assembly of
galaxies. Cosmological numerical simulations are needed to estimate their
visibility time-scale (among other properties) in order to reconstruct the past
merger history of galaxies. In the present work, we analyze a hydrodynamical
cosmological simulation to build a comprehensive interpretation of the
properties of fine structures. We make a census of several types of LSB fine
structures by visual inspection of individual snapshots at various time. We
reconstruct the evolution of the number of fine structures detected around an
early-type galaxy and we compare with the merger history of the galaxy. We find
that most of fine structures are associated with major and intermediate mass
merger events. Their survival time scale ranges between 0.7 and 4 Gyr. Shells
and streams remain visible for a longer time than tidal tails. These estimates
of survival times provide clues to interpret the shape and frequency of fine
structures observed in deep images in terms of mass assembly. We find that the
detectability of stellar streams is the most sensitive to the surface
brightness limit. We see 2-3 times more streams with a surface brightness cut
of 33 mag arcsec$^{-2}$ than with 29 mag arcsec$^{-2}$. The detection of shells
display a strong dependence on the projection angle.
