  We present the study of a magnitude limited sample (mB < 16.6 mag) of 13 late
type galaxies (LTGs), observed inside the virial radius, Rvir 0.7 Mpc, of the
Fornax cluster within the Fornax Deep Survey (FDS). The main objective is to
use surface brightness (SB) profiles and g-i colour maps to obtain information
on the internal structure of these galaxies and find signatures of the
mechanisms that drive their evolution in high-density environment, which is
inside the virial radius of the cluster. By modelling galaxy isophotes, we
extract the azimuthally averaged surface brightness profiles in four optical
bands. We also derive g-i colour profiles, and structural parameters like total
magnitude and effective radius. For 10 of the galaxies in this sample, we
observe a clear discontinuity in their SB profiles, derive their break radius
(Br), and classify their disc-breaks into Type-II (down-bending) or Type-III
(up-bending). We find that Type-II galaxies have bluer average (g-i) colour in
their outer discs while Type-III galaxies are redder. Br increases with stellar
mass and molecular gas mass while decreases with molecular gas-fractions. The
inner and outer scale-lengths increase monotonically with absolute magnitude,
as found in other works. In Fornax, galaxies with morphological type 5< T< 9
(~60 % of the sample) are located beyond the high-density, ETG-dominated
regions, but no correlation found between T and the disc-break type. The main
results of this work suggest that the disc-breaks of LTGs inside the virial
radius of the Fornax cluster seem to have arisen through a variety of
mechanisms, which is evident in their outer-disc colours and the absence of
molecular gas beyond their break radius in some cases. This can result in a
variety of stellar populations inside and outside the break radii.
