  We consider the possibility that neutrino masses arise from the exchange of
dark matter states. We examine in detail the phenomenology of fermionic dark
matter in the singlet-triplet scotogenic reference model. We explore the case
of singlet-like fermionic dark matter, taking into account all co-annihilation
effects relevant for determining its relic abundance, such as fermion-fermion
and scalar-fermion co-annihilation. Although this in principle allows for dark
matter below 60 GeV, the latter is in conflict with charged lepton flavour
violation (cLFV) and/or collider physics constraints. We examine the prospects
for direct dark matter detection in upcoming experiments up to 10 TeV.
Fermion-scalar coannihilation is needed to obtain viable fermionic dark matter
in the 60-100 GeV mass range. Fermion-fermion and fermion-scalar coannihilation
play complementary roles in different parameter regions above 100 GeV.
