  We discuss the net quark and isovector fluctuations as well as off-diagonal
quark flavor susceptibilities along the chiral phase transition line in the
Nambu--Jona-Lasinio (NJL) model. The model is formulated at non-zero quark and
isospin chemical potentials with non-vanishing vector couplings in the
iso-scalar and iso-vector channels. We study the influence of the quark
chemical potential on the quark flavour susceptibilities in detail and the
dependence of the results on model parameters as well as on the quark mass. The
NJL model findings are compared with recent lattice results obtained in
two--flavor QCD at finite chemical potential. On a qualitative level, the NJL
model provides a consistent description of the dependence of quark number
fluctuations on temperature and baryon chemical potential. The phase diagram
and the position of the tricritical point in the NJL model are also discussed
for different parameter sets.
