  The application of the nonperturbative renormalisation group approach to a
system with two fermion species is studied. Assuming a simple ansatz for the
effective action with effective bosons, describing pairing effects we derive a
set of approximate flow equations for the effective coupling including boson
and fermionic fluctuations. The case of two fermions with different masses but
coinciding Fermi surfaces is considered.
  The phase transition to a phase with broken symmetry is found at a critical
value of the running scale. The large mass difference is found to disfavour the
formation of pairs.
  The mean-field results are recovered if the effects of boson loops are
omitted. While the boson fluctuation effects were found to be negligible for
large values of $p_{F} a$ they become increasingly important with decreasing
$p_{F} a$ thus making the mean field description less accurate.
