  By using a mean field approach, based on the Popov approximation, we
calculate the temperature dependence of the condensate fraction of an
interacting Bose gas confined in an anisotropic harmonic trap. For systems
interacting with repulsive forces we find a significant decrease of the
condensate fraction and of the critical temperature with respect to the
predictions of the non-interacting model. These effects go in the opposite
direction compared to the case of a homogeneous gas. An analytic result for the
shift of the critical temperature holding to first order in the scattering
length is also derived.
