  In the paper we consider a hydrodynamical description of a nonideal Bose gas
in one-loop approximation. We calculate an effective action which consists of
mean field contributions and first quantum correction. This provides the
equations of motion for the density and velocity of the gas where both mean
field contributions and fluctuations are presented. To fulfill the calculation
we make use of the formalism of functional integrals to map the problem to a
problem of quantum gravity to benefit from a well-developed technique in this
field. This effective action provides all correlation functions for the system
and is a basis for a consideration of dynamics of the gas. Response functions
are briefly discussed. Applications to the trapped bosons are reviewed.
Together with Ref.\cite{IS} the paper provide complete description of the
condensate fraction and the deplition in the case of Bose condensed gases.
