  Whenever and wherever one talks of dark matter, one does so when and where
there is a luminous matter and a dynamical issue to be settled. We promote this
observation to the status of an axiom and assume that there is a dark companion
to every luminous matter and there are orders to this companionship. To pursue
the proposition in a formal and quantitative manner, we consider the anomalous
rotation curves of spiral galaxies. From the available observations, we infer
the gravitational potential prevailing in the outer parts of the galaxy and,
thereof, construct the tt- component of the metric of the embedding spacetime.
Next we examine a perfect fluid candidate as the dark companion and solve the
relevant GR equations. We are able to determine the strength and the
distribution of the dark fluid that accompanies a point baryonic mass. Finally,
we argue that the whole paradigm can be explained just as well in terms of an
alternative theory.
  Keywords: Dark matter; Alternative GR; Spiral galaxies, rotation curves of
