  I consider the observed rotation curves of 12 gas-dominated
low-surface-brightness galaxies -- objects in which the mass of gas ranges
between 2.2 and 27 times the mass of the stellar disk (mean=9.4). This means
that, in the usual decomposition of rotation curves into those resulting from
various mass components, the mass-to-light ratio of the luminous stellar disk
effectively vanishes as an additional adjustable parameter. It is seen that the
observed rotation curves reflect the observed structure in gas surface density
distribution often in detail. This fact is difficult to comprehend in the
context of the dark matter paradigm where the dark halo completely dominates
the gravitational potential in the low surface density systems; however it is
expected result in the context of modified Newtonian dynamics (MOND) in which
the baryonic matter is the only component. With MOND the calculated rotation
curves are effectively parameter-free predictions.
