  The acoustic analogue of the geometry of curved spacetime realised in a
classical fluid becomes Lorentz violating in the presence of viscosity. We
study how this effective Lorentz violation affects acoustic superradiance from
the ergosphere of a rotating sonic black hole formed in such a fluid. It turns
out that Lorentz violation imposes an upper bound on frequencies of acoustic
perturbations that can get scattered from the ergosphere. Incidentally, this
upper bound is same as that on the spectrum of superradiant frequencies. This
study also reveals how superradiance is in general modified when the wave
propagates through a dispersive and dissipative medium. Our result is valid
only upto linear order in the coefficient of viscosity and is thus a first
approximation to the full solution, focussing on the key qualitative features.
