  There has been a surge of recent interest in the role of anisotropy in
interaction-induced phenomena in two-dimensional (2D) charged carrier systems.
A fundamental question is how an anisotropy in the energy-band structure of the
carriers at zero magnetic field affects the properties of the interacting
particles at high fields, in particular of the composite fermions (CFs) and the
fractional quantum Hall states (FQHSs). We demonstrate here tunable anisotropy
for holes and hole-flux CFs confined to GaAs quantum wells, via applying
\textit{in situ} in-plane strain and measuring their Fermi wavevector
anisotropy through commensurability oscillations. For strains on the order of
$10^{-4}$ we observe significant deformations of the shapes of the Fermi
contours for both holes and CFs. The measured Fermi contour anisotropy for CFs
at high magnetic field ($\alpha_\mathrm{CF}$) is less than the anisotropy of
their low-field hole (fermion) counterparts ($\alpha_\mathrm{F}$), and closely
follows the relation: $\alpha_\mathrm{CF} = \sqrt{\alpha_\mathrm{F}}$. The
energy gap measured for the $\nu = 2/3$ FQHS, on the other hand, is nearly
unaffected by the Fermi contour anisotropy up to $\alpha_\mathrm{F} \sim 3.3$,
the highest anisotropy achieved in our experiments.
