  The sequence of prominent fractional quantum Hall states up to $\nu$=5/11
around $\nu$=1/2 in a high mobility two-dimensional electron system confined at
oxide heterointerface (ZnO) is analyzed in terms of the composite fermion
model. The temperature dependence of $\Rxx$ oscillations around $\nu$=1/2
yields an estimation of the composite fermion effective mass, which increases
linearly with the magnetic field. This mass is of similar value to an enhanced
electron effective mass, which in itself arises from strong electron
interaction. The energy gaps of fractional states and the temperature
dependence of $\Rxx$ at $\nu$=1/2 point to large residual interactions between
composite fermions.
