We investigate magnon spin transport in epitaxial nickel ferrite (NiFe2O4, NFO) films grown on magnesium gallate spinel (MgGa2O4, MGO) substrates, which have a lattice mismatch with NFO as small as 0.78%, resulting in the reduction of antiphase boundary defects and thus in improved magnetic properties in the NFO films. In nonlocal transport experiments where platinum (Pt) strips function as magnon spin injectors and detectors, enhanced signals are observed for both electrically and thermally excited magnons, and the magnon relaxation length (lambda(m)) of NFO is found to be around 2.5 mu m at room temperature. Moreover, at both room and low temperatures, we present distinct features from the nonlocal spin Seebeck signals which arise from magnon-polaron formation. Our results demonstrate excellent magnon transport properties (magnon spin conductivity, lambda(m), and spin mixing conductance at the Pt/NFO interface) of NFO films grown on a lattice-matched substrate which are comparable with those of yttrium iron garnet. Published by AIP Publishing.