  A direct and complete measurement of isotopic fission-fragment yields of
$^{239}$U has been performed for the first time. The $^{239}$U fissioning
system was produced with an average excitation energy of 8.3 MeV in one-neutron
transfer reactions between a $^{238}$U beam and a $^{9}$Be target at Coulomb
barrier energies. The fission fragments were detected and isotopically
identified using the VAMOS++ spectrometer at the GANIL facility. This
measurement allows to directly evaluate the fission models at excitation
energies of fast neutrons, relevant for next-generation nuclear reactors. The
present data, in agreement with model calculations, do not support the recently
reported anomaly in the fission-fragment yields of $^{239}$U and confirm the
persistence of spherical shell effects in the Sn region at excitation energies
exceeding the fission barrier by few MeV.

Nuclear Experiment