  Electron-like carriers in bismuth are described by the Dirac Hamiltonian,
with a band mass becoming a thousandth of the bare electron mass along one
crystalline axis. The existence of three anisotropic valleys offers electrons
an additional degree of freedom, a subject of recent attention. Here, we map
the Landau spectrum by angle-resolved magnetostriction, and quantify the
carrier number in each valley: while the electron valleys keep identical
spectra, they substantially differ in their density of states at the Fermi
level. Thus, the electron fluid does not keep the rotational symmetry of the
lattice at low temperature and high magnetic field, even in the absence of
internal strain. This effect, reminiscent of the Coulomb pseudo-gap in
localized electronic states, affects only electrons in the immediate vicinity
of the Fermi level. It presents the most striking departure from the
non-interacting picture of electrons in bulk bismuth.
