  We study finite-volume effects on the masses of the ground-state octet
baryons using covariant baryon chiral perturbation theory (ChPT) up to
next-to-leading order by analyzing the latest $n_f=2+1$ lattice Quantum
ChromoDynamics (LQCD) results from the NPLQCD collaboration. Contributions of
virtual decuplet baryons are taken into account using the "consistent" coupling
scheme. We compare our results with those obtained from heavy baryon ChPT and
show that, although both approaches can describe well the lattice data, the
underlying physics is different: In HBChPT, virtual decuplet baryons play a
more important role than they do in covariant ChPT. This is because the virtual
octet baryon contributions to finite-volume corrections are larger in covariant
ChPT than in HBChPT, while the contributions of intermediate decuplet baryons
are smaller, because of relativistic effects. We observe that for the octet
baryon masses, at fixed $m_\pi L$ ($\gg1$) finite-volume corrections decrease
as $m_\pi$ approaches its physical value, provided that the strange quark mass
is at or close to its physical value, as in most LQCD setups.
