Anti-phase boundary (APB) domains resulting from the orthorhombic (o(1), Ibmm (No. 74)) to orthorhombic (o(2), Pbnm (No. 62)) phase transformation at similar to 290 degrees C in pressureless-sintered barium cerate (BaCeO3) ceramics have been investigated by transmission electron microscopy and large-angle convergent beam electron diffraction (LACBED). APB exhibiting symmetric pi-fringe patterns in both bright-field and dark-field images, lying in {011) with the fault vector R=1/2 < 111 >, were determined adopting the invisibility criteria of 2 pi g.R=0 or 2n pi. The curved boundaries due to symmetry change can be related to the low symmetry phase by a pure translation upon phase transition. The displacement vector, R, relating the domains is the translational symmetry element from the origin to the lattice point that was lost upon transition. The formation of such domains induced by the o(1)-> o(2) phase transition is discussed in terms of change in the Bravais lattice and loss of lattice point upon the transition. The identification has also confirmed the existence of a higher symmetry orthorhombic o(1) phase along the transition sequence of R3c -> Ibmm -> Pbnm. The increased spatial frequency of APB domains is attributed to A-site ordering due to vacancies created by BaO loss and/or disordering of the B-site substitutional defects generated extrinsically when doped with either a Y3+-acceptor or a Nb5+-donor.