Sequence-specific transcription factor which is part of a developmental regulatory system that provides cells with specific positional identities on the anterior-posterior axis. First detected at 12.5 hours post-fertilization (hpf) in dorsal presomitic mesoderm and in the neural keel, extending to the ventral somitic mesoderm during tail budding. At 16-19 hpf, restricted to the posterior end of the somitic mesoderm. Also expressed in the developing pectoral fins from 34 hpf, with progressive localization to the periphery. Belongs to the Abd-B homeobox family.