Myoblast-specific protein that mediates myoblast fusion, an essential step for the formation of multi-nucleated muscle fibers (PubMed:25078621, PubMed:28681861, PubMed:28161523, PubMed:30016436). Actively participates in the membrane fusion reaction by mediating the mixing of cell membrane lipids (hemifusion) upstream of mymx (By similarity). Localizes on the cell surface of myoblasts. Specifically expressed in the developing somites, concomitant with muscle differentiation. Homozygous knockout animals are viable (PubMed:28681861). While, larval and early juvenile fish show no overt phenotype, adult animals are small and develop craniofacial deformities (PubMed:28681861, PubMed:30016436). Mutant embryos lack fast-twitch myoblast fusion at 24 hours post-fertilization (hpf) (PubMed:25078621, PubMed:28681861, PubMed:28161523, PubMed:30016436). No alteration in the organization of slow-twitch myofibers, that do not fuse (PubMed:28681861, PubMed:30016436). In adults, fast-twitch musculature shows variably-sized hypotrophic fibers with variable degrees of fatty infiltration compared to wild-type siblings (PubMed:28681861, PubMed:30016436). Belongs to the TMEM8 family. According to a report, morpholino knockdown in embryos is lethal (PubMed:25078621). Other publications report that morpholino knockdown animals are viable (PubMed:28681861, PubMed:28161523, PubMed:30016436).