The electric organs first appear when the embryo is long, at which time it has distinct eyes, pectoral and pelvic fins, and external gills. At an embryonic length of , the gill clefts close dorsally, leaving the gill slits beneath the disc as in all rays. At the same time, the four blocks of primordial cells that make up each electric organ rapidly coalesce together. The embryo's pectoral fins enlarge and fuse with the snout at a length of , giving it the typical circular electric ray shape. When the embryo is long, the external gills are resorbed and pigmentation develops. The embryo can produce electric discharges by a length of . The strength of the discharge increases by a magnitude of 105 over the course of gestation, reaching 47–55 volts by an embryonic length of , close to that of an adult.