page_title: Japanese sleeper ray
section_title: Biology and ecology
hierarchical_section_title: Japanese sleeper ray / Biology and ecology
caption_attribution_description: Blotchy swell shark (Cephaloscyllium umbratile)
context_page_description: The Japanese sleeper ray is a species of electric ray in the family Narkidae. It is common in the inshore and offshore waters of the northwestern Pacific Ocean from southern Japan to southern China. Growing up to 40 cm long, the Japanese sleeper ray has a nearly circular pectoral fin disc colored reddish to chocolate brown above, sometimes with darker or lighter spots, and lighter brown below. The spiracles behind its small eyes have raised, smooth rims. Its short and muscular tail bears a single dorsal fin positioned aft of the rounded pelvic fins, and terminates in a large caudal fin.
  Inhabiting shallow, sandy areas near rocky reefs, the Japanese sleeper ray is a bottom-dwelling predator of invertebrates. Like other members of its family, it can produce a strong electric shock from its electric organs for defensive purposes. Females give live birth to litters of up to five pups. The gestating young are sustained at first by yolk, and later by histotroph. The International Union for Conservation of Nature has listed this species as Vulnerable, due to its susceptibility to trawl fisheries that operate intensively throughout its range.
context_section_description: Fairly inactive in nature, the Japanese sleeper ray spends much of its time lying buried on the sea floor. It can produce an electric shock of 30–80 volts to ward off predators, which include the blotchy swell shark (Cephaloscyllium umbratile). Its electric organs are composed of electrocytes, which are specialized cells derived from muscle fibers that are filled with a jelly-like substance. These electrocytes are stacked in vertical columns, with many columns making up each electric organ; this arrangement functions essentially like batteries connected in parallel. The diet of the Japanese sleeper ray includes benthic invertebrates. A parasite of this species is the tapeworm Anteropora japonica (Yamaguti, 1934) Subhapradha, 1955.
  The Japanese sleeper ray is viviparous, with the developing embryos nourished initially by yolk and later by histotroph ("uterine milk") produced by the mother. Females bear litters of up to five pups in early summer; the newborns measure 10 cm (3.9 in) long and are lighter and more uniform in color than the adults. Sexual maturity is reached at a length between 23–37 cm (9.1–14.6 in) for males, and at around 35 cm (14 in) for females.
caption: The blotchy swell shark is a predator of the Japanese sleeper ray.
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