Numbfish
Hypnos monopterygium
The numbfish is a ray with a distinctive double lobed, flattened body shape, two small rounded dorsal fins located at the rear of the body and a very short rounded tail. They have small eyes which are raised when active and their colouration can vary from a light pink to brown to black. The numbfishes most characteristic feature is a pair of kidney shaped electric organs located on either side of the head, which have the ability to deliver a powerful electric shock when touched. The electric current is produced by a chemical reaction radiating from the nerves and is believed to be the first scientific report of electricity. This electric shock is a valuable defense against potential predators as well an effective food gathering strategy. It allows the numbfish to feed on comparatively large prey of crabs, worms and fish, which they first stun, wrap their fleshy lobes around then consume whole with their greatly expandable mouth. They are noctournal and are usually covered by sand with only their eyes and spiracles protruding during the day. Females tend to be larger than males, and the give birth to a small litter of live pups (vivipoous). Numbfish grow to a maximum length of 60 centimetres.
The numbfish is endemic to Australia. They found inhabiting sand and mud bottoms in shallow inshore bays and estuaries from Broome, WA to Caloundra, Qld, but is absent from Tasmanian waters. They are also known to occur in depths of up to 200 metres.
Other common names include: Australian numbfish, coffin ray, crampfish, electric ray, numb ray, numbie, short-tail electric ray, torpedo.
Occurrence at the Busselton Jetty:
Numbfish are seen infrequently from the underwater observatory. As they are noctournal creatures, they are often observed moving from one resting place to another, where they hastily wriggle into the sand. On occasion they come very close to the windows of the observatory, even swimming straight into the windows, indicating that they may have poor eyesight and rely on other senses for navigation.
Image by: S. Daniels
