Dinner time

Last updated 14:17 23/11/2009

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Matthew Williamson, of Ardgowan School, asks: How do stingrays eat their food when they are facing the ground?

Malcolm Francis, a fisheries scientist with the National Institute of Water and Atmospheric Research, Wellington, responds:

At first sight, the answer is simple. Stingrays feed on small animals (shellfish, crabs, worms) that burrow in the sand and mud. The mouth of stingrays is on the underside of the head, so it faces the bottom where its prey live.

But it's more complicated than that. Stingrays need to pump water through their gills to breathe.

Most fish and sharks take in water through their mouths and pump it out of their gill slits. If stingrays did this, they would suck in mud and sand while breathing. Instead, they have a hole behind each eye called a spiracle. They breathe by sucking water in through the two spiracles and pumping it out through the gills.

Stingrays use this current of water to assist their feeding: they jet water out of the gills at high pressure (like a water blaster) and wash away the sand and mud covering their prey! They can breathe and feed at the same time.

Send questions to Ask-A-Scientist, PO Box 31-035, Christchurch 8444, or email questions@ask-a-scientist.net

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