Where do you begin with an animal whose mouth looks like a face, whose face is split into two – half at the top, and half the bottom; who can breathe with either part – from spiracles behind the eyes, or gills behind the mouth; whose teeth are scales; whose scales are teeth-like (denticles)?
When stingrays hunt, they lose sight of their prey – their eyes are bad, and their prey is often underneath them. To find and feel clams, mussels, crabs and fish, the rays rely on electroreceptors in their skin, or, as National Geographic puts it, “special gel-filled pits”. They literally inhale their food, gulping down the electric signal. As they do this, they breathe through the spiracles behind their eyes, which work less efficiently than their gills. Do they get a little light-headed, breathing as if through a towel, feeling the electricity brighten, speed up, then die?
“Maybe it’s like feeling the presence of someone hiding in a dark room,” says the narrator of a YouTube video explaining how this electric sense works. “Every time a fish opens its mouth to breathe, it exposes its mucous membranes to the salty water, creating a tiny voltage that disappears every time the mouth closes.” In this way (that fish mouth movement is called, grossly, “buccal pumping”) each fish produces an electric frequency of two hertz: the same as the number of breaths.
The pores on the stingray’s face are called “ampullae of Lorenzini”. They’re dark, and give the ray the appearance of a five o’clock shadow’s worth of stubble. The gel in the pores is highly conductive. It carries the particular signal to cells that read it, and tell the ray what it is: prey just big enough, and alive enough, to swallow whole. Like a fish mouth, a clam, too, opens and closes; a crab draws saltwater over the gills on its carapace.
Stingrays are venomous. Most venomous creatures store their poison in a gland. Not the stingray, whose venom is in its very tissue. It has no bones. Poisonous tissue, electric senses: where do you begin?
At Heron Island, on the Great Barrier Reef, I saw young stingrays. They were very pale gold, the same colour as the sand. They shuffled in groups of four, or seven, or 12, where the almost waveless ocean met the flat beach. Seen through the impossibly clear water, they seemed almost transparent, figures of clear metal bumping up against the water’s edge, like ghosts trying to cross into the living world.
• Helen Sullivan’s first book, Calcium-Magnesium, will be published in Australia in 2023
