Monday, September 17, 2012

Eggs and Burritos: How a Stingray Gets Born

Our exhibit was recently blessed by the arrival of two baby cownose stingrays! Say hello to Theodore and Madeline, born only one day apart to our female cows Wilma and "Zebra" (unofficially we call her this because of her unique scar patterning).

Theo, leading the pack.

Maddy, smiling for the camera.

Cownose rays, like most elasmobranchs (that's the sharks & ray family), give a specialized kind of live birth called "ovoviviparity" (which pretty much means egg-live-birth). Ovoviviparity is a bit different from our mammalian viviparous reproductive strategy. There is no placenta, nor umbilical cord, instead there is an internal egg that hatches partway through gestation. 

NB: Inside the womb, a stingray baby's pectoral fins are furled up like a little burrito, which is precisely what we call stingray fetuses. 

After birth, the mother and baby separate completely, leaving the baby to fend for itself. Luckily, it's born as a miniature version of the adult, complete with a miniature venomous barb!

The baby is born with a bit of yolk still in its belly, so it may not start eating on its own for up to two weeks! This can prove frustrating for a zookeeper, such as myself, who needs to tube feed a baby stingray that doesn't start eating a few days after birth. 

Tube feeding involves restraining a tiny, slippery, and surprisingly strong little stingray upside down underwater while forcing a tube down its esophagus and into the spiral valve (a ray's modified extra-muscular stomach). It's unpleasant for all parties involved. But it ensures that the baby loses no weight and stays nourished while it figures out what eating is, and how to go about doing it. 

Fortunately, both Madeline and Theodore are eating well on their own and are steadily gaining weight! We feed them tiny pieces of capelin, shrimp, and squid. Capelin is the least popular fare, as it is the most nutritious, and I suspect the stingray's equivalent of broccoli. 

Our babies are fenced off in their own pen, so that visitors don't scratch their delicate skin, and the adult rays don't stress or bully them. Sometimes they get to go on recess in the main adult pool. Once the babies are big enough, they will graduate to full-time status in the main pool. Until then, they are working on building their strength by swimming in a little fever (the technical term for a group of stingrays) round and round the baby pen all day long. 

"The Gang" - Bubba, Oliver, Pip, Smudge, Lily, Lorenzo, Theo, and Madeline!


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