How does a manta foetus breathe?

The giant oceanic manta ray is the largest member of the ray family. Giant rays are live-bearing but, because they are not mammals, they have neither placenta nor umbilical cord. How, then, does the developing foetus get oxygen?
Giant oceanic mantas are very impressive. The rays can be up to seven metres wide and four metres long; there’s no overlooking this animal! Not much is yet known about the giant manta. For example, mantas bear live young, but don’t have a placenta or an umbilical cord. The big question has been how the foetus gets oxygen. An answer was available in the Okinawa Churaumi Aquarium in Japan, where a pregnant giant manta, just under four metres wide and weighing 400 kg, was examined using ultrasound. The images obtained clearly showed the foetus repeatedly opening and closing its mouth, meaning that oxygen is taken out of the fluid in the uterus. This form of breathing is also called ‘buccal pumping’ or ‘throat breathing ’. The muscles of the throat help to suck water (containing oxygen) in and squeeze it past the gills.

After the birth, this system changes. The young manta switches to a different method of breathing called ram ventilation. As the ray swims with its mouth open, water flows past its gill slits. The researchers suggest that the rapid reduction in size of the spiracle (breathing hole) in young giant mantas could be caused by the change in breathing method.

The article describing this research was published in the journal Biology Letters.