Aquaria: A new research field for shark reproductive science

 

Taketeru Tomita

Okinawa Churashima Research Institute, Okinawa Churaumi Aquarium

 

Among the foremost difficulties confronting shark research is the necessity for exceedingly large-scale facilities to maintain live specimens. Given this limitation, the study of shark physiology, particularly reproductive physiology, has generally been conducted on a limited number of small-sized species, and consequently, this has probably contributed to an underestimation of the diversity of reproductive mechanisms in sharks. However, public aquaria, including the Okinawa Churaumi Aquarium, have provided a novel option for overcoming this problem.

Here, I present some recent discoveries on the reproductive biology of sharks. The first example relates to an investigation of a pregnant female white shark caught in 2014, which revealed that the uterus secretes a lipid-rich “milk” that may serve as a source of nutrition for developing embryos. This finding would thus indicate that some shark species may have a “lactation” mechanism, which is generally considered a mammalian characteristic. The second example is that of pregnant female tawny nurse sharks whose ultrasound examination revealed that their embryos have a strong swimming capacity and frequently migrate between the left and right uterus.

Based on our current understanding of the reproductive physiology of sharks, we developed an “artificial uterus” for sharks. Using this device, we can maintain embryonic sharks in an artificial environment until they grow to a sufficient birth size. Such technology provides a novel option for the medical treatment of premature shark embryos in public aquaria, which would be particularly valuable concerning the conservation of threatened species.