Tunas have been collected and maintained in captive pens and holding tanks for both commercial and research purposes for over forty years (Harada et al., 1971; Brill, 1999). The Tuna Research and Conservation Center (TRCC) of the Monterey Bay Aquarium and Stanford University has maintained both yellowfin tunas, Thunnus albacares, starting in 1995, and bluefin tunas, Thunnus orientalis, for the last four years. The focus of research at the TRCC is for both physiological studies of tunas and the testing of new electronic tagging technologies. Physiologically healthy specimens are critical to both endeavours and the technology of keeping tunas in captivity is reviewed?.