Giant Manta Ray

Mantas have the highest brain-to-body mass ratio of any fish, with enlarged regions associated with learning, vision and social behaviour. They return to cleaning stations on a schedule and appear to recognise individual divers; one contested study reported self-directed behaviour in front of a mirror. Almost nothing about them has been learned in a tank, because the species is oceanic and effectively unkeepable — the research is done in open water, on the animal's terms.

The market driver is the gill plate, dried and sold in southern China as a tonic with no clinical basis. A single large manta is worth more dead over a weekend than alive over a decade of dive tourism, and because females mature late and bear roughly one pup every two to three years, targeted fishing collapses a local population fast and it does not come back within a human career.