What animals tend to suffer from mental illnesses when in captivity?

Most (all actually) of the intelligent Animals suffer from various degree of mental illnesses in captivity. Specially Great apes like Gorillas, orangutans, chimpanzees, and bonobos suffer serious mental illness in captivity.

Like humans, Elephants, Killer Whales and also all species of great apes are highly social self aware animals. They are very intelligent and suffer greatly in Captivity. They get depressed, psychologically disturbed, frustrated and start to harm each other, become sick.

Kiska, a young female orca, was captured in 1978 off the Iceland coast and taken to Marineland Canada, an aquarium and amusement park. Orcas are social animals that live in family pods with up to 40 members, but Kiska has lived alone in a small tank since 2011. Each of her five calves died. To combat stress and boredom, she swims in slow, endless circles and has gnawed her teeth to the pulp on her concrete pool.

The neural cruelty of captivity: Keeping large mammals in zoos and aquariums damages their brains

Almost 75% of primates in captivity die within the first 20 months mostly due to depression and psychological problems. Many zoos even heavily use antipsychotic drugs like Haldol, and antidepressants and antianxiety medications like Prozac to keep them docile and not-psychotic!

Orcas are complex, intelligent and are animal with cognitive abilities. They are one of the most highly social, communicative, and culturally complex animals on the planet.

Captivity causes extreme emotional suffering for Orcas by depriving them social interactions and also many other required things such as enough space, environmental enrichment, social stability, and the opportunity to perform natural behavior such as swimming long distances. The confined space in captivity is physically as well as psychologically harmful to orcas, and. In captivity they tend to display aggression, self-injury, and also an increased rate of mortality because of stress, physical & psychological trauma.