Thought this was some interesting info:
Note: From Wikipedia (which is a useful although somewhat dubious)
Tilikum, sometimes misspelled Tillikum, is a bull Orca who lives at SeaWorld Orlando. He was captured near Iceland in November 1983 at about two years of age. Tillikum measures 22 feet 6 inches long and weighs in at 12,300 pounds (as of 2007). His pectoral fins are six and one half feet long, his massive flukes curl under, and his 6-foot-tall dorsal fin is flopped completely to his left side, and weighs close to 200 pounds. He is the largest Orca in captivity and also the most successful sire in captivity, with 13 offspring, 10 of which are still alive. His name means friend in Chinook Jargon, usually spelled Tillicum and also meaning "people/tribe" or "kin".
Tillikum was first sent to live at Sealand of the Pacific near Victoria, British Columbia. There, he lived with two older females named Haida II and Nootka IV. While living in British Columbia, Tilikum sired his first calf when he was about eight or nine years old. His first son, Kyuquot, was born to Haida II on December 24, 1991. Just a few months prior to the birth of Kyuquot, Tilikum was involved in an incident which resulted in the death of a trainer. Twenty-year-old Keltie Byrne, who worked at the park, slipped and fell into the tank with the whales. Tillikum, a pregnant Haida II, and Nootka IV grabbed her in their mouths and tossed her to each other, presumably playing. Keltie drowned. The orcas had never had humans in the water with them before. Haida II and Nootka IV were overprotective of the newborn calf and aggressive towards Tillikum, who was forced into the small medical pool. Because of his huge size, Seaworld requested an emergency transfer to their facility. Tilikum was moved to SeaWorld Orlando, Florida in January 9, 1992; he has been there ever since. Sealand of the Pacific closed soon thereafter.
Since his arrival at SeaWorld, Tilikum has sired many calves with many different females. His first calf, born in Orlando, was to Katina. Katina gave birth to Taku on September 9, 1993. Tillikum's other calves are: Nyar (born 1993, died 1996), Unna (1996), Sumar (1998), Tuar (1999), Tekoa (2000), Nakai (2001), Kohana (2002), Ikaika (2002), Skyla (2004), and Malia (2007). In 1999, Tillikum began training for artificial insemination (AI). In early 2000, Kasatka who resides at SeaWorld San Diego was artificially inseminated using his sperm. She gave birth to Tillikum's son, Nakai, on September 1, 2001. On May 3, 2002, another female in San Diego, named Takara, bore Tilikum's calf through artificial insemination.
Tilikum was at the scene of another death on July 6, 1999, though evidence suggests the Orca may not have been at fault. A 27-year-old man was found floating naked in Tilikum’s pool, apparently killed by a combination of hypothermia and drowning. He had visited SeaWorld the previous day, stayed after the park closed, and evaded security to enter the Orca tank. Investigators determined that the man, either before or after death, had been bitten by Tillikum.
Tilikum never takes part in water work with trainers, not necessarily due to aggression, but because he doesn't necessarily realize his own strength. Tilikum is the feature of the show "Believe" where the audience and trainers chant "Shamu" as Tillikum soaks the audience.
On February 24th, 2010 Tilikum was involved in a third incident, when a 40-year-old experienced trainer was killed. The trainer drowned following a popular Dine with Shamu show as at least two dozen tourists looked on from above a whale tank and from an underwater viewing area. SeaWorld executive Chuck Tompkins confirmed what witnesses saw, that the trainer was pulled into the water by Tilikum. The trainer was finishing up a session with Tilikum, the largest whale in SeaWorld's collection and its only mature male, following the Dine with Shamu show."
In another article, it states that it is captive killer whales not only are more susceptible to physical deformities, but those that were not born into captivity display more aggression to people and other whales. This is due to the stress of living in a small tank.
Those born into captivity also have problems, such as having a low life span.
Maybe orcas are not suitable for these environments at all, and the practice should be stopped.