A trainer at the SeaWorld park in Orlando, Florida, has died after being attacked by a killer whale.
A SeaWorld executive said the trainer was rubbing the whale's head, when the seven-metre, six-tonne male orca grabbed her and pulled her into the water.
The Orange County Sheriff's Office said it was too early to tell if she had been attacked by the whale, adding that early accounts indicated she could have slipped and fallen into the tank.
BBC News website readers have been sending in their thoughts.
If you keep a top predator in a confined space for long periods it will suffer psychological damage. This animal was merely displaying normal behaviour for a killer whale. The clue is in the name.
Richard Linley, Sheffield, UK
Sadly, such incidents clearly demonstrate that wild animals belong in the wild, their natural environment. They ought not to be used as entertainment puppets for ignorant spectators.
Marianna Galea Xuereb, Dingli, Malta
This is a terrible incident and I deeply feel for the woman's family and friends. However, whales are primarily wild animals and apex predators. Domestication of such a species can only be partly resolved. The animal's instincts will remain latent and create a tension within the animal. It is absurd and cruel for such creatures which are native to the vast ocean habitat to be kept in confined spaces.
Sharon Jones, Nice, France
While it is sad that a person has been killed, the incident is a clear illustration that killer whales are wild creatures, not meant to be kept for entertainment. Using such beautiful animals in this way is appalling in this day and age.
Margaret Lowndes, Harpenden, Herts, UK
Firstly my sympathies to the trainer's family. It's to be expected really - these are wild animals that have been forced to perform tricks. If people want to see these gorgeous whales, then go out on a boat and see them in the wild.
Helen, Liverpool, UK
After seeing the remarkable documentary film The Cove I am convinced that dolphins, porpoises and killer whales should not be exploited as circus performers for commercial reasons. These animals are much too intelligent and it is now known that living in small spaces is very stressful and dangerous to their health.
Eugene Rapi, Gävle, Sweden
I think keeping wild animals captive and teaching them circus tricks is cruel and degrading, and accidents of this nature are the result. The whale is not to blame; it is the culture of thinking that animals are only on this planet for the benefit of mankind that is at the root of this tragedy.
Jen Manning, Folkestone, UK
Surely these kind of events go to show that these mammals should not be kept in captivity, and should be free. They travel thousands of miles and it was never going to be natural for them to go into a tank and perform tricks. How many more people have got to be killed and mammals suffer before these kind of shows are stopped?
Bridgette Burnett, Swansea, South Wales, UK
Tears all around. Animals confined unnaturally, people die needlessly... for what? So we can watch nature jump at our command? Enough is enough. Put them back in the sea.
Earnest Thompson, Seattle, US
It's about time people realised that God was not a fool to separate humans from wild animals. That's exactly why wild animals live in jungles and seas, and we live in cities.
Dicksongitau, Nairobi, Kenya