Animal activists in the US have reacted angrily after a shark being used in an advert for the Kmart chain died of apparent stress.The white-tipped shark died in an outdoor pool in Los Angeles.The People for the Ethical Treatment of Animals (Peta) said whistleblowers had informed it of the death.The American Humane Association (Aha), which had its member at the shoot and certified it, said everything possible was done for the shark's safety.Peta said it had asked Kmart to stop using wild animals in commercials. 'Sensitive animals'Peta's Vice-President Lisa Lange told Associated Press signs of stress had been seen in the shark when actors jumped in and out of the pool in the suburb of Van Nuys on 6 March.The 5ft (1.5m) shark received adrenaline injections and was given oxygen but died after being removed from the pool."Again, it appears that no-one on set is protecting animals from exploitation, suffering, and death,'' Ms Lange said.In a letter to the Aha, Peta wrote: "Sharks are sensitive animals who, in captivity, require a highly specialised and controlled environment. Given the delicate nature of this species, why would the Aha approve the transport and use of this animal?"Karen Rosa, senior adviser for the film and television unit of the Aha, told Reuters: "We honestly don't know why the animal died. It was not being mistreated. It was not being harmed."She said "specialised aquatic veterinarian care" was immediately insisted upon but the animal could not be saved.Kmart is investigating the incident.Howard Riefs, a spokesman for Kmart owner Sears Holdings, said in a statement: "We take this matter seriously and safety is always our paramount concern."