Two dolphins at a zoo in Switzerland died a "slow and painful" death after partygoers fed them a heroin substitute at a weekend-long rave on the premises.
According to the Mirror, the dolphins, called Shadow and Chelmers, died within five days of each other in November 2011 after park bosses at the Connyland marine park in Lipperswil rented land near their training pool to organisers of a weekend rave.
It was originally believed that the techno music pumping out from the club just yards from the dolphins' pool had caused their deaths.
But toxicology tests carried out by the forensics institute in St Gallen show that the heroin substitute Buprenorphin was present in the dolphins' urine.
According to The Sun, Dutch marine biologist and dolphin expert Cornelis van Elk said: "Opiates are extremely dangerous for underwater mammals and would never be used in any legitimate treatment.
"The reason is that dolphins are conscious breathers, which means they actively decide when to come to the surface to breathe.
"Even when sleeping, there is part of the brain that automatically controls the breathing instinct in the same way as it does for people when asleep.
And Connyland zookeeper Nadja Gasser revealed harrowing details of the dolphins' deaths, describing them as "horrendous".
According to the Mirror, she told local media: "The death was very drawn out and painful. The death went on for over an hour. It was horrendous. I have not been able to sleep since.
"When we went to start the dolphin training we noticed the same thing that had happened to Shadow was happening with Chelmers.
"He was drifting under the water and was clearly in trouble and so we jumped into the water. We tried to hold him. He was shaking all over and was foaming at the mouth.
"Eventually we got him out of the water. His tongue was hanging out. He could hardly breath. He was given adrenalin, but it didn't help. After an hour the dolphin died."
Outraged animal activists have said they warned Connyland and local planners who gave the rave a green light of the dangers to the animals before the event.
Connyland has consistently denied any wrong-doing.
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