A CONTROVERSIAL rave held at a Swiss zoo went horribly wrong when party-goers fed dolphins a heroin-like substance.

Toxicology results have confirmed suspicions the dolphins, named Shadow and Chelmers, were given the drug Buprenorphine, which drowned them by suppressing their natural instinct to surface for air, the UK’s Sun reported.



The rave was held at the Connyland marine park in Lipperswil, Switzerland, last November. At first it was thought that the blaring techno music had caused their deaths.



Dutch marine biologist and dolphin expert Cornelis van Elk said opiates were extremely dangerous for underwater mammals.



“The reason is that dolphins are conscious breathers, which means they actively decide when to come to the surface to breathe,” he said.



“Drugging them with opiates causes this part of the brain to switch off, with fatal consequences.”



Connyland zookeeper Nadja Gasser said the dolphins suffered a horrific and slow death.



“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,” Gasser said.



“The death went on for over an hour. It was horrendous. I have not been able to sleep since.”



Animal rights activist said they had warned the zoo about the dangers of the event.



Connyland has denied any wrongdoing.

