Chippie is now swimming south

Conger eels are common in coastal waters around Scotland and mature between the ages of five and seven.

When they are ready to breed, the eels stop eating, lose their teeth and begin a long migration south to an area in the Atlantic between the Azores and Gibraltar.

The eels are known to congregate in deep water, where they spawn before dying.

Before his departure, Chippie, who is believed to be around six or seven years old, had been showing the classic signs of wanting to find a mate.

He had not been eating and had begun swimming around the tank more, convincing staff it was time for him to leave.

'Fraught moment'

Claire Matthews, education officer at the aquarium, said the operation had been a "total success", although there was a "fraught moment" when it looked as if the 40kg eel was not going to allow himself to be caught.

She said: "It was a bit tense. The bag didn't have a huge opening and he swam around it several times.

"Eventually we persuaded him to go in and pulled the bag as tight as possible. After that, it was plain sailing."

Claire Matthews: "It couldn't have gone better"

Once in the bag, Chippie was lifted by crane out of the open-top tank and across to the sea a short distance from the aquarium.

He was then freed by divers wearing snorkels and began his journey to the Azores.

Ms Matthews added: "He swam in the right direction and everything, so we were pleased.

"The staff did a great job and the conditions were excellent and it couldn't have gone better.

"The rest is down to Chippie, he has got to make his own way there."

She added: "People came in on their day off and there were tears and everything.

"We went in to feed the fish afterwards as we normally do on a Wednesday and it was a bit weird realising there was no more Chippie."