A fish enthusiast from East Dunbartonshire has described the death of his prized Japanese koi carp collection as a “massacre”.

Steven Smith from Milngavie, who has reared the prized fish for almost 40 years, believes otters were responsible for the destruction of the creatures, worth about £10,000.

Mr Smith found the koi, some of them beheaded and others with their tails bitten off, scattered around his garden at the weekend.

He told BBC Radio Scotland’s Drivetime programme that he is devastated.

The 75-year-old’s wife, Yvonne, discovered the dead fish beside the pond in the couple’s back garden on her way to work.

She then alerted her husband, who said the scene was “horrendous”.

He said: “The first thing I saw was what I thought was a bunch of leaves. When I got closer it turned out to be one of the koi.

“As I stepped over the wall I noticed there were a couple to the left, more to the right, and when I looked in the pond there was no movement at all.”

He said the scene got worse the further he walked.

“I took a walk around the pond and almost every fish that I had was lying there headless, fins ripped off them, faces ripped off them,” he said. “It was just a massacre as far as I was concerned.”

At first Mr Smith thought it had been an attack from a heron.

But after posting his discovery on social media, friends said it could have been otters or mink.

“As far as I believe,” he said, “it was otters.”

Mr Smith said he lost his entire collection of 25 fish – 13 carcasses were scattered beside his ornamental pond that he built himself, 12 others were missing.

The former roofer estimates he has spent around £10,000 over the years building up his hobby, and more on creating the perfect environment for them.

He said he cherished the fish as pets.

“I am totally heartbroken,” he said. “People have dogs, they have cats, but I have fish. I could interact with my fish.

“I would hand-feed them. The biggest one, he would feel the vibrations of me coming over, then the rest would come over. It was like feeding a baby.

“His name was Baby Jaws – he was a metre long and I have had him for 35 years.”

East Dunbartonshire Council said they knew of only one other case in recent years where a koi owner in Bearsden believed their fish had been targeted by otters.

Otters are protected under law and the local authority advise a number of measures to help protect koi ponds from predation by the species like electric and mesh fencing.

Grace Yokon, who is director of the International Otter Survival Fund, believes either otter or mink could be responsible as “both will tackle fish.”

She said: “It’s important that anyone [who] has ponds with koi carp or any other fish in, that they understand that basically what they’ve got is a feeding table.

“If you leave a table out with sandwiches and nice cakes on it, and come back, they are not going to be there – and anyone who has these ponds has got to protect them.”

Otters have been spotted in recent years in the River Kelvin in the west end of Glasgow with some also being sighted further north where the river meets the Allander Water.

Experts from the International Otter Survival Fund believe it is possible otters could have travelled to near Mr Smith’s home which is close to the Allander Water in Milngavie as their territory is up to 40km (25 miles).

Mr Smith, who describes sitting by his pond watching his koi fish as his “happy place”, told the BBC he was torn about what to do now as he is fearful if he gets more koi the otters will return.