Owners of outdoor goldfish in suburbs of Swansea have been told to cover their ponds to deter a mystery predator.
One theory is a mink may be responsible for the attacks
Since the late summer, an unknown animal has been preying on ponds in back gardens across the Killay and Derwen Fawr areas, killing dozens of fish.
Members of a gardening club believe a mink or possibly an otter is responsible and are urging people to protect their ponds.
Following an attack that left around a dozen of their neighbour's Koi carp decapitated, Alma and Ray Jenkins have covered the pond at their home on Dylan Road in Killay with mesh.
The couple say they know of at least eight incidents in the area in the past six months, but believe there could be many more that have gone unreported.
"It's been happening across the area since the late summer," said Mrs Jenkins.
"There are many different opinions about what it could be but we have been told it could be a mink or possibly an otter.
"Our neighbour lost his Koi carp on Christmas Eve.
"It was like a slaughterhouse. There was blood and fish remains everywhere but just the heads were taken.
"It is an awful thing to see. The fish are a sitting target in a fish pond.
"You go out and you hear people talking about it.
"We are great gardening enthusiasts and know several people in our club who have lost their fish."
According to the Wildlife Trust of South and West Wales, both mink and otters are likely to be found in the area.
A spokesman said the organisation was receiving an increasing number of complaints about otters preying on fish ponds as the numbers of the mammals in the region increased.
He said it was probably more likely that an otter was responsible, but he could not rule out that the culprit was a mink.