There was horror, there was outrage – and just a little scepticism – when a flesh-eating piranha was said to have blocked a sewer in Telford.

A variety of mystery fish were found by investigators from Severn Trent Water after people complained of a fishy smell coming into their homes, according to the Shropshire Star.

Workmen were sent to clear the "piles of meat-eating piranhas", and speculated that the culprit "was someone who became bored of their pet fish and decided to get rid of them by flushing them away".

Matt Final and Jay Slater, who went to investigate the sewers for Severn Trent, said, in a statement released by the company: "We've certainly seen some weird things in the sewers over the years but we were a little shocked to remove piranhas! You wouldn't think a fish of this size would fit down a toilet, but this is just one example of amazing things we find blocking the sewers."

However, Star readers were quick to question the findings when the story was published alongside a photograph of the offending fish. Reader Lyndsey Bird was the first to comment: "Those are not piranhas, they appear to be some sort of cichlid, possibly Malawian. Piranhas have extremely small scales and a fused lower jaw. Not to mention the fin and body structure is all wrong.

"Having been an avid fishkeeper for many years as well as having a degree in marine and freshwater biology, I get extremely frustrated when fish are mislabled, especially when everyone jumps to the piranha as a default for a large fish."

Another reader, Adam Firth, added, with some conviction: "That's not a piranha. It's a type of tilapia."

Following several hours of fevered speculation on how a piranha had found itself in a Shropshire sewer, a fish expert confirmed that the fish was indeed a tilapia, a commonly farmed breed.

Asked if the water company was sure it was a piranha, Sarah-Jayne O'Kane, a spokeswoman for Severn Trent Water said: "No, we're not. Apparently it's a tilapia, which isn't quite as exciting."

Nonetheless it had been a hair-raising experience for the workmen involved, she said. "It scared out guys to death – they were told by a neighbour that someone had been flushing piranhas down the toilet. And you have to admit, it looks quite like a piranha."

Whatever the provenance, or breed, of the offending fish, the message remained the same, she said: "At the end of the day people shouldn't be flushing fish down the toilet, it causes blockages and can make it very smelly for your neighbours."

This is the second recent sewer blockage in the Shropshire area. In January the company reported sewers in Ditton Priors, near Bridgnorth, were blocked by piles of pants.