Now there’s a blog post title you don’t read every day. Without wishing to alarm people, you (or at least approximately half the population) might like to be aware that a small, piranha-like fish called the pacu – but also referred to as the ‘ball-cutter’ owing to its reputation for biting off men’s testicles – has been found in European waters. The fish is in fact related to the piranha but its teeth are very different – more like a human’s, in fact, than the pointed, razor-sharp teeth of piranhas. It also has a crushing jaw that is capable of breaking up seeds and nuts (please forgive the pun!).Although traditionally found in South America, and common to the Amazon and Orinoco basins, last month a Scandinavian fisherman retrieved a 21-centimetre pacu from the Øresund Sound between Sweden and Denmark. This prompted the National History Museum in Denmark to advise swimmers in the Sound to keep their swimwear on.

Furthermore, this week the fish has been found in the River Seine, according to a newsletter from the Paris Prefecture of Police. Although not normally a danger to people, the pacu can grow up to 90 centimetres in length and weigh as much as 25 kilogrammes, and its fearsome reputation for biting off male genitalia has even allegedly caused some men to bleed to death.

So, next time you’re going for a dip – particularly if it’s in the Seine or the Øresund Sound – you may just want to bear this in mind…