There appears to be no definitive answer. Some scientists bestow the honour on the Wels catfish (a 127kg individual was caught in Italy in 2015); others claim the title belongs to the Beluga sturgeon.

Still others nominate the mangar, a little-known relative of the common barbel and a voracious predator whose name translates as ‘pike-like wolf barb’. This behemoth inhabits the Tigris-Euphrates river system, and is the biggest freshwater fish in Turkey – one caught in 2001 apparently weighed in at 111kg.