According to Official Guinness Records,
The most people gutting fish simultaneously is 1,000 and was achieved by the people of Santoña, in Cantabria, Spain on 1 May 2011. A long table was set up in the streets of Santoña, where a 1,000 participants took part in gutting and preparing anchovy fish. Each participant was given the following kit: apron, gloves and hair cap; and the following tools: nets, scissors, plates, cloth, oil, a water container, a tin and toothpicks. The event lasted for 50 minutes as all the participants gutted and prepared 2 fish each.
For a complete list of 2011 records, please visit 2011 Guinness Records in Spain.