In 1100 A.D., there were more than 540,000 eels paid in rent in England every year. Most were due at the beginning of Lent.
Nifty map and more at English Eel-Rents: 10th-17th Centuries - Historia Cartarum
Nifty map and more at English Eel-Rents: 10th-17th Centuries - Historia Cartarum