Six skippers admitted making illegal landings of £15 million worth of fish, prosecutors said.
Robert Polson, 47, David Hutchison, 64, Thomas Eunson, 55, Allen Anderson, 54, John Irvine, 66, and Allister Irvine, 61, all from Shetland, pleaded guilty to taking part in the fraud at the High Court in Glasgow.
The skippers overfished herring and mackerel in the waters around Shetland and lied about how many fish they landed to try and get past the annual fishing quotas.