Sea lice remain one of the main problems in salmon farming, with estimated costs of treatment and losses of fish running to several million pounds each year in Scotland alone. The use of chemical methods by the industry has brought adverse publicity and wrasse (cleaner fish) present an alternative, environmentally friendly means of biological control. As a result, the demand for wrasse has spawned a new inshore fishery, and this has led to calls for more information on the population dynamics and size of stocks. Attempts are also being made to rear wrasse for stocking. As a consequence there is considerable interest in cleaner fish technology from fish farmers and research workers. This book draws together the latest information on the biology and culture of wrasse, and the use of wrasse in controlling sea lice.