The use of lumpfish (Cyclopterus lumpus L.) to control sea lice (Lepeophtheirus salmonis Krøyer) infestations in intensively farmed Atlantic salmon (Salmo salar L.)

The salmon louse is an ectoparasitic copepod that causes major economic losses in the Atlantic salmon aquaculture industry. To assess the efficacy of lumpfish grazing on attached sea lice on Atlantic salmon, six sea cages (5 × 5 × 5 m) were each stocked with 120 Atlantic salmon with a mean ± SD weight of 619 ± 49 g. Two of the cages were further stocked with 12 lumpfish (10% density) and two with 18 lumpfish (15% density) with a mean ± SD weight of 54.0 ± 7.2 g. Two cages without lumpfish acted as controls. Sea lice infestation levels were recorded every other week for 54 days. To determine the diet preferences of lumpfish in the cages, gastric lavage was performed every 2 weeks. No differences in salmon or lumpfish growth between test groups and controls were observed. There were clear signs of lumpfish grazing on sea lice, with significantly lower average numbers of pre-adult, mature males and females stages of Lepeophtheirus salmonis per salmon. Lumpfish reduced the mature female stage of L. salmonis to levels equal to or lower than the counts recorded prior to the start of the study. There were no significant differences between the treatments (10% and 15% densities) in grazing efficacy. There was clear evidence of grazing from the results of gastric lavage, with 28% of all lumpfish found to have ingested sea lice on the last sampling day. Overall, the present results indicate that lumpfish is a suitable cold-water option for biological delousing of Atlantic salmon.