Towards a better understanding of the evacuation time of salmon lice (Lepeophtheirus salmonis) in lumpfish (Cyclopterus lumpus)

Cleaner fish are utilised as a preventive control measure against sea lice infestations in salmon farms. In recent years, lumpfish (Cyclopterus lumpus) has been the most commonly deployed cleaner fish species in Norway. However, there have been few studies aiming to quantify the cleaning effect of lumpfish. There are many studies which document the number of sea lice in lumpfish stomach contents. These numbers cannot be used to infer the cleaning efficacy of lumpfish without also knowing the evacuation time of sea lice in lumpfish. In this study, we aimed to replicate an experiment of the evacuation time for salmon lice (Lepeophtheirus salmonis) in lumpfish. We found a median evacuation time of 50 h, and a mean evacuation time of 65 h. Combining with the data from the previous experiment, we found a median evacuation time of 31 h, and a mean evacuation time of 49 h. Interestingly, we found significantly slower digestion for adult female salmon lice than for other motile salmon lice. This implies that if lumpfish consumed the same (absolute) number of lice in different stages of lice, then one would expect more adult female lice in the stomach contents, as these require a longer time to be fully evacuated. This study is an important contribution to further understand the digestion time of salmon lice in lumpfish, which ultimately can be combined with an estimated number of salmon lice in the stomach contents of lumpfish to estimate a cleaning effect.