Cleaner fish are widely used to combat sea lice on farmed Atlantic salmon. Unlike wrasse, lumpfish are native to the Faroe Islands, making them the only cleaner fish species used in the local salmon production. The number of lumpfish used in the Faroe Islands has been gradually decreasing since 2020. Mostly due to high mortalities and difficulties in verifying their effect. Routine welfare monitoring of lumpfish includes stomach content analysis to assess their consumption of sea lice. However, estimating lumpfish efficiency based on this method is challenging due to uncertainties about the digestion time for salmon lice in lumpfish , complicating the assessment of lumpfish efficacy.
Two 12-day trials were conducted at two different temperatures (6°C and 9°C), each involving 64 lumpfish in batches of eight. Lumpfish were fed a single salmon louse, with six receiving a preadult II or adult male louse and two receiving an adult female louse. Lumpfish were fed lumpfish feed once or twice daily throughout the experiment.
The results showed no apparent difference in the proportion of lice recovered at different temperatures (Figure 1). However, lice were still detectable in the stomachs after 12 days. Notably, while all preadult II/adult males were fully digested by day 12, adult female lice were still present (Figure 1). This suggests that estimating lumpfish efficacy based on stomach content analysis should consider the developmental stages of lice.
These findings contrast with recently published results on the same subject, particularly regarding digestion time and differences in digestion rates among developmental stages of s almon lice. This emphasizes the complexity of accurately estimating the efficacy of cleaner fish in controlling sea lice infestations. Further research is needed to better understand and optimize the use of cleaner fish in aquaculture practices.