Using a length-weight relationship based on wild lumpfish (Cyclopterus lumpus L.) for estimation of body condition of lumpfish in salmon cages

The use of lumpfish (Cyclopterus lumpus L.) as cleaner fish in Atlantic salmon aquaculture has emerged as a promising solution to combat the issue of sea lice infestation, as they have proven effective under the right conditions. The aquaculture industry, however, is facing challenges in ensuring the welfare and survival of lumpfish in salmon cages. Part of the welfare monitoring of lumpfish is the estimation of body condition. Previous research on standard length-weight relationships for lumpfish has primarily relied on the growth patterns of lumpfish in salmon cages, which might not align with the natural growth patterns of the fish. In this study, we argue for another perspective: using the standard weight of wild lumpfish to estimate the body condition of lumpfish in salmon cages. We assert that this approach aligns more closely with the natural growth pattern of the fish and may offer a more accurate representation of their condition. Our findings show significant differences in growth patterns between wild lumpfish, which show positive allometric growth, and those in salmon cages, which show slightly negative allometric growth. The findings underscore the importance of using appropriate length-weight relationships for lumpfish in aquaculture to ensure an accurate assessment of their body condition.