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 welfare monitoring of lumpfish in salmon cages is estimation of body condition. Previous research on standard length-weight relationships for lumpfish has primarily relied on growth patterns of lumpfish in salmon cages, which might not align with the natural growth patterns of the fish. Therefore, a correct species-adapted method is required to accurately estimate the body condition of lumpfish in salmon cages. In this study, we argue for a different approach: calculating the standard weight for lumpfish based on length-weight relationships observed in wild lumpfish. We assert that this approach aligns more closely with the natural state of the fish and may offer a more accurate representation of their condition. Our observations revealed a considerable difference in the length-weight growth patterns of wild lumpfish and lumpfish in salmon cages. Wild lumpfish displayed a positive allometric growth pattern, while the lumpfish in salmon cages displayed a slightly negative allometric growth pattern. The difference in growth patterns between wild lumpfish and lumpfish in salmon cages has important implications for the assessment of lumpfish body condition in aquaculture settings.
In conclusion, this study highlights the necessity of using appropriate length-weight relationships for lumpfish in salmon cages to accurately assess their body condition.