Assessment of growth and sea lice infection levels in Atlantic salmon stocked in small-scale cages with lumpfish

• We assessed the growth of Atlantic salmon in the presence of lumpfish.
• No effect on feed consumption was seen.
• Small lumpfish had no effect on growth in salmon.
• Feed conversion ratio and growth were negatively affected when reared with large lumpfish.
• Sea lice grazing efficiency was dependent on the size of the lumpfish.

Growth and performance of Atlantic salmon in the presence of lumpfish were assessed in two studies. In the first study, six sea cages (5 × 5 × 5 m) were each stocked with 120 Atlantic salmon with a mean (± SD) weight of 619 (± 49) g and reared for 159 days. Control cages were without lumpfish, while two of the cages were stocked with 12 lumpfish (10% density), and two with 18 lumpfish (15% density) with a mean (± SD) weight of 54.0 (± 7.2) g. The lumpfish were removed from the cages after 56 days, but feed consumption and growth of the salmon were monitored for another 12 weeks until 17 November 2012 to investigate possible long term effect from the presence of lumpfish on growth performance of the salmon. In the second study, six sea cages (5 × 5 × 5 m) were each stocked with 80 Atlantic salmon with a mean (± SD) weight of 2400 (± 220) g and reared for 60 days. Two of the cages were further stocked with 4 lumpfish (5% density), and two with 8 lumpfish (10% density) with a mean (± SD) weight of 360 (± 30) g. Two cages without lumpfish acted as controls. In both studies sea lice infestation levels were recorded every other week. In the study with small salmon and lumpfish, the presence of lumpfish did not have any negative short- or long-term effects on feed conversion ratio (FCR) or specific growth rate (SGR) in salmon. However, when large salmon were reared together with large lumpfish, FCR was lower and SGR higher in the control cages compared to the two lumpfish treatments. Significantly lower sea lice infection levels were seen on Atlantic salmon when reared together with small lumpfish compared to the control group without lumpfish, whereas this trend was not as clear when reared with larger lumpfish.