Efficient sea-lice control remains one of the most important challenges for the salmon farming industry. The use of wrasse (Labridae) as cleaner fish offers an alternative to medicines for sea-lice control, but wrasse tend to become inactive in winter. Lumpfish (Cyclopterus lumpus) continue to feed on sea-lice at low temperatures, and commercial production has escalated from thousands of fish in 2010 to well over 30 million juveniles deployed in 2016. However, production still relies on the capture of wild broodstock, which may not be sustainable. To meet global industry needs, lumpfish production needs to increase to reach c. 50 million fish annually and this can only come from aquaculture. We review current production methods and the use of lumpfish in sea cages and identify some of the main challenges and bottlenecks facing lumpfish intensification. Our gap analysis indicates that the areas in most need of research include better control of maturation for year-round production; formulation of appropriate diets; artificial selection of elite lines with desirable traits; and development of vaccines for certified, disease-free juvenile production. The welfare of farmed lumpfish also needs to be better quantified, and more information is needed on optimal densities and tank design. Finally, the risk of farmed lumpfish escaping from net pens needs to be critically assessed, and we argue that it might be beneficial to recover cleaner fish from salmon cages after the production cycle, perhaps using them as broodstock, for export to the Asian food markets or for the production of animal feeds.

Abstract. Ocean acidification, caused by rising concentrations of carbon dioxide (CO2), is widely considered to be a major global threat to marine ecosystems. To investigate the potential effects of ocean acidification on the early life stages of a commercially important fish species, European sea bass (Dicentrarchus labrax), 12 000 larvae were incubated from hatch through metamorphosis under a matrix of two temperatures (17 and 19 °C) and two seawater pCO2 levels (ambient and 1,000 μatm) and sampled regularly for 42 days. Calculated daily mortality was significantly affected by both temperature and pCO2, with both increased temperature and elevated pCO2 associated with lower daily mortality and a significant interaction between these two factors. There was no significant pCO2 effect noted on larval morphology during this period but larvae raised at 19 °C possessed significantly larger eyes and lower carbon:nitrogen ratios at the end of the study compared to those raised under 17 °C. Similarly, when the incubation was continued to post-metamorphic (juvenile) animals (day 67–69), fish raised under a combination of 19 °C and 1000 μatm pCO2 were significantly heavier. However, juvenile D. labrax raised under this combination of 19 °C and 1000 μatm pCO2 also exhibited lower aerobic scopes than those incubated at 19 °C and ambient pCO2. Most studies investigating the effects of near-future oceanic conditions on the early life stages of marine fish have used incubations of relatively short durations and suggested that these animals are resilient to ocean acidification. Whilst the increased survival and growth observed in this study supports this view, we conclude that more work is required to investigate whether the differences in juvenile physiology observed in this study manifest as negative impacts in adult fish.

The mussel (Mytilus edulis) is successfully grown in aquaculture in Europe. Mussels are usually sold live and wet storage is becoming more common. In this study, oxygen demand and ammonia excretion were assessed at increasing water temperatures and different post-harvest situations. This information was used to calculate minimal flow rates per unit biomass of live mussels sufficient to keep oxygen above 5 mg L −1 or 50% saturation, and avoid accumulation of ammonia in commercial wet storage. In this study, rope-grown mussels were kept out of water for 8 h to simulate harvesting conditions and then re-immersed in holding tanks at 5, 10 and 15 • C. Oxygen and ammonia concentrations were measured immediately after mussels were re-immersed (0 h), after 6 h and then every day for 3 days. After this period, the mussels were again kept out of water for 48 h to simulate long-distance transport and once again re-immersed for the same period as before. In the first 6 h after re-immersion, the oxygen consumption was between 7.5 and 12.2 μmol g −1 h −1 (dry flesh) and after this period it decreased to a standard level of around 4.0 ± 0.9 μmol g −1 h −1 and was independent of temperature. There were no major differences in oxygen consumption between mussels having spent 8 and 48 h out of water at any of the subsequent water temperatures used for re-immersion. In contrast, the ammonia excretion showed greater differences according to temperature and time out of water. Ammonia excretion was lowest at 5 • C (<0.01 μmol g −1 h −1). The implications of these results for the industry and authorities are discussed considering the water flow rate, depuration specifications and energy costs.

Ocean acidification, caused by rising concentrations of carbon dioxide (CO₂), is widely considered to be a major global threat to marine ecosystems. To investigate the potential effects of ocean acidification on the early life stages of a commercially important fish species, European sea bass (Dicentrarchus labrax), 12 000 larvae were incubated from hatch through metamorphosis under a matrix of two temperatures (17 and 19 °C) and two seawater pCO₂s (400 and 750 μatm) and sampled regularly for 42 days. Calculated daily mortality was significantly affected by both temperature and pCO₂, with both increased temperature and elevated pCO₂ associated with lower daily mortality and a significant interaction between these two factors. There was no significant pCO₂ effect noted on larval morphology during this period but larvae raised at 19 °C possessed significantly larger eyes and lower carbon:nitrogen ratios at the end of the study compared to those raised under 17 °C. These results suggest that D. labrax larvae are resilient to near-future oceanic conditions. However, when the incubation was continued to post-metamorphic (juvenile) animals (day 67–69), fish raised under a combination of 19 °C and 750 μatm pCO₂ were significantly heavier and exhibited lower aerobic scopes than those incubated at 19 °C and 400 μatm. Most other studies investigating the effects of near-future oceanic conditions on the early life stages of marine fish have used incubations of relatively short durations and suggested these animals are resilient to ocean acidification. We propose the durations of these other studies may be insufficient for more subtle effects, such as those observed in this study, to become apparent. These findings may have important implications for both sea bass in a changing ocean and also for the interpretation of results from other studies that have shown resiliency in marine teleosts exposed to higher atmospheric concentrations of CO₂