Ozone (O3) is a powerful oxidant that has been used in both the aquaculture and water treatment industries to improve water quality and reduce pathogens during pretreatment, treatment of effluent, as a continual treatment during RAS operations, and for bivalve depuration. As ozone can be toxic to aquatic organisms, the technology has also been investigated to destroy invasive or nuisance species, and other research has also highlighted negative effects of residual ozone on water courses. Ozone and ozone‐produced oxidants used in aquaculture operations have therefore typically been removed from water prior to entry into tanks holding stock animals. However, a growing body of research has identified direct application of ozone, here defined as exposure of residual ozone and ozone‐produced oxidants to cultured species of finfish, shellfish and live feeds across various life stages. This approach appears to be increasingly employed as a beneficial technology due to proven enhancement of hygiene and water quality, provided dosages or concentrations are appropriate to maintain animal health and welfare. This review paper concentrates on the observed benefits and drawbacks of direct ozonation, influencing factors and future considerations for standardisation and uptake of the technology.

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.

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The feeding rate and behaviour of whelks (Buccinum undatum) offered cockles (Cerastoderma edule) in laboratory experiments were examined. When presented with cockles in a range of sizes (10-40 mm), 14 B. undatum (34.6-88.3 mm), held individually in aquaria, consumed a wide size range of cockles. Small whelks (,40 mm) consumed cockles (,23 mm), whereas large whelks, (.60 mm) ate a greater number of larger cockles (.30 mm) and a wider size range of cockles (12-40 mm) than smaller whelks. The majority (90%) of the shells of the predated cockles were undamaged and the few (,10%) that were damaged showed only slight abrasions to the anterior and posterior shell margin. Filmed observations of B. undatum feeding on C. edule showed a method of attack that has not previously been reported and involved the use of the whelk's foot to asphyxiate the cockle or to pull the shell valves apart. No filmed evidence was found for the previously reported shell 'wedging' technique for prising open the closed shell valves of C. edule, although 10% of the shells of consumed cockles in feeding experiments had damaged shell margins.