The climate is still changing

It is December 2020, the year is almost at its end with the world is still facing the effects of COVID-19 and its resulting disruption. Simultaneously, a series of interesting scientific debates concerning the possible unexpected side-effects of pandemic management on climate change are now proliferating. Wishes and hopes have been expressed about the possible temporary benefits of a partial reduction in greenhouse gas emissions. The possibility to use the anticipated recovery phase as a platform to transform the current challenges into opportunities to transit towards a more sustainable world is now a new prospective priority. Whilst we have no reason not to be optimistic when it comes to the current pandemic, we have to note that climate change, with its resulting effects on ocean warming, ocean acidification, extreme and unpredictable weather conditions, rising sea levels and salinity variations, is still happening. We should not be distracted from maintaining a focus on these phenomena which are directly impacting the aquaculture sector. In addition to the immediate and logical effects that such changes could have on aquaculture activities and practices, there are two, somewhat unexpected, effects that have been put forward in recent publications. The first one pertains to the alarming association between antimicrobial resistance in aquaculture-related bacteria and warmer temperatures that has been recently reported by Reverter et al. (2020). Whilst the authors of this study clearly outline that the causes and effects of this association are still numerous, unclear and complex, it can be argued that the existing changing environmental conditions on farms are increasing the occurrence of conditions favouring disease outbreaks and therefore favouring an increased application of antimicrobial agents. This observation is a somewhat unpredicted consequence of how climate change can further affect aquaculture, and – with a cascade effect – generating a series of possible secondary effects on environmental and societal health. This observation is prompting further impetus towards the R&D efforts of the aquaculture sector in the development and refinement of possible solutions and climate change adaptation remedies. When the relocation of a farm to an area with more suitable environmental conditions, or the adoption of new cultured species better equipped to cope to the new conditions is not possible, other remedial strategies must be identified. These can span from improved – and more cost-effective – vaccination strategies, to the implementation of targeted selective breeding, the use of adaptive nutrition strategies, the identification and effective use of bioactive compounds, probiotics and other immune stimulants, which can all contribute in reducing the occurrence of diseases outbreaks, and therefore minimising the use of antimicrobial agents. What is evident is that increased knowledge, targeted research activities and solutions are needed, as the climate is still changing, and aquaculture needs to adapt. The second recent observation of another unexpected effect of climate change, which could directly affect aquaculture, arises from a study by Colombo et al (2020), who hypothesised that global warming could significantly reduce the availability of the health-promoting omega-3 long-chain polyunsaturated fatty acid and docosahexaenoic acid (DHA). This is because the de novo synthesis of DHA in algae, which sit at the base of aquatic food chains, could reduce when temperature increases. DHA is an extremely important nutrient, with a plethora of physiological roles and health-promoting effects in animals and in humans. Currently, considering the constantly increasing share of aquaculture over wild fisheries on the total fish and seafood availability, aquaculture is possibly the largest source of edible DHA for humanity. However, aquaculture is also a user of this precious nutrient, which is already in relatively short supply. Several strategies have been developed and are at different stages of implementation and commercialisation to reduce the dependence of aquaculture on wild-derived DHA, traditionally coming from fish meal and fish oil from wild fisheries. These comprise of improved aquafeed formulations and feed management strategies, new raw materials containing omega-3 long-chain polyunsaturated fatty acids, such as single cell oils and the oil extracted from GM oilseed crops, nutritional programming and selective breeding, shifts to aquaculture species with more efficient in vivo DHA biosynthetic capabilities and other approaches in earlier stages of development. Nevertheless, the impact of climate change on global DHA availability will further exacerbate this problem, and aquaculture must face the challenge of delivering this health-promoting nutrient to humans, whilst significantly reducing its utilisation from wild-derived sources. Again, what is evident is that increased knowledge, targeted research activities and