12/11/2021 | Extreme temperature events caused by climate change are becoming more intense and frequent. For fish, temperature is the most important abiotic factor controlling and limiting their development and physiology at all stages of aquaculture. A new study with participation of the Experimental Aquaculture WG summarises the effects of extreme temperatures on various physiological responses of aquaculture fish and discusses the consequences for fish growth and reproduction.
What was the initial question of the study?
Andreas Kunzmann: Climate change is already clearly noticeable in Europe, especially in southern Europe. We wanted to know how fish in aquaculture, which cannot simply migrate further north like their wild relatives, react to the higher temperatures. We also wanted to know whether their reactions might be financially noticeable for fish farmers.
What exactly did you study?
Andreas Kunzmann: Sea bass is a typical aquaculture fish in the Mediterranean. We exposed it to very different temperatures in many successive experiments in the laboratory (slow vs. rapid temperature increase, also lower temperatures) and this in combination with different salt contents. Then we determined growth, health and a whole range of physiological parameters (blood components, enzymes, gene expression) and compared them with control animals.
What are the new findings?
Andreas Kunzmann: The sea bass is quite adaptable. While there are still few immediate reactions at the organism level (growth, health), the effects of stress at the organ and cell level can already be seen very clearly. Energy consumption increases, the first limits of stress tolerance become apparent. We have also clearly seen that it is essential to take several reaction parameters into account.
What conclusions can be drawn from this?
Andreas Kunzmann: In the long run, temperature and salinity stress will also affect feed conversion, growth performance, health and reproduction of the fish. So the fish farmer has to think about how to adapt his aquaculture to climate change. One possibility is the clever selection of suitable sites. Another is the administration of probiotic substances in the feed, which definitely reduces short-term stress effects.
What could be the impact on aquaculture?
Andreas Kunzmann: The "wild" sea bass stocks will very likely leave their traditional areas and migrate further north if temperatures continue to rise. It is possible that fish farmers will have to migrate behind with their production sites. Land-based production can adjust environmental parameters such as temperature or salinity in a controlled way, but this would make production much more expensive. Nutritional measures should be explored as a potential option to combat extreme temperature stress and an innovative and adapted fish feed should be developed.
Why is the study relevant to the general public?
Andreas Kunzmann: Basically, we learn a lot about the effects of climate change from relevant studies on animals. The adaptive capacity of marine organisms is amazingly great, but it has clear limits. Future food security is inconceivable without products from the sea and especially without aquaculture.
Publication
Islam, Md Jakiul, Slater, Matthew James and Kunzmann, Andreas (2021) Responses of aquaculture fish to climate change‐induced extreme temperatures: A review. Journal of the World Aquaculture Society.
Contacts 
Working Groups