Note: We acknowledge the fact that climate change is a complex issue and hard to predict. Forecasting climate change’s impacts on aquaculture is equally complex. This blog post is based on carefully selected studies and suggests the potential impacts of climate change on farmed fish.
We live in a time of a changing climate. Some places become increasingly hot and dry, while others flood (IPCC, 2014). In 2013, extremely high temperatures led to massive fish kills for milkfish farmers in the Philippines (White, 2013). Hot temperatures stress fish and can destroy farmers' livelihoods by eradicating whole stocks (White, 2013). But not only the Philippines are affected. Fish farmers around the world note the rising sea levels, extreme weather events, and increasingly challenging farming conditions. In the past few years, the aquaculture sector started further exploring the effects of climate change on farmed fish. The resulting message is clear: “The issues relating to climate change can significantly affect the welfare of farm animals” (RSPCA, 2015).
We can prepare fish to withstand the changes ahead by improving their resilience. And the key to better resilience is higher welfare.
The world is changing ...
Long, dry, hot summer months followed by sudden temperature changes and flooding - this is global warming messing with our climate. Increasingly severe storms and bigger waves damage open ocean fish farms and make it hard for farmers to reach their facilities to tend to fishes’ needs (Barange et al., 2018 - Chapter 23). Farmers keeping their fish in inland ponds are also not spared from climate change, as floods and droughts can deteriorate water quality in their ponds (Peck et al., 2020; Holmyard, 2014).
Open ocean sea cages like this cobia fish farm in Vietnam are at significant risk of destruction from extreme weather events.
Furthermore, warmer air means warmer water, both in inland and offshore fish farms (Holmyard, 2014). The problem with warmer water is that it holds less oxygen. To survive, fish need oxygen as much as humans, and small-sized ponds and lakes especially run the risk of oxygen depletion (Barange et al., 2018 - Chapter 1).
High temperatures also increase the risk of algal blooms. These can be either toxic (harmful algal bloom) or non-toxic. During toxic blooms, a sudden increase in plankton and algae depletes the water of its oxygen, frequently creating “dead zones” (i.e., zones of low oxygen levels, unsuitable for marine life). Scientists have found that if temperatures increase by 5°C, we can lose up to 60% of the 694 fish species they investigated (Vaughan, 2020).
Higher temperatures deplete oxygen in the water. Low oxygen levels leave fish in a constant state of suffocation.
… with serious implications for farmed fish.
Amidst all these changes live billions of fish. Each species thrives in specific water temperature ranges. If temperature changes permanently remain outside of a fish’s tolerable range, they enter a constant state of stress, also called allostatic overload. Combating stress requires energy, so fish will compensate for this energy loss by eating more. Feed already accounts for 25-85% of production costs without this added stress (Rola & Hasan, 2007). Increased hunger is not only stressful for the fish, but also requires farmers to invest more money in feed.
Another side effect of increased stress is suppressed immune function. Remember the last time you were in the middle of a stressful project? Perhaps you got sick with a cold as your body reacted to little sleep and a lot of cortisol (the stress hormone). Fish are no different. They can only cope with excessive stress for so long before their immune system weakens. This eventually leaves them increasingly vulnerable to diseases and parasites that they would have combated well under normal circumstances (Holmyard, 2014).
The biggest challenge of climate change lies in more frequent and more intense disease and parasite outbreaks. And the usual answer to more disease is the use of more antibiotics. Chilean salmon producers already give their fish over ten times more antibiotics than are used for chickens (Scott, 2019). High doses of antibiotics can lead to antibiotic resistance both in fish and humans - a concerning side-effect of global warming in aquaculture (Reverter et al., 2020).
Stress leads to a weakened immune system and the need for medical treatment. A cycle that can be broken by improving welfare.
Wild fish are affected by these developments as much as farmed fish. During past extreme weather events, the price for prey species such as anchovy has almost doubled (Bertrand et al., 2020). These species are processed into fishmeal and fish oil (FMFO), which is then fed to carnivorous fish in fish farms. Reduced availability and higher prices of FMFO could push farmers to either farm fewer carnivorous species or change fishes’ diet altogether. If feeding is not adjusted in the fish's best interest, less or different feed can leave them hungry.
Climate change may interrupt the freshwater supply in many areas. As water becomes more scarce, different sectors will compete over this resource (FAO, 2020, Barange et al., 2018 - Chapter 21). Aquaculture systems relying on external freshwater input will feel this shortage.
Furthermore, fish farming and processing requires boats, trucks, and other machines that rely on gasoline. With reduced future availability, oil prices will likely rise, forcing aquaculture facilities to find alternative methods of transport to keep costs down.
Who is most affected?
Fishes in open aquaculture operations such as sea cages, ponds, and raceways are directly exposed to the elements, and therefore the forces of climate change. Extensive aquaculture systems (e.g., small, backyard ponds) are particularly vulnerable because farmers generally spend little time monitoring and controlling such systems. Changes in water quality or poor welfare indicators can thus be missed easily. On the other hand, highly controlled systems such as Recirculating Aquaculture Systems have more control over changing environmental parameters and can regulate temperatures and oxygen content accordingly.
Some fishes may also experience short-term positive results when, for example, they are farmed in areas that are usually too cold for them. Yellowtail Kingfish struggle during the colder winter months in South Australia and may find warmer winters favorable. Of course, this only holds true as long as the summer temperatures stay within their tolerable range (Kolkovski & Sakakura, 2004).
Specific impacts will vary across regions and with species’ individual requirements. The fact that climate change impacts some species more than others may induce a shift in the species farmed, increasing the pressure on more resilient species. This shift in farmers’ focus holds serious welfare risks because some species can tolerate inappropriate conditions without indicating their discomfort.
What can we do?
Climate change is a complex problem that will have to be addressed by the international community. However, even if emissions stopped today, global warming will not halt. Farmers need to take action today to alleviate the stress on farmed fish in the future:
Improving fish welfare right now
Checking the water quality and environmental parameters at least once per day to identify any changes and immediately alleviate risks.
Reducing stocking densities to minimize infection spread and allow fish to recover more quickly.
Reducing the overall stress on fish to make them more resilient. Appropriate feed, minimal handling, adequate water quality, and the presence of positive experiences are just a few ways to improve resilience and brace aquaculture for the increased stressors ahead.
Planning ahead: When building a new facility, farmers should work with scientists to determine the future long-term climate change impacts in the desired area.
Changing tactics: Farmers could farm more omnivorous species to avoid reliance on FMFO, a feed source that may become scarce and expensive.
Giant gourami gasping for air. Scenarios like this can be avoided by decreasing stocking density and monitoring water quality regularly.
Frequent disease outbreaks, damaged facilities, and reduced revenue are the future of an aquaculture industry that does not brace itself for climate change. Unfortunately, the full extent of climate change’s impacts is not totally clear. What is clear, however, is that fish farmers can begin increasing their operational resilience by improving fish welfare today.