Fish Farming: A Polluting Practice?

Fish farming, or aquafarming, is the breeding and rearing of aquatic animals in captivity for food. It is often regarded as a more sustainable alternative to meat production, but it can have significant environmental consequences. The pollution emitted from fish farms damages natural waterways and ecosystems and kills wild animal populations. This paragraph will explore the ways in which fish farming causes pollution and its impact on the environment.

Fish waste and uneaten food

In addition to fish waste, uneaten food in fish farms can also contribute to pollution. Uneaten food can release toxic ammonia and nitrite as it decomposes, which can be dangerous to fish, especially in newer aquariums where nitrifying bacteria have not had a chance to develop fully. The decomposition process also lowers the dissolved oxygen content in the water, which can stress the fish. Furthermore, uneaten food can clog filters, reducing circulation and further decreasing oxygen levels. This can lead to poor water quality, stunting the growth of fish, causing their colours to fade, and lowering their resistance to disease.

The impact of fish waste and uneaten food on the environment is influenced by the species being farmed, the intensity of production, and the location of the farm. Regulatory agencies have recognised the issue of nutrient and effluent buildup and have implemented measures to mitigate it, such as siting fish farms in areas with strong currents to disperse effluent.

To reduce the impact of fish waste and uneaten food, it is important to feed fish according to their number and size rather than the size of the tank. Removing uneaten food after a few minutes and fasting fish for a day or two each week can also help. Choosing the right types of food, such as plant-based food for herbivores, can minimise excess waste from undigested food.

While fish farming has been criticised for its environmental impact, it is important to note that it was initially intended to increase food security. With the world's growing population and appetite for seafood, aquaculture has become a significant source of seafood, and it can be more sustainable than meat production if done right. However, there is a need for continuous improvement and the adoption of sustainable practices to minimise the negative effects of fish waste and uneaten food on the environment.

Antibiotics and pesticides

Fish farming is responsible for a massive amount of waste, which causes water pollution when released. Fish farms are often crowded, and when one fish gets sick, the disease spreads to many others. To prevent this, antibiotics are administered generously, and in many countries, routinely. The use of antibiotics in aquaculture is a significant contributor to antimicrobial resistance (AMR), which poses risks to both humans and the environment. Antimicrobials are only partially taken up by fish, and their residues can end up in aquatic systems, altering microbial communities and affecting their functions. The presence of antimicrobial residues and antimicrobial-resistant bacteria and genes in the environment contributes to the emergence and spread of AMR. This has led to rising rates of antibiotic resistance in humans, with antimicrobial-resistant infections causing an estimated 35,000 deaths per year in European Economic Area countries.

The use of pesticides in fish farming can also have negative consequences. While pesticides are effective at eradicating targeted pests, they can be harmful to other organisms, especially when applied without oversight or management. Pesticides can spread quickly beyond the immediate food chain to the rest of the marine environment and to birds that prey on fish. The unauthorized use of pesticides and drugs has been reported by Chinese farmers to increase production and save on feed costs.

In addition to the direct impacts on human and environmental health, the use of antibiotics and pesticides in fish farming can also have socioeconomic implications. The presence of antimicrobial residues in food of animal origin can create challenges in international trade, as seen with the detection of antibiotics in imported fish and shrimp from China.

To address these issues, measures to reduce the use of antibiotics and pesticides in fish farming are essential. Expanded monitoring of antimicrobials in waterways can help identify pollution hotspots and better assess the impacts on humans, animals, and the environment. Risk analysis has emerged as a critical tool for assessing and managing the safety of aquaculture products, ensuring that the sector produces safe food for consumers.

Escape of non-native fish

Fish farming, or aquaculture, has been criticised for its negative environmental impact, particularly the escape of non-native fish. This can occur due to accidental release during operations, damage to cages, or attacks by predators. While recapture methods have been employed, they have only been partially effective, and the effects of a fish spill can be immediate and irreversible.

Non-native fish can bring new diseases and parasites that local fish are not resistant to, impacting natural marine habitats and causing death and potential species extinction. For example, farmed salmon are prone to infection from sea lice, which can spread beyond the confines of fish farms. Introducing invasive species can cause catastrophic damage, as they compete with native species for food and space, introduce new pathogens, and alter the food chain.

The escape of non-native fish can also lead to genetic impacts through interbreeding with wild populations, potentially weakening their adaptability to the environment. This can disrupt the balance of the marine ecosystem, with non-native fish preying on local species and potentially wiping out entire populations.

To mitigate these issues, regulatory agencies have implemented measures such as siting fish farms in areas with strong currents to disperse waste and periodically moving farms to prevent concentrated environmental impacts. Additionally, the use of underwater cameras and regular inspections by divers helps monitor and prevent fish escapes.

While fish farming has faced criticism for its environmental impact, it is important to note that when done sustainably, it can be a solution to increasing food security and addressing the strain on wild fisheries.

Pollution from chemicals

Fish farming uses a combination of fertilizers, antibiotics, and pesticides, which can make the water runoff highly toxic. This toxic water flows into local waterways and eventually back into the ocean, polluting marine ecosystems and water for human consumption. The use of antibiotics in fish farms contributes to rising antibiotic resistance in humans, as people consume food laden with antibiotic-resistant bacteria. Pesticides, while effective at eradicating targeted pests, can be harmful to other organisms, especially when applied without oversight or management. Beyond the immediate food chain, pesticides can spread quickly to the rest of the marine environment and to birds that prey on fish.

One of the most common chemicals found in fish is mercury, which can cause neurological issues in humans when consumed in high doses. The global trade of fish and fish products has led to concerns about the transfer of contaminants via food exports and imports, and the subsequent contamination of local and regional food webs. For instance, research has shown that 84% of PCB exposure in sub-Saharan fish consumers could be attributed to fish imported from Western and Northern Europe.

Pollutants such as polychlorinated biphenyls (PCBs) and mercury may be elevated in certain marine fish species or in fish-meal-based diets for mariculture. PCBs, widely used in electrical transformers and building products until banned in the 1970s and 1980s, remain elevated in marine fish, especially in coastal areas of Western Europe and the eastern USA. Fish farmed in seawater mariculture systems and fed wild-caught fish-meal are also exposed to PCBs and other persistent organic pollutants (POPs) from multiple sources.

The specific site of a fish farm dictates the scope of its environmental impact. Cage systems in existing and open waters are more likely to spread fish waste, uneaten food, and chemicals into surrounding waters, increasing the risk of algal blooms that deplete oxygen and create "dead zones". Fish farms are often situated in or near sensitive coastal ecosystems, which can be irreparably damaged by pollution.

Destruction of natural habitats

Fish farming has been linked to the destruction of natural habitats, with serious environmental implications. One of the main ways in which this occurs is through the conversion of sensitive natural habitats into fish farms. For example, the establishment of tropical prawn farms has historically caused significant damage to delicate coastal mangrove forests, resulting in the loss of vital ecosystem functions such as natural coastal flood defences, nursery habitats for young fish, and water filtration.

The high density of fish in fish farms leads to nutrient and waste buildup, which can deplete the water of oxygen, creating algal blooms and "dead zones" where much of the aquatic life is killed. This waste, along with uneaten food and harsh chemicals used to treat the fish, is discharged directly into ecologically fragile coastal waters, further destroying local ecosystems. The waste from fish farms can also cause large blankets of green slime to form on the water's surface, which depletes oxygen and contributes to the creation of "dead zones".

Additionally, fish farms can act as breeding grounds for diseases and parasites, which can then spread to wild fish populations. For example, sea lice parasites from high-density farmed salmon can infect and harm juvenile wild salmon in surrounding water systems. Escaped farmed fish can also interbreed with wild fish, resulting in hybrid offspring with reduced chances of survival. These escapees compete with wild fish for food and resources, further adding pressure to already vulnerable wild populations.

The impact of fish farms on natural habitats is influenced by factors such as the species being farmed, the intensity of production, and the location of the farm. While some argue that fish farming can be made more sustainable through the implementation of new strategies and technologies, others emphasize the inherent environmental impact of the industry and the need to reduce the consumption of fish.

Frequently asked questions