Aquaculture – the term given to the cultivation of saltwater and freshwater organisms, under controlled farm conditions – is the fastest-growing food production system in the world. But with rapid expansion comes a huge challenge: how does the industry balance the need to meet continually increasing demand, while managing the risks of unprecedented growth?

While no stranger to criticism, aquaculture is seen by some as a conceivable “blue revolution” for its potential to help feed the growing human population with high quality food and valuable animal proteins. It undoubtedly represents an opportunity to reduce pressure on marine resources and create millions of jobs, but it also raises a number of sustainability concerns.

Trends in aquaculture

In the last few decades, aquaculture has expanded tremendously in almost all regions of the world. Global production grew from 5 million tonnes in 1980, to 67 million tonnes in 2013. While the trend in increased agricultural productivity since the “green revolution” is slowing down, aquaculture has only just started to exploit its potential. The decline of wild fish stocks, globalisation and the development of new technologies lead to extensive opportunities in the fish farming sector.

But as with agriculture, will the overexpansion and intensification of aquaculture affect the future of marine habitats and resource availability?

Reasons for concern

There are a number of interconnected issues which arise out of current aquaculture production, spanning environmental impacts, food security and sovereignty.

Today, we are repeatedly told by media and NGOs, that half of the fish we eat comes from aquaculture. However, this only tells us part of the story. Carnivorous fish, such as salmon and tuna, eat other fish, particularly small pelagic fish like sardines and anchovies. These are critical to the aquatic food chain, but they are increasingly used as fishmeal and fish oil to sustain both aquaculture and livestock. It is currently estimated that 36% of all fish landed, is used for the production of fishmeal and fish oil. Many species cultivated in intensive systems, such as salmon, require more wild fish as inputs than the farmed fish produced, a phenomenon described as the ‘fishmeal trap‘.

Linked to this is an ethical problem associated with producing high-value fish, fed with small pelagic fish caught by fisheries in developing countries, especially when we consider that these small fish represent a cheap source of valuable animal proteins for the rural poor.

Further concerns include discharges from farming sites, the problem of aquaculture escapees, the spread of pathogens, and the heavy use of antibiotics in intensive production systems. Nitrogen wastes and untreated waste water, contaminated with uneaten feed and fish faeces, contribute to nutrient pollution near coastal ponds and fish cages.

In some cases, aquaculture affects wild fish stocks with biological pollution. For instance, farmed salmon can escape from net pens and increasing evidence shows that escapees may alter the genetic makeup of wild populations of salmon, which are inherently adapted to their natal spawning grounds. Such genetic alteration could exacerbate the decline of many locally endangered populations. Finally, the movement of fish stocks from intensively farmed environments increases the risk of spreading pathogens to wild fish.

The magnitude of these effects varies considerably among aquaculture systems. For instance, herbivorous and omnivorous species like carp, tilapia and catfish can be farmed without the use of modern compound fish-based feeds. Production of these species can potentially compensate for the shortfall in ocean harvests as marine fisheries deteriorate, reducing pressures on marine resources globally.

But unfortunately, current intensive production systems of most species, including both herbivores and omnivores, rely heavily on added feeds. This is due to high density stocking, at which level they cannot be supported by natural food sources.

Over time, intensive fish farming has promoted the growth of several bacterial diseases, which has led to an increase in the use of antibiotics. It is not easy to determine current levels of antimicrobial use in aquaculture, because different countries have different distribution and registration systems. However, there is evidence suggesting that the presence of antibiotic-resistant bacteria in the fish we eat is a potential public health threat.

Aquaculture can also play a role in the displacement of pre-existing activities and habitats. The replacement of mangrove forests with shrimp ponds in tropical estuaries is a well-known example of displacement, denounced by many environmental NGOs. Mangrove forests serve as nurseries that provide food and shelter to many juvenile finfish and shellfish, and generally improve habitat conditions of coral reefs and seagrass beds. Another significant impact is related to the social transition of mangrove dependent communities to globalised production systems which are often based on few and large multinational aquaculture companies. This may result in loss of local community knowledge and increased inequality.

Prospects for sustainable aquaculture

Certification is a valuable instrument for steering commercial aquaculture towards sustainability. But only a very small proportion of world aquaculture production – less than 5% in 2013 – is currently certified.

A recent publication, Certify Sustainable Aquaculture?, argues that certification is only one tool for charting a sustainable path for aquaculture. Other instruments include local government action to design better policies and regulations, as an example, for site and species selection, implementation of the best system for aquaculture, and the management of effluents.

Small-scale rural and peri-urban aquaculture, along with innovative technologies which are currently receiving considerable research attention – such as recirculating aquaculture, aquaponics, integrated multi-trophic aquaculture – will all contribute to securing future fish supplies, especially at a local level.

It is also vital that the public and private sector are committed to reducing the widespread confusion among consumers, by giving them accurate information on the conditions and impacts of aquaculture so that they can make informed decisions about what they eat and the industries they support.

But there are many issues, particularly in relation to public health and working conditions, which are critical to the overall sustainability of aquaculture. To move forward, these require detailed research in line with the rate at which the industry is gaining momentum.

Raising the sustainability profile of aquaculture demands the understanding of scientists and decision-makers from varied sectors and geographies, exploring the interactions between fishery and aquaculture and between global and local dynamics.

It is clear that as fish farming expands, we must avoid the mistakes exemplified in the green revolution and the rapid intensification of agriculture, aiming to engage the ensuing blue revolution in a positive cycle of sustainability from its earliest days.

Photograph: WorldFish

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