Photo by Artur Rydzewski

Image by Artur Rydzewski

First of all, what is aquaculture?

The FAO (Food and Agriculture Organization) defines aquaculture as the farming of aquatic organisms such as fishes, crustaceans, molluscs, aquatic plants and aquatic photosynthetic organisms.

Aquaculture farming implies individual or corporate ownership of the cultivated stock and involves the enclosure of the species in a secure system. The farming methods are remarkably diverse and are practiced in different environments including fresh, brackish and marine water, and entail human interventions such as stocking, feeding and protection from predators.

Seafood is a nutritious diet, offering a rich source of protein, as well as unsaturated fats, vitamins, minerals and trace elements. This is why aquaculture has existed for thousands of years. The origins of raising fish and cultivating aquatic plants are attributed to Chinese communities that developed before 1000 B.C. [1] (in other words, more than 3000 years ago!). Soon, these practices spread to other places. Ponds for both sacred and commercial fish around the Sumerian temples can be traced back to 2500 B.C. Fish farming was also practiced by the ancient Greeks and Romans, which later became part of the food production system of the Christian monasteries of Central Europe. The culture of aquatic organism farming experienced a continuous expansion to different regions of the world, but it was in the 1970s that its large-scale industrial intensification reached its peak.

Today, almost 600 aquatic species are cultivated throughout the world [2]. Table 1 shows the top 10 species currently cultivated. More information on other important species can be found on the FAO’s site. While these are the ones recorded in the databases, it is believed that the total number of species may actually be considerably higher, as some countries do not publish their activities comprehensively for either market reasons or because the species are not adequately identified as separate species. China for example, which is believed to cultivate around 200 different species, lists only 90 of them. It is further expected that the number of cultivated species will continue to increase in the coming years, as there is a large number of other species that are still at the research stage to complete their full life cycle in captivity.

Table 1: Top 10 ASFIS species items by quantity in world aquaculture, 2017. Source: FAO Global Fishery and Aquaculture Production Statistics 1950–2017 (v2019.1.0), published through FishStatJ (March 2019). Available at http://www.fao.org/fishery/statistics/software/fishstatj/en.

With over 114 million tons produced in 2018, aquaculture has become the most developed food industry in recent decades, surpassing fishing in 2016 [2]. The depletion of wild fishery stocks, rising global populations, a continuing demand for fish and international trade has driven aquaculture’s tremendous expansion during the last decades, in terms of both production volume and value.

Figure 1 shows the global aquaculture production in 2013. Asia accounts for 91.24% of global management, with China (by far) being the world’s largest producer. In fact, most statistics exclude China’s production, as this is the only way to display data from other producing countries. The graph further shows that the rest of the leading aquaculture countries also belong to the Asian continent, followed by some European (Norway), African (Egypt) or Latin American (Chile) countries.

Fig. 1Map of global aquaculture production in 2013. Source: Ottinger et al., (2016). Ocean & Coastal Management.

Some effective tools for consulting data related to the aquaculture sector are:

They include datasets on production, trade and consumption. Data can be extracted and aggregated according to different levels of details and international standard classifications.

Threats from the high increase in aquaculture production

The intensification and industrialization of aquaculture has increased the threats to aquatic environments.

Aquaculture production comprises different types of systems. Cages or net pens floating directly in aquatic environments such as lakes, rivers, fjords or in the open ocean (offshore) are an important part in aquaculture production, currently accounting for 63% of total production (!). Fig. 2 and 3 adequately illustrate the main environmental risks of this type of intensive systems in aquatic environments:

Fig. 2Main environmental risks of marine aquaculture. Source: Right from the start: Open-ocean aquaculture in the United States. Ocean Conservancy Report (2011) [4]. Fig. 3: Environmental impacts of open-ocean aquaculture. Source: Hutchings et al., (2012). Environmental Reviews. [5].

Some of the most important ones are:

Release of nutrients to the receiving environment

 This is one of the most important impacts. It is caused by the discharge of nutrients from the feeding and excretion processes of cultured organisms (uneaten food and waste products).

It induces organic enrichment, which decreases oxygen concentration and causes mortality of wildlife. This produces “dead zones” and important alterations in the benthos, the biological communities living at the bottom of aquatic ecosystems. Furthermore, the release of organic and inorganic nutrients can produce microalgae blooms (eutrophication) and imbalances in aquatic food chains. You can see more in this short documentary about the industrial salmon cages in Nova Scotia!

Feed manufacture: fish meal and fish oil

Fish meal and fish oil are the main ingredients contained in aquaculture feed. They are dependent on fisheries and create situations of overfishing and overexploitation of natural aquatic resources. For several years, possible alternative ingredients to be used as feed have been investigated, but on a large scale, this has not yet become a reality. You can go deeper into the alternatives to fish meal by watching Ashild Krogdahl’s lecture (Norwegian University of Life Sciences) during the aquaculture breakout session at the World Nutrition Forum 2016 in Vancouver.

Introduction of invasive species

This is a global reality. Many of the species cultivated in aquaculture do not belong to the ecosystems where they are farmed. This is the case, for example, for the Atlantic salmon (Salmo salar) culture in Chilean fjords. The introduction of invasive species causes the emergence of new diseases in wild populations (parasites and pathogens imported into the aquatic environment). Furthermore, escapes of organisms in open water systems are common, e.g. due to the breakage of nets, human failures or adverse environmental conditions. Consequently, leaks of invasive species into an environment where they do not belong cause a competition for food and habitat thereby increasing the mortality of wild populations and reducing the health of local fauna and flora. In the following documentary from Patagonia Films you can see the impact of salmon aquaculture on Chilean coasts:

Drugs and chemical contamination

Antibiotics, parasiticides, antifouling paints, hormones, pigments, anesthetics, cleaning products and other chemicals flow out of aquaculture cages and can affect wild populations, food webs and the ecosystem in general.

Natural predator control

To protect cultured organisms, aquaculture companies create “predator control programs”. These involve the control and killing of wild organisms such as birds, sharks, or even mammals (such as sea lions), which are often protected species.

Loss of biodiversity

All the above impacts the biodiversity of aquatic ecosystems, which in turn implies considerable risks for the health of the environment and the ecosystem’s balance. A 2019 study by the University of Manitoba (Canada) further determined additional adverse environmental effects of global aquaculture productivity, such as greenhouse gas emissions (GHG), modifications of hydrological patterns, a decline in natural resources, competition for land and water, habitat destruction, mangrove deforestation or biotic depletion (which means the declining of wild fish populations) [6].

The road towards sustainability

Today, many aquaculture production systems and technologies are moving towards a sustainable development by considering the right balance between the environment, the social and the economic sphere. So, let’s see some!

Recirculating aquaculture systems (RAS)

RAS are high-tech systems based on the reuse and treatment of water, through the application of mechanical and biological processes. They are closed systems on land that manage to reduce water consumption and the release of nutrients into the environment [7]. These systems work almost independently from the aquatic environment (some of them only need a 1% change of the total water per day). This allows the control of all water parameters (temperature, oxygen etc.) and offers the possibility to grow any species anywhere in the world, with exceptionally low environmental risks. In contrast, these systems are difficult to manage and entail high technological complications. In recent years, they have become highly relevant. It is estimated that by 2030, more than 40% of the world’s aquaculture production will be generated in RAS. Have a look at how RAS systems work!

Integrated Multi-trophic Aquaculture systems (IMTA)

IMTA systems are based on the cultivation of species of different trophic levels. The trophic level is where an organism is located with respect to those fed by solar energy sources (Fig. 4). A food web starts at trophic level 1 (primary producers) and finish with carnivores or predators at level 5 or 6. All food webs have the same basic levels, but the type and the number of species are very different between ecosystems and aquatic regions.

Fig. 4: A typical marine food web. Source: University of Waikato. Available at: https://www.sciencelearn.org.nz/.

In IMTA systems, the nutrients discarded by the main cultivated species (usually a carnivorous species from the top of the pyramid) are recycled by other groups of organisms from lower levels (bioremediators), i.e. invertebrates (sea cucumbers, sea urchins, polychaetes, molluscs) and plant organisms (macroalgae, microalgae, aquatic plants).

Figure 5 shows a conceptual model for an IMTA system [8]. Small orange dots and orange arrows show the flow and uptake of inorganic dissolved nutrients from the salmon finfish net pen towards the kelp rafts. White arrows show the direction of the water currents within an IMTA system. Green dots and arrows show the flow and uptake of organic particulate nutrients by filter feeders (scallops, mussels) and deposit feeders (sea cucumbers, sea urchins, sea worms). Depictions for organic nutrients are shown for both fine (represented by smaller and lighter green dots) and large (represented by larger and darker green dots) particles.

Fig. 5Conceptual model for an IMTA system. Source: Reid et al., (2020). Reviews in Aquaculture.

This type of cultivation can reduce the environmental impact of aquaculture. But not only that! It also helps to diversify production, allows for an efficient use of resources, reduces economic risks and fosters social acceptance of the activities.

However, such an ideal application of an IMTA system in the aquatic environment is often difficult. At the same time, they are complex systems and depend on species that can live together and feed from  the metabolic discharges of the main species cultivated. The hydrodynamic conditions of the aquatic environment (temperature, pH, salinity or the intensity and direction of waves and tides) and the extent of bioremediation organisms that must be implemented must also be taken into account. As an example, a 2009 study about the environmental impacts and bioremediation systems in Chilean fjords concluded that to mitigate the effect of nitrogen (N) discharges from a salmon farm (producing 1500 tons/year), the implementation of 50-60 Ha of macroalgae (Gracilaria chilensis and Macrocystis spp) is necessary to reduce the 80% of the N released by the salmon farm. And it must be considered that salmon farming occupies only 0.8 Ha [9].

That is why in recent years, IMTA systems have also been incorporated into RAS systems (where discharges are much more controlled than in open systems). Here there is an example of marine polychaetes as bioremediators in marine recirculating aquaculture systems (RAS-IMTA).

Do you want a more visual explanation of IMTA concept? Watch in the following video the IMTA conceptual site fly-through (left), or the Ocean Forest concept (right)!

Organic/ecological aquaculture

Organic aquaculture favors the use of renewable resources, the respect for natural mechanisms for controlling pests and diseases and the management of the generated waste products. It focuses on animal welfare and the use of natural foods.

Organic aquaculture meets the following requirements:

  • Less damage to the aquatic environment
  • Use of pollutant-free water
  • Absence of genetically modified organisms (GMOs)
  • Low culture density
  • Maintenance of typical species behavior
  • Animal health based on prophylactic measures (rather than medication)
  • Use of oxygen to improve animal welfare (not to increase culture density)
  • Feeding from sustainable sources
  • Health guarantees

The organic standards required by the EU Organic Regulation are the legal basis for the control of organic farming and food processing in Europe and regulate how the word ‘organic’ can be used.

Other important practices to bring aquaculture closer to sustainable development are: plans for sustainable extraction of wild juveniles for cultivation, design of containment systems to avoid leaks, the search for sustainable diets with alternative ingredients, sustainable management of waste and spills, biofloc systems, non-use of harmful antifouling products and antibiotics and use of alternative energy sources.

Future perspectives

The rapid development of aquaculture has made it a vital source of human nutrition and contributed to food security. If aquaculture is to become a sustainable method however, the bad practices associated with these activities must be avoided.

The concept of a Blue Economy emerged in 2012 at the Rio + 20 Conference. It involves the sustainable development of aquaculture through ecosystem integrity. It is an innovative, integrated and multi-sectoral approach to managing aquatic resources to obtain the greatest possible amount of ecosystem goods and services through the use of oceans, inland waters and wetlands, while providing social and economic benefits (Fig. 6).

It aims at a coordinated management for inclusive growth that contributes to all three pillars of sustainable development (social, economic and environmental) and to the alleviation of poverty, hunger and malnutrition [10]. In particular, marine ecosystem services (i.e. fishing, tourism, etc.) generate more than 60% of the economic value of the global biosphere. The global community recognizes this value and has increasingly focused its efforts on developing the economic capacity to make use of aquatic ecosystems, and the services they provide, in a sustainable manner.

Fig. 6Potential social, economic and environmental benefits from finfish, shellfish and seaweed production under the Blue Economy of coastal and marine aquaculture. Source: Ahmed & Thompson (2019).

In short, aquaculture has provided the human population with an invaluable source of food, and continues to do so. But it shouldn’t come at any price! It must be strongly regulated and aim at a sustainable development of natural resources if we want to preserve the environmental health of our waters. To conclude, I leave you with this inspiring webinar – Aquaculture and marine conservation: looking for a common challenge? – that took place on June 25, 2020, led by Dr. Raphaëla le Gouvello, an expert in marine conservation working for the International Union for Conservation of Nature (IUCN). It is worth listening to!

What are your thoughts? Should we pursue the road of aquaculture? Let us know in the comment section!

Ressources:

  1. Nash, C. (2010). The history of aquaculture. John Wiley & Sons. 227 pp. Oxford, UK.
  2. FAO Food and Agriculture Organization of the United Nations. The state of world fisheries and aquaculture. In Meeting the Sustainable Development Goals; FAO: Rome, Italy, 2018.
  3. Ottinger, M., Clauss, K., & Kuenzer, C. (2016). Aquaculture: Relevance, distribution, impacts and spatial assessments–A review. Ocean & Coastal Management, 119, 244-266.
  4. Ocean Conservancy. Right from the start: Open-ocean aquaculture in the United States. Ocean Conservancy Report, March 2011.
  5. Hutchings, J. A., Côté, I. M., Dodson, J. J., Fleming, I. A., Jennings, S., Mantua, N. J., … & Weaver, A. J. (2012). Climate change, fisheries, and aquaculture: trends and consequences for Canadian marine biodiversity. Environmental Reviews, 20(4), 220-31.
  6. Ahmed, N., Thompson, S., & Glaser, M. (2019). Global aquaculture productivity, environmental sustainability, and climate change adaptability. Environmental management, 63(2), 159-172.
  7. Zhang, S. Y., Li, G., Wu, H. B., Liu, X. G., Yao, Y. H., Tao, L., & Liu, H. (2011). An integrated recirculating aquaculture system (RAS) for land-based fish farming: The effects on water quality and fish production. Aquacultural Engineering, 45(3), 93-102.
  8. Reid, G. K., Lefebvre, S., Filgueira, R., Robinson, S. M., Broch, O. J., Dumas, A., & Chopin, T. B. (2020). Performance measures and models for open‐water integrated multi‐trophic aquaculture. Reviews in Aquaculture, 12(1), 47-75.
  9. Buschmann, A. H., Cabello, F., Young, K., Carvajal, J., Varela, D. A., & Henríquez, L. (2009). Salmon aquaculture and coastal ecosystem health in Chile: analysis of regulations, environmental impacts and bioremediation systems. Ocean & Coastal Management, 52(5), 243-249.
  10. Ahmed, N., & Thompson, S. (2019). The blue dimensions of aquaculture: A global synthesis. Science of the total environment, 652, 851-861.

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