Farmed fish supply roughly one-third of worldwide seafood consumption, and that number is increasing every day. With a rapidly growing global population, accompanied by a burgeoning demand for food, the farming industry is finding greater utility in aquacultures.
The aquaculture industry, also known as fish-farming, incorporates traditional husbandry with modern technology. Farmed fish are raised in man-made pens or other enclosures in natural bodies of water, where they are bred under controlled conditions governing water quality, nutrition, therapeutics, and prophylactics. Such tactics give farmers the tools to manipulate the environment according to the specific needs of different species of fish. However, while fish farming as a whole may sound like an efficient method of satisfying the global seafood demand, there are various tradeoffs between different types of aquacultures.
The biological process behind aquaculture farming seems simple: feed the fish, the fish grow, harvest the fish, repeat. However, it is necessary to delve deeper, to the atomic level, in order to discover one of the major disadvantages of fish farming. When any organism feeds, waste from the food must be excreted. This waste is generally high in nitrogen and phosphorous molecules. While these elements are usually necessary to sustain an ecosystem, an overabundance of nitrogen and phosphorous will organically pollute the water. Fish farming, which yields water that is highly dense in nutrients, contributes to a phenomenon known as eutrophication.
Eutrophication is a form of bio-pollution whereby a surplus of nutrients from organic waste, above a level of 0.1 mg/L of phosphorous and 25 mg/L of nitrogen, leads to the over-enrichment of a body of water. Aquacultures yield nutrient-dense water, which can be released into neighboring ecosystems. In a healthy ecosystem, these excess nutrients are consumed by zooplankton, bacteria, and bottom filter feeders. However, when this organic matter piles up in excess, these decomposer organisms proliferate and their respiration consumes oxygen. At first, these organisms consume the oxygen in bottom sediments, but then start to seek out higher oxygen stores, creating hypoxic zones, areas low in oxygen. These hypoxic zones can lead to the deaths of benthic organisms (organisms that dwell near the seabed), lower numbers of fish in an environment, impediment of fish migrations, and decreased biodiversity.
To preserve this biodiversity, researchers, environmentalists, and seafood manufacturers alike are working to find an alternative to aquaculture that is both environmentally friendly and economically efficient. Surprisingly, their potential solution to eutrophication lies in farming even more organisms.
While seemingly counterintuitive, this paradoxical proposal involves adopting a new method of fish-farming: integrated aquaculture. Unlike conventional fish farming, Integrated Multi-Trophic Aquacultures (IMTAs) farm multiple species in a way that mimics a natural ecosystem. This practice includes combining traditionally grown fish with extractive species. Extractive species, such as seaweed and shellfish, are able to feed on the nutrients from fish waste and in turn, grow and generate an oxygen-rich environment. In an IMTA, multiple species are cultivated in proximity to each other, allowing waste from one organism to be recycled as food for another.
Application of IMTAs has already found traction in smaller fishing communities in Southeast Asia. The world’s growing seafood favorite, shrimp, is being farmed in Cà Mau, Vietnam through the Mangroves and Markets (MAM) program. The MAM project utilizes a shrimp farming model that integrates shrimp farms into local mangrove forests, which are natural bio-filters. The program has reaped both environmental and economic benefits. MAM has not only employed a sustainable method in farming shrimp, but has fostered the reforestation and protection of species in the mangrove forests. In addition, small-scale Vietnamese shrimp farmers are able to utilize a more efficient farming system, and, through bonuses for their efforts in environmental protection, are able to compete with larger-scale fisheries. Shannon Lim, managing director of a IMTA-based seafood company in Singapore, has said, “[Why spend] $30,000 on stuff [when] a lobster will do it for you?” Many independent fish farmers in Southeast Asia have been able to find success with IMTAs, affirming its ecological and economic boons.
MAM has not only employed a sustainable method in farming shrimp, but has fostered the reforestation and protection of species in the mangrove forests.
While IMTAs have found proponents in small-scale fishermen, they have yet to be fully implemented into larger aquacultures. Opponents of IMTAs argue that while integrated aquacultures seem profitable in theory, the systems cannot be pragmatically implemented on a larger scale. Unlike traditional fish farming methods, IMTAs require a significant amount of planning and engineering. IMTAs must be engineered to maximize the complementing ecological functions of different species. As such, these species must be carefully selected and monitored so that nutrient levels are within the healthy limits. The complexity of integrating species from different species is labor- and skill-intensive. This is an additional financial cost for large-scale fishing companies, mitigating the economic feasibility of integrated aquacultures.
In addition to the economic drawbacks of IMTAs, existing environmental policies do not encourage fisheries to implement IMTAs into their industries. Unlike the fishmongers of Cà Mau, large-scale fisheries are not rewarded through bonuses such as tax benefits and subsidies. Without the assistance of governmental incentives, the fishing industry has no motivation to implement an eco-friendly method of manufacturing. Both voluntary and mandatory actions are necessary to carry out integrated aquaculture systems on a larger scale.
Without the assistance of governmental incentives, the fishing industry has no motivation to implement an eco-friendly method of manufacturing.
Because a majority of IMTAs have only been used in smaller systems, integrated aquaculture is still largely in the developmental stage. Further research is necessary to maximize the potential efficiencies of these systems. A variety of new species are being studied to analyze their possible feeding niches within an IMTA system. Optimized species combinations and species interactions are being researched alongside market demand and commercialized potential of promising aquaculture organisms.
The IMTA system may not be a panacea for the burgeoning global seafood shortage, but its potential towards the solution of eutrophication still remains at the forefront of aquaculture design. At the very least, we can hope that smaller-scale fish farms will help lead the way in promoting integrated aquaculture and discovering new methods in aquaculture sustainability.