Chem321:Aquaponics
This is the 2013 paper by Tom Fuchs. Aquaponics
The global production and sale of fish is an often over-looked issue in discussions regarding sustainable business practice. Fish stock in the world will play a pivotal role in our future as populations grow and wealth reaches more segments of the global population. According to the Food and Agriculture Organization (FAO) of the United Nations, fish provides 3 billion people globally with almost 20% of their intake of animal protein, and from the 1960s to 2009 average per capita food fish consumption in the world has increased from 9.9kg to 18.4kg (FAO 2012). Increases in fish demand due to growing wealth in mainland China has had a significant impact on this change. As global populations continue to grow, the sustainable production of fish for human consumption must be carefully watched. Problems associated with overfishing and wasteful aquaculture practice must be carefully monitored and procedural changes must take place so that the fish can continue to serve as a viable source of animal protein for generations to come. One example of a promising new technology in fish-stock production is a method of fish farming known as aquaponics. This is a system which intertwines the management of resources and waste in fish farming with the growth of crops via hydroponics – thus reducing harmful wastes associated with traditional fish farming. As scientific inquiries continue to optimize this burgeoning technology, our chances of producing fish sustainably for generations to come will grow.
Overfishing, or the catching of fish faster than the rate of reproduction, is a significant problem faced by ecosystems affected by today’s global economy. United Nations reports suggest that commercial fish populations of cod, hake, haddock, and flounder in the Atlantic region have fallen by as much as 95% in the last decade alone (United Nations 2004) and that over 70% of the world’s fish species are either fully exploited or depleted (FAO 2012). Other reports suggest that global fishery catch is operating at 2.5 times a level considered to be sustainable (Monterey Bay Aquarium).
Other foreshadowing trends have been observed, such as the declining rates of fish catches across the globe. Although new technologies such as GPS tracking allowed fisheries to increase rates of fish catch for a long time, in many places peak rates of catches were reached many years ago. Total fish production had declined continuously in the Northwest Atlantic, Northeast Atlantic, and Northeast Pacific temperate fishing areas from the early and mid-2000’s to around 2010 (FAO 2012). Rates of fish catches in the Mediterranean Black Sea have been declining by 15% since 2007, and in the Southwest Atlantic an even more significant trend has been observed since 2007, reaching as much as a 30% decline (FAO 2012). It is also worth mentioning that the destruction of fish populations does not only affect fish. The depletion of populations of large fish and the subsequent depletion of populations of fish lower on the food web can have pervasive effects on the surrounding ecosystems and forms of life, such as seabirds and marine mammals (Monterey Bay Aquarium). Marine fishing historically has been carried out unsustainably, as seen in examples such as the collapse of the New England Cod industry (Monterey Bay Aquarium), and continues to be practiced at rates which cannot be supported indefinitely by natural ecosystems.
In the wake of growing demands for fish and slowing rates of catch in fisheries, the production process of fish farming, also referred to as aquaculture, has grown dramatically since the 1970’s. In the last three decades alone, world fish production for human consumption through aquaculture has expanded by almost 12 times (FAO 2012). This growth in aquaculture production is majoritively a result of the growth of the industry in Asia and especially China. In 2010, global aquaculture fish production reached an all time high of almost 60million tons, 60% of which occurred in China (FAO 2012).
Aquaculture growth seems like a very good solution to the problems associated with overfishing. With the growth of aquaculture it would seem that we are no longer depending on the naturally growing populations of fish in large bodies of water. Fish farming appears to give us control over the amount of fish we produce and helps us to meet the growing demands of increasing national populations. Despite the glowing allure of a seemingly limitless production process, there are shortcomings of the aquaculture industry which have not been adequately addressed since the explosion of its popularity. Fish farming was the low hanging fruit grabbed to solve a problem of increasing demand for seafood – and there are better alternatives, despite being harder to reach.
One major problem associated with the aquaculture industry is the use of fishmeal for the production of carnivorous species. A large afferent feedstock used for the production of farmed carnivorous species of fish is fishmeal. Fishmeal, at least in part, is actually produced from the remains of smaller fish which are caught in fisheries (Goldburg et al., 2005). This implies that the production of farmed fish actually requires vast inputs from protein derived from natural ecosystems. The use of small fishery caught fish as feed for aquaculture production may contribute to the depletion of natural aquatic resources – which is already under tremendous stress. For instance the two most popular farm-raised fish in the United States are salmon and tilapia, both of which are carnivorous species commonly raised using fishmeal (Virgin Islands Aquaponics Institute).
Additional concerns regarding fish feed used for production in aquaculture arises following the analysis of dangerous contaminants found in farm-raised fish. A study published in 2004, examining the contents of over 2 tons of farm-raised salmon and wild salmon, showed that farmed-raised salmon in Northern Europe, North America, and Chile had significantly higher concentrations of organochlorine contaminants when compared to wild salmon (Hites et al., 2004). An example of an organochlorine that is commonly known is DDT, famed for its disastrous use as a pesticide. Other examples include dicofol, cyclodienes, and aldrin. This difference in concentration of potentially harmful substances may be a result of improper regulation of the development and use of fishmeal. It is worth mentioning though, that concentrations of beneficial fatty acids are significantly higher in farmed salmon than in wild (Foran et al., 2005), and although regulation of fish feed is not at its current best, the United Nations FAO recently launched the Southeast Asia Fisheries Improvement Project (FIP). This project is aimed at regulating the fish feed industry in Southeast Asia, which is a large producer of feed for fish farmed globally (Aquaculture Stewardship Council). Projects such as this will help lead us into an era of more sustainable fish feed production.
More problems associated with the fish farming industry arise due to the unsustainable production and disposal of waste. Aquaculture systems produce continuous wastes associated with fallen feed, excretion, and respiration. Components of such waste include phosphorus, carbon, and nitrogen (Wu 1995). The nitrogen waste is often found in the form of ammonia (Rakocy et al., 2011). At high concentrations, ammonia can be toxic – reacting with water to produce ammonium hydroxide, which is corrosive and can cause cell damage (New York State Department of Health). This can be a concern for those working at aquaculture ponds, though should not be considered a risk for the average person.
The environmental impact of fish-farming depends on many variables, including species, stock density, feed type, and the hydrography of the site (Wu 1995). In general, the largest measured effects from waste of caged fish have been the result of high pollution loading of organics and nutrients such as carbon, nitrogen, and phosphorus. Of the feed input into the culture system, 23%, 21%, and 53% of each of these elements respectively are found to have accumulated in the bottom of sediments to an area usually confined to about 1 kilometer (Wu 1995). The organic matter which settles on the sea bed leads to the development of anoxic conditions. Sediment oxygen demands have been found to be up to 5 times higher than control and total metabolism is reported to be 10 times higher than control (Wu 1990a, & Holmer et al., 1992). The anoxic conditions produced and increased nutrient levels may have negative effects on the biodiversity of the surrounding area and on bodies of water as it breaches the natural capacity for those bodies of water to assimilate the waste. For instance, a study published in 2000 showed that macrofaunal communities in the Mediterranean were affected up to 25 meters away from the site of fish farming cages, often reflecting reduced biodiversity. These changes, however, varied from site to site (Karakassis et al., 2000). In addition to the effects of waste from fish farming on the biodiversity of the area, antibiotics used in fish farms have reflected changes in levels of antibiotic resistant bacteria. For instance, up to 100% of exytetracycline-resistant bacteria have been observed in marine sediments near fish farms following medication (Torsvik et al., 1988), a resistance which persists for more than 13 months after treatment (Samuelsen et al., 1992).
Experiments in more sustainable designs for aquaculture sites have been yielding quite promising results. One example of a more sustainable aquaculture practice, which will be discussed less here, is that of the integration of rice paddies with aquaculture plants. Because aquatic animals traditionally are found living within rice paddy ecosystems, this practice is actually quite ancient in its use in Asia and only recently has become a more directed scientific endeavor (Martin 2005). The success of a system like rice paddy aquaculture is due to the ecological interactions between the vegetative growth, pond bacteria, and aquatic animals.
This sort of sustainable ecological interaction between fish, bacteria, and vegetation is exactly what allowed for the development of the system of aquaponics. The word aquaponics is a reference to the joint use of both aquaculture and hydroponics in a cyclic ecological/industrial system for the production of both fish and vegetation. Hydroponics is a plant growth system which does not require soil. Water is cycled past the roots of plants to provide continuous and controlled delivery of nutrients such that water is highly conserved and plant growth can be optimized. This is all carried out in greenhouse temperature controlled environments such that plants can be grown within the confines of climate areas which would normally not sustain the growth of the selected plants (Rakocy et al., 2011).
In an aquaponics system, the waste produced by fish excrement and feed sediment is run through the roots of plants stemmed in gravel following aerobic bacterial breakdown of the toxic ammonia buildup. The bacteria convert the nitrogen containing ammonia to nitrites which is then converted to nitrates by micro-organisms on plant roots and rock surfaces. The nutrients found in the water from the fish-feed sediment and fish excrement then act as fertilizers, helping to enable the growth of the plants – and in conjunction the gravel and plants provide a natural filtration process for the water running through. Notably though, the plant growth still requires that the water be supplemented with calcium, potassium, and iron (Rakocy et al., 2011). The plants that grow through this hydroponic system, such as vegetables, herbs, or flowers, can then be sold for additional revenue. The removal of wastes from the water thanks to the bacteria and plant growth allows for the water to be re-cycled back to the fish ponds (Rakocy et al., 2011). The water is commonly returned to the fish ponds via waterfall so that oxygen can be resupplied to the water prior to its return to the fish. With these systems, the sludge which settles at the bottoms of the fish ponds is frequently vermicomposted. This means that the sludge is introduced to various worms so that it may be converted to a nutrient rich organic fertilizer which can then be used in other sectors of plant growth (Virgin Islands Aquaponics Institute).
The primary benefit of the aquaponics system is that it is closer to a closed system than any other form of fish production. Instead of introducing more waste to external ecological systems, all the wastes produced by the fish-feed and fish excrement are converted to useful forms and re-used for the viable growth of plants and vegetables. In addition to this immense benefit, there are a wide range of other benefits to the aquaponics system which allows for it to be a more sustainable alternative to other fish production systems. The controlled temperature environments of the greenhouses, often through use of finned-coil heat exchangers, allow for these systems to be viable in a range of otherwise unviable locations – and can allow for the continuous growth of fish in more temperate environments despite changes in climate from season to season (Lund 2006). Additionally, a very small space is required for an aquaponics greenhouse. The most efficient designs have consisted of connected structures of greenhouses, each covering 0.5 to 1.0 acres (Lund 2006). This small size allows for aquaponics systems to have a future in local production of fish in both rural and urban environments. If aquaponics systems are brought closer to the cities they are providing meat for, then financial and environmental costs of transportation can be greatly reduced, such as the cost of oil and the effects of greenhouse gas emissions.
A significant pitfall and criticism for an aquaponics system is that when producing carnivorous fish such as salmon and tilapia, they still mostly rely on fishmeal to be used as feed. This means that the growth of larger fish in the aquaponic ponds still relies on catches of smaller fish by fisheries in natural ecosystems – and thus potentially contributing to the problems associated with overfishing. This may be addressed in the future through experimental ingenuity such as supplementation of fishmeal with protein-rich plants that are grown within the aquaponic systems themselves. One such example has been attempted where duckweed, a plant with the protein equivalent of commercial fish feeds, was grown by aquaponic methods and then fed back to the tilapia in the ponds. The tilapia was able to grow OK on a diet of duckweed alone and grew better when their feed was supplemented with fish feed (Virgin Islands Aquaponics Institute). Another viable solution to problems associated with overfishing of small fish for use as fishmeal would be to make better use of bi-catch of global fisheries. Reports by the United Nations FAO suggest that 18-40 million tons of bi-catch is killed and discarded each year (FAO 1998). If we are to find methods to utilize bi-catch in the production of fishmeal, then it may provide a sustainable alternative to the use of small fish.
Another important consideration in the use of these small aquaponics systems is that they often provide an extremely confined space for the life and growth of the fish produced. Rearing tanks containing Nile tilapia, in which the fish are cultured for 24 weeks, hold an average of 77 fish for every cubed meter of space, and rearing tanks containing red tilapia average 154 fish for every cubed meter of space (Rakocy et al., 2011). These close quarter environments are certainly far from the natural environments from which these fish are commonly found and it is unlikely that the fish take comfort in these packed ponds. The design and development of future aquaponic systems is an important step towards a more sustainable future in which fish can continue to be provided for human beings – but we must also take into account the ethical concerns raised. Though there is likely an optimal ratio of space used to healthy fish reared, this ratio may not coincide with the rights of the animal to live a life of reduced suffering. It may be very likely that to address the questionable caging of farm-grown fish we will have to accept either a future in which people must limit their animal protein consumption – or pay more for each pound of fish they purchase. As arbiters of the future of our planet and of the future of meat production – it is our duty not only to create food production systems which can sustainably provide for future generations and reduce environmental impacts, but also to create this future in a morally righteous manner. These careful balances present us with a challenge, but not an insurmountable one.
The systems level thinking associated with the development of aquaponics-style fish farming allows for fish producers to maintain business practice which follows the effects of all steps of production. An aquaponics system in which the majority of the waste is either filtered by plant growth or converted to viable soil fertilizer reduces the environmental effects of fish production to a small fraction of its former function. The possibility of then feeding back protein-rich plants grown within the aquaponic system itself to the fish in the rearing ponds opens up new doors for the reduction of feedstock necessary for the growth of commercial fish. This in turn could help us alleviate the stresses of overfishing from marine ecosystems. There is invariably still room for improvement in the design of aquaponic systems – and an increase in the global use of these systems may further push innovation in the field. Overfishing is a legitimate problem which in the long run could vastly reduce the amount of fish available as animal protein for growing global populations and it will take initiatives towards the use of integrated systems such as aquaponics to capably meet the demands of future generations.
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