Chapters 10.8

10.8 - Investing in Aquaculture to Improve Food Security for Subsistence Farmers

Rameen Jafri, University of Guelph, Canada

Suggested citation for this chapter.

Jafri,R. (2022) Investing in Aquaculture to Improve Food Security for Subsistence Farmers, The Encyclopedia for Small Scale Farmers. Editor, M.N. Raizada, University of Guelph, Canada. http://www.farmpedia.org

Background on Aquaculture

Aquaculture is the practice of breeding and harvesting aquatic species in a closed and controlled environment (World Fisheries Trust, 2008; Naylor et al., 2021). Aquaculture has existed for thousands of years, with the earliest recorded instances in First Nations’ clam gardens, and the introduction of carp to Chinese earthen rice paddies (World Fisheries Trust, 2008). Modern aquaculture techniques, however, are systematic and require deeper knowledge of aquatic life cycles, nutritional and environmental requirements, and species productivity (World Fisheries Trust, 2008).

Globally, fish is not farmed as intensively as other animal proteins. Unlike land animals, fish have a near equal feed-to-body mass ratio (Bourne, n.d). Where cattle require 6.8 lbs of feed to produce one pound of meat, fish only require 1.1 lbs (Bourne, n.d). As they have a lower demand for natural resources, fish populations naturally replenish faster than livestock populations do. As human intervention is not generally required to meet demands, half of the global yield is harvested from the wild, a practice that is depleting wild fish populations (NOAA, 2019).

Among farmed fish, the most common families are the cyprinids and the barbels (stomachless and toothless fish, notably carps and minnows), who make up a quarter of global aquaculture production (Cai et al., 2017). Tilapias and catfish follow, making up 10% of global production collectively. The members of these families are popular choices for aquaculture as they are high value or high producing species, and are relatively low maintenance (Cai et al., 2017). Conversely, salmon and shrimp are high value species but are less common as they require more maintenance (World Fisheries Trust, 2008; Cai et al., 2017). As such, aquaculture represents the opportunity to generate income and decrease reliance on fish imports (World Fisheries Trust, 2008).

Aquaculture in practice

Aquaculture generally comes in two forms: open and closed systems. Commercial aquaculture can be carried out in both, and generally requires labour and machinery to closely monitor water conditions (Lawson, 1995). Importantly, commercial open systems require constant adjustment as the water conditions (nutrient balance, acidity, salinity, etc) can change as the current does. As such, this method tends to be expensive. Commercial or large-scale open systems are typically large nets submerged under water with monitors suspended above the water level. The design and layout differ based on location, water depth/temperature, ecosystem, and fishery specific goals. This method is preferred commercially because the water flowing through the nets removes waste and mitigates disease spread (Lawson, 1995; National Geographic).

Small scale aquaculture (or extensive) is a much less costly form of open system aquaculture, and can be adapted to any location (World Fisheries Trust, 2008). The trade-off is that this method involves heavy reliance on natural feed, thus yields are typically lower. In practice, cow manure is introduced to small lakes and ponds with little water flow. Nutrient cycling within the pond ecosystem will provide food for the few fish growing there, and their feed will consist of zooplankton and insects (special feed is not added). To scale up this method, a process called intensification can occur (where prepared feed is added). However, due to its reliance on nature, adding nutrients in feed can disrupt the cycle and create nutrient imbalance in the ecosystem (World Fisheries Trust, 2008). As such, to increase yields while minimizing costs, a solar pump and biological filter can be added to the system to facilitate movement for treatment and minimize toxicity due to overnutrition (DeLong & Losordo, 2012).

Feed and Nutrition

In aquaculture, feed is chosen depending on the method employed. In open systems, the water is naturally circulated and already contains some nutrients (Craig & Helfrich, 2017). As such, supplemental feed is used to compensate for any nutritional deficiencies that may be inhibiting fish development. In closed systems, water is treated and cleaned prior to circulation. As the fish cannot freely forage, they must be provided a complete diet. Complete feeds typically contain 18-50% protein, 10-25% fats, and 10-25% carbohydrates. The exact amounts depend greatly on the fish species and its developmental stage. Additionally, the feed must contain all the micronutrients (vitamins and minerals) that the organisms require for healthy development.

Of the macronutrients in fish feed (both supplemental and complete), protein tends to be the most essential (and expensive) component (Craig & Helfrich, 2017). As a result, fish meat is a good source of protein. Carp, tilapia, and salmon contain between 23-26 g protein per 100 g (FoodData, 2019). Generally, carnivorous fish tend to have higher protein requirements than herbivorous and omnivorous fish like carp and tilapia (Craig & Helfrich, 2017). As such, carnivorous fish are less commonly farmed. Additionally, fish in their early developmental stages have higher protein requirements than mature fish do. Of the amino acids in most feeds, lysine and methionine are most commonly supplemented as plant proteins in the feed (soybean based especially) lack them. Fish have high protein requirements because they excrete ammonia (NH3) as a waste product, which can cause them to lose up to 65% of their nitrogen to the environment (Craig & Helfrich, 2017).

Environmental Sustainability and Waste Management

The ammonia compound equilibrates between two forms, ammonia (NH3) or the ammonium hydroxide ion (NH4+) (EPA, 2021). The form it takes depends greatly on the water temperature and acidity. In warmer water and in basic (high pH) conditions, the compound tends to exist as NH3. In high concentrations, this form can be toxic to aquatic life. When the concentration is high, it is difficult for aquatic species to excrete excess ammonia, so it builds up in their muscles and blood, eventually killing them. Additionally, high concentrations of ammonia can also promote the growth of nitrogen-fixing bacteria and algae in the water, which reduces the dissolved oxygen content. This suffocates other aquatic species that are competing for the oxygen (EPA, 2021).

Due to the undesirable effects of excess ammonia in aquatic systems, it is essential to manage nitrogen levels. Two general methods for managing the excess nutrients in wastewater are irrigation and treatment. Nitrogen is an essential nutrient for plant growth because plants cannot fulfill their life sustaining functions (like creating food) without it (Raizada, 2017; EPA, 2021). As such, ammonia rich water can be a good source of valuable nutrients (EPA, 2021). This principle is adopted in a branch of aquaculture called aquaponics. In commercial aquaponics, plants are suspended above the water level in grow beds, with roots free floating in the nutrient rich water (USDA, 2016). This method of gardening is soilless. In practice, the aquaculture water is drained into a reservoir with nitrifying bacteria that will convert the ammonia into nitrates which are essential for plants. The nitrate rich water is then pumped directly into the grow beds where the nutrients are depleted by the plants and cycled back into the aquaculture (USDA, 2016). This closed system is preferred in drier regions where water is scarce. Low-commitment open system waste management could simply be pumping the water directly into soil where plants are grown. This method would promote plant growth but can cause nutrient leaching into underground reservoirs and can be expensive as water removed from the aquaculture would constantly need to be replenished (Raizada, 2017; USDA, 2016).

The second water treatment method is significantly less labour intensive and may be favoured in early aquaculture stages. This method takes advantage of Nitrosomonas and Nitrobacter bacteria families (DeLong & Losordo, 2012). Nitrosomonas convert ammonia (NH3) into nitrite (NO2), while Nitrobacter converts the nitrite into nitrate (NO3). Biological filters compactly house these bacteria on a non-corrosive material (plastic, fibreglass, ceramic, rock) with a large surface area. The medium is arranged in stacked sheets where water can flow through to be treated. Biological filters rely on natural processes that are not mechanized; energy is only inputted in pumps that facilitate water circulation through the filter. As such, this method tends to be slower and less suitable for large scale commercial water treatment. Unlike other types of filters, biological filters require little initial investment. To start one, a medium (non-corrosive filter), a pump, and small amount of ‘starter’ bacteria are required. The bacteria can be added onto the filter and added into the reservoir. Soon after their introduction, they will colonize the biofilter and treat the water. Importantly, starter bacteria can be sourced from an existing system or from the wild. Both sources can potentially introduce pathogens into the system and should be carefully evaluated before adoption (DeLong & Losordo, 2012).

In its simplest form, aquaculture can just be a carp or tilapia pond. Adding a biological filter and solar powered pump are two low cost and effective ways to provide ideal conditions for fish development while improving yields. For a long-term operation, pH testing strips (litmus paper) and nutrient testers are important tools to monitor conditions (USDA, 2016). Electrical conductivity (EC) readers are used to monitor dissolved nutrients and salinity, but tend to be very costly (USDA, 2016; Opiyo et al., 2018). However, a single device can be shared amongst nearby farmers to down-average the cost (Raizada, 2017; Opiyo et al., 2018). Small-scale aquaculture practiced like this does not require much equipment and is relatively low risk (Opiyo et al., 2018). As the project scale and income increase, more expensive testing equipment and more efficient filters can be purchased to further increase yields. However, the system is fully functional with the limited, inexpensive equipment mentioned above.

Economic Prospects

In Sub-Saharan Africa, small-scale aquaculture makes up 95% of the aquaculture industry (Machena & Moehl, 2001). In this form, fish are harvested from small lakes or ponds (closed systems) and rely on family/community labour. Small-scale aquaculture is not mechanized and does not require special machinery. In practice, it only requires a clean body of water, nutritious feed, and healthy baby fish (fingerlings). This method is suitable for family and small community use, but does not capitalize on the Sub-Saharan climate that favours a year long growing season, and the region’s underutilized water stores (Machena & Moehl, 2001).

Aquaculture can take many forms, and design is heavily dependent on environmental conditions and resource availability (World Fisheries Trust, 2008). Regions with long monsoon seasons may favour open system aquaculture as rainwater can be used to replenish aquaculture, and semi-arid regions may favour closed system aquaculture as water is scarce (World Fisheries Trust, 2008; Shava & Gunhidzirai, 2017). In either case, a little investment in infrastructure can increase yields and stimulate the local economy (Opiyo et al. 2018). As the industry is so underexploited, the demand for aquatic products greatly exceeds the supply. As such, the products are high value and can serve as a low-commitment additional income source for subsistence farmers.

Conclusions

The aquaculture industry in many developing nations is severely underexploited, largely due to lack of government financial support and investment (KMAP, 2019). In countries where it has been adopted, it has failed almost solely due to lack of farmer connections to feed suppliers, lack of transport routes to consumers and retailers, and insufficient training. As such, government support to subsidize the costs for feed and enable access to healthy fingerlings would greatly increase yield which could support the local economy as a high value product; alternatively, the fish could be consumed to alleviate nutritional deficiencies (KMAP, 2019). Importantly, as populations grow, demand for protein does as well (Naylor et al., 2021). As such, young children and pregnant women are increasingly unable to acquire the nutrients they need for healthy development (Naylor et al., 2021).

There is considerable potential for economic growth, environmental conservation, and nutritional supplementation by adopting aquaculture in rural areas (Opiyo et al. 2018). Aquaculture represents a low maintenance, low commitment, and profitable venture for subsistence farmers around the world (Naylor et al., 2021). By removing physical capacity from the economic equation, aquaculture can promote gender equality and empower women (Raizada, 2017).

Practical Resources to Get Started

Purdue Aquaponics: Cut Water Usage https://www.youtube.com/watch?v=26xpMCXP9bw Overview of aquaponics (focus on natural resource consumption)

Aquaponics - How To Do It Yourself! https://www.ncrac.org/video/aquaponics-how-do-it-yourself Video, walks through practical applications and benefits of aquaponics

Aquaculture Systems - A Basic Overview https://www.youtube.com/watch?v=8pMxhXdrEo8 Video, provides information on subsets and different forms of aquaculture

How to start fish farming in Zimbabwe https://www.youtube.com/watch?v=6qE3KtmnWIc Small scale aquaculture details specific to those in rural areas

Botswana Fish Farming (Aqua Culture) https://www.youtube.com/watch?v=Bdv2HI72zgg A large scale commercial aquaculture in Botswana

Marine Nutrient Cycle and Energy Flow https://www.youtube.com/watch?v=G1yPrfDaijE Provides overview with images of nutrient cycling and impacts on aquatic life

References

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