Aquaponics, the combination of fish and plant cultivation in recirculating systems, has gained popularity. Now, a newsgroup on the Internet (aquaponicsrequest@townsqr.com — subscribe here) holds regular discussions on various aspects of aquaponics. Starting in 1997, the Aquaponics Journal has been publishing informative articles, conference announcements, and product advertisements on a quarterly basis. Two major suppliers of aquaculture and hydroponic equipment have added aquaponic systems to their catalogs. Numerous school districts have incorporated aquaponics into their science curricula for educational purposes. Additionally, two short courses on aquaponics have been introduced, and while commercial aquaponic operations are still relatively small in number, they are on the rise.
Aquaponic systems are recirculating aquaculture systems that involve growing plants without soil. The purpose of recirculating systems is to raise a large number of fish in small amounts of water by treating the water to eliminate harmful waste products and then reusing it. By reusing the water multiple times, safe nutrients and organic matter accumulate. These by-products can be put to good use by incorporating them into secondary crops that have economic value or provide some benefit to the primary fish production system. Systems that grow additional crops using by-products from the primary species production are known as integrated systems. If the secondary crops consist of aquatic or terrestrial plants grown alongside fish, this integrated system is referred to as an aquaponic system.
Plants in closed recirculating systems receive rapid growth from dissolved nutrients that come from either fish excretion or the breakdown of fish waste by microbes. These systems have minimal water exchange, less than 2 percent, which leads to the accumulation of dissolved nutrients at concentrations similar to hydroponic nutrient solutions. Among these nutrients, nitrogen can reach very high levels in recirculating systems. Fish release waste nitrogen, in the form of ammonia, directly into the water through their gills. Ammonia is then converted by bacteria into nitrite and ultimately into nitrate. While ammonia and nitrite are harmful to fish, nitrate is relatively safe and considered the ideal nitrogen source for the growth of higher plants like fruiting vegetables.
Aquaponic systems have a number of benefits. Plants in these systems retrieve dissolved waste nutrients, which reduces the amount of waste discharged into the environment and extends water usage by removing nutrients through plant uptake. This, in turn, decreases the need for water exchange, ultimately reducing costs in arid climates and heated greenhouses where water or heated water is a major expense. Additionally, the presence of a secondary plant crop that obtains most of its necessary nutrients at no cost improves the system’s potential for profitability. With the daily application of fish feed, plants receive a consistent supply of nutrients, eliminating the need to discharge and replace depleted nutrient solutions or adjust nutrient solutions as in hydroponics. The plants also remove nutrients from the culture water, negating the necessity for separate and pricey biofilters. Furthermore, aquaponic systems require less monitoring of water quality compared to separate hydroponic or recirculating aquaculture systems. There are also cost savings in shared operational and infrastructural expenses like pumps, reservoirs, heaters, and alarm systems. Additionally, the intensive and integrated production of fish and plants requires less land than ponds and gardens. However, aquaponic systems do require significant capital investment, moderate energy inputs, and adept management skills. In order to be profitable, niche markets may be necessary.
System Design
Aquaponic systems are designed similarly to recirculating systems. However, aquaponics includes a hydroponic part and may not have a separate biofilter or foam fractionators to remove fine and dissolved solids. If aquaponic systems are built according to the recommended design ratio, the levels of fine solids and dissolved organic matter typically do not require foam fractionation. The key components of an aquaponic system consist of a fish-rearing tank, a component to remove settleable and suspended solids, a biofilter, a hydroponic part, and a sump.
In order to reduce organic matter in the fish-rearing tank, the effluent is treated initially. This treatment focuses on removing settleable and suspended solids. Following this, the culture water undergoes treatment to eliminate ammonia and nitrate through a biofilter. Subsequently, the water flows through the hydroponic unit where plants absorb certain dissolved nutrients, and bacteria that grow on the sides of the tank and the underside of the polystyrene sheets remove additional ammonia and nitrite through fixed-film nitrification. Ultimately, the water is collected in a reservoir known as a sump and then returned to the rearing tank. The location of the sump may vary. If elevated hydroponic troughs are utilized, the sump can be positioned after the biofilter. In this scenario, water would be pumped up to the troughs and then flow back to the fish-rearing tank by gravity.
It is possible to configure the system in a way that redirects a portion of the flow to a specific treatment unit. For instance, after removing solids, a small side-stream flow can be sent to a hydroponic component, while the majority of the water goes through a biofilter and back to the rearing tank.
By incorporating plant support media such as gravel or sand, the biofilter and hydroponic components can be merged together. If the plant production area is sufficiently large, raft hydroponics, which involves using floating sheets of polystyrene and net pots for plant support, can also serve as an effective biofiltration method. The combination of biofiltration and hydroponics is advantageous in aquaponics as it eliminates the need for a separate biofilter, reducing costs. Alternatively, a different design integrates solids removal, biofiltration, and hydroponics within a single unit. The hydroponic support media, such as pea gravel or coarse sand, serves the dual purpose of capturing solids and providing surface area for fixed-film nitrification. However, it is important not to overload the unit with suspended solids when using this design approach.
Fish Production
Tilapia is the fish species that is most commonly cultured in aquaponic systems, although channel catfish, largemouth bass, crappies, rainbow trout, pacu, common carp, koi carp, goldfish, Asian sea bass (barramundi), and Murray cod have also been used in some aquaponic systems. However, it is mostly tilapia that is used in commercial systems. Most freshwater species, including ornamental fish, can thrive in aquaponic systems as they can tolerate crowded conditions. However, hybrid striped bass is known to perform poorly in these systems due to their intolerance towards high levels of potassium, which is often added as a supplement to promote plant growth.
What Are The Best Fish For A Small Aquaponics System?
When considering the best fish for aquaponics, it is advisable to choose small species that will not outgrow the tank as they mature. By selecting small fish that do not grow excessively, you can prevent overcrowding in your fish tank. Here are a few small fish species worth considering for your small aquaponic system.
Tetra fish are to be thought of in a step-by-step manner.
The tetra fish is a popular and diverse type of freshwater fish, with many different species such as Diamond, cardinal, rainbow, bloodfin, emperor, lemon, ember, and neon tetras. They can grow up to 2.5 inches in length and are best suited for medium-capacity tanks. They typically do not get along well with other fish species. Tetra fish can survive in water with pH levels between 5 and 8, and prefer warmer temperatures ranging from 68F to 82F. They are not edible and are valued solely as pet fish. One of the benefits of having tetra fish is how easy they are to raise and breed.
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The ideal choice for a small aquaponics system is the guppy fish, which is known for its resilience and ability to thrive in various water conditions. Guppies come in different species, such as Endler and rainbow guppy, and can be found worldwide, making them easily accessible for aquaponic setups. These fish can tolerate slight changes in temperature and pH, with the ideal range being between 72F to 78F and a pH of 6.7 to 8.5. Guppies typically reach a maximum length of 2.4 inches. While guppies have the advantage of being edible, their small size poses challenges in effectively cleaning their insides.
Goldfish are aquatic creatures belonging to the family Cyprinidae. They are known for their bright colors and are commonly kept as pets in aquariums. Goldfish have a distinct body shape and can be distinguished from other fish species by their large eyes and double tail. They primarily originate from East Asia and have been selectively bred over centuries to develop various color and fin patterns. Goldfish are omnivorous and feed on a variety of foods, including plants, insects, and small crustaceans. They have a relatively short lifespan compared to other fish, typically living for only a few years. Despite their popularity as pets, goldfish require proper care and a suitable aquatic environment to thrive.
Goldfish are ideal for a typical aquaponic system as they produce a significant amount of waste, which provides high nutrients for the plants. Their growth can reach up to 12 inches long depending on the conditions they are kept in, particularly in ponds where they tend to get larger. Goldfish are hardy creatures that can survive in fluctuating environments. To promote their best survival, it is recommended to maintain temperatures between 23oC to 50oC and a pH level ranging from 7 to 8.4. A notable advantage of goldfish is their ability to consume a wide range of fish food, including vegetables.
What Are The Best Fish For A Large Aquaponics System?
Below are some of the best fish suitable for large tanks in an extensive aquaponics system.
Tilapia is a type of fish species.
This type of fish is found all over the world and is commonly found in grocery stores and restaurants due to its high edibility. Tilapia can grow up to 8 inches in length and can be easily bred and raised on a small or large scale. They reach maturity at a rapid pace, with a harvestable size of six months. They thrive in temperatures ranging from 80oF to 85oF and in water with a pH level of 6 to 9. Tilapia are resilient creatures that can tolerate changing environments, making them ideal for aquaponic systems. One advantage of tilapia is their rapid reproduction, making them suitable for larger hydroponic systems. However, a downside of keeping them is that they require warmer temperatures.
Catfish are a type of fish that are known for their long, whisker-like barbels. They are commonly found in freshwater environments and are known for their scavenging behavior. Catfish are adept at locating food sources by their keen sense of smell. They are opportunistic feeders and will consume a variety of prey, including smaller fish, insects, crustaceans, and plant matter. Due to their adaptability and hardiness, catfish are popular among anglers and are often stocked in recreational fishing ponds.
Similar to tilapia, catfish are able to survive in warmer temperatures, but they can also endure colder temperatures. They are able to thrive in temperatures ranging from 65oF to 90oF and in a pH level between 7 and 8. Each catfish requires 8 gallons of water. The diet of catfish consists of proteins, pellets, and homemade fish food. Due to their resilient nature, catfish are capable of surviving in fluctuating temperatures and pH levels. They are relatively easy to raise and breed. Catfish primarily feed at the bottom of tanks, which makes them suitable for larger systems that have ample horizontal space. Their rate of growth is rapid, allowing for harvest at approximately three months of age. A main drawback of catfish is their high demand for protein-rich food. Additionally, their lack of scales makes them more delicate.
Koi, also known as nishikigoi, are a colorful fish species that originated in Japan. They are a type of carp that have been selectively bred for their vibrant colors and patterns. Koi are highly valued and are often kept in ponds or outdoor water gardens as ornamental fish. They require careful maintenance and a well-regulated environment to thrive. Koi can live for several decades and are known for their long lifespan. They are popular among fish enthusiasts and are also seen as a symbol of good luck and prosperity in many cultures.
Koi fish have a long lifespan of up to 30 years and can grow to be over three feet long when fully matured. Their large size makes them a great fit for larger systems. If you have more than five mature koi fish in your aquaponics tank, you will need over 1000 gallons of water. Koi are able to survive in temperatures ranging from 65oF to 78oF and prefer a pH level of 6.5 to 8. They have a varied diet, which can include vegetables along with other fish food. Koi are highly resilient to diseases and can withstand changes in temperature. However, a notable drawback of koi fish is their tendency to produce excessive waste as they age. As a result, regular cleaning is necessary to maintain the efficiency of your system.
In order to make a profit and recuperate the significant investment and operational costs of aquaponic systems, it is crucial to run both the fish and hydroponic vegetable components at maximum production capacity continuously. The critical standing crop, which refers to the maximum amount of fish biomass a system can support without impeding fish growth, must be maintained in order to efficiently utilize space, optimize production, and minimize fluctuations in the daily feed input. There are three methods for stocking fish biomass near the critical standing crop: sequential rearing, stock splitting, and multiple rearing units.
Sequential rearing
Sequential rearing is a method that involves culturing multiple cohorts of fish in a single rearing tank. When one cohort reaches the desired size for market, it is selectively harvested using nets and a grading system. Consequently, an equal number of fingerlings are immediately restocked in the same tank. This system presents three challenges: firstly, the periodic harvests cause stress to the remaining fish and may potentially trigger disease outbreaks; secondly, stunted fish manage to avoid capture and end up accumulating in the system, thereby wasting space and feed; finally, maintaining accurate stock records over time is difficult, resulting in a high level of management uncertainty and unpredictable harvests.
Stock splitting
Stock splitting is a technique that involves keeping a high number of fingerlings in a tank and dividing the population in half when the tank is full. This method is used to prevent stunted fish and improve stock inventory. However, this process can be stressful for the fish unless a “swimway” is constructed to connect all the tanks. The fish can be guided into the swimway through a hatch in the tank wall and moved to another tank using movable screens. When swimways are used, estimating the exact number of fish in each population becomes challenging because they cannot be weighed or counted. An alternative approach is to use screens to crowd the fish and then pump them to another tank with a fish pump.
Multiple rearing units
The entire population is transferred to larger rearing tanks when the initial tank reaches the critical standing crop. This can be done by herding the fish through a hatch between adjoining tanks or by using “swimways” that connect distant tanks. Multiple rearing units typically consist of two to four tanks and are connected to a shared filtration system. Once the largest tank is harvested, the remaining groups of fish are moved to the next largest tank, while the smallest tank is restocked with fingerlings. Another variation of the multiple-rearing unit concept involves dividing a long raceway into compartments with movable screens. As the fish grow, their compartment is expanded and moved closer to one end of the raceway where they will eventually be harvested. It is important for these compartments to be cross-flow raceways, with influent water entering through a series of ports on one side and effluent water exiting through a series of drains on the other side. This ensures that the water quality remains consistently high throughout the raceway.
One alternative approach involves using multiple tanks that are of equal size. Each tank is dedicated to a specific age group of fish and remains stationary throughout the production cycle. While this system may not efficiently utilize space during the initial growth stages, it offers the benefit of uninterrupted fish growth and eliminates the need for labor in fish movement.
Solids
It is necessary to remove most of the fecal waste produced by fish before it enters the hydroponic tanks. Other sources of particulate waste in the system include uneaten feed and organisms like bacteria, fungi, and algae. If this organic matter builds up in the system, it will decrease levels of dissolved oxygen (DO) as it decomposes, resulting in the production of carbon dioxide and ammonia. If there are deep deposits of sludge, they will decompose without oxygen and release highly toxic gases such as methane and hydrogen sulfide, which can harm fish.
Suspended solids play a significant role in aquaponic systems. When these solids enter the hydroponic component, they can accumulate on plant roots, creating anaerobic zones that hinder nutrient uptake through active transport, which relies on oxygen. Nonetheless, some accumulation of solids can be advantageous. As microorganisms decompose these solids, they release inorganic nutrients crucial for plant growth into the water, a process known as mineralization. Mineralization provides various essential nutrients. When there aren’t enough solids for mineralization, more nutrient supplementation is necessary, increasing the system’s operating expense and management complexity. However, it may be feasible to minimize or eliminate the need for nutrient supplementation by increasing fish stocking and feeding rates relative to plants. Additionally, solids have the benefit of generating microorganisms that decompose them, which are antagonistic to plant root pathogens and contribute to maintaining healthy root growth.
Solids Removal
The primary factor in determining the suitable device for removing solids in a specific system is the organic loading rate, which includes the daily feed input and feces production. The plant growing area is of secondary importance. If the system has a high organic loading due to a large number of fish compared to the plant growing area, it is advisable to use a highly efficient solids removal device like a microscreen drum filter. This filter captures fine organic particles and removes them from the system through backwashing after a few minutes. In this setup, the dissolved nutrients from the fish or the mineralization of very fine particles and dissolved organic matter could sufficiently nourish the plants. On the other hand, if there are only a small number of fish relative to the plant growing area, solids removal may not be necessary as more mineralization is required to produce enough nutrients for the plants. However, it is crucial to prevent the accumulation of unstabilized solids on the tank bottom, as it can result in the creation of anaerobic zones. To address this issue, a reciprocating pea gravel filter can be used. This filter is designed with flood and drain cycles, spreading incoming water evenly over the entire gravel bed surface. It ensures that solids are distributed evenly in the gravel and are exposed to high levels of oxygen (21 percent in the air compared to 0.0005 to 0.0007 percent in fish culture water) during the drain cycle. This promotes microbial activity and increases the rate of mineralization.
Biofiltration
The removal of ammonia, a waste product excreted by fish through their gills, is a major concern in aquaponic systems. If not removed, ammonia will accumulate and become toxic. The process of nitrification, also known as biofiltration, is used to remove ammonia. During this process, ammonia is first oxidized to nitrite, which is toxic, and then to nitrate, which is less toxic. Two groups of bacteria, Nitrosomonas and Nitrobacter, facilitate this two-step process. These nitrifying bacteria grow as a film, known as biofilm, on the surface of inert material or adhere to organic particles. Biofilters, which contain media with a large surface area, are used to support the growth of nitrifying bacteria. Various substrates such as sand, gravel, shells, or plastic media have been used in aquaponic systems for biofilters. For optimal performance, biofilters require a temperature range of 77 to 86 F, a pH range of 7.0 to 9.0, saturated dissolved oxygen (DO), low biological oxygen demand (BOD) of less than 20 milligrams per liter, and a total alkalinity of 100 milligrams per liter or more. Nitrification is an acid-producing process, so an alkaline base must be added regularly to maintain a stable pH, depending on the feeding rate. It is necessary to remove dead biofilm to prevent media clogging, water flow issues, decreased DO levels, and reduced biofilter performance.
Pest and Disease Control
The use of pesticides to control insects on aquaponic plant crops is not recommended. Even if the pesticides are registered, they would still pose a threat to fish and would not be allowed in a fish culture system. Similarly, the use of therapeutants to treat fish parasites and diseases should be avoided because vegetables have the potential to absorb and concentrate them. The common practice of adding salt to treat fish diseases or reduce nitrite toxicity is harmful to plant crops. Instead, nonchemical methods of integrated pest management should be employed. These methods include utilizing resistant cultivars, predators, pathogens, antagonistic organisms, physical barriers, traps, and manipulation of the physical environment. Enclosed greenhouse environments offer more opportunities to implement biological control methods compared to exterior installations. For instance, parasitic wasps and ladybugs can be utilized to effectively control white flies and aphids.
Crop production in aquaponic systems is made more challenging by the prohibition on the use of pesticides. Nonetheless, this restriction guarantees that crops grown in aquaponic systems will be produced in an environmentally friendly manner and will be free from pesticide residues. One significant benefit of aquaponic systems is that crops are less vulnerable to soilborne diseases. The plants cultivated in aquaponic systems may possess a higher resistance to diseases that commonly affect plants in traditional hydroponics. This increased resistance may be attributed to the existence of organic matter in the culture water, creating a stable growing environment that harbors a diverse array of microorganisms, some of which may actively combat plant root pathogens.
