The recognition of the benefits of aquatic food for human nutrition and health, and its role in future sustainable diets, is dependent on the global aquaculture sector’s contribution towards increasing the quantity and quality of fish supplies by 2030. This growth should not only involve increasing production and diversity of species but also the diversification of systems. It is important to highlight that fish from aquaculture has only recently become a topic of discussion in food security and nutrition debates and future strategies and policies, underscoring its importance in preventing malnutrition in the future due to its protein, unsaturated fat, mineral, and vitamin content. Many African nations are increasingly promoting aquaculture to address their current and future food production challenges. Even in Europe, there is a current lack of self-sufficiency in fish supply, with an unbalanced domestic supply and increasing dependence on imports. Therefore, it is imperative to prioritize the successful and sustainable development of global aquaculture for both global and European economies. The concept of sustainability encompasses environmental acceptability, social equitability, and economic viability. Aquaponic systems offer a sustainable solution by combining animal and plant production systems in a cost-efficient, environmentally friendly, and socially beneficial manner. Staples and Funge-Smith define sustainable development as the equilibrium between ecological and human well-being, and it is only recently that an ecosystem approach is being recognized as a key area for research in the case of aquaculture.
Aquaculture has experienced significant growth over the past 40 years and is considered a promising solution for meeting future global food demands. Global aquaculture production is increasing at an annual rate of 6%, and it is projected to account for 63% of worldwide fish consumption by 2030, with a population estimate of nine billion by 2050. In Europe, this growth is expected not only in the marine sector but also in terrestrial production. However, several challenges need to be addressed for the continued development of aquaculture. These include reducing the use of antibiotics and other treatments, improving aquaculture systems and equipment efficiency, diversifying fish species, and promoting sustainable practices in feed production and utilization. There is also a need to shift away from fishmeal in feed and address the issue of “fish-in-fish-out” ratios. Efforts have been made since the 1960s to promote sustainability in the aquaculture sector, including the development of more sustainable feed formulas, reducing feed waste, and improving feed conversion ratios. While aquaculture is recognized as a more efficient animal production sector compared to terrestrial animal farming, there is still room for improvement in terms of resource efficiency, species diversification, and adopting an ecosystem approach that considers biological potential and environmental and societal factors. To support the anticipated growth of aquaculture, there will be a need for increased feed production. Approximately three million additional tons of feed will be required annually by 2030. Research into replacing fishmeal and fish oil with plant-based and terrestrial alternatives for animal feed formulas is also necessary.
The animal and aquafeed industries are a part of the global production sector, which is also the main focus of future development strategies. According to Alltech’s annual survey, the total animal feed production surpassed 1 billion metric tons in 2016, representing a 3.7% increase from the previous year despite a 7% decrease in the number of feed mills. In terms of production, China and the USA dominated the industry and accounted for 35% of the world’s total feed production. The survey further reveals that the top 10 producing countries possess more than half of the world’s feed mills (56%) and contribute to 60% of the total feed production. This concentration in production makes aquafeed production susceptible to global market volatility as many key ingredients used in commercial aquaculture feeds are internationally traded commodities. For instance, the price of fishmeal is projected to double by 2030, while fish oil is expected to increase by over 70%. This highlights the significance of reducing the reliance on these ingredients in fish feed and increasing interest and focus on new or alternative sources.
While there have been advancements in the development of offshore platforms for aquaculture production, there is also a significant focus on marine and freshwater recirculating aquaculture systems (RAS). These systems are preferred because they use less water per kg of fish feed, resulting in increased fish production and reduced environmental impacts associated with aquaculture, such as decreased water usage. RAS can also be integrated with plant production in aquaponics systems, which can easily fit into local and regional food system models and can be practiced in or near densely populated areas. The three major physical inputs for aquaponic systems are water, energy, and fish feed. Approximately 5% of the feed is not consumed by the fish being farmed, while the remaining 95% is ingested and digested. Out of this amount, 30-40% is retained and converted into new biomass, while the remaining 60-70% is released in the form of feces, urine, and ammonia. On a global scale, an average of 1 kg of feed (containing 30% crude protein) releases approximately 27.6 g of N, and 1 kg of fish biomass releases about 577 g of BOD (biological oxygen demand), 90.4 g of N, and 10.5 g of P.
Aquaponics is a fast-growing sector that is well-suited to address various political and socio-economic challenges. These challenges include the need for food security and nutrition, the establishment of self-sufficient regions for fish production, and the focus on global feed production and ingredients in the aquaculture industry. Additionally, there is a push for agricultural innovation that promotes biodiversity and sustainability within the circular economy. Furthermore, there is an increasing demand for locally produced foods. These aspects align with the recommendations of the International Union for the Conservation of Nature, which emphasizes the importance of localizing aquaculture production and implementing a circular approach. This includes the establishment of quality control programs for new products and by-products, as well as processing local fish feed within regions. Aquaponics, specifically small-scale farms, can serve as examples for the implementation of the bioeconomy and local-scale production. It allows for the utilization of organic matter that may not be suitable for other purposes, such as farmed insects and worms, macro- and microalgae, fish and by-product hydrolysates, agro-ecology-produced plants, and locally produced bioactives and micronutrients. This approach helps to reduce the environmental impact and move towards zero waste generation, while still ensuring high-quality food production of fish and plants. Furthermore, aquaponics serves as a multidisciplinary learning platform for sustainable production and the valorization of bioresources, as demonstrated by the ‘Islandap Project’.
Sustainable Development of Fish Nutrition
In order to achieve sustainable development in fish nutrition in aquaculture, it is necessary to address the challenges presented by aquaponics, which is becoming increasingly important for producing high-quality food. One approach to influencing the accumulation of nutrients and reducing the need for artificial and external nutrient supplementation in aquaponics is by manipulating the nitrogen, phosphorus, and mineral content of fish diets. Rakocy et al. suggest that fish and feed waste can provide most of the necessary nutrients for plants if the optimal ratio between daily fish feed input and plant growing areas is maintained. However, the solid fish waste, known as “sludge,” in aquaponic systems results in a loss of approximately half of the available nutrients, especially phosphorus, which could be used for plant biomass production. Limited information is available on this topic. While the goal of sustainability in fish nutrition in aquaculture will eventually be achieved through the use of customized diets, fish feed in aquaponics must currently meet the nutritional requirements of both fish and plants. Increasing sustainability will involve reducing dependence on fishmeal (FM) and fish oil (FO) and incorporating new, low-carbon footprint, high-energy raw natural ingredients. To preserve biodiversity and promote the sustainable use of natural resources, the use of wild fisheries-based FM and FO in aquafeeds should be limited. However, substituting dietary FM with alternative ingredients may alter fish performance, health, and final product quality. Therefore, research in fish nutrition is focused on efficiently using and transforming dietary components to provide the essential nutrients needed for optimal growth performance and sustainable and resilient aquaculture. Replacing FM, which is an expensive but high-quality protein source in fish diets, is not simple due to its unique amino acid profile, high nutrient digestibility, palatability, sufficient micronutrient content, and lack of anti-nutritional factors.
Numerous studies have demonstrated the successful substitution of FM with soybean meal in aquafeeds. However, the presence of anti-nutritional factors like trypsin inhibitors, soybean agglutinin, and saponin in soybean meal restrict its use and hinder its ability to replace FM in large quantities for farming carnivorous fish. Furthermore, replacing FM with plant meals in fish diets at high rates can decrease nutrient bioavailability in fish, leading to changes in the final product quality. Consequently, this substitution may have undesirable impacts on the aquatic environment and hinder fish growth due to reduced levels of essential amino acids (particularly methionine and lysine) and decreased palatability. Gerile and Pirhonen found that completely replacing FM with corn gluten meal significantly impaired the growth rate of rainbow trout, but it had no effect on oxygen consumption or swimming capacity.
The presence of large amounts of plant material can impact the quality of pellets and complicate the manufacturing process during extrusion. Many plant-derived nutrient sources used in fish feeds contain anti-nutritional factors that interfere with fish protein metabolism, affecting digestion and utilization. This can result in increased nitrogen release in the environment, which can harm fish health. High levels of phytic acid in diets also disrupt phosphorus and protein digestion, leading to excess nitrogen and phosphorus being released into the environment. The intake and digestibility of nutrients, as well as the composition of fish waste, can vary depending on the species of fish and the levels of nutrients in the diet. As a result, it is important for aquaponics to consider the optimal levels of anti-nutritional factors in the fish diet and the effects of adding minerals like zinc and phosphate. Additionally, it should be acknowledged that using plant material as an alternative to fishmeal in aquafeeds may have ecological consequences, as plants require irrigation, which can result in nutrient run-off from fields.
By incorporating non-ruminant processed animal proteins (PAPs) derived from monogastric farmed animals (such as poultry and pork) that are suitable for human consumption at the point of slaughter, terrestrial animal by-products could be utilized as a substitute for FM and contribute to the circular economy. These PAPs have a higher protein content, more desirable amino acid profiles, and fewer carbohydrates compared to plant-based feed ingredients. Additionally, they lack anti-nutritional factors. Research has shown that meat and bone meals can serve as a good phosphorus source for Nile tilapia when included in their diet. However, due to the risk of bovine spongiform encephalopathy (mad cow disease), its use in the feed of ruminant animals is strictly prohibited. To address sustainability concerns, certain insect species like the black soldier fly (Hermetia illucens) can be utilized as an alternative protein source in fish feed diets. Insect farming offers significant environmental benefits, including reduced land and water requirements, lower greenhouse gas emissions, and high feed conversion efficiencies. Nevertheless, further research is needed to assess the quality, safety, and potential risks to fish, plants, people, and the environment.
It is important to note that fish rely on their feed to obtain essential nutrients required for their metabolism and growth, as they cannot synthesize them. However, there are certain animal groups that have symbiotic microorganisms capable of providing these nutrients even in nutrient-deficient diets. When the microbial supply of essential nutrients matches the demand, fish can benefit the most. Not getting enough nutrients limits fish growth, while an excess can be harmful as fish need to neutralize the toxicity caused by non-essential compounds. The extent of microbial function and the underlying mechanisms vary among different fish species and are largely unknown. It is worth mentioning that an aquatic animal’s gut microbiota has the potential to play a crucial role in providing necessary nutrients and achieving sustainability in fish farming. Further research in this area will aid in selecting ingredients for fish feeds that promote diversity in gut microbiota, thus enhancing fish growth and ensuring their health.
Research into the utilization of alternative plant and animal protein sources and low-trophic fish feed ingredients is ongoing. The substitution of marine-sourced raw ingredients in fish feed, which could be used directly for human food purposes should decrease fishing pressure and contribute to preserving biodiversity. Low trophic-level organisms, such as black soldier fly, which may serve as aquafeed ingredients may be grown on by-products and waste of other agricultural industrial practices given different nutritional quality meals, thereby adding additional environmental benefits. However, efforts to succeed with the circular economy and the recycling of organic and inorganic nutrients should be handled with care since undesirable compounds in raw materials and seafood products could increase the risk to animal health, welfare, growth performance, and safety of the final product for consumers. Research and continuous monitoring and reporting on contaminants of farmed aquatic animals in relation to the maximum limits in feed ingredients and diets are essential to inform revisions in and introductions of new regulations.
Feed Ingredients and Additives
Protein and Lipid Sources for Aquafeeds
Since the late 20th century, there have been significant changes in both the composition and manufacturing of aquafeeds. These changes were driven by the desire to improve the economic profitability of aquaculture and minimize its environmental impact. However, the main catalyst for these changes is the necessity to reduce the reliance on fishmeal (FM) and fish oil (FO) in aquafeeds. FM and FO have traditionally made up the largest portion of feeds, particularly for carnivorous fish and shrimp. This need for change has arisen partly due to overfishing and, more significantly, the growing global aquaculture industry, which requires alternative proteins and oils to replace FM and FO in aquafeeds.
The composition of fish feeds has changed significantly over time. In the 1990s, the proportion of FM in diets for carnivorous fish like Atlantic salmon was >60%, but it has now decreased to <20% in modern diets. Similarly, the FO content has decreased from 24% to 10%. As a result, the fish-in-fish-out ratio for salmon and rainbow trout, also known as the FIFO ratio, is now below 1. This means that less than 1 kg of fish is needed in the feed to produce 1 kg of fish meat. Consequently, carnivorous fish culture today is a net producer of fish. On the other hand, feeds for omnivorous fish species with lower trophic levels, such as carp and tilapia, may contain less than 5% FM. Farming these low trophic fish species is more environmentally sustainable compared to higher trophic species. In 2015, the FIFO for tilapia was 0.15, and for cyprinids (carp species), it was only 0.02 (IFFO). However, it’s important to note that completely replacing total FM in the diets of tilapia and salmon is not possible without significantly affecting production parameters.
Currently, the primary sources of proteins and lipids in fish feed are plants. However, other sectors, such as meat and poultry by-products and blood meal, also contribute to this supply. Waste and by-products from fish processing, including offal and waste trimmings, are also often used to produce fish meal (FM) and fish oil (FO). Nevertheless, EU regulations prohibit the use of FM from a specific species as feed for that same species. For example, salmon trimmings cannot be included in FM used for feeding salmon.
The replacement of FM and FO with other ingredients can impact the quality of the product sold to customers. Fish is known for its health benefits, particularly its high levels of poly and highly unsaturated fatty acids. Seafood is especially valued as the sole source of EPA and DHA, omega-3 fatty acids that are essential nutrients for various bodily functions. If FM and FO are substituted with land-based products, the quality of the fish meat will be directly affected, particularly its fatty acid composition. The proportion of omega-3 fatty acids, especially EPA and DHA, will decrease, while the levels of omega-6 fatty acids will rise due to the increase of plant material replacing FM and FO. Consequently, the health advantages of consuming fish are partially diminished, and the product served may not meet consumers’ expectations. However, fish farmers can address the issue of decreased omega-3 fatty acids in the final product by incorporating finishing diets with a high FO content during the last stages of cultivation.
The possibility of using genetically engineered plants that produce EPA and DHA, such as genetically modified Camelina sativa, is a new and interesting option for replacing FO in fish feeds. This plant, also known as camelina, gold-of-pleasure, or false flax, naturally contains high levels of omega-3 fatty acids. By utilizing oil from genetically modified Camelina sativa, salmon were successfully grown with significantly elevated concentrations of EPA and DHA. It is important to note that the use of genetically modified organisms in human food production requires regulatory approval and may not be a viable short-term solution.
Insects can now be used as a substitute for FM in aquafeeds due to recent changes in EU legislation. The allowed insect species for this purpose include black soldier fly, common housefly, yellow mealworm, lesser mealworm, house cricket, banded cricket, and field cricket. These insects must be reared on specific permitted substrates. Growth experiments conducted on various fish species indicate that using meal made from black soldier fly larvae as a replacement for FM does not necessarily impair growth and other production factors. Conversely, replacing FM with meal made from yellow mealworms can only be done partially in order to prevent a decline in growth. However, substituting FM with insect meal can result in a reduction of omega-3 fatty acids since they lack EPA and DHA.
Microalgae generally have beneficial amino acid and fatty acid profiles, including EPA and DHA, unlike insects. Nonetheless, there is significant variation in this regard between different microalgae species. Promising outcomes have been observed in replacing some FM and FO in aquafeeds with specific microalgae. It can be anticipated that the utilization of microalgae in aquafeeds will rise in the future, even though cost limitations may impede their widespread use.
This brief description of potential feed ingredients suggests that there are numerous options available to partially substitute FM and FO in fish feeds. Generally, FM has an ideal amino acid profile for most fish species, and FO contains DHA and EPA, which are extremely difficult to obtain from oils derived from land-based sources, although this situation may be altered in the future through genetic engineering. Nonetheless, the acceptance of GMO products by legislation and customers must come first.
The Use of Specialist Feed Additives Tailored for Aquaponics
Developing aquafeeds specifically for aquaponic systems is more difficult compared to traditional aquaculture feed development. This is because aquaponic systems require the aquafeeds to not only provide nutrition to the cultured animals but also to the cultured plants and the microbial communities within the system. Currently, aquaponic practice involves using aquafeeds that are formulated to optimize the nutrition for the cultured aquatic animals. However, these feeds also need to consider the nutrient requirements of the plant production component, as they are the main source of nutrients in aquaponic systems. This becomes particularly important in commercial-scale aquaponic systems, where the productivity of the plant component greatly affects the overall profitability of the system. Improving the production performance of the plant component can significantly enhance the profitability of the entire system.
The overall objective of developing customized aquaponic feeds is to create a feed that achieves a balance between supplying extra nutrients to plants and ensuring adequate functioning of the aquaponic system (such as maintaining water quality for animal production, biofilter and anaerobic digester performance, and nutrient absorption by plants). To achieve this, the ultimate customized aquaponic feed may not be ideal for either aquatic animal or plant production separately, but would instead be ideal for the entire aquaponic system. The ideal point would be determined according to overall system performance parameters, such as measures of economic and/or environmental sustainability.
One of the main difficulties in increasing production output from aquaponic systems that are connected is the relatively low concentrations of both macro- and micro-plant nutrients, primarily in the inorganic form, in the recirculating water compared to traditional hydroponic systems. This deficiency in nutrients can lead to nutrient deficiencies in plants and lower rates of plant production. Another challenge is the substantial amount of sodium chloride present in traditional fishmeal-based aquafeeds and the potential buildup of sodium in aquaponic systems. Various approaches can be devised to tackle these issues, such as technological solutions like decoupled aquaponic systems, direct nutrient supplementation through foliar spray or addition to the recirculating water, or cultivating plants that are more tolerant to salt. A novel approach involves developing custom aquafeeds specifically designed for use in aquaponics.
To address nutrient shortages for plants in aquaponics, specific adjustments need to be made to the aquaponic feeds. These adjustments aim to increase the availability of nutrients for plants by either increasing the concentrations of specific nutrients after they are excreted by the cultured animals or by making the nutrients more bio-available after excretion and biotransformation, allowing for rapid uptake by the plants. However, achieving increased nutrient excretion is not as straightforward as supplementing higher quantities of desired nutrients to the aquaculture diets. This is because there are several factors within an integrated aquaponic system that need to be taken into consideration, and these factors can often conflict with one another. For instance, while optimal plant production requires higher concentrations of certain nutrients, certain minerals like specific forms of iron and selenium can be toxic to fish even at low concentrations. Therefore, these minerals have maximum allowable levels in the circulating water. In addition to the total nutrient levels, the ratio between nutrients (such as the P:N ratio) is also important for plant production. Imbalances in nutrient ratios can result in the accumulation of certain nutrients in aquaponic systems. Furthermore, even if an aquaponic feed increases plant nutrient levels, it is still crucial to maintain the overall water quality and pH within acceptable limits. This ensures acceptable animal production, efficient nutrient absorption by plant roots, proper functioning of biofilters and anaerobic digesters, and prevents the precipitation of important nutrients like phosphates, as this would make them unavailable to plants. Achieving the overall balance required for the system is not an easy task, as there are complex interactions between different forms of nitrogen in the system (NH3, NH4 +, NO2 −, NO3 −), the system pH, and the various metals and ions present.
Transform Fish Waste Into Food For An Aquaponics Garden
Aquaponics, which has its origins in ancient China and Mexico, is being increasingly recognized globally as a method for producing locally sourced food, according to David Landkamer, an aquaculture specialist at the Oregon State University Sea Grant Extension program. He frequently receives inquiries from individuals interested in initiating small-scale aquaponics ventures in their backyards or even establishing commercial aquaponics farms. Landkamer mentioned that hobbyists have the opportunity to begin their aquaponics journey with kits that can be purchased online or from hydroponics supply stores.
Aquaponics systems consist of a fish tank, trough, or outdoor pond alongside a soil-free bed designed for plant growth. The fish container can be constructed from a variety of materials such as fiberglass, glass, concrete, or plastic. The size of the containers can vary, ranging from a 20 to 40-gallon plastic tote to a larger, deep and wide plastic aquarium measuring approximately 4 to 5 feet deep and 6 to 10 feet wide. According to Landkamer, it is recommended to use kits in a temperature-controlled environment, such as a greenhouse or inside your home. To fill the plant bed, one can opt for either clay or gravel pebbles, or alternatively grow plants on foam or bamboo “rafts” that float on the water, as suggested by Landkamer.
In addition to the tank and bed, every system depends on the subsequent customizable elements: an area for removing solids, a system for biofiltration that cultivates beneficial bacteria responsible for decomposing fish waste, a water sump and pump, and an aeration system. A water sump functions as a reservoir where water is gathered and subsequently reintroduced to the rest of the system via a pump.
He said that aquaponics farmers often utilize cost-effective sources of warmth, like solar greenhouses or hot compost, in order to ensure the water temperatures are suitable for the fish and plants, depending on the fish species chosen.
“These systems require monitoring to make sure everything is in balance and running smoothly,” Landkamer said. “You have to pay attention and see how well the fish are feeding, how well the plants are growing, and see whether the water is circulating properly.”
In addition to fish and plants, the aquaponics system also produces “good” bacteria naturally. These bacteria play a vital role in converting the harmful substances present in fish waste into nutrients that can be used by the plants. Although you do not need to introduce these bacteria separately, it is advisable to use a testing kit to monitor the levels of oxygen and nutrients in the water, according to Landkamer.
He said that Tilapia are the most commonly raised fish in aquaponics systems. Landkamer also suggests catfish, trout, common carp, koi, sunfish, goldfish, barramundi, Murray cod, and crayfish. He advised selecting freshwater species and mentioned that they can be fed standard diets specifically designed for each species. These diets can be obtained from feed suppliers or pet stores, he added.
Even for personal use, you must obtain a transport permit from the Oregon Department of Fish and Wildlife to raise fish such as tilapia. According to Landkamer, these permits are easily available online or from licensed fingerling sellers.
