1 A WICKED PROBLEM

The global population continues to grow with projections of reaching 9.5 billion by 2050. That growth will be accompanied by an estimated 40–75% increase in total protein demand, 72% arising in countries currently identified as developing where 70% of that estimated population is expected to reside in urban areas (National Research Council of the National Academies (NRC), 2015). In these areas, higher socioeconomic levels will be achieved, generating a greater demand for animal-sourced protein. To address this demand, animal agriculture production will need to increase by 250–300 million m.t.

The goal of global food security in response to the projected increase in global population must be readjusted with a collective conviction of sustainability that is composed of several goals (NRC, 2010) that produce positive results based on environmental, economic, and societal return, now and for future generations. The results depend on overcoming many inherent challenges that arise from different demands and levels of efficiency of current production systems which are influenced by the reality of significant depletion of essential natural resources and the ongoing global changes in consumptive preference of different protein sources. Existing production systems contribute different levels of carbon footprints in the form of greenhouse gases (GHG) which are responsible for climate change and its adverse effects on environment such as mean increases in global temperature and changes in weather patterns. In addition, the potential effects of intensification of current production systems on animal health and safety have become a very relevant issue of concern (FAO, 2009). Even with future advances in technology designed to further promote efficiency in intensive management practices, the existing conditions of food production will not be able to successfully address the increasing global protein demand due to limited land and freshwater resources (NRC, 2015). Collectively, the issues are complex, uncertain, interdependent, controversial, and subject to a variety of opinions such that a definitive point that yields an ideal/model solution can never be reached. This scenario is defined as a wicked problem (NRC, 2015). By its very nature, a wicked problem can only be positively confronted by substantial adjustments that somehow relieve the underlying levels of disruptive interrelationships to produce the best possible outcome.

A key element in the holistic approach toward meeting global food security is achieving a desired balance sought within the components of the wicked problem. Sources of meat produced for human consumption differ in how each of the different production systems impacts the environmental, economic, and societal tiers of sustainability. Multiple challenges will arise in seeking the establishment of regional and country based food policies based on sustainability guidelines that include decisions about sources of protein to be directly consumed versus those to be included in feed formulations. Qualitative and quantitative changes in human consumption of different protein sources, both existing and newly developed, will be an inevitable end product. Therefore, what we grow, what we feed to animals, and what we eat should become subject to dynamic change.

2 SUSTAINABLE AQUACULTURE AND AQUAFEEDS

The anticipated increase in demand for seafood protein fits well with the overall demand for animal derived sources of protein. In comparison to other animal production systems, aquaculture has the greatest overall efficiency. For example, the production of CO₂ per kg (carbon footprint) of farmed beef is 90% higher than that resulting from 1 kg of salmon (Marine Harvest, 2017). In addition, the percent protein retention and edible meat produced per equivalent amount of feed fed to salmon and other fish exceed that of beef, pork and to a lesser extent poultry (Tidwell, 2012). Despite these notable characteristics, this approach will still require novel management strategies that do not further deplete the dwindling supply of available land and freshwater water resources.

The contribution of aquaculture production continues to increase and occupy an important part of all global animal agriculture production and offers a path to the balance that is needed to positively address the wicked problem. As of 2018, global aquaculture production as part of the total global fisheries (animal derived seafood) had risen to 45.8% from 9% in 1980 (FAO, 2020). Seafood produced in marine production systems amounted to 37.5% of total aquaculture production. In addition, the percentage of human consumption of total global seafood arising from culture fisheries is 52%, exceeding that derived from traditional hunter/capture fisheries (42%). The global aquaculture production of 82 million tons in 2018 is estimated to increase by 33% to 109 million tons by 2030. This latter amount followed by ongoing annual increases that include greater realization of the potential of marine fish farming, will be a noteworthy sustainable solution to an overall global meat demand estimated to be 250–300 million m.t. by 2050 (NRC, 2015).

Fish and crustaceans, as fed species, composed 55.2% (61.8 million tons) of the total global aquaculture production in 2017 (FAO, 2019). By 2025, it is estimated that 73.15 million tons of aquafeed will be needed to meet the estimated levels of production of fed species (Boyd et al., 2020). Therefore, sustainable aquafeeds, based on choice of ingredient composition, play a fundamental role in the overall goal of meeting the increase in seafood demand via sustainable aquaculture production. For the new generation of sustainable aquafeeds, “the sustainability of diets goes beyond nutrition and environment as to include economic and socio-cultural dimensions” (FAO, 2010). Additionally, meeting the need for sustainable aquafeeds for fed production systems is influenced by many confounding and competitive factors that drive other agricultural production systems. What pathways and solutions are needed to ensure that sustainable aquafeeds will be sufficiently available to realize the opportunities that aquaculture offers? Management strategies will need to evolve to at least sustain and increase aquaculture production levels, particularly in response to the effects of climate change (D'Abramo & Slater, 2019). Therefore, ingredient composition of aquafeeds will correspondingly have to evolve as part of a dynamic process to ensure sustainability. A comprehensive review of characteristics of alternative aquafeed, policy directions, and tradeoffs in meeting sustainability goals is provided by Mitra (2021).

3 EVOLVING AND EVER-DYNAMIC PARADIGMS

To meet the principle of aquafeed sustainability, changes prompted by a holistic approach that involves use of feed ingredients characterized by reliable availability, minimal imports, comparatively low carbon footprint and, most definitely, policy to meet standards of quality assurance are needed. In pursuit of economic sustainability, variables such as cost of each ingredient, potential for scalability of production, level of import dependency, and logistics of transport must be included in decisions concerning use of ingredients that can be recognized as sustainable. Choice of ingredient composition of feeds used in other agricultural animal production systems will correspondingly influence the selection of ingredients for fed aquaculture systems and must be addressed. In fact, even the pet food industry may interfere financially by procuring conventionally used feed ingredients as well as those being evaluated as potential alternatives at higher prices because consumers (pet owners) are willing to endure higher retail prices per volume of feed.

Efficient fulfillment of qualitative and quantitative levels of essential dietary nutrients, nutrient digestibility and assimilation and manufacturing practices is the overarching goal of aquafeed production. This paradigm must forsake the idea that an ingredient is “essential.” All actions regarding changes in constituent ingredients must be based on the results of nutritional research rigorously conducted with a strong a priori recognition that sustainability must be the principal guiding factor. Enhanced growth achieved by interaction/synergism between or among nutrient sources per se and the role of specific aquafeed additives, as influenced by the characteristics of a specific production system, must be focal areas of investigation. For example, the beneficial effects of recognized dietary probiotic and prebiotic additives to sustainability as revealed through qualitative and quantitative changes in the microbiome (D'Abramo, 2018) must be weighed against the additional cost of inclusion.

An example of the evolution of compositional changes in feed ingredients of formulated feeds is aptly described as the movement from Aquafeed 1.0 to Aquafeed 2.0 by Columbo and Turchini (2021). This “upgrade” was principally realized by significant reductions in the amount of fishmeal and fish oil used as sources of protein and lipid respectively in aquafeed formulations for those species that seemingly "required" fishmeal and fish oil as major feed ingredients. Viewed holistically, this notable achievement introduces a complementary benefit of increasing the volume of fish product available for direct human consumption. Other ingredients with noteworthy potential to contribute to advances in the development of aquafeed are protein sources derived from single cell (bacteria/fungi/algae) culture and insect meals. These ingredients are commonly produced via the use of agricultural or biotechnological waste as a nutrient source. Single cell protein sources and insect meal offer an added advantage because nutrient composition can be altered via the nutrient source(s) provided for growth. Rendered products, such as poultry by-product, blood and feather meals, are principal sources of dietary protein and other nutrients and are currently used as ingredients in aquafeed formulations. These products have proven to be sources of good growth and health when added at comparatively high levels (Bureau, 2006; Trushenski & Lochmann, 2009). Whether currently used or in pilot production stages, all of these ingredients are derived directly or indirectly from waste and have characteristically lower carbon footprints.

Aquafeeds have been successful in negating the ecological concept that species occupying higher levels on the food chain are associated with lower efficiency and therefore less attractive for sustainable farming (Cottrell et al., 2021). For example, a reduction in trophic level (3.48–2.42) achieved for farming of salmon, a piscivorous fish, is testimony to the ability to increase feed efficiency from adjustments of mixtures of ingredients and other additives to meet nutritional requirements for desired growth rates. Increases in feed efficiency of aquatic species can continue to be realized as new ingredients are identified and incorporated into feeds due to their sustainable properties.

4 CIRCULAR BIOECONOMY—USE OF WASTES

Globally, food loss and waste annually contribute 8% of the total anthropogenic contributions to global warming as measured by equivalent production of CO₂ (FAO, 2011). Cycling of waste with the goal of an impactful minimization of waste generated over time is defined as circular economy. The use of waste as an aquafeed ingredient or as an independent nutrient source is more specifically termed circular bioeconomy. While the re-use of nutrients and resources by integrating various aquatic and terrestrial crops dates back to the earliest aquaculture systems, the need for efficient management of waste products in current production systems, particularly intensive systems, is greater than ever. As part of the holistic strategy, use of waste in the formulation and manufacture of aquafeeds would most likely improve sustainability. Circular bioeconomy is proposed as being the eventual driving force toward Aquafeed 3.0 (Columbo & Turchini, 2021). Integrated aquaculture (IA), specifically integrated multitrophic aquaculture (IMTA), is a distinctive example of a circular bioeconomy. Waste products from one fed organism are provided as nutrient sources to grow another plant or animal (non-fed) that occupies a different habitat niche. With two production species, production efficiency is increased due to the amount of aquafeed fed being the same for the combined production of two species (Boyd et al., 2020). The prospects of IMTA systems has been demonstrated in the results of recent laboratory research whereby satisfactory growth of a marine shrimp species was exclusively maintained through provision of the egesta of sea urchins (Jensen et al., 2019). However, with the exception of invertebrate integration (scallops) to macroalgae sites in Sanggou Bay, China (Shi et al., 2013), the management and financial feasibility of commercial-scale IMTA production have yet to be demonstrated. Neori, Shpigel, Guttman, and Israel (2017) reviewed the early evolution of polyculture to IMTA and discussed the challenges of optimizing multiple crops that are coupled into a single system. In fact, as stated by Knowler, Chopin, Martinez-Espineira, Neori, et al. (2020), results of field-testing have yet to establish any widespread acceptance to prompt commercial endeavors. However, assessment of aquaponic recirculating systems that operate on the principal of IMTA do indicate the potential for economic viability under specific conditions (Greenfeld, Becker, McIlwain, Fotedar, & Bornman, 2018).

With addition of specific organic matter to pond production systems, rich sources of food (bioflocs) are produced and consumed by the cultured organisms. Feed efficiency is increased because the amount of aquafeed needed can be reduced while still meeting desired production goals. For some management practices, supplemental feed (corn gluten meal pellets) designed as a supplemental nutrient source for terrestrial animal production is routinely introduced as a nutritionally incomplete source to aquaculture production ponds. Some of this nutrient source is consumed directly and the remaining uneaten feed pellets rapidly fragment into small particles which are consumed by benthic organisms which grow and reproduce. Thus, two sources of nutrients, feed and natural pond biota, in tandem satisfy nutritional requirements (D'Abramo & New, 2010). These latter two examples demonstrate how a desired growth rate and product can be achieved using reduced levels of a directly fed feed.

5 RECOMMENDATIONS

The magnitude of impact of aquafeed is truly founded in the efficiency and flexibility of selected feed ingredients and different approaches to meeting nutritional requirements. These characteristics aptly interface with the high efficiency of aquatic animal production. Founded in efficiency and balance, transformational changes must be openly and collectively embraced and ultimately prevail.

Tacon, Metian, and McNevin (2021) offer guidelines for future development of aquafeeds as they relate to issues of sustainability. Required, recommended, or encouraged points of action about ingredient selection and quality, feed manufacture, and feeding practices are offered, some of which complement, repeat, or extend what I have presented. Aquaculture nutritionists, feed manufacturers, and farmers themselves must heed this information in an effort to continue to improve management practices, including those already identified as sustainable. Researchers must operate under some common guidance. Otherwise, scientific literature that is confusing and ultimately of little or no value in application is a source of undesirable interference. A sustainability-based effort in aquafeed ingredient research is well illustrated by the recent evaluation of the environmental impact of the use of insect meal in aquafeeds (Tran, Van Doan, & Stejskal, 2021). Additionally, many potential plant-derived feedstuffs such as wheat and corn gluten meals are by-products of production processes and have nutrient qualities that require further research for use in meeting nutritional requirements. The processing of protein sources via fermentation can improve quality by yielding a product that is digested more efficiently and therefore becomes a promising ingredient in sustainable aquafeeds (Dawood & Koshio, 2019). As part of a holistic approach to sustainability and food security, the aforementioned feedstuffs offer the opportunity to use feed grade rather than food grade (for human consumption) ingredients in feed formulations. If these and possibly other similarly derived feedstuffs are judged satisfactory, then more plant protein potentially becomes available to serve as a direct source for human consumption.

The ominous conditions that confront us obviously demand a widespread, swift and steadfast response founded in a highly collaborative effort and responsible oversight. A comprehensive system of regulation of quality of feed ingredients must be established in those countries where such control does not exist. Intellectual property issues related to feed additives must be negotiated whereby gainful advances are not impeded. Collaboration and sharing of information between publicly funded academic and private sector researchers and cooperation among feed manufacturers must be established to realize maximum benefits. These visions of progress must be complemented by supportive efforts of those who are involved with sourcing of feed ingredients and the intricacies of feed supply chains which are high risk and require efficient management for delivery. Whatever might be the source of ingredients for production of sustainable aquafeeds, these efforts must be complemented by effective feeding/feed management practices, in an effort to reduce waste and further increase efficiency in a highly sustainable production system like aquaculture. Although not an exclusive panacea, sustainable aquafeed production combined with novel feeding systems will play significantly vital roles as components of long-term, sustainable aquaculture production practices.

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