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Written by the Editorial Team of Aquaculture Magazine
Feed-food competition is a current but unsustainable practice in aquaculture, where resources are allocated to feed humans to animal feed instead. This study analyzes feed-food competition in aquaculture using natural trophic levels (TLs) and species-specific human-edible protein conversion ratios (HePCRs).
In the future, the role of aquaculture in circular food systems will most likely consist of a balanced mix of species at different natural trophic levels (TLs) and from different aquaculture systems, depending on the by-products available. In this paradigm, farm animals, including aquaculture species, should not consume human edible biomass but instead convert by-products from crops, livestock, and fisheries that are inedible for humans, into edible biomass.
In addition to these by-products, animals in circular food systems can also convert plant-based food waste and grass resources into food.
The fish-in: fish-out ratio (FIFO) is an indicator for feed efficiency of aquaculture species, which differs greatly among species. Over the years, the FIFO has decreased to around 0.3 for global aquaculture due to a growing trend to replace fishmeal with plant-based protein sources, such as soy protein concentrate.
These replacement ingredients often cause feed-food competition because they can be used directly as 20 diet even when consumed in small amounts. They are also the main source of essential omega-3 long chain polyunsaturated fatty acids in food. Plant-based ingredients, such as soya-bean-based ingredients, could influence feed-food competition in
directly by increasing land use for the production of animal feed instead of human food.
“Fish and shellfish are rich in macronutrients and micronutrients and can be a valuable addition to a healthy human diets. Farmed fish convert feed into food relatively efficiently, with Atlantic salmon having a feed conversion efficiency similar to that of chicken.”
To determine the unique role of aquaculture in the transition towards healthy and circular food systems, more insight is needed into feed food competition in global aquaculture. One way to do so is to explore an animal’s natural ability to upgrade specific by-products into food, which is determined by animal species, breed, and production-system intensity.
Aquaculture species at higher trophic levels — omnivores and carnivores species — have diets more similar to those of humans and are well adapted to convert fish or other animal-based by-products into food.
The study aims to understand feed food competition in aquaculture by using the Human Edible Protein Conversion Ratio (HePCR) to quantify the net contribution of farmed fish to the supply of human edible protein. HePCR equals the ratio of human edible protein in feed (input) to the human edible protein in the animal product (output). The research focuses on the current status and trends in aquaculture production based on TLs and calculated HePCRs of current intensive aquaculture systems.
Methods
The study first reviewed generic data on aquaculture production by retrieving production (wet weight) and economic data (USD) at global and continental levels from FishstatJ. Then, it selected the 50 species produced most (in wet weight).
To quantify the relative contribution of each TL to current global aquaculture production (in kg wet weight and edible protein), aggregated by species groups, the researchers categorized production data of the 50 aquaculture species produced most by TL range. Each species’ natural TL (1–5) was based on information from FishBase (Figure 1), a good
data source for the trophic ecology of finfish.
The protein content of individual fish species was collected from the U.S. Department of Agriculture (USDA) database. The protein contribution was based on raw fish, and cooking losses were not included.
The trend in the mean TL of aquaculture production globally and by continent from 1980–2019 was quantified. Data on annual production and the natural TL of the 25 species produced most (wet weight) globally and categorized them by
continent.
To embed HePCR results in the existing aquaculture literature, the protein conversion ratio (PCR) was calculated as an indicator of feed efficiency. Four case-study species — three finfish (one from each natural TL) and one crustacean — chosen based on two criteria: having the highest economic value and being produced in intensive systems.
Consequently, the study selected Atlantic salmon (TL 4–5), common carp (TL3–4), Nile tilapia (TL 2–3), and white
leg shrimp (TL 2–3).
“In conclusion, the study provides valuable insights into feed-food competition in aquaculture, highlighting the importance of understanding the conversion efficiency of human edible feed protein into aquatic protein.”
The study focuses on the diet composition of Atlantic salmon, common carp, Nile tilapia, and white leg shrimp for intensive cultivation in 2020. The diet composition was based on confidential surveys with five people active in the aquaculture feed industry. The crude protein content of diet ingredients was calculated based on the International Aqua
culture Feed Formulation database.
The human edibility of each feed ingredient was defined as either food competing or non-food-competing based on Sandström et al. (2022) and Mottet et al. (2016). Both studies reported the same human edibility for most ingredients, except for soya bean meal and fishmeal.
Sandström et al. considered fishmeal made from whole fish food-competing but fishmeal made from fish by-products
non-food-competing, while Mottet et al. (2016). considered all fishmeal non-food-competing. Furthermore, while soy protein concentrate is food competing, soya bean meal is considered non-food-competing because it is a by-product of soya bean oil production, and the meal is used almost entirely as a feed ingredient.
For the human edibility of the output of the species, the study focused on the current habits of eating primarily fillets. To represent protein quality, the digestible indispensable amino acid score (DIAAS) was in cluded for the mean ingredient composition of the four selected aquaculture species.
“Animal-based ingredients included blood meal, feather meal, fishmeal, krill meal, meat and bone meal, poultry meal, plant-based ingredients like cassava meal, corn bran, corn gluten meal, distillers grains, faba beans, gar protein, pea flower, pea protein concentrate, rice bran, soy lecithin, soybean meal, sunflower meal, wheat gluten meal, wheat meal, wheat bran, and wheat flour.”
The Food and Agriculture Organization of the United Nations (FAO) recommends the DIAAS as a measure of protein quality. The DIAAS reflects the content of the first limiting indispensable amino acid in a feed/food ingredient relative to the requirement for the same aminoacid by humans. The amino acid requirement pattern for a 6-month to 3-year-old child was used as the reference protein’s amino acid profile, similar to studies by Laisse et al. and Ertl et al., and as recommended by the FAO.
The DIAASs of feed ingredients were extracted from Ertl et al. or, if not included by them, estimated using their method. Due to a lack of data on the human ileal amino acid digestibility of fish fillets, the DIAASs of the case-study species were calculated based on amino acid scores from the USDA, assuming an amino acid digestibility of 94% for fillets/meat.
In conclusion, the study highlights the importance of considering the human edibility of feed ingredients in aquaculture production. By focusing on the grow-out phase and incorporating the DIAAS score, the study contributes to the understanding of the nutritional value of fish in aquaculture.
Results
Global aquaculture productions have seen a 50% increase in volume, with Asia dominating the sector at 90%, followed by the Americas (4%), Europe (3%), Africa (2%), and Oceania (0.2%). Africa showed the highest growth over the previous decade (130%), more than 2.5 times that of China. The continent (Asia) and country (China) that produced the
largest volume had the lowest economic values, while the continents with the lowest volumes (Oceania, Europe, and the Americas) had the highest economic values.
The contribution of each aquaculture species group to global aquaculture production in 2019 varied (Figure 2). TL 2-3 produced the mostwet weight (59%) and edible protein (60%), dominated by freshwater fish and molluscs. Aquaculture species at lower TL (TL 1–3) contributed less to global protein production than to global aquaculture wet-weight volumes.
This is due to their high water and low protein content, while fish from low TLs have lower edible yields than at higher TLs.
Over the past 40 years, the mean natural total length (TL) of aquaculture species increased slightly, but it differed greatly among regions, especially China and Europe. In Europe, it increased due to the large increase in production of diadromous fish, particularly Atlantic salmon, over the past 35 years.
However, the mean TL of aquaculture species in Asia/China remained relatively low and stable over the past 30 years due to higher growth of production of freshwater fish, molluscs, and aquatic plants than other species groups.
In scenario 1, Atlantic salmon had the highest percentage of food-competing ingredients in the diet (45%), as soy rotein concentrate was the primary protein source (Figure 3).
The study analyzed the feed-food competition in aquaculture diets of common carp, whiteleg shrimp, and Nile tilapia. Food-competing ingredients provided the most edible protein, while food-competing ingredients provided the least. In scenario 2, soya bean meal and fishmeal food-competing increased the percentage of human edible protein for all diets, ranging from 49% to 65%.
Atlantic salmon and whiteleg shrimp had the highest percentages of food-competing ingredients, followed by livestock by-products, gluten meals, and cereal bran.
“The conversion ratios of the case study species ranged from 3.4 to 8.7, with Atlantic salmon converting protein the most efficiently. Differences in PCR among species were caused by differences in the FCR, edible yield, and protein content of the feed.”
Atlantic salmon had the lowest FCR and highest fillet/meat yield. In scenario 1, Atlantic salmon consumed more human edible protein than it produced, while other species had lower values due to the higher quality of fillet protein. In scenario 2, all four species were net consumers of protein, with HePCRe increasing to 2.0 – 4.6 and HePCRd increasing to 1.7 – 3.5.
The range of HePCRe/d overlapped, indicating smaller changes in the human edibility of protein in salmon diets compared to other species. This study serves as a starting point for exploring and analyzing feed-food competition for additional species, systems, and locations.
Discussion and conclusions
The study focuses on the potential of aquaculture to produce food while avoiding feed-food competition. It uses TLs as a starting point to analyze feed-food competition, as the natural ability of an animal to upgrade specific by-products into food can determine its role in a circular food system.
In both Europe and the Americas, Atlantic salmon was the species at a high TL, whose production was largest and grew the most rapidly, driving the increase in average produced natural TL. Feeding compound feeds has generally resulted in aquaculture diets with an effective TL lower than that of natural diets (natural TL).
This decrease may appear positive if assuming that diets at lower TLs generally cause less feed-food competition because they include more plant-based ingredients and less fishmeal. However, when fishmeal is replaced by soy protein concentrate, as for salmon, the positive impact on feed-food competition is not apparent because soy protein concentrate is human edible and has higher protein quality (i.e., a higher DIAAS) than fishmeal.
“As a result, species at a naturally high TL, such as salmon, continue to receive relatively higher quality (plant-based) ingredients, resulting in highly human edible diets.”
When investigating feed-food competition in the present study, classifying soya bean meal and fishmeal as either food-competing or non-food-competing ingredients had large influence on the net contribution to protein supply of the four
aquaculture species. Soya bean meal is considered inedible, but its production is the main mean trophic level of aquaculture production by continent.
This causes indirect feed-food competition, as the land used to produce soya bean meal could have been used to grow food crops for direct human consumption. Fishmeal does not require land, but its production can lead to overfishing and greenhouse gas emissions.
Replacing soya bean meal in aqua culture feeds would reduce feed-food competition in aquaculture drastically. When soya bean meal and fishmeal were considered food-competing, Nile tilapia, which has a low TL, had the highest HePCR, while Atlantic salmon, which has a high TL, had the lowest HePCR. This may seem surprising, but it can be explained by its relatively high growth rate and feed efficiency.
“Intensive aquaculture systems do not optimally align with the natural ability of species at a low TLs to upgrade lower quality by-products or natural biomass. For these species, extensive systems and ecological intensification, such as nutritious ponds, are better suited.”
The study focuses on feed-food competition in aquaculture, which accounts for only 1.2% of global feed consumption compared to cattle (73%), pigs (20%), and poultry (7%).
However, it represents a larger percentage (3.8%) of global human-edible feed consumption, likely due to the high protein requirements of fed aquaculture species. The most significant gain to reduce feed-food competition is to be made with livestock.
Comparing the Human-Edible
Protein Conversion Ratio (HePCR) of livestock and aquaculture is hampered by differences in metabolism and housing. The most logical comparison is with monogastric species, such as poultry and pigs. When comparing their HePCR ratios, broilers (HePCRe∼ 5.2) and industrially produced pigs (HePCRe∼ 4.5) have higher HePCRs than the aquaculture species examined.
The study attempted to approach feed-food competition scenarios in aquaculture using all available information and objective criteria, but improvements are always possible.
Factors such as complete feed formulation, feed quantity and growth rate, feed quantity and growth rate, and protein efficiency were considered.
“Future studies could focus on the entire life cycle of one specific system and species, as HePCR depends on the animal, its feed and efficiency, and the definition of human edible products.”
Another limitation of this study was related to its scope, as it focused only on intensive systems to enable comparison of HePCRs between species at low versus high TLs and between aquaculture and livestock.
Most aquaculture species are produced in extensive or semi-intensive systems, especially finfish species at a low TL, in which they can obtain some of their nutritional requirements from the natural environment.
As the efficiency of converting by products is affected by species as well as production systems, comparative case studies of specific species and production systems are needed.
“In conclusion, the study highlights the importance of reducing feed-food competition in aquaculture and the need for more detailed estimates of HePCRs for selected aquaculture species in intensive production systems.”
Animals can play a crucial role in circular food systems by upgrading by-products, and the transition to wards circular systems should focus on minimizing feed-food competition for both livestock and aquaculture. To ensure a net contribution of aquaculture to food security, focus should be placed on feed efficiency metrics such as Feed Conversion Ratio (FCR) and HePCR.
For example, Atlantic salmon consume more protein than they produce (HePCR > 1), indicating the importance of HePCR.
In recent years, an increasing number of animal and plant-based by-products have been used as aquaculture feeds. Livestock by-products and fishmeal from fish by-products could replace 99% of the fishmeal made from whole fish. Novel protein sources to replace fishmeal, such as insects, algae, and yeasts, should not be incorporated into aquaculture feeds. A combination of novel protein sources and by-products could replace current food-competing ingredients.
To encourage the feed industry to develop and apply innovations to increase by-product use, the government could develop targets for the inclusion of by-products in aquatic feeds for feeding companies or tax the use of food-grade feed materials.
Certification schemes such as the Aquaculture Stewardship Council, Best Aquaculture Practices, and Safe Feed/Safe Food (SF/SF) Certification Program could include targets for the inclusion of by-products in aquatic feed. To monitor the efficacy of these policies or certification schemes, indicators of feed-food competition, such as HePCR, are needed.
A final strategy to optimize the role of aquaculture in the food system is to increase the edible yield of harvested species. If humans would consume not only fillets but also all edible parts, the HePCR e/d would decrease by 27% for Atlantic salmon, 37% for common carp, 21% for whiteleg shrimp, and 35% for Nile tilapia. Consuming a larger fraction of the fish has an environmental benefit, as it allows for better use of all raw materials and primary resources used through the life cycle of the fish.
“The role of aquaculture in circular food systems will most likely consist of a balanced mix of species at different Total Lengths (TLs) and from different aquaculture systems, depending on the by-products available. As the natural Total Length (TL) is not the only factor that influences feed-food competition, future research should focus on including more species (e.g., diets, FCRs) and systems (e.g., intensities).”
This study focuses on the role of farm animals in a circular food system and the potential benefits of aquaculture for the global food system. The authors acknowledge the contributions of three anonymous reviewers and Micheal Corson for
their valuable comments and suggestions. The research was supported by Wageningen University as part of Anne-Jovan Riel’s PhD project.
The study also discusses the use of fish as feed and the environmental impact of animal source foods. The authors also discuss the importance of isotopic baselines in evaluating fish trophic position in Mediterranean lagoons. The authors also discuss the utilization of feed resources in the production of Atlantic salmon (Salmo salar) in Norway and the comparison between Atlantic salmon post-smolts rear and pre-smolts rear.
The authors also discuss the role of aquaculture in reducing the environmental impact of animal-based food production. They discuss the use of aquaculture as a sustainable food source and the potential benefits of using aquaculture feeds as a feed source.
The study concludes that aquaculture can contribute to the global food system by increasing the availability of food and reducing the environmental impact of animal-based food production. The authors emphasize the need for further research and development in this area to ensure the sustainability of aquaculture practices.
This is a summarized version developed by the editorial team of Aquaculture Magazine based on the review article titled “FEED-FOOD COMPETITION IN GLOBAL AQUACULTURE: CURRENT TRENDS AND PROSPECTS” developed by: VAN RIEL, A.; NEDERLOF, M.; CHARY, K.; WIEGERTJES, G. and DE BOER, I. – Wageningen University & Research, The Netherlands.
The original article was published, including tables and figures, on JUNE, 2023, through REVIEWS IN AQUACULTURE.
The full version can be accessed online through this DOI: 10.1111/raq.12804.
