Protein Sources in Aquaculture Feed: Quality and Nutrition
Updated: Feb 11, 2022
Introduction
“Feeding fish to fish”; this is, feeding wild fish meal (FM) and fish oil (FO) to aquaculture fish as “aquafeed”. This “Fish In, Fish Out” (FIFO) ratio, which Tacon and Metian (2008) used to show that more fish (in the form of FM and FO) is being consumed by fish than is produced by the aquaculture industry. For example, these authors calculated that it takes 4.9 tons of wild fish to produce every ton of salmon, therefore the FIFO ratio is 4.9:1, showing an inefficient and wasteful production of salmon. However, Tacon and Metian did not consider the proportion of FM and FO being used, with salmon using more FO than FM. To provide for the high FO requirement more FM is produced, resulting in left-over FM, but this excess FM is not “thrown away” in the aquaculture supply chain. However, in their calculation, FM is “thrown away” which resulted in a high FIFO ratio. Additionally, the percentage of FM derived from otherwise inedible fish by-products (e.g., offal) rather than whole feed fish (i.e., edible + inedible fish parts1 ) was not taken into account (International Fishmeal and Fish Oil Organisation (IFFO), 2017). Jackson (2009) corrected the calculation and generated a more realistic FIFO of 1.4:1, a much lower value than what was originally asserted to the public.
Even though widely quoted, the FIFO metric has shown to be an invalid tool for calculating the efficiency of aquaculture production, primarily because it does not consider the nutritional quality (e.g., amino acids) of FM and FO in aquafeeds (IFFO, 2017). Nonetheless, an additional 37.4 million tons of aquafeed will be required by 2025 (Hua et al., 2019), and given that limited supply and rising demand are causing a price increase of FM and FO (Nunes et al., 2014), companies are seeking alternative protein sources (e.g., plant-based ingredients, aquaculture byproducts, insect meal) for their aquafeed products. Specifically, alternative protein sources that can compete, nutritionally, with the high protein level and essential amino acid profile of high-quality FM.
Deciding on the right protein source that is both safe and meets the nutritional requirements of fish species can be challenging. The following factors should be considered when choosing a protein source for use in aquaculture feed.
Ingredient quality
Target species protein requirements
Regulatory challenges
These three factors are discussed in detail below.
Ingredient quality
The physical, chemical, and nutritional quality of aquafeed ingredients is influenced by the source of the raw material used, including production and harvesting costs, as well as the cost of processing, storage and transportation of the final product (Table 1). For example, if soybean meal is undercooked during the manufacturing process, it will contain antinutritional factors such as trypsin inhibitor and lectin; on the other hand, overcooked soybean meal will result in damaged amino acids, particularly lysine, resulting in reduced biological availability and, consequently, lower product quality. Also, dehulled soybean meal will have higher a protein content than non-dehulled soybean meal. (Tangendjaja, 2015).
The specifications provides knowledge concerning the exact composition of raw materials and the levels of toxic substances normally present (Chow, 1980). Quality control methods, including testing the parameters specific to the protein source, is necessary to ensure that minimum specifications are met. For instance, a urease activity test uses urea phenol red solution that produces a red color when soybean meal is undercooked (the amount of red color indicates the degree of undercooking). When there is no red color at all, it is possible that soybean meal has been overcooked, and this can be evaluated by the percentage of protein solubilized in 0.2% KOH (Tangendjaja, 2015). However, other protein sources would require different evaluations. For instance, when using animal by-products, Salmonella contamination is a major concern and although Salmonella can be eliminated during the rendering process, possible re-contamination may occur (Tangendjaja, 2015). As a result, it is important that Salmonella is tested for in animal by-product meals.
Table 1. Factors that affect the quality of protein ingredients for aquaculture (adapted from Tangendjaja, 2015)
Quality Factors | Description (how quality is affected) | Cost Effectors |
Natural variation or growing conditions where the ingredients are produced | Plant derived ingredients: The chemical composition and nutritive value is influenced by agronomic background (soil fertility, fertilizer application), plant variety, season, and environment. Animal derived ingredients: Different types of fish would influence the protein level and amino acid content, while fish harvested at certain seasons and latitudes would impact the oil content of the fish meal. | Cost of land/use of land (e.g., rental), seed, labor to maintain and harvest, machinery rental, cost of transportation to processing plant and destination, pesticides and fertilizer. Cost of obtaining fish (overhead of vessels for harvesting and preliminary processing), fuel, labor, refrigeration and storage. |
Manufacturing process | During ingredient production: Processing techniques, such as removal of bone in a rendering plant would influence the chemical composition of meat and bone meal produced. Different heat applications during toasting of soybean would affect the residual heat-labile antinutrient factors and can cause a decrease in amino acid and protein digestibility. | Cost of final processing (heat and frozen storage) and added ingredients (antioxidants, vitamin and mineral mixes, antibiotics), labor. |
Storage and transportation condition | Poor storage conditions, resulting in degradation: May occur during storage resulting in reduced quality, for example, the fat in animal by-product meals may undergo oxidation, resulting in rancidity. High temperature: Will cause the Maillard reaction and reduce amino acids digestibility during storage. | Cost of possible specialized storage, cost storage containers (e.g., bags or barrels with liners), warehousing costs, quality checks by inspectors and analytical laboratory, determination of stability. |
Adulteration and contamination | Adulteration: Economic adulteration with materials of lesser quality. Contamination: May occur from improperly cleaned equipment or storage containers such as, but not limited to pesticides or mycotoxins. | Cost of secure and quality storage areas, quality control checks by analytical laboratory, inspectors, etc. |
The Hazard Analysis Critical Control Point (HACCP) methodology is intended to reduce the risk of unsafe food products, but can also improve product quality. The FDA guidance document, “Fish and Fishery Products Hazards and Controls Guidance (Fourth Edition – March 2020)”, can help processors of fish and fishery products identify hazards that are associated with their products and formulate control strategies. Additionally, safety assessments are necessary to ensure that the feed ingredient does not introduce contaminants into the fish’s diet that result in health concerns for the consumer.
Target species protein requirements
Proteins consist of linkages of individual amino acids. There are 20 primary amino acids and of those, 10 are “essential” amino acids (EAAs) that fish cannot synthesize on its own (or is incapable of synthesizing sufficient amounts) and must obtain them from exogenous sources (NRC, 2011). According to the National Research Council (NRC) (2011), all fish and shrimp require the same 10 EAAs: arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. The nutritional value of the protein is dependent not just on its amino acid composition, but also on its digestibility, i.e., how much of a nutrient in an ingredient can the fish actually digest and absorb (USDA, 2016). High-quality fish meal is an ideal protein source for aquafeed because it has a high protein level (60 – 72%), high digestibility (>95%) and an excellent source of essential amino acids (EAAs) (Table 2). Alternative protein ingredients, on the other hand, may have a comparable protein level to high-quality FM, but might be less digestible and/or deficient in one or more EAA. For instance, FM and soy protein concentrate are highly digestible, but other ingredients, like Zophobas morio (superworm) meal, is very high in protein but low in available protein (Table 2). This is because digestibility is dependent on the raw material, as well as other factors, e.g., intrinsic composition of an ingredient, processing (Table 1). The minor differences in digestibility can often be adjusted for during diet formulation (USDA, 2016).
Table 2. Comparison of protein level, digestibility and EAA profile of protein sources for use in aquafeed.
Protein Source | Protein Level | Protein Digestibility | EAA Profile(a) |
|---|---|---|---|
High-quality fish meal | 60–72%(b) | >95%(b) | Excellent |
Plant-base protein | 15–50%(c) | Varies greatly 77–96%(b) | Deficient in certain EAAs:
|
Insects | 40–63%; defatted insect meal can contain up to 83%.(e) | Varies greatly HI meal: 81.10–97%(f) TM meal: 79.19–92%(f) ZM meal: 50.53%(f) | The EAA patterns of insects are taxon-dependent:
close to soybean EAA profile.(g) |
EAA=Essential Amino Acid; FM=Fish Meal; HI=Hermetia illucens; TM=Tenebrio molitor; ZM=Zophobas morio.