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McLean, E., 2023. Feed Ingredients for Sustainable Aquaculture. In: Ferranti, P. (Ed.), Sustainable Food Science: A Comprehensive Approach, vol. 4. Elsevier, pp. 392–423.
https://dx.doi.org/10.1016/B978-0-12-823960- 5.00085-8.
ISBN: 9780128239605
Copyright © 2023 Elsevier Inc. All rights reserved.
Elsevier
4.23 Feed Ingredients for Sustainable Aquaculture
Ewen McLean,Aqua Cognoscenti LLC, West Columbia, SC, United States
© 2023 Elsevier Inc. All rights reserved.
4.23.1 Introduction 393
4.23.2 Alternative Proteins 394
4.23.2.1 Rendered Meat Products 394
4.23.2.2 Meat and Bone Meals (MBM) 394
4.23.2.3 Poultry By-Product Meals (PBM) 394
4.23.2.4 Feather Meals 395
4.23.2.5 Blood Meals 395
4.23.2.6 Fishery and Aquaculture By-Products 396
4.23.2.7 Amphipod and Krill Meals 396
4.23.2.8 Insect Meals 397
4.23.2.9 Safety Issues 397
4.23.2.10 Microbes 397
4.23.2.11 Parasites 400
4.23.2.12 Mycotoxins and Heavy Metals 400
4.23.2.13 Annelids 401
4.23.2.14 Single-Celled Products (SCP) 401
4.23.2.15 Microalgae 401
4.23.2.16 Fungi and Yeasts 402
4.23.2.17 Bacteria 402
4.23.2.18 Plant Proteins (VP) 402
4.23.2.18.1 Soybean Meal 402
4.23.2.18.2 Corn and Wheat Gluten Meals 405
4.23.2.18.3 Concentrates and Isolates 405
4.23.3 Anti-nutritional Factors and Mycotoxins 406
4.23.4 Exogenous Enzymes 406
4.23.4.1 Phytases 406
4.23.4.2 Carbohydrases 407
4.23.4.3 Lipases 408
4.23.4.4 Proteases 408
4.23.4.5 Enzyme Blends 408
4.23.5 Alternative Oils 408
4.23.6 Vitamins and Minerals 409
4.23.7 Pigments 409
4.23.8 Nutrient Sensing and Feed Stimulation 410
4.23.9 Pre-, Syn-, Pro- and Post-biotics 410
4.23.10 Outlook 410
References 411
Abstract
Due to the precarious status of globalfisheries the aquaculture sector has come under pressure to move away from its addiction tofishmeal (FM) andfish oil (FO) as feed ingredients, toward more sustainable alternatives. This chapter provides a brief overview of animal, microbial and plant-based feedstuffs that have been examined as FM/FO substitutes. Other than classic rendered meat products, attention is given to insect meals and issues surrounding their safety. Single celled products, including fungi and yeasts, bacteria, and microalgae are examined as sources of protein, lipid, pigments and enzymes. Plant- based proteins and lipid sources are also examined. Feed additives such as exogenous enzymes (phytases, lipases, proteases and carbohydrases) are evaluated as potential aquafeed ingredients as too are pigments, chemoattractants and palatants.
Discussion is provided on pre-, pro- and synbiotics. Examples of the application of these various ingredients are considered with reference to over 50 species of cultivated organism.
4.23.1 Introduction
Seafood plays a critical role in human nutrition and global food security, representing a valuable source of macro- and micronu- trients of fundamental value to a healthy and varied diet (Mohanty et al., 2019;Hicks et al., 2019). Since 1961, annual growth in per capitafish consumption has doubled from around 10 kg per year to over 20 kg per year today (IFAD, 2019;FAO, 2020). What is remarkable about thisfigure is that over the same timeframe the world’s population grew from about 3 billion to 8 billion. Global demand forfish over this period, therefore, jumped 5-fold. Several factors underpin the global increase in seafood consumption, including improved living standards and income, enhanced educational attainment, and heightened health consciousness. The health benefits associated with seafood are well documented and include cardiovascular protection, reduced risk of cancers, bene- ficial effects on a variety of neurodegenerative disorders and, among others, involvement in resolving inflammatory-autoimmune diseases (Alhassan et al., 2017;Cederholm, 2017;Venugopal and Gopakumar, 2017;Calder, 2018;Fard et al., 2019;Sarojnalini and Hei, 2019). In the coming decades world population growth is expected to slow, but by 2050, it is nonetheless projected to reach around 10 billion (UN, 2022). If the same patterns of seafood consumption are to be maintained as today (although it has been suggested that per capita intake may increase;Cai and Leung, 2017), then an additional 50þmillion tons of seafood would be required. Depending on scenario employed, this demand could be achieved, provided certain boundaries are not crossed, catastro- phes are avoided, and specific conditions are fulfilled (Béné et al., 2015;Costello et al., 2020;FAO, 2020). The principal method of increased seafood production will be through aquaculture (e.g., Gentry et al., 2017;Troell et al., 2017;Garlock et al., 2020), although worrywarts to this prediction exist (e.g.,Belton et al., 2020;Sumaila et al., 2021). Indeed, several challenges hinder pros- pects for aquaculture expansion, with the severity and type of obstructions differing geographically, with type of aquaculture prac- ticed (marine, freshwater, brackish), and species farmed (algae, invertebrate, vertebrate). Continued growth and sustainability of the aquaculture sector will be dependent on the availability and/or repurposing of suitable terrestrial and aquatic habitats. In the marine, it has been estimated that globally over 11.4 million km2are available and suitable forfinfish aquaculture, and around 1.5 million km2for shellfish production (Gentry et al., 2017). While suitable space is available in both tropical and temperate zones, however, the common nature of the seascape and its multiuser character has led to conflicts. These have included those between aquaculturists and traditionalfishers, conservationists, environmentalists, coastal property owners, the tourism and recre- ational sectors, within shipping, military and power generation domains, and others. Similar tensions have been witnessed regarding freshwater aquaculture especially with respect to policy development and ownership and control of land and water rights.
Even given these complications, however, aquaculture development remains an attractive proposition for many countries.
Other than providing increased food security and independence, aquaculture alleviates poverty in many areas of the world, and generates an important source of export income. Employment in the aquaculture sector is open to those of varying educational attainment and physical ability, is gender neutral, and presents opportunities in coastal communities where work prospects may otherwise be limited. Aquaculture relieves the pressure on wildfisheries and can even be used to enhance, supplement and assist in their recovery (McLean, 2021a,b), thereby safeguardingfishers facing vessel decommissioning, quotas and collapsing stocks.
Growth in the aquaculture sector also stimulates expansion in support and services industries (McLean, 1998). Non-fed, multi- trophic and integrated aquaculture has proven beneficial in the reduction of eutrophication caused by agricultural runoff, enhanced nutrient cycling and rates of denitrification. Advances in technology permit production of aquatic animals even in water-poor regions due to water recirculation techniques. Such practices also enable animal containment, thus reducing genetic pollution and risks of disease dissemination.
Even given the undisputed advantages presented by aquaculture, the sector remains one of the most disputed animal protein production systems in the world (Bush, 2018). Feeds, and especially their marine ingredients, have become a topic of attention in terms of questioning industry sustainability. Because of its high nutrient density, excellent profile of essential amino acids, high palatability, and digestibility, fishmeal (FM) has traditionally represented the mainstay protein ingredient of aquafeeds whereasfish oil (FO), due to its fatty acid composition, has represented the core lipid. These products are derived mainly from so-called forage species taken by industrialfisheries. However,fluctuations in their catch due to natural (e.g., El-Niño Southern Oscillation events) and anthropogenically-induced climate change, overfishing, and a greater proportion being used for human food, has led to increases in the price of FM/FO (Pincinato et al., 2020). Consumers have become more aware and informed about sustainability and recognize that industrialfishing operations can cause severe disruptions to ecosystems, including losses to biodi- versity (Pauly and Zeller, 2016;Shannon and Waller, 2021), and are responsible for at-sea discards, which may represent 10.8% of global catch (Gilman et al., 2020). Together with human rights infringements in the commercialfishery, aquaculture, and supply chain sectors (Lewis et al., 2017), and animal welfare issues (Eriksen, 2003), all these concerns ultimately play roles in consumer purchasing decisions. Seafood buyers are also becoming more knowledgeable of the range of potential contaminants that may impact food safety; including those of raw materials used during aquafeed production (Glencross et al., 2020a,b). These worries have resulted in the creation of a sustainability imperative driven by consumers who demand safe, ethically, and environmentally responsive food production systems. The aquafeed industry represents a critical reaction hub in helping to achieve such a goal and has already started to focus on the use of a diversity of non-marine proteins and oils in efforts to substitute FM/FO (Gatlin et al., 2007;Gasco et al., 2018). Nevertheless, the aquafeed sector retains a significant dependency upon marine products (Boyd et al., 2022) and it is likely that this addiction will remain for some time.
Although attempts to remove animal proteins fromfish feeds has a long history (Almy and Robinson, 1920), it was not until the late 1980s that the aquafeed industry started to contemplate FM replacement more earnestly. This resulted partly due to increased competition from the agricultural and pet feed industries, a decline in industrialfishery production, increasing costs of FM and,
more recently, due to ethical considerations. Over the last twenty or so years, there has been a steady decline in the use of FM and FO in aquafeeds (Tacon and Metian, 2008;Sprague et al., 2016;IFFO, 2017;Tacon, 2020) and this trend continues. The FM industry uses around 20 million tons of raw material per year of which 14 million tonnes are wholefish and 5.6 million tonnes by-product.
This material is used to produce aroundfive million tons of FM and a million tons of FO, three-quarters going into aquafeeds, illus- trating the continued importance of marine resources to the sectors’food account (Konar et al., 2019). However, because the avail- able quantities of FM and FO will become scarcer as demand increases, the feed industry has turned to alternative raw materials to satisfy growing needs. This ingredient substitution includes transition to a variety of plant-based proteins, animal by-products, and novel ingredients (e.g.,Bulfon et al., 2015;Sprague et al., 2017;Hua et al., 2019;Kok et al., 2020;Hua, 2021;Agboola et al., 2021;
Lorenzo and Simal-Gandara, 2022). While aquacultured species do not have a conditional need for FM and FO (Wilson, 2002;
Sargent et al., 2002), their diets must comprise an optimal mixture of nutrients to satisfy requirements. This is not as easy as it seems since, of the 230 or so aquacultured species (Metian et al., 2019), a basic understanding of nutritional requirements is known for just a handful. Moreover,findings in one species are not necessarily transferable to another (Oliva Teles et al., 2020). An expanded feed formulators pantry, therefore, while making aquafeed composition more complex, does provide greaterflexibility in choosing ingredients that match known requirements of a species. Nevertheless, nutrient substitutions must not dim animal performance, compromise health, impact processing, storage, or consumer acceptance. Most important, nutrient alternatives must be socially and economically viable.
4.23.2 Alternative Proteins
4.23.2.1 Rendered Meat ProductsThe use of unprocessed terrestrial animal products by aquaculturists has an extended history (Hayford, 1921;Gutsell, 1939), with especially salmonid hatcheries employing slaughterhouse by-products. By the mid-1950s,Grassl (1956)reported on the growth of trout fed either on wet chopped meats or dry pelleted animal/vegetable feeds, supplemented with beef liver as a vitamin source. He observed no difference between the two groups even when the pellet was fed at 50% the amount recommended for raw feeds.
Following these trials various hatcheries adopted pelleted feeds containing rendered animal rations. Rendering transforms materials from the animal industry into stable and safe products. The process may commence with the crushing and grinding of unused mate- rial followed by cooking which removes moisture, releases fats, and kills microbes. Fats are separated by draining and pressing with the balance being ground into a powder, creating the meal. Meal production may incorporate various side processes such as rotary drying used for feather and blood meal. Although early on, some feeding trials with rendered pelleted products experienced issues with digestibility, these initial problems have largely been overcome (Bureau, 2006). Because rendered meals and derivative fats are less expensive than FM and FO, they have found extensive use by the aquafeed sector. It is well to remember that around 40% of the live weight of animals used for human food remains unconsumeddwithout rendering the unexploited parts of the animal would be squandered as landfill or otherwise. The following provides brief overview of the various meals available, examples of their appli- cation to aquacultured organisms and potential concerns, where these exist, relating to their use.
4.23.2.2 Meat and Bone Meals (MBM)
Meat and bone meals generally have lower protein and higher fat and ash levels than meat meals. Moreover, the quality of MBM varies considerably between rendering plants and the profile pf essential amino acids and macrominerals differ to that of meat meals, often being deficient in methionine (Met) and isoleucine (Ile). The crude protein (CP) content of MBM varies, depending on source, between 47% and 54%. Apparent protein digestibility of MBM is also lower than FM, and the product may negatively influence the pelleting process (Hertrampf and Piedad-Pascual, 2000). MBM has been used successfully to replace around 20% FM with higher proportions being used when supplementary amino acids are employed during diet formulation.El-Sayed (1998)re- ported no differences in growth performance of Nile tilapiaOreochromis niloticuswhen MBM was employed with wheat bran to replace FM and similar responses were observed in snakeheadOphiocephalus argus(Yu et al., 2015) with 20% FM replacement, and Pacific whiteleg shrimpLitopenaeus vannamei fed mixtures of MBM with poultry by-product meal (PBM) and blood meal (Ye et al., 2011). The high ash content of MBM increases intestinal transit time resulting in higher feed intake and decreased feed efficiency and growth in African catfishClarias gariepinusand Nile tilapia (Goda et al., 2007;Xavier et al., 2014), although when used with channel catfishIctalurus punctatusfingerlings, no such impacts were measured (Li et al., 2020). The cost savings of feeds incorporating MBM, even when growth performance is negatively impacted, however, are offsetting (Moutinho et al., 2017). Nevertheless, the use of MBM is restricted in some countries. For example, EC Regulation 999/2001, which was enacted to prevent, control, and eradicate transmissible spongiform encephalitis (BSE), prohibits the use of rendered animal by-products not intended for human consumption in aquafeeds (EC, 2001). This regulation remains in effect for ruminant by-products but has been amended, to permit use of PBM (EC, 2017) and insect proteins (EC, 2021).
4.23.2.3 Poultry By-Product Meals (PBM)
PBM is of high nutritional value, being rich in amino and fatty acids, macro and micronutrients. PBM comprise heads, gizzards, viscera, feet, undeveloped eggs and natural mortalities. High variation is thus encountered in chemical composition among
samples (Kerr et al., 2019), which may result not only due to the characteristics and makeup of the raw material, butflow of by- product to the hopper, the type, condition and maintenance of equipment employed, variations in temperature during process- ing and even plant management (Ferroli et al., 2000). Together with deficient content of conditionally essential amino acids (EAA) including Met, phenylalanine (Phe), and threonine (Thr), these variables may explain reported differences in product digestibility and growth when employed as a substitute for FM in aquacultured organisms (Gaylord and Rawles, 2005;Shapawi et al., 2007;Parés-Sierra et al., 2014). Two grades of PBM are available for aquafeedsviz.feed and pet food grade. The feed grade product is generally considered as being of lower quality, containing higher ash and lower protein content but, due to its lower cost, is more frequently employed. A helpful overview of the impact of PBM on a broad range of species is con- tained inGasco et al. (2018). Some trials have demonstrated the feasibility of total replacement of FM with PBM, without effect on growth, animal health or fillet eating qualitydirrespective of changes in fillet fatty acid profiles (Nengas et al., 1999;
Webster et al., 2000; Sealey et al., 2011; Hernández et al., 2014; Sabbagh et al., 2019; McLean et al., 2020a,b,c, 2022;
Galkanda-Arachchige et al., 2020;Randazzo et al., 2021).
4.23.2.4 Feather Meals
Poultry represents around 39% of global meat production with approximately 9.2 billion broilers being produced annually. A major by-product of the poultry rendering industry are feathers, which are formed of keratin proteins and thus decompose slowly.
Feather-based products have found wide use in various industrial processes ranging from glues to microbial growth media and the production of enzymes. Feather meal is produced by partial grinding under elevated heat and pressure which sterilizes and partially hydrolyzes and denatures the protein. While generally considered to possess a poor amino acid balance and digestibility, it is inexpensive and has been extensively used in animal feed rations (Firman, 2006). In commercial and academic trials feather meal has been successfully used to replace up to 25% FM in fish feeds without negative effects on growth or feed efficiency (Bureau, 2006) although contradictions to thesefinding appear in the literature (e.g.,Jasour et al., 2017;Chen et al., 2019;Ade- lina et al., 2020). More recent studies with European seabassDicentrarchus labraxhave reported 75% FM replacement with hydro- lyzed feather meal without impacting growth, feed intake, feed conversion (FCR) or protein efficiency (PER) ratios. Moreover, the study authors (Campos et al., 2017), observed no effects of FM replacement on whole body composition or assessed immune parameters. An interesting trial with longarm river prawns Macrobrachium tenellumdemonstrated that feather meal produced strong attractant responses relative to other assessed meals (Montoya-Martínez et al., 2018). If this characteristic were authentic, dietary incorporation of feather meal might assist in enhancing the palatability of poorly accepted feeds for freshwater prawns and perhaps, other species. Research push has centered attention on novel methods of processing feather meal, and this has resulted in more digestible products that improve nutrient retention and amino acid utilization (Pfeuti et al., 2019;Ren et al., 2020;Pool- sawat et al., 2021;Kumar, 2021).
4.23.2.5 Blood Meals
Blood is a valuable by-product of the animal rendering process. Traditionally blood is vat cooked and dried into a meal which is then used in livestock feeds. Blood meals are high in protein but due to palatability issues and poor amino acid balance their use has been restricted. New procedures for processing, as exemplified by spray andflash-drying, have, however, improved palatability and amino acid availability which has enhanced interest in using blood meals as an alternative protein supply. Nevertheless, laboratory trials appear to indicate variability in receptivity to such feeds by different species. For example, substitution of FM with bovine or donkey blood meal in African sharptooth catfishClarias gariepinusdiets, at anything above 7%, had a negative effect on growth and feed conversion and altered antioxidant enzyme functions (Ogunji et al., 2020; Ogunji and Iheanacho, 2021). Remarkably, complete replacement of FM with blood meal in diets for the same species has been reported to be without effect on growth, survival and feed conversion (Agbebi et al., 2009). Infingerling black carpMylopharyngodon piceusin which 20%–100% replacement of die- tary FM was examined, depressions in growth were observed together with reductions in gut trypsin activity (Twahirwa et al., 2021).
In marked contrast,Gao et al. (2020)reported that 50% substitution of FM with blood meal did not affect growth performance, feed conversion or survival, but did reduce intestinal fold height and visceral somatic index in common carpCyprinus carpio. When blood meal was used to replace 50% of dietary FM in Nile tilapia diets, augmented growth, improved feed conversion and equiv- alent survival to controls was recorded (Mokolennsang et al., 2021). Interestingly, when replacing FM at 25% and 75% levels, feed intake was significantly lower than controls, but animals returned equivalent growth. Incorporation of driedfish blood meal at 4%– 16% in diets for Pacific whiteleg shrimp resulted in decreased growth and feed intake but did not impact survival when compared against FM control groups (Pranama et al., 2018). Noteworthy was that inclusion offish blood meal had a marked effect on diet stability resulting in greater feed loss than experienced with controls. Also of note was that in contrast to thefindings ofTwahirwa et al. (2021), significantly increased trypsin activity was measured in animals receiving thefish blood meal-containing diets. In using chicken plasma meal to replace FM at 50–150 g/kg diet,Li et al. (2019)found that largemouth bassMicropterus salmoidesexperi- enced decreased feed intake and growth depression at the highest level of inclusion. Furthermore, at 150 g/kg diet the plasma meal reduced lysozyme activity, the classical complement pathway and respiratory burst suggesting a negative effect of the meal on animal health.
4.23.2.6 Fishery and Aquaculture By-Products
Co-products from mollusk processing may include digestive glands, gills, mantle, reproductive organs and shells whereas, for crus- tacea, shells, legs, heads, and meat portions may remain unused. By-products from farmed and processedfish may include natural mortalities, heads, frames, trimmings, bellyflaps, tails and skin, viscera and blood (Arvanitoyannis and Kassaveti, 2008). Each of these unexploited goods contain high quality feed components including feed stimulants, valuable pigments, omega 3 polyunsat- urated fatty acids (PUFAs), and others. These products can be employed in feed formulae with only basic processing steps. For example, meals derived from clams and squid have been employed at various levels of incorporation in aquafeeds for crustacea andfish without negative impacts on growth (Naik et al., 2001;Córdova-Murueta and García-Carreño, 2002;González-Felix et al., 2014;Mithun et al., 2019). Red swamp crayfishProcambarus clarkiiby-product meal, comprising washed, ground and dried (60C) exoskeleton and appendages (33% protein), with an amino acid profile that fulfills the requirements of Nile tilapia, was used to replace 25%–100% dietary FM. Four months feeding resulted in growth depression at the higher levels of inclusion, asso- ciated with renal tubular degeneration, glomerular atrophy and blood congestion, but a replacement of 25%–50% FM in the feed was deemed acceptable (El-Hady et al., 2019). Numerous other studies have illustrated the utility of various shrimp meals and silages in replacing dietary FM for shrimps, tilapias, carps, catfishes, salmonids, and others (Cruz-Suarez et al., 1993;Fox et al., 1994;Fagbenro and Bello-Olusoji, 1997; Ozogul, 2000;Nwanna, 2003; Cavalheiro et al., 2007;Leal et al., 2010; Fall et al., 2012;Al-Jader and Al-Khshali, 2021). Like shrimp carcasses,fishery processing by-products, discards, or unsold inventory, can also be rendered or ensiled and stabilized using co-drying with, for example, wheat bran (Goddard et al., 2003). Kotzamanis et al. (2001)used minced trout offal containing 15% CP and 11% fat as a substitute for FM in gilthead breamSparus auratadiets and observed similar growth and body composition at the end of a 72-day trial. When used to replace 50% dietary FM in African catfish feed, marinefish viscera had no impact on growth, protein efficiency ratio or production when compared against commercial feeds or an experimental FM-based diet, irrespective of whetherfish were reared in concrete raceways or earthen ponds (Oké and Abou, 2016;Oké et al., 2016). Viscera meals, derived from milkfishChanos chanos(Mamauag and Ragaza, 2016), skipjackKatsu- wonus pelamis(Chotikachinda et al., 2013;Iranshahi et al., 2011) and Atlantic bluefinThunnus thynnus(Gümüs et al., 2011) tunas, squid (Mai et al., 2006) and others have all been successfully employed to replace dietary FM. Additional methods of processing fishery co-products include the use of enzymes, such as alcalase, to produce mollusk, crustacean andfish protein hydrolyzates, and fermentation, following inoculations of bacteria (Dawood and Koshio, 2020). Some of these products have been shown to increase growth and immunity when used to replace FM in crustacean andfish feeds (González-Felix et al., 2014;Hernández and Olvera- Novoa, 2017;Zynudheen et al., 2020;Siddik et al., 2021;Teoh and Wong, 2021) and several authors have isolated a variety of secretagogues and growth factors from hydrolyzates and processing side streams (Cancre et al., 1999;Välimaa et al., 2019).Kou- soulaki et al. (2009,2012)reported that inclusion of stickwater from FM production in plant-supplemented Atlantic salmonSalmo salardiets resulted in growth stimulation without impacting body composition.
4.23.2.7 Amphipod and Krill Meals
Koops et al. (1979)observed that rainbow trout fed an Antarctic krillEuphausia superbameal-based feed performed equally well to fish maintained on a FM-based diet. However, later research determined that the krill contained very high levels offluoride, and this raised alarm that the trout muscle may have accumulatedfluoride. Subsequent trials determined that mostfluoride accumulated in the trout’s scales and skeleton (Tiews et al., 1981). Thefluoride was discovered to be highest in the krill carapace and most of the content could be removed by acid extraction. Dietary calcium supplementation also reducesfluoride uptake by100% (Hansen et al., 2011). Both partially deshelled and whole krill meals have been investigated as replacers for FM in Atlantic salmon, and substitution with deshelled krill meal did not impact growth performance relative tofish fed a FM-based feed. Whole krill meal feeds, however, had a negative effect on growth and caused a reduction in trypsin activities in the pyloric and mid intestine (Hansen et al., 2010). In an earlier study (Moren et al., 2006) no adverse effects of growth were observed with either Atlantic salmon or Atlantic codGadus morhuawhen fed Arctic Thysanoessa inermisor Antarctic krill or amphipodThemisto libellulameal. However, high levels of copper and cadmium, exceeding EU standards for feedstuffs, were detected in krill and amphipod meals respectively.
When Antarctic krill meal was used to replaced 50% of FM in European sea bass diets, no negative impacts to growth or muscle fatty acid composition were seen (Torrecillas et al., 2021). Contrary to other studies, when examined in gilthead sea bream feeds, increasing FM substitution with krill meal decreased growth and feed intake (Moutinho et al., 2019). In Pacific whiteleg shrimp diets, 100% replacement of FM with Antarctic krill meal provided equivalent growth (Nunes et al., 2011) and a number of trials indicate that krill meal at low incorporation can act as feeding stimulants (vide infra). Interestingly,Leonardi et al. (2021)reported that 3% inclusion of high protein krill meal in a low-cost diet improved growth of Pacific whiteleg shrimp to the extent that cost was reduced by 10 ¢ kg1versus a commercial feed.
Frozen amphipodsElasmopus pectenicrushave proven useful as feeds for the lined seahorseHippocampus erectus(Vargas-Abúndez et al., 2018) andPlatorchestia platensis-based diets equaled the performance of FM feeds for another ornamental speciesPoecilia retic- ulata(Appadoo and Saudagur, 2007). When used as a paralarval octopusRobsonella fontanianafeed, the tube-building amphipod Jassa marmoratagrew heavier than those fed onArtemia(Gonzalez et al., 2011).Gammarus pulexmeals substituting<75% FM in gray mulletMugil cephalusfeeds, provided equivalent growth to the full FM diet (Ashour et al., 2021), while 100% replacement of FM using a marine amphipod had no negative effects on the performance of juvenile turbot (Alberts-Hubatsch et al., 2019). In marked contrast, feeding Atlantic cod on a weaning diet containing 25%–100% Norwegian sea amphipodThemisto libellulameal resulted in
decreased weight gain and an increase in deformities (Opstad et al., 2006). Tiger prawnPenaeus monodonjuveniles fed liveGrandi- dierella megnaestocked at various densities grew at rates like those of commercial feeds (Sulaeman et al., 2020).
4.23.2.8 Insect Meals
Various lines of evidence suggest that ancient hominins relied on insects as an important protein source (Bodenheimer, 1951;
Ramos-Elorduy, 2009;Ko, 2016;Lesnik, 2018). Even today it is estimated that insects form part of traditional diets for around 2 billion people (van Huis et al., 2013) with over 2100 species being consumed in over 110 countries (Mitsuhashi, 2017). Although the nutritional value of edible insects varies greatly, differing with metamorphic stage, habitat, diet, and method of processing (Table 1;Oonincx et al., 2015;Koutsos et al., 2019), many express high levels of protein and fat (Table 1). It is because of this, that interest in employing insects as ingredients for animal feeds has intensified (van Raamsdonk et al., 2017;Berg et al., 2017;
Feng et al., 2017;de Souza-Vilela et al., 2019;Sogari et al., 2019a,b;van Huis, 2020;Madau et al., 2020;Hawkey et al., 2021). Their potential use as alternatives to FM in aquafeeds has likewise garnered increased attention (Table 1;Sánchez-Muros et al., 2016;
Ankamah-Yeboah et al., 2018;Lock et al., 2018;Karthick Raja et al., 2019;Shaikhiev et al., 2020). However, the use of insects in aquaculture is not a recent innovation. Integratedfish production systems are frequently encountered in Asia and perhaps one of the earliest examples of using insects to supportfish growth was seen in mulberry dyke-fish pond systems which originated some 2500 years ago (Ruddle and Zhong, 1988). These production platforms employ mulberry as feed for silkworms (Bombyx mori) which, in turn, provide fertilizer for ponds in the form of excreta, and sloughed skins and pupae, as food forfish. Even water used in the extraction of silk from silkworm cocoons is reused, yielding 5 kgfish m1(Hu and Yang, 1984). It is not too surprising, there- fore, tofind that some of the earliest studies to examine the use of insects in modern, prepared formulations, used silkworm pupae either as meals or in powder form (Kim, 1974;Akiyama et al., 1984).
More recent interest in the application of insect-based products has grown for a variety of reasons, not least the global expansion of insect farming operations. Industrial ventures now provide a more reliable and uninterrupted supply of raw materials of known composition and acceptable quality. As well, the nutritional profile of many insect species is not unlike FM, and considered supe- rior, in many respects, to that of plant proteins (Nogales-Mérida et al., 2019). Insect proteins are also highly palatable and digestible (Sánchez-Muros et al., 2016) and defatting technologies enhance their processability (Sindermann et al., 2021). Insect farming systems offer potential to reduce land occupation, and water and energy consumption per unit of production (Rumpold and Schlüter, 2013; Dobermann et al., 2017) and thereby satisfy the demands of conservationists and consumers. The variety of substrates upon which insects can be reared, include industrial, market, and institutional (e.g., schools, hospitals, prisons, etc.) food scraps, household and animal wastes, such as offal and manure, and by-products from breweries, vintners and other industries (Verner et al., 2021).Table 1, while not exhaustive, provides examples of insect species employed in feed trials with a selection of aquacultured animals. These have included studies in which FM components of diets have been partially or entirely replaced. In general, the response offish and shrimp to insect-based meals has been positive with differences in response seemingly being dependent on meal/feedstock origin, species used, and level of dietary inclusion employed. Comprehensive reviews have been pre- sented regarding insect composition and meal digestibilities (van Huis et al., 2013;Nogales-Mérida et al., 2019) and the reader is directed to excellent reflections of,Sánchez-Muros et al. (2016)andHua (2021)on the impacts of insect meals on the performance of cultivated species.
4.23.2.9 Safety Issues
Although clearly offering high potential as aquafeed ingredients, there are several safety concerns surrounding the use of insects. As with other food and feed production systems (e.g.,Glencross et al., 2020a,b), vulnerabilities during rearing, harvesting, processing and post-handling exist. In particular, the bioaccumulation, growth and transmission of microorganisms, parasites and mycotoxins represent worries. However, organic contaminants, including dioxins, PCBs, DDT and pesticides, together with heavy metals, also pose hazards for transfer to feeds and later accumulation and transmission to consumers. Just asfish can pass on diseases to humans (McLean et al., 2020d), the potential exists for the transfer of microbial and sapronotic diseases from insects tofishes.
4.23.2.10 Microbes
Studies on the microbial safety of insects used for human consumption, while unusual, have been reported but appraisal of risks associated with the transfer of microbes from insects to feeds, and thence consuming animals, are scarce indeed. Research on insects as food for humans has revealed very high levels of generally Gram-negative (Micrococcusspp. andLactobacillusspp.) microbes (105– 106 cfu/g), and especially fecal coliforms, from both larvae and adult stages. However, neitherSalmonellaspp. norListeria monocy- togeneswere detected (Giaccone, 2005). Nonetheless,ClostridiumandListeriaspp. have both been detected in processed crickets and grasshoppers (Garofalo et al., 2017;Wynants et al., 2017). Several bacteria that are known to occur in the insect gut are of clinical significance. For example,Klebsiella pneumoniaean opportunistic pathogen of humans, occurs in the intestine of migratory locusts, while the insect pathogen,Spiroplasmaspp., can cause neurodegenerative diseases in humans and animals (Bastian et al., 2012). A listing of other potential pathogenic microbes found in various species that may be of concern when employing insect-based prod- ucts in aquafeeds is provided bySchlüter et al. (2017)and the relationship between insects and carriage of zoonoticSalmonellaspp.
diseases has been considered by Wales et al. (2010). Trials in which different methods of insect storage and processing were
Table 1 Examples of insect species and developmental stage employed as supplementary protein sources or replacement forfishmeal (FM) in diets of various species of culturedfishes and crustaceans
Insect Stage
% Protein/fat
content Test species Observations References
Hermetia illucens Tenebrio molitor Gryllodes sigillatus Blatta lateralis
PP L I I
40/33 56/25 61/19 55/26
Rainbow trout 20% inclusion rate. No effect on survival.
YGrowth withG. sigillatus(P<0.05).
[Growth withH. illucensandT. molitor(P<
0.05).
YIntestinal fold height withTm/Gs,[inHi
Józefiak et al. (2019a)
H. illucens L 44–6/17–22 Atlantic salmon 85% of protein. No effect on growth, survival, or body composition.
YDigestibility of AAs
100% replacement offishmeal. No effect on digestive enzyme activity, feed intake or FCR and body composition. Sensory analysis revealed[ Rancidflavor
Belghit et al. (2018,2019)
Bombyx mori L Chum salmon [FE @ 5% FM substitution (P<0.05) Akiyama et al. (1984)
H. illucens T. molitor
L L
40/33 56/25
Siberian sturgeon 50% FM substitution had no effect on growth, survival, or intestinal fold height.
Beneficial (?) impact (P<0.02) was discerned on gut microbiome.
Józefiak et al. (2019b)
H. illucens F 21/6 Channel catfish [wt gain, FI (P<0.05) No difference in survival
Yildirim-Aksoy et al. (2020a) Acheta domesticus
Zophobas morio
A 22/4.6 19/18.3
European perch 25% replacement of FM (50:50 mix of insect meals) resulted inYgrowth, SGR, andK(P<
0.05)
Changes in fatty acid profile
Tilami (2019)
H. illucens F 18.5/5.3 Hybrid tilapia 30% inclusion caused no change in body composition or survival
No effect on serum chemistry or hematology [Growth, PER and apparent protein utilization
(P<0.05) versus control diet.
Serum complement activity higher than controls (P<0.01)
F-based diets had better survival following challenge withFlavobacterium columnareand at the 30% level, againstStreptococcus iniae
Yildirim-Aksoy et al. (2020b)
Imbrasia belina A 57/13 Mozambique tilapia 60% inclusion rate
YSGR (P<0.05) but equivalence in wt gain and FI, FCR and PER
Rapatsa and Moyo (2017)
Musca domestica L 37.5/19.8 Nile tilapia Identical SGR, FCR, growth and PER YSurvival (P<0.05)
[Hemoglobin (P<0.05)
Ogunji et al. (2008)
Nauphoeta cinerea Gromphadorhina
portentosa Gryllus assimilis Zophobas morio T. molitor
A A A L L
39/23 37/13 40/18 30/33 29/32
Nile tilapia Differences in digestibility coefficients between insect meals for all nutrients (P<0.0001)
Fontes et al. (2019)
H. illucens 30/5 Nile tilapia No differences in growth, FI, survival, or hematology.
Skin and mucus lysozyme and peroxidase[(P<
0.05)
Tippayadara et al. (2021)
H. illucens PP Turbot High meal inclusionYgrowth, FI (P<0.05)[ Kroeckel et al. (2012) T. molitor L 52/10 Red seabream [Growth (P<0.05) versusfishmeal diet
[Survival afterEdwardsiella tardachallenge
Ido et al. (2019)
M. domestica L 67/8.5 Red seabream YGrowth (P<0.05) Hashizume et al. (2019)
Table 1 Examples of insect species and developmental stage employed as supplementary protein sources or replacement forfishmeal (FM) in diets of various species of culturedfishes and crustaceansdcont'd
Insect Stage
% Protein/fat
content Test species Observations References
T.molitor L Blackspot seabream No impact on FCR, SGR, FI, texture, growth
Fillet pHY
Change in ventral skin color (P<0.05) No impact on proximate composition but EPAY
(P<0.05)
Sn3/Sn6 FA ratio was linearlyYwithT. molitor presence
Iaconisi et al. (2017)
T. molitor L Gilthead seabream YGrowth, SGR @ 50% FM substitution (P<
0.05)
Piccolo et al. (2017) T. molitor L 53/21 European seabass YGrowth, SGR @ 50% FM substitution (P<
0.05)
Gasco et al. (2016) H. illucens PP European seabass No impact on growth, FI, FE, survival or AA
digestibility
Magalhães et al. (2017)
A. domesticus A N.S. African catfish Ygrowth, SGR (P<0.05) Nnaji and Okoye (2005)
Gryllus bimaculatus A 40/12 African catfish 100% replacement of FM[WBC, total protein, globulin and lysozyme activity (P<0.05) Enhanced survival onAeromonas hydrophila
challenge
Taufek et al. (2018)
Acheta domesticus A N.S. Walking catfish YGrowth, RG, FCR (P<0.05) Johri et al. (2011)
H. Illucens L 42/12 Barramundi 100% replacement of FM substantiallyYGrowth
(P<0.05) [FCR (P<0.05)
Altered EAA profiles favoring His and Arg
Kataya et al. (2017)
H. Illucens L 44/17 Barramundi 30% replacement CP
No differences in growth, SGR, FCR, survival or serum lysozyme.
Suppressive effect ofH. illucensoil on bactericidal activity v.fish oil (P<0.05)
Upregulation of IL-1band IL-10 gene expression Gut and skin mucin cells increased (P<0.05) Changes in FA composition tofillet
Hender et al. (2021)
H. illucens PP 41/17 Zebrafish 50% FM replacementYgrowth and expression of
igf1 andigf2 (P<0.05)
Altered profiles of fatty acids (P<0.05) and n3:n6 ratios
No impact on gut morphology but liver exhibited steatosis
Zarantoniello et al. (2019)
Oryctes rhinoceros A 73/12 Puyu
Goldfish Common carp Oscar
Overall poor performance v. control [Growth
[Growth
Overall poor performance v. control
Kamarudin et al. (2007)
B. mori L N.S. Speckled shrimp YDigestive efficiency Sumitra-Vijayaraghavan et al.
(1978) H. Illucens L 34/26 Freshwater prawn Equivalent growth and survival
YFCR
Tiu and Ratliff (2012)
M. domestica L Chinese shrimp [Growth (P<0.05)
[n3:n6 ratio in muscle (P<0.05)
Zheng et al. (2010) Bombyx mori
T. molitor A. domesticus H. illucens
P L A L
45/29 54/29 64/19 37/14
Giant river prawn [Growth vfishmeal (P<0.03) [Survival
McCallum et al. (2020)
T. molitor 45/42 Narrow-clawed
crayfish
50% substitution of FM increased growth, SGR, PER, and molt frequency (P<0.05) YFCR and survival (P<0.05)
Mazlum et al. (2021)
H. illucens L 52/15 Pacific white shrimp @ 36% of dietary protein,Ygrowth, SGR (P<
0.05)
FI and survival unaffected
Cummins et al. (2017)
(Continued)
examined (Klunder et al., 2012), determined that boiling for 5 min was an efficient way to eliminate Enterobacteriaceae but not spore-forming microbes. Roasting, on the other hand, did not kill all Enterobacteriaceae. The same authors observed higher levels of spore-forming bacteria and Enterobacteriaceae in insects that had been crushed, presumably due to their release from the gut.
Freeze-drying and blanching have been reported to reduce aerobic mesophilics, yeast and mold counts for a variety of species (Megido et al., 2017). Importantly,Megido et al. (2017)also discovered that insects derived from unregulated or illegal markets were highly contaminated by microbes to the extent that these would need a processing step before use.
4.23.2.11 Parasites
There are comparatively few reports of the transfer of parasites from insects to other animals when eaten whole thereby suggesting that, under controlled conditions of production, and following processing into meals, they pose limited if any risk of disease.
Gałe˛cki and Sokół(2019)analyzed farmed crickets, mealworms, migratory locusts and cockroaches as transporters of various para- sites. They reported that the different species were colonized by various developmental forms of parasites specific to insects includingNosemaspp.,Gregarinespp.,Nyctotherusspp.,Steinernemaspp.,H. diesigni, andThelastomaspp. Parasitic protists, such as the Gregarinasina, that colonize the digestive tract and body cavity of cockroaches and other species are characterized by swollen abdomens associated with a putrid smell indicative of septicemia (Lopes and Alves, 2005). It may be possible for the compounds responsible for putridity to transfer to meals and ultimately impact palatability of feeds.
4.23.2.12 Mycotoxins and Heavy Metals
Mycotoxin contamination of insect feedstock represents a concern since they can bioaccumulate and may pass on to feeds and their consumers. This is because mycotoxins are very heat stable (Bullerman and Bianchini, 2007). However,Mancini et al. (2020)did not observe dangerous accumulations of aflatoxin B1 (afB1), ochratoxin A (OTA) or fumonisin B1 when larvae ofTenebrio molitor were fed cereal-based diets. Correspondingly, neither black soldierfly or mealworm accumulated deoxynivalenol (DON), zearale- none (ZEN) afB1, or OTA when feed was spiked at 25 times the limits set by the EU (Carmenzuli et al., 2018). Nonetheless, increased research on mycotoxin accumulation is desperately needed since other studies have reported toxicological impact of mycotoxins on the development of various insect larvae, includingT. molitor(Reiss, 1973;Davis et al., 1975;Davis, 1982). The potential forH. illucensto accumulate various elements from optimized feeds was examined byProc et al. (2020)who reported biomagnification of Ba, Bi, Cu, Fe, Hg, Mg, Mo, Se and Zn at all stages of development, while Ca, Cd, Ga, Mn, P and S were only accumulated in some developmental stages. Other studies with various insects have similarly demonstrated their propensity for metal accumulations (Fels-Klerx et al., 2018). Another issue that requires consideration in using insects as feed include possible presence of allergens which may have significance for those working in direct production, processing and storage and indirectly during feed manufacture (Ribiero et al., 2021).
A major concern that haunts the insect in feeds industry is their lack of competitiveness. At the time of writing this chapter, pro- cessed insect meals were more expensive than the highest quality FMs. Their use in aquafeeds, therefore, are restricted. At the present time 5% substitution of FM using black soldierfly meal results in a 10% increase in the cost of commercial diets (personal commu- nication, Boyd Way, Dainichi Corporation, August 19th,2021). This has led to some to tout the immunomodulatory effects of insect meals and the presence of growth factors rather than their alternate protein potential. Equally, there have been reports of Table 1 Examples of insect species and developmental stage employed as supplementary protein sources or replacement forfishmeal (FM) in diets of
various species of culturedfishes and crustaceansdcont'd
Insect Stage
% Protein/fat
content Test species Observations References
T. molitor Pacific white shrimp 100% substitution
Dietary replacement resulted in linear increase in lipids (P<0.05)
Color and musclefirmness unaltered
Panini et al. (2017)
T. molitor L 36/7 Pacific white shrimp 100% replacement of FM Identical performance for growth
[Phenoloxidase (P<0.0001) v. FM following V. parahaemolyticuschallenge and 60%
reduction in mortality.
Motte et al. (2019)
B. mori P N.S. Disk abalone 100% replacement of FM with SBM/CGM @ 2:1
ratio
[Survival and growth (P<0.05)
Cho (2010)
A¼adult, AAs¼amino acids, EAA¼essential amino acids, F¼frass, FCR¼feed conversion ratio, FE¼feed efficiency; FI¼feed intake, I¼imago,K¼condition factor, L¼ larvae, N.S.¼not stated, P¼pupae; PER¼protein efficiency ratio, PP¼prepupae.
negative effects of insect meals on intestinal histology and uncharacterized changes in the gut microbiome. Clearly if used as an ingredient other than as an alternative protein/fat source, then it is vital that more, directed, in-depth studies are required.
4.23.2.13 Annelids
Aquacultured polychetes are employed as bait, pet food, for assisting biofiltration and remediation of aquaculture wastes (Palmer, 2010) and can be used to enrich earthen ponds (Carvalho et al., 2007). As a valuable source of PUFA (Jerónimo et al., 2021), they are also used as components of maturational diets for broodstockfish and shrimp (Parthiban et al., 2006;Deenarn et al., 2020). As an element of feeds, they enhance coloration in ornamental species (McLean et al., 2015), and growth in shrimp andfish when compared against FM-based diets (Zheng et al., 2008;Salze et al., 2010). The major limitation to the use of polychetes in aquafeeds relates to low commercial production, even though their reproductive cycle is enclosed and controlled, methods for the cryopres- ervation of gametes are available, and an understanding of their nutrition acquired.Pombo et al. (2020)provide an overview of the current state-of-art of the sector.
Earthworms represent another annelid that have been successfully evaluated for their remedial action of aquaculture side- streams (Marsh et al., 2005). Depending on species, and method of processing, earthworm protein content varies from 60% to 70% while fat levels are 3%–10% (Sabine, 1983;Musyoka et al., 2019). Protein levels may differ depending on culture substrate employed, production system and processing methods used. Earthworm meal-based diets have been evaluated in a wide range of aquacultured species, at various levels of inclusion (Musyoka et al., 2019). Results from these trials indicate good digestibility (94þ%), amino acid and mineral profiles (Hertrampf and Piedad-Pascual, 2000), but reduced growth in test subjects, possibly due to palatability issues when employed above 50% inclusion levels (Musyoka et al., 2019). Nonetheless, higher weight gains have been reported for walking catfish Clarias batrachus (Ghosh, 2004), common carp (Ngoc et al., 2016; Nandeesha et al., 1988), obscure snakeheadParachanna obscura(Vodounnou et al., 2016), rohuLabeo rohita(Mohanta et al., 2016), rainbow trout Oncorhynchus mykiss(Tacon et al., 1983;Velasquez et al., 1991), giant freshwater prawnMacrobrachium rosenbergii(Dube et al., 2002) and others, in which earthworm meal was used at<50% inclusion levels. Cost-benefit analysis, comparing production costs of Nile tilapia juveniles fed either a FM-based or earthworm meal was highly favorable, recording a 20% reduction in cost per kilo produced (Gbai et al., 2018). Similar studies, with the same species, comparing earthworm bedding meal against freshwater shrimp (Caridina nilotica) meal, reported even higher profitability for the bedding meal, even with a slightly reduced growth rate. Some studies have attempted to manipulate the nutritive quality of earthworms by enhancing their docosahexaenoic acid (DHA) content (Kumulu et al., 2018).
4.23.2.14 Single-Celled Products (SCP)
SCP originate from several microbial sources that include various microalgae, fungi, protists and bacteria. These organisms and their products are viewed as excellent candidates for aquafeeds since they do not require extensive areas of land or water for production, and can be grown, liberated from seasonal and climatic constraint, throughout the year. Generation of SCP is also seen as environ- mentally gratifying since some of the processes employ greenhouse gases such as CO2(algae) and CH4(bacteria) during produc- tion. SCP have been employed in aquafeeds for over a century but in recent decades new technologies have emerged that enable their mass production and novel methods have been developed to improve biomass processing. Often, the feedstocks employed for organismal growth are considered as“waste streams”from other processes or industriesdbut this is an absurdity. There is no such thing as waste and this is elegantly demonstrated by nutrient recovery from and bioconversions of agricultural by- products, restaurant, supermarket and institutional discards, and other coproducts, coincidentally saving on landfill, using microbes. The by-product used for such processes nevertheless has enormous influence on the economic viability of production.
Ritala et al. (2017)provide a useful overview of production systems, substrates and processes used and a consideration of their economic viability. Several recent reviews provide coverage of the wide variety of SCP available, their production and application to aquacultured organisms (Shah et al., 2018;Glencross et al., 2020a,b;Jones et al., 2020;Jannathulla et al., 2021;Sharif et al., 2021). Here, a distinction is made between SCP and pre-, pro- and synbiotics, which are considered separately.
4.23.2.15 Microalgae
Cultured microalgae are employed during larval rearing of mollusks, crustaceans, andfishes both as a direct source of food and as feed for live prey, such as rotifers, copepods andArtemia(Støttrup and McEvoy, 2003). Methods for microalgal cultivation have a long history (e.g.,Pringsheim, 1924) and, more recently, they have been used to produce biofuels (Halim et al., 2012;Mishra et al., 2022), edible oils (Xue et al., 2021) and pigments (Ambati et al., 2019), and have gained use in cosmetics (Yarkent et al., 2020) and functional foods (Barros de Medeiros et al., 2021). The application of microalgae to produce biodiesel and other prod- ucts creates a large by-product, following processing, which may facilitate their consumption as a major aquafeed ingredient.
Indeed, replacing the FM component of aquafeeds with defatted microalgal biomass has proven successful in a wide range of fish and some crustaceans (Shah et al., 2018;Chen et al., 2021a,b;Nagappan et al., 2021). The amino acid profiles of microalgae deemed most suitable for aquafeeds compare favorably to other reference proteins, although some deficiencies, such as that for Met, have be encountered (Nagappan et al., 2021). Additionally, the microalgal cell wall is high in cellulose which may hinder complete digestion and assimilation (Ahmad et al., 2020). This may explain the reduced growth of Atlantic salmon observed bySørensen
et al. (2017)when using defattedNannochloropsis oceania-based feeds. The same authors also recorded reduced feed intake, FCR, lipid and energy retention and health of thefish. Similar reductions in FCR were also reported byKiron et al. (2016)in substituting FM withDesmodesmussp. These authors likewise detected changes in the expression of various genes in the distal intestine of salmon that were, nevertheless, apparently without impact on overallfish gut health. Together with natural pigments, some microalgae have the advantage of containing high levels of n-3 LC-PUFA (DHA/eicosapentaenoic acid {EPA}), immunostimulants, antioxidants, and antimicrobial compounds. Nevertheless, as cautioned byTibbetts (2018), several technical gaps still exist regarding raw mate- rials, including incomplete knowledge of biochemical composition and the heterogenous nature thereof; some studies have provided inconsistent and contradictory findings (Table 2). Before the aquafeed industry can economically incorporate microalgae-based ingredients more completely into commercial feeds, therefore, more focused research is needed to examine life-cycle-based performance of target species fed feeds comprising various species of microalga, and at varying levels of incorporation.
4.23.2.16 Fungi and Yeasts
Numerous studies withfish and shrimp have demonstrated the utility of fungal and yeast biomass, and/or their derivatives, as FM replacers for aquafeeds (Zhong et al., 1992;McLean and Craig, 2004;McLean et al., 2006;Lunger et al., 2006,2007a,b;
Pérez-Pascual et al., 2020; Karimi et al., 2018, 2021; Patsios et al., 2020). In addition to supporting good growth, even when incorporated up to 100% FM replacement, several trials have also reported heightened immune response (Agboola et al., 2021;Richard et al., 2021,Table 2). These reactions, especially with yeast-based feeds, likely result due to their being a rich source of protein, B-complex vitamins, complex carbohydrates, including glucans, and nucleotide content (Craig and McLean, 2006). Since yeast is a by-product of the brewing industry this SCP represents considerable potential as an alternative, economically viable ingredient. Moreover, trials have also determined a null-effect of yeast-based feeds onfillet quality (Estévez et al., 2021). Summary schemes for production and processing methods during solid-state and submerged fermentation are presented byKarimi et al. (2018)andSar et al. (2021), as too are comparisons of amino acid and fatty acid profiles between fungal species, FM and other alternative proteins.
4.23.2.17 Bacteria
Processes currently employed to produce bacterial products are varied, with some concentrating on excreted products (e.g., amino acids, enzymes) and others on bacterial cells themselves. Bacterial cultures are typically obtained by fermentation of an organic carbon source, such as a sugar or alcohol. The culture is then harvested, and the broth separated from cells. Cultures can be scaled to commercial-size fermenters (50,000 L and up) which achieve high cell densities. After dewatering, the biomass produced is spray- dried to obtain a dry,fine, free-flowingflour suitable for feed manufacture using extrusion technologies. The quality of bacterial proteins as feed ingredients has been documented in various species using growth and digestibility trials (Table 2). Nonetheless, various factors influence the ultimate composition of bacterial meals and the performance characteristics thereof (Glencross et al., 2020a,b). Replacement of 50% of FM in diets for Nile tilapia (Viola and Zohar, 1984) with bacterial meal (Methylophilus meth- ylotrophus) had no impact on growth. AndPerera et al. (1995)reported successful replacement of 25% FM using bacteria meal with rainbow trout. Sixty-six percent substitution of FM with purple phototrophic bacteria sustained equivalent growth and survival to FM-based feed in barramundiLates calcarifer(Delamare-Deboutville et al., 2019). Bacteria not only provide an alternative protein source for aquafeeds but can also be harnessed to provide specific molecules, such as taurine which is appreciated as an important and often limiting nutrient in many species (Salze and Davis, 2015). Bacteria are also employed in biofloc systems which remove excess nitrogen, thereby improving water quality and reducing system water exchange. Bioflocs also provide a feed supplement, thus reducing system feed inputs and may have probiotic-like immunological benefits (reviews:Dauda, 2020;El-Sayed, 2021;Mugwa- nya et al., 2021).
4.23.2.18 Plant Proteins (VP)
Vegetable proteins (VP) are often deemed sustainable as alternatives for FM and other animal protein sources and are widely used in contemporary aquafeeds (Gatlin et al., 2007). A comprehensive consideration of VPs that have been evaluated as FM alternatives is presented inHertrampf and Piedad-Pascual (2000). As well, some reviews consider the application of specific plant species as alter- nate protein sources (e.g.,Li and Robinson, 2006;Enami, 2011;Mosha, 2018;Sonta et al., 2019; Abdel-Latif et al., 2022). VP are generally considered imperfect FM replacers, especially for carnivorous species, due to their lower digestibility, lack of some EAAs such as lysine (Lys) and methionine (Met), and the presence of antinutritional factors (ANFs;Table 3).
4.23.2.18.1 Soybean Meal
Of all VPs it is soybean meal (SBM) and its derivatives that are conspicuous, being commonly used in commercial feeds and widely tested experimentally infish and shrimp. They are however, only employed at a level up to 30% dietary protein mainly due to their low protein content (54% CP;Hertrampf and Piedad-Pascual, 2000) and presence of ANFs and non-soluble carbohydrates. SBM
Table 2 Examples of single cell proteins used as partial or total replacement forfishmeal (FM) in aquafeeds and their impacts on various species of aquacultured organism
Species
%
Protein Test animal Observations Reference
Scenedesmus almeriensis 43 Gilthead sea bream 38% replacement of FM without impacting feed intake or wt gain, SGR, FCR, PER, gut histology, or digestive enzymes. Decreased HSI and VSI (P<0.05).
Vizcaíno et al. (2014)
Chlorella vulgaris Giant FW prawn PL Increased SGR (P<0.05), enhanced immunity and resistance toAeromonas hydrophilainfection (P<
0.05).
Maliwat et al. (2017)
Spirulina maxima 61 Common carp 100% substitution of FM, improvement in enzyme activities
Nandeesha et al. (1998) Catla 100% substitution of FM did not impact growth, SGR,
survival FCR or PER (P>0.05).
Nandeesha et al. (2001) Rohu !00% substitution increased growth, SGR, FCR, and
lowered PER (P<0.05)
Nile tilapia 100% FM substitution levelYgrowth and SGR, HSI and VSI (P<0.05)
Velasquez et al. (2016) Goldfish 100% replacement of FMYgrowth and SGR, PER, FI
(P<0.05)
Cao et al. (2018) Arthrospira platensis 58 Pacific white
shrimp
75% replacement of FM had no effect on growth, FCR, SGR, PER or survival. At 100% however, differences (P<0.05) were seen for wt, and SGR which were lower and FCR which was higher.
Macías-Sancho et al. (2014)
Saccharomyces cerevisiae 55 Rainbow trout 40% replacement of FM had no effect on gut health, growth, or nutrient digestibility
Vidakovic et al. (2020) Atlantic salmon 40% replacement of FMYgrowth, FCR, NRE (P<0.05)
and increased feed intake, VSI and FCR (P<0.05)
Øverland et al. (2013) Nile tilapia Complete replacement of FM without impact Nhi et al. (2018) Panga 45% FM replacement had no effect on growth or feed
efficiency, meat quality or hematology.
Pongpet et al. (2016)
Goldfish Substitution of 45% FM Gümüs et al. (2016)
NuPro® 54 Pacific white
shrimp
No difference in wt gain or survival v. FM control ponds, lower size variation for NuPro fed animals.
McLean et al. (2006) Channel catfish Wt gain and SGR depressed v. FM (P<0.05).
Whole-body fatYin NuPro fedfish (P<0.05)
Peterson et al. (2012) Cobia No effect on wt gain, feed efficiency, biological indices,
orfillet composition when used as a replacement for 40% FM.
Lunger et al. (2007a)
Pirarucu At 8% of diet no differences in wt gain, FCR, HSI, VSI or feed intake.
Increases (P<0.05) in WBC counts for thrombocytes, leukocytes, lymphocytes, and monocytes.
Hoshino et al. (2020)
Methylophilus methylotrophus 81 Mirror carp [Growth and SGR v FM (P<0.05), enhanced FCE (P<
0.05) no effect on proximate composition but reduced NPU (P<0.05)
Atak et al. (1979)
Rainbow trout 80% replacement of FM had no effect on growth or body composition
Kaushik and Luquet (1980) Methylobacterium extorquens
(KnipBio)
70 Rainbow trout 25% CP no difference in survival, weight gain, FCR, or body composition
Hardy et al. (2018) Pacific white
shrimp
Smallmouth grunt
100% replacement of FMYgrowth and FCR (P<0.05) 50% replacement of FM had no effect on growth, SGR,
survival, FCR or gut microbiome
Tlusty et al. (2017)
Atlantic salmon Digestibility coefficients higher than FM-based feeds Salze and Tibbetts (2021) Brevibacterium lactofermentum
Bacterium glutamaticum
71 69
Rainbow trout When used at 16% as fed,Ygrowth and feed efficiency (P<0.001) v. FM.B. l.larger thanB. g.and higher GSI/HSI (P<0.05)
Kiessling and Askbrandt (1993)
(Continued)
causes enteritis of the distal intestine of carnivores, and especially in salmonids (Merrifield et al., 2011), and indigestible non- soluble carbohydrates impact gut evacuation rates and fecal pellet quality (Hardy, 2009). SBM proteinase inhibitors and lectins are decreased by heating during pellet extrusion whereas other ANFs can be reduced by alcohol extraction (Krogdahl et al., 2010).Dersjant-Li (2002)reviews the application of SBM in aquafeeds.
Table 2 Examples of single cell proteins used as partial or total replacement forfishmeal (FM) in aquafeeds and their impacts on various species of aquacultured organismdcont'd
Species
%
Protein Test animal Observations Reference
Clostridium autoethanogenum N/A Black sea bream No difference in weight gain, survival, SGR or HSI when fed at 58.2% replacement of FM. Feeding rate and PER lower (P<0.05). Phosphorus retention efficiency higher (P<0.05).
Chen et al. (2020)
Largemouth bass 54% replacement of FM resulted in reduced growth, PRE, lipid retention and protease activity and higher FCR (P<0.05). Intestinal folds were also reduced in height (P<0.05)
Yang et al. (2021a)
Escherichia coli Mozambique tilapiaYGrowth, FCR, NPU (P<0.05) when incorporated as 15%–20% replacement of FM
Davies and Wareham (1988) Methylococcus capsulatusþ
Alcaligenes acidovoransþ Bacillus brevisþ B. firmus
Atlantic salmon At 20% FM replacement, no differences in growth, feed intake or mortality, or apparent digestibilities of nitrogen, fat and energy. There was no difference between FM and bacteria meal groups for pigmentation or organoleptic analyses.
Berge et al. (2005).
Dried fermented bacterial biomass
N/A Florida pompano No difference in growth when replacing 13% FM Rhodes et al. (2015) Microbial biomass N/A Tiger prawn 10% of diet[growth, survival and FCR P<0.05) Glencross et al. (2014) Rhodobacter sphaeroides
Afifella marina
54 48
Pacific white shrimp
5% of diet[growth after 60 d (P<0.05) but no differences in SGR, FCR or survival.
Chumpol et al. (2018)
FCE¼food conversion efficiency, FCR¼food conversion ratio, FI¼feed intake, FM¼fishmeal, FW¼freshwater, GSI¼gonadosomatic index, HSI¼hepatosomatic index, NPU¼net protein utilization, NRE¼nitrogen retention efficiency, PER¼protein efficiency ratio, PL¼post-larvae, VSI¼viscerosomatic index, WBC¼white blood cellswk¼ week, wt¼weight.
Table 3 Examples of commonly encountered anti-nutritional factors in alternative plant proteins and their impact onfish and shrimp physiological control processes
Plant source Antinutritional factors Physiological effects
Soybean meal Antiproteases, lectins, phytic acid, saponins, allergens, antivitamins, phytoestrogens.
YGrowth and feed conversion Cottonseed meal Gossypol, antivitamins, phytoestrogens, phytic acid,
cyclopropenoic acid.
YGrowth,
Sunflower oil cake Antiproteases, saponins, arginase inhibitor. YGrowth,
Mustard oil cake Glucosinolates, tannins. YDigestibility,Ygrowth,
Canola meal Glucosinolates, aflatoxin, tannins, phytic acid, antiproteases.
YDigestibility,Ygrowth,
Sesame meal Antiproteases, phytic acid, aflatoxin. YGrowth,
Peanut Antiproteases, phytic acid, lectin, saponins. YGrowth,
Wheat Antiproteases, phytic acid, lectin. YGrowth,
Maize Antiproteases, phytic acid. YGrowth,
Barley Antiproteases, phytic acid, lectin. YGrowth,
Lupin seed meal Antiproteases, phytoestrogens, saponins, alkaloids. YDigestibility,Yfeed intake,Ygrowth Pea seed meal Antiproteases, tannins, lectins, phytic acid, cyanogens,
antivitamins.
YDigestibility,Ygrowth, Alfalfa seed meal Antiproteases, phytoestrogens, aflatoxin, antivitamins,
saponins.
YGrowth,
Duckweeds Antiproteases, cyanogens, tannins, gossypol YDigestibility,Ygrowth,
Water hyacinth Antiproteases, cyanogens, saponins, tannins, phytic acid. YDigestibility,Ygrowth,
Water lettuce Antiproteases, saponins, tannins. YDigestibility,Ygrowth,
