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Intensive production of mainly carnivorous fish has resulted in fish feeds containing high levels of fishmeal and fish oil, with Europe requiring around 1.9 million tonnes a year. Although this use of fishmeal was initially the recycling of waste from fishing through the use of bycatch and trimmings, due to the rapid development of aquaculture this reliance on fishmeal and fish oil is environmentally unsustainable. This has resulted in other sources of fish feed being investigated. This literature review will focus on microalgae; the composition in terms of nutritional quality, the current methods of production and associated costs along with potential future uses such as feed in aquaculture.
I N C O R P O R AT I N G f I s h fA R m I N G T e C h N O l O G y September | October 2013 The potential of microalgae meals in compound feeds for aquaculture International Aquafeed is published six times a year by Perendale Publishers Ltd of the United Kingdom. All data is published in good faith, based on information received, and while every care is taken to prevent inaccuracies, the publishers accept no liability for any errors or omissions or for the consequences of action taken on the basis of information published. ©Copyright 2013 Perendale Publishers Ltd. All rights reserved. No part of this publication may be reproduced in any form or by any means without prior permission of the copyright owner. Printed by Perendale Publishers Ltd. ISSN: 1464-0058 The International magazine for the aquaculture feed industry Fatten up your bottom line. Bühler high-performance animal and aqua feed production systems are used by leading companies around the world. 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FEATURE The potential of microalgae meals in compound feeds for aquaculture by Nathan Atkinson, MSc Sustainable Aquaculture Systems student, Fish Nutrition and Aquaculture Health Group, Plymouth University, United Kingdom I ntensive production of mainly car- totrophs and are characterised by their lack Marine microalgae are the dominant nivorous fish has resulted in fish feeds of roots, leaves and presence of chlorophyll a. primary producers in aquatic systems and containing high levels of fishmeal and They range in size from microscopic individual account for a similar level of carbon fixation as fish oil, with Europe requiring around cells called microalgae to seaweeds that can terrestrial plants (40-50%) but represent only 1.9 million tonnes a year. Although this use be greater than 30 m in length (Qin 2012). 1 percent of the planetary photosynthetic of fishmeal was initially the recycling of waste from fishing through the use of bycatch and trimmings, due to the rapid development of aquaculture this reliance on fishmeal and fish oil is environmentally unsustainable. This has resulted in other sources of fish feed being investigated. This literature review will focus on microalgae; the composition in terms of nutritional quality, the current methods of production and associated costs along with potential future uses such as feed in aquaculture. Algae overview Marine algae are distributed from the Figure 1: Percentages (dry weight basis) of protein, lipid and carbohydrate in polar regions to tropical seas in nutrient rich microalgae. The range of values is shown by range bars (Brown 1997) and poor environments. Algae are photoau- table 1: amino acid profile of different algae as compared with conventional protien sources and the WHo/Fao (1973) reference pattern (g per 100 protein) Source Ile leu Val lys Phe tyr Met Cys try thr ala arg asp Glu Gly His Pro Ser WHo/Fao 4.0 7.0 5.0 5.5 6.0 3.5 1.0 egg 6.6 8.8 7.2 5.3 5.8 4.2 3.2 2.3 1.7 5.0 - 6.2 11.0 12.6 4.2 2.4 4.2 6.9 Soybean 5.3 7.7 5.3 6.4 5.0 3.7 1.3 1.9 1.4 4.0 5.0 7.4 1.3 19.0 4.5 2.6 5.3 5.8 Chlorella vulgaris 3.8 8.8 5.5 8.4 5.0 3.4 2.2 1.4 2.1 4.8 7.9 6.4 9.0 11.6 5.8 2.0 4.8 4.1 Dunaliella bardawil 4.2 11.0 5.8 7.0 5.8 3.7 2.3 1.2 0.7 5.4 7.3 7.3 10.4 12.7 5.5 1.8 3.3 4.6 Scenedesmus obliquus 3.6 7.3 6.0 5.6 4.8 3.2 1.5 0.6 0.3 5.1 9.0 7.1 8.4 10.7 7.1 2.1 3.9 4.2 arthrospira platensis 6.7 9.8 7.1 4.8 5.3 5.3 2.5 0.9 0.3 6.2 9.5 7.3 11.8 10.3 5.7 2.2 4.2 5.1 aphanizomenon sp. 2.9 5.2 3.2 3.5 2.5 - 0.7 0.2 0.7 3.3 4.7 3.8 4.7 7.8 2.9 0.9 2.9 2.9 14 | InternatIOnal AquAFeed | September-October 2013 FEATURE microalgae and table 2: oil contents of some microalgae (Demirbas 2007) resulted in reviews being published Microalgae oil content (wt% of dry about specific sub- basis) jects such as genetic engineering of algae (Qin 2012), poten- Botryococcus braunii 25-75 tial use as biofuel Chlorella sp. 28-32 (Demirbas 2011) Crypthecodinium cohnii 20 and novel methods Cylindrotheca sp. 16-37 to measure such Dunaliella primolectra 23 important com- ponents such as Isochrysis sp. 25-33 protein (Slocomb Monallanthus salina >20 2012). nannochloris sp. 20-35 This interest and nannochlorosis sp. 31-68 knowledge in the neochloris oleoabundans 35-54 area has allowed aquaculture to nitzschia sp. 45-47 essentially piggy back Phaeodactyhum tricornutum 20-30 the research being Schizochytrium sp. 50-77 performed by the tetraselmis sueica 15-23 biodiesel industry and even act syner- biomass (Stephenson 2011). Microalgae are gistically with it by sometimes directly consumed by humans as consuming the by- health supplements due to this high nutritional products produced value and abundance (Dallaire 2007) but this (Ju 2012). Currently is relatively rare. microalgae have As carnivorous fish ingest algae as a food been used in aqua- source (Nakagawa 1997) there has been a culture as food move to utilise them for fish feed. Currently additives, fishmeal 30 percent of the world algal production is and oil replace- used for animal feed (Becker 2007) but the ment, colouring of use in aquaculture is mainly for larval fish, salmonids, inducing molluscs and crustaceans (FAO 2009a). As biological activities mentioned above, the fishmeal and oil use in and increasing the aquaculture is unsustainable and algae have nutritional value of the potential to reduce this dependence. This zooplankton which is due to the algae being photosynthetic so are fed to fish lar- they have the ability to turn the sun’s huge vae and fry (Dallaire amount of energy, 120,000 TW of radiation, 2007). into protein, lipids and nutrients. More energy Although the from the sun hits the surface of the earth biodiesel industry in one hour than the energy used in one has been conduct- year and this is a huge amount of untapped, ing a large amount sustainable energy can be exploited by algae. of research, this This is a relatively new area of research but has mainly been has many positive aspects that give it a large focused towards amount of potential for future use. species that have high lipid contents Microalgae whereas species in The term ‘microalgae’ is often used to aquaculture must refer specifically to eukaryotic organisms, both be of appropriate from freshwater and marine environments but size for ingestion can include prokaryotes such as cyanobacteria and be read- (Stephenson 2011). Microalgal production ily digested. They has received some attention recently due to must also have its potential use as a biofuel (Slocomb 2012), rapid growth rates, use in animal feed, human consumption and be able to be cul- recombinant protein technology (Becker, tured on a mass 2007; Potvin and Zhang 2010; Williams and scale, be robust Laurens, 2010). This has resulted in a huge enough to cope amount of knowledge and research into with fluctuations September-October 2013 | InternatIOnal AquAFeed | 15 THE SPECIAL WORLD OF LEIBER YEAST... REAL BRE WER S YEAST ’ “Made Germanin y” For Leiber`s specialty yeast products, “Made in Germany” is a seal of quality. Multibiotic effect of Leiber yeast - vitality, health and performance for fish. www.leibergmbh.de Leiber GmbH · Hafenstraße 24, 49565 Bramsche, Germany · Tel +49 (0) 5461 9303-0 · Fax +49 (0) 5461 9303-28 · www.leibergmbh.de · firstname.lastname@example.org FEATURE in temperature, light and nutrients and result in an overestimation of the true protein Vitamins have a good nutrient composition (Brown content (Becker 2007). Microalgae also contain vitamins which can 2002). The non-protein nitrogen can be up to 12 be beneficial to the health of the consumer but percent in Scenedesmus obliquus, 11.5 percent vary greatly between species (Brown 2002). Varying nutritional values in Spirulina and 6 percent in Dunaliella. Even This variation is greatest for ascorbic acid The nutritional value of any algal species with this overestimation the nutritional value (Vitamin C), which varies from 1-16mg g dry depends on its cell size, digestibility, produc- of the algae is high with the average qual- weight (Brown & Miller, 1992), but other vita- tion of toxic compounds and biochemi- ity being equal, sometimes even superior, to mins typically show a 2-4 x difference between cal composition. This, along with differences conventional plant proteins (Becker 2007) species (Brown et al., 1999) (Figure 3). among species and method of production, (Table 1). Despite the variation in vitamin C all the explains the variability in the amount of The amino acid composition of the species would provide an adequate supply to protein, lipids and carbohydrates, which are protein is similar between species and is cultured animals which are reported to only 12-35 percent, 7.2-23 percent, and 4.6-23 relatively unaffected by the growth phase require 0.03-0.2 mg g-1 of the vitamin in their diet percent respectively (FAO 2009a) (Figure 1). and light conditions (Brown et al., 1993a, (Durve and Lovell, 1982). However every species b). Aspartate and of algae had low concentrations of at least one glutamate occur in vitamin (De Roeck-Holtzhauer et al., 1991) so a the highest concen- careful selection of a mixed algal diet would be trations (7.1-12.9%) necessary to provide all the vitamins to cultured whereas cysteine, animals feeding directly on microalgae. methionine, tryp- tophan and histidine Algae in aquaculture occur in the lowest The use of algae as an additive in aqua- concentrations (0.4- culture has received a lot of attention due 3.2%) with other to the positive effect it has on weight gain, amino acids ranging increased triglyceride and protein deposi- from (3.2-13.5%) tion in muscle, improved resistance to Figure 2: Average percentage compositions of the long- chain PUFAs docosahexaenoic acid (DHA; 226n-3), (Brown 1997). disease, decreased nitrogen output into eicosapentaenoic acid (EPA; 20:5n-) and arachidonic acid the environment, increased fish digestibility, (20;4n-6) of microalgae commonly used in aquaculture. Lipids physiological activity, starvation tolerance Data compiled from over 40 species from laboratory of The lipids in micro- and carcass quality (Becker, 2004; Fleurence CSIRO Marine Research. algal cells have roles as 2012). Li (2009) showed that the addition both energy storage of dried microalgae in the diet, albeit at low molecules and in the forma- concentrations 1.0-1.5 percent, resulted in tion of biological membranes increased weight gain of the channel catfish and can be as high as 70 (Ictalurus punctatus) along with improv- percent dry weight in some ing the feed efficiency ratio and levels of marine species (Stephenson poly-unsaturated fatty acids. Ganuza (2008) 2011) (Table 2). Under rapid showed that algal oil can be an alternative growth conditions these lipid source of DHA (docosahexaenoic acid) to levels can drop to 14-30 per- fish oil in gilthead seabream (Sparus aurata) cent dry weight, which is a microdiets although it did not allow for the level more appropriate for complete substitution of fisheries products aquaculture. These lipids are due to the low EPA (eicosapentaenoic acid) composed of polyunsaturated levels in the species of algae used. fatty acids such as docosa- These were at relatively low-level inclu- hexaenoic acid (DHA), eicos- sions; at greater levels it can have a detri- apentaenoic acid (EPA) and mental effect. At 12.5 percent inclusion algae arachidonic acid (AA) (Brown caused reduced growth performances in rain- Figure 3: Concentrations of different vitamins in 2002) and in high concen- bow trout and at 25 percent and 50 percent microalgae in µg g-1. Graph adapted from Brown trations; most species have this substitution of fish feed caused nutritional 2002 with data collected from Seguineau et al., 1996 and Brown et al., 1999 percentages of EPA from 7-34 deficiencies that led to decreased growth, percent (Brown 2002) (Figure feed efficiency and body lipids (Dallaire 2007). 2). Levels of algal inclusion of 15 percent This level of fluctuation can be influenced by These fatty acids are highly sought after and 30 percent also reduced feed intake and the culture conditions (Brown et al., 1997) but and as they currently cannot be synthesised growth rate in Atlantic cod (Walker 2011). rapid growth and high lipid production can be in a laboratory and are usually obtained As Atlantic cod are known to have a robust achieved by stressing the culture. through fish oil and are a limiting factor in digestive system it was suggested that this was vegetable oils such as palm, soybean and due to reduced palatability which could be an Protein rapeseed oil use in aquaculture. The fatty issue for algal use in aquaculture. Most of the figures published in the litera- acid composition is associated with light High levels of inclusion does not cause ture on the concentration of algal proteins are intensity, culture media, temperature and such negative effects in all species raised in based on estimations of crude protein and pH. Appropriate measures and control, along aquaculture, 50 percent replacement did as other constituents of microalgae such as with the suitable selection of a species, is not have a negative effect on shrimp (Ju nucleic acids, amines, glucosamides and cell necessary to produce algae with the desired 2012), but is generally experienced among wall materials which contain nitrogen; this can lipid level and composition. finfish. 16 | InternatIOnal AquAFeed | September-October 2013 FEATURE Algae production portion of photo protective pigments which The production of algae, in particular would improve the light-dependant reactions microalgae, is a rapidly developing industry and selecting for algae with small antennas due to the biofuel research that is currently which is fundamental to achieving high yields taking place. The annual world production of in biomass dense cultures (Stephenson 2011). all species is estimated to be 10,000 t year-1 This research is essential as the production (Richmond, 2004) with the main limit to pro- costs of microalgae are still too high to duction currently being the cost. Production compete with traditional protein sources for costs are currently range from US$4-300 per aquaculture (Becker 2007). kg dry weight (FAO 2009a) depending on the type of production method employed Benefits and obstacles (Table 3). Algae have a great potential for use in There has been a shift away from typical sustainable aquaculture as they are not only a systems such as outdoor ponds and raceways source of protein, lipids and have other nutri- to large-scale photobioreactors which have a tional qualities but they are phototrophic so much higher surface area to volume ratio and produce these directly from sunlight. Producing could potentially reduce the production cost 100 tons of algal biomass also fixes roughly (Brown 2002). These photobioreactors could 183 tons of carbon dioxide which has obvious yield 19,000 - 57,000 litres of microalgal oil per implications in this period of climate change. improving the nutritional value of rotifers acre per year, which is over 200 times the yield The production does not always require and not as algae as a potential replacement from the best performing vegetable oils (Chisti freshwater, compete for fertile land and are of fishmeal and fish oil. There is also interest 2007), and reduce the cost of algal oil from not nutritionally imbalanced with regard to into storing algal pastes which have extended $1.81 to $1.40 per litre (Demirbas 2011). the amino acid content like soybean. shelf life (2-8 weeks) or the use of defatted However, for algal oil to be competitive There are still some obstacles such as the microalgae meal from the biodiesel industry. with petrodiesel, it should be less than $0.48 powder-like consistency of the dried biomass The use of algae in aquaculture is a promis- per litre. This is achievable through economies and applications to feed manufacture, the ing and young area of research and when of scale (Demirbas 2011) and would make it a production costs and pests and pathogens compared to agriculture, which has increased cheap and sustainable oil for the aquaculture that will effect large scale algal cultivation crop productivity by 138 percent in a 50 year industry. There are also other developments sustainability (Hannon et al., 2010), which is an period, it demonstrates the great potential that such as increasing the specific activity of the area that little is known about. algae has. enzyme RUBISCO which would increase There still needs to be many feeding trials yields, transgenic studies, increasing the pro- as the majority of research has focused on References available on request x i n Ri to sk Myco M YC OF I X t en a nag eM M Mycofix ® More protective. Mycotoxins decrease performance and interfere with the health status of your animals. Mycofix is the solution for mycotoxin risk management. ® mycofix.biomin.net Naturally ahead September-October 2013 | InternatIOnal AquAFeed | 17 This igital e-print s art f he eptember ctober 013 dition f nternational d r i p o t S |O 2 e o I LINKS Aquafeed magazine. 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