They are what they eat - Enhancing the nutritional value of live feeds with microalgae


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Live feeds are often essential for larval fish. Live feeds are proven to be essential first-feed for many larval fish, essentially all those that hatch from small eggs with limited yolk reserves and often immature feeding and digestive functions. Live feeds provide larval fish with essential nutrients that are naturally ‘microencapsulated’ in bite-sized packages. They include a high proportion of easily-assimilated free amino acids and free fatty acids, as well as digestive enzymes and beneficial bacterial microfloras in the gut contents of the prey. The swimming activity of live prey also stimulates feeding responses in larval fish, a vital concern because small larvae with very limited metabolic reserves can quickly starve if they do not promptly begin feeding actively.

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They are what they eat - Enhancing the nutritional value of live feeds with microalgae

  1. 1. May | June 2013They are what they eat - Enhancingthe nutritional value of live feeds withmicroalgaeThe International magazine for the aquaculture feed industryInternational 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 ofinformation published.©Copyright 2013 Perendale Publishers Ltd.All rights reserved.No part of this publication may be reproduced in any formor by any means without prior permission of the copyright owner. Printed by Perendale Publishers Ltd. ISSN: 1464-0058INCORPORATINGf ish farming technolog y
  2. 2. www.oj-hojtryk.dkDie and roll re-working machinesO&J Højtryk A/SØrnevej 1, DK-6705Esbjerg ØCVR.: 73 66 86 11Phone: +45 75 14 22 55Fax: +45 82 28 91 41mail: info@oj-hojtryk.dkO&J HØJTRYK A/S endeavours to be a powerful, vigorousand energetic company. With our customers needs and theimmediate environment as our point of departure, we wantto be a trendsetter in our core area of business - MechanicalEngineering - Re-working of Dies and Rollers for themanufacture of Feedstuffs and Biopellets, as well as the saleand delivery of wearing parts in connectionwith Roller Re-working - as well as toremain open to new initiatives andbusiness opportunities.O&J HØJTRYK A/S has drawn up astrategy plan setting out guidelines forhow we as an organisation must conductand develop ourselves in order to makeour mark, not just in the present, but also in thefuture.O&J HØJTRYK A/S must achieve success by adaptingto the conditions of the market more quicklyand efficiently than our competitors. As a serviceorganisation we must, in relation to our customers,attach great importance to our own vitality and efficiencyby constantly living up to the ever-growing demands made onthe services we provide.
  3. 3. “Today the most costly andperhaps least understood livefood are the unicellular algae”- Dhert & Sorgeloos 1995Live feeds are often essential for larval fish. Live feeds are proven to be essential first-feed for many larval fish, essentially all those that hatch from small eggs with limited yolk reserves and often immature feeding and digestive functions. Live feeds provide larval fish with essential nutrients that are naturally ‘microencapsulated’ in bite-sized packages. They include a high proportion of easily-assimilated free amino acids and free fatty acids, as well as digestive enzymes and beneficial bacterial microfloras in the gut contents of the prey. The swimming activity of live prey also stimulates feeding responses in larval fish, a vital concern because small larvae with very limited metabolic reserves can quickly starve if they do not promptly begin feeding actively. The natural live foods of such larvae are of course microplankton, both zooplankton and (although often not appreciated) phytoplank-ton. Natural zooplankton assemblages are often highly diverse and may include protozoa, rotifers, arroworms, microcrustaceans such as copepods, and eggs and larvae of nearly every group of marine animals including sponges, coelenterates, polychaetes, various crusta-ceans, molluscs, echinoderms, and even fish. This diverse array of prey organisms supplies multiple sources of essential nutrients. But it can be very difficult to obtain sufficient natural plankton to supply the needs of a hatchery, and natural plankton can introduce predators, parasites and pathogens. Hatchery-cultured live feeds are therefore the only practical and safe feed for many larval fish.Use of live feeds in aquacultureBy far the most commonly-used live feeds in hatcheries are rotifers (Brachionus spp.) and brine shrimp (Artemia) (Conceição et al. 2010), with some use of copepods such as species of Acartia, Calanus, Tisbe, and Parvocalanus. Although copepods gener-ally provide better nutritional value, their culture presents so many difficulties that they are not commonly used in hatcheries (Drillet et al. 2006, 2011). Rotifers can read-ily be mass-cultured at high densities and can double their numbers in a day. Rotifers are smaller than newly-hatched Artemia, which can be too large for some larvae. Artemia are most convenient because their resting eggs (cysts) can be purchased and hatched when needed, but newly-hatched Artemia nauplii do not begin to feed until after the first molt, so their nutritional value depends entirely on the nutritional environ-ment of the previous wild generation that produced the eggs. One study found that the content of the important omega-3 Poly-Unsaturated Fatty Acid (PUFA) EPA in Artemia cysts from the same source can vary as much as 44-fold (Dhert & Sorgeloos 1995). Such variations mean that the nutri-tional content of newly hatched Artemiamay be largely unknown, and only after the first molt can their nutritional value be improved by feeding.It is important to understand that nei-ther Brachionus rotifers nor Artemia are truly marine organisms. Rather they are found in ‘saline’ habitats, which are mostly inland environments with often extreme seasonal variations in temperature, salinity, and even availability of water. Adaptation to such extreme conditions has endowed these species with characteristics that are very useful in aquaculture, such as tolerance of a wide range of culture conditions, rapid asexual reproduction by parthenogenesis (Brachionus), and formation of resistant rest-ing cysts (Brachionus and Artemia). They are also relatively omnivorous and do not have stringent nutritional requirements, and so can be fed on low-cost feeds such as yeast, starch, rice bran, and dried Spirulina (cyano-bacteria).It may be no surprise that feeding larvae only one or two species of hatchery-pro-duced live feeds might not provide adequate nutrition. But the underlying cause of such nutritional inadequacy is often the low quality of the low-cost food sources used to pro-duce the live feeds. It is therefore necessary to choose carefully the food sources used for hatchery-produced live feeds if they are to provide adequate nutritional support for larval fish.They are what they eatEnhancing the nutritional value oflive feeds with microalgaeby Eric C Henry PhD, research scientist, Reed Mariculture Inc., USA12 | InternatIonal AquAFeed | May-June 2013FEATURE
  4. 4. Innovations for a better world.Bühler AG, Feed & Biomass, CH-9240 Uzwil, Switzerland, T +41 71 955 11 11, F +41 71 955 28, www.buhlergroup.comFatten up your bottom line. Bühler high-performance animal and aqua feed productionsystems are used by leading companies around the world. These producers know theycan rely not just on the technology itself, but also on the support that accompanies it. Aservice combining local presence with global expertise both lowers feed mill operatingcosts and increases capacity utilization. To find out more, visit
  5. 5. Limitations of formulated feedsfor live feed productionFormulated feeds offer low cost and con-venience, but they have fundamental short-comings. Zooplankton, including rotifers and Artemia, can feed only on micro particles of appropriate size (from bacteria to 10 µm for Brachionus [Baer et al. 2008, Vadstein et al. 1993], and from bacteria to 28 µm, with the optimum about 8-16 µm for Artemia [Makridis and Vadstein 1999, Fernández 2001]). It is difficult to produce dry feeds that provide uniform particle sizes, and even when uniform dry particles can be produced they can be subject to clumping when dispersed into water for feeding. But probably the most criti-cal shortcoming of dry feeds is rapid leaching of water-soluble nutrients; the smaller the par-ticle, the faster nutrients are leached out. Not only are leached nutrients unavailable to the live feeds, they can cause fouling of the water.Rotifer BrachionusplicatilisAlgae concentrate (ReedMariculture Tetraselmis 3600)May-June 2013 | InternatIonal AquAFeed | 13FEATURE
  6. 6. Lipid emulsions of high-PUFA oils may be used to improve the fatty acid profile of live feeds. Although their contents are not subject to leaching, lipid droplets are prone to stick to surfaces, including the walls of the culture tank and the live feed organisms themselves. Lipid enrichment protocols therefore often must include a rinsing step to clean the rotifers or Artemia of adhering lipid droplets, which would otherwise foul the larval tank. Short-term feeding of oil emulsions results in lipid-enriched rotifers with high EPA and DHA levels, but, they are prone to rapid loss of their gut contents and acquire an extreme lipid:protein ratio (Dhert et al. 2001). Moreover, it has been shown that when the rotifers are collected on screens, as they are for rinsing, this mechanical stress can cause ejection of the nutritious gut contents that were ingested during enrichment feeding (Romero-Romero & Yúfera 2012), defeating the purpose of the enrichment.Advantages of microalgaeMicroalgae are the base of the plankton food web, and their great biochemical diver-sity is the source of the high nutritional value of natural zooplankton. As the natural food of zooplankton, microalgae offer a number of advantages over formulated feeds. They are natural ‘microencapsulation’ particles bounded by a cell membrane that retains the nutri-tious contents. They naturally contain a wide spectrum of nutritional components, such as essential amino acids, PUFAs, sterols, vitamins, and phytopigments. Different species provide a wide range of cell sizes and nutritional factors, as well as components that enhance digestion and immune functions (Guedes & Malcata 2012). Some strains have been found to have antibacterial effects (Austin & Day 1990, Kokou et al. 2012, Regunathan & Wesley 2004).Selecting the right microalgaeAlthough hundreds of microalgae strains have been tested as feeds for aquaculture, fewer than 20 are in widespread use (Guedes & Malcata 2012). Because these strains vary so greatly in their nutritional profiles, careful consideration is necessary in order to select the most nutritionally appropri-ate strains. Such algae as Spirulina, Chlorella, Haematococcus, and Dunaliella are easily mass-produced because they can be cultivated in open ponds at low cost, but they all lack the omega-3 PUFAs EPA and DHA that are essential for production of live feeds that provide adequate nutrition to marine fish. High-PUFA algae in wide use include strains of Nannochloropsis (Eustigmatophyceae), favoured for rotifer production and green-water; Tetraselmis (Prasinophyceae); Isochrysis and Pavlova (Prymnesiophyceae); Thalassiosira, Chaetoceros, and Skeletonema (diatoms); and Rhodomonas (Cryptophyceae).Although the PUFA content of many strains has by now been well-documented, sterol profiles have been more challenging to characterise because there is far more strain-to-strain variation, even among strains suppos-edly of the same spe-cies, as revealed in a recent investigation of over 100 diatom strains (Rampen et al. 2010). Protein content is less variable, with a study of 40 strains of microalgae in seven algal classes finding consistently high contents of essential amino acids (Brown et al. 1997). Vitamin contents of microalgae also appear to be con-sistently high (Brown & Miller 1992, Brown et al. 1999, De Roeck-Holtzhauer et al. 1991).Although various nutritional components have been well-documented in many strains, it remains difficult to assemble complete nutritional profiles of many strains so that the optimal combination of strains can be selected for a particular application. It is unfortunate that so many studies of the nutritional per-formance of microalgae have tested single strains as the only feed, when it should be obvious that no single strain is likely to provide an optimal nutritional profile comparable to that provided by a natural phytoplankton assemblage. In practice, microalgae have repeatedly been shown to dramatically improve the PUFA content of rotifers and Artemia (Chakraborty et al. 2007, Ferreira et al. 2008, Kjell et al. 1993, Lie et al. 1997, Øie et al. 1994, Reitan et al. 1997), which frequently results in improved larval performance. But it is important to recognise that the high nutritional quality of enriched live feeds can be maintained after delivery to the larval tank only by application of ‘greenwater’ techniques. Unless microalgae are added to the larval tank water, the live feed organisms quickly begin to starve, and can metabolize a significant fraction of their biomass before they are eaten by the larvae. The algal cells themselves can also function as live feeds, since they have been shown to be eaten and digested by larvae (Reitan et al. 1997, Van Der Meeren et al. 2007), and may Nauplius stage of copepodParvocalanus crassirostris14 | InternatIonal AquAFeed | May-June 2013FEATURE
  7. 7. also stimulate digestive enzyme production (Cahu et al. 1998).Production of microalgaeDespite the many advantages of microalgae, their wider use is hampered by difficulties in culturing, storage, and high costs. Microalgae culture can consume a significant fraction of the resources of a hatchery, and requires special equipment, skilled labour, and a large alloca-tion of space that is unproductive during the seasons when live feeds are not needed. Low-cost open-pond culture methods carry high risks of contamination and culture failure due to the impossiblity of tightly con-trolling culture conditions, and the most highly prized high-PUFA strains such as Isochrysis and Pavlova require indoor culture. It is very difficult to synchronize microalgal production with live feed requirements to prevent feed shortages or wasteful overpro-duction, and it is difficult to accurately dose algae cultures directly into live feed cultures. If the algae are harvested and concentrated, the tightly-packed cells can deteriorate rapidly in refrigerated storage. Some microalgae have been freeze- or spray-dried, but dried cells are subject to protein denaturation, and when they are rehydrated the leaching of water-soluble substances can rapidly deplete their nutritional value, as with other dry feeds. Microalgae concentratesThe best solution to these problems can be the use of commercially-available refrigerated or frozen algae concentrates or ‘pastes’ (Guedes & Malcata 2012, Shields & Lupatsch 2012). These products, which are actually viscous liquids, have proven to be effective feeds for rotifers, Artemia, shellfish and other filter-feeders, as well as for greenwater applications. In products formulated to provide a long shelf-life, the concentrated microalgae are suspended in buffer media that pre-serve cellular integrity and nutritional value, although the cells are non-viable. When concentrates with well-defined biomass densities are employed, the algae can be accurately dosed into live feed cultures with a metering pump, and non-viability confers the advantage that the products pose no risk of introducing exotic algal strains. The best refrigerated products typi-cally have a shelf-life of 3-6 months, and frozen products several years. This means that a reliable supply of algae can be kept on hand, available for use in any season or if an unexpected need arises. Algae costs become predictable, and often prove to be less than on-site production when total production costs and inefficiencies are accounted for.Although costs of liquid algae concen-trates are higher than for dried algae or formulated feeds, they offer all the nutritional advantages of live cultures. The nutritional quality of live feeds can be no better than the food sources used to produce them. Success of early larvae is so critical to the success of a hatchery that even a relatively small improvement in survival or growth rate can yield great benefits.OutlookLive feeds remain indispensable for larviculture of many fish. Although micro-algae are among the costliest food sources used to produce live feeds, their many advantages justify the cost for hatcheries producing high-value fish. Research contin-ues to better characterise the nutritional properties of various algae strains and to optimise algae production technologies. We can anticipate that introduction of novel algae strains and nutritionally-opti-mised combinations of strains, along with improved feeding protocols, will ensure that microalgae remain the food of choice for production of the highest-quality live 2013 | InternatIonal AquAFeed | 15FEATURENaturally aheadMYC OFIXMycotoxin RiskMan a g e MentMycofix®More protective.Mycotoxins decrease performance and interferewith the health status of your animals.Mycofix®is the solution for mycotoxin risk
  8. 8.• See the full issue• Visit the International Aquafeed website• Contact the International Aquafeed Team• Subscribe to International AquafeedThey are what they eatEnhancing the nutritional value of live feedswith microalgaeControlling mycotoxins withbindersUltravioletwater disinfection for fishfarms and hatcheriesNiacin– one of the key B vitamins for sustaininghealthy fish growth and productionVolume 16 Issue 3 2013 - mAY | Ju NeINCORPORATINGfIsh fARmING TeChNOlOGyThis digital re-print is part of the May | June 2013 edition of InternationalAquafeed magazine. Content from the magazine is available to view free-of-charge, both as a fullonline magazine on our website, and as an archive of individual features onthe docstoc website.Please click here to view our other publications on purchase a paper copy of the magazine, or to subscribe to the paperedition please contact our Circulation and Subscriptions Manager on the linkabove. INFORMATION FOR ADVERTISERS - CLICK HERE