September | October 2012

The use of algae in fish feeds as alternatives to fishmeal

The International magazine for the aquaculture feed industry

International Aquafeed is published five 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 2012 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

Fishmeal is very extensively usedin feeds for fish as well as otheranimals. A recent global surveyestimatedaquacultureconsumption

of fishmeal at 3724 thousand tonnes in2006 (Tacon and Metian 2008). Now it isbecomingincreasinglyevidentthatsuchcon-tinuedexploitationof this natural resourcewillultimatelybecomebothenvironmentallyandeconomicallyunsustainable.

Any satisfactory alternative feed ingre-dients must be able to supply compara-ble nutritional value at competitive cost.Conventional land-based crops, especiallygrains and oilseeds, have been favouredalternativesduetotheirlowcosts,andhaveproved successful for some applicationswhen they were used as substitutes fora portion of the fishmeal. But even whenthese plant-based substitutescan support goodgrowth theycancausesignificantchangesinthenutritionalqualityofthefishproduced.

Why algae?Thereadermaywonderwhy

algae, includingbothmacroalgae(‘seaweeds’)andmicroalgae(e.g.phytoplankton), and which arepopularly thought of as ‘plants’,would be good candidates toserve as alternatives to fishmealin fish feeds. One fundamentalconsideration is that algae arethe base of the aquatic foodchains that produce the foodresources that fish are adapt-ed to consume. But often it isnot appreciated that the bio-chemical diversity among differ-ent algae can be vastly greaterthan among land plants, evenwhen ‘Blue-Green Algae’ (e.g.Spirulina), more properly calledCyanobacteria, are excluded

from consideration. This reflects the veryearlyevolutionarydivergenceofdifferentalgalgroupsinthehistoryoflifeonearth.Onlyoneof the many algal groups, the Green Algae,produced a line of descent that eventuallygaverisetoallthelandplants.Thereforeitcanbedifficulttomakemeaningfulgeneralisationsabout the nutritional valueof this extremelydiversegroupoforganisms;ratheritisneces-sary to consider the particular qualities ofspecificalgae.

Protein and amino acidsFishmeal is so widely used in feeds

largely thanks to its substantial contentof high-quality proteins, containing all theessential aminoacids.Acritical shortcom-ing of the crop plant proteins commonlyusedinfishfeedsisthattheyaredeficientin certain amino acids such as lysine,

methionine, threonine, and tryptophan (Liet al.2009),whereasanalysesoftheaminoacid content of numerous algae havefound that although there is significantvariation, they generally contain all theessentialaminoacids.Forexample,surveysof 19 tropical seaweeds (Lourenço et al.2002) and 34 edible seaweed products(Dawczynski et al. 2007) found that allspeciesanalysedcontainedalltheessentialaminoacids,andthesefindingsareconsist-ent with other seaweed analyses (Roselland Srivastava 1985, Wong and Peter2000,Ortizet al.2006).

Analysesofmicroalgaehave foundsimilarhigh contents of essential amino acids, asexemplified by a comprehensive study of40 species of microalgae from seven algalclassesthatfoundthat,“Allspecieshadsimilaraminoacidcomposition,andwererichinthe

essentialaminoacids”(Brownet al.1997).

TaurineOne often-overlooked

nutrient is the non-proteinsulphonic acid taurine, whichis sometimes lumped withamino acids in discussionsof nutrition. Taurine is usu-ally an essential nutrient forcarnivorousanimals, includingsomefish,but it isnot foundin any land plants. However,although taurine has beenmuch less often investigat-ed than amino acids, it hasbeen reported in significantquantities inmacroalgaesuchas Laminaria, Undaria, andPorphyra (Dawczynski et al.2007, Murata and Nakazoe2001) as well as certainmicroalgae, for example thegreen flagellate Tetraselmis(Al-Amoudia and Flynn1989),theredunicellularalga

The use of algae in fish feeds as alternatives to fishmeal

by Eric C. Henry PhD, Research Scientist, Reed Mariculture Inc., USA

table 1: nutritional profiles of rotifers enriched using optimized protocols based on culture using reed Mariculture rotiGrow Plus® and enriched with n-rich® feeds

n-rich® feed type High Pro® Pl Plus® Ultra Pl®

applications

Moderate PUFa;

overnight gut-load

maintenance

overnight or 2-6 hr

enrichment

extreme DHa 2 hr enrichment

Composition of Biomass

lipid (Dry wt. % of Biomass) 35% 44% 66%

DHa (% of lipids) 37% 41% 44%

ePa 5% 2% 0.5%

ara 1.0% 1.0% 1.2%

total PUFas 45% 45% 48%

Protein 38% 32% 18%

Carbohydrate 19% 15% 7%

ash 8% 9% 10%

Dry weight Biomass 9% 9% 9%

10 | InternatIOnal AquAFeed | September-October 2012

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September-October 2012 | InternatIOnal AquAFeed | 11

Porphyridium(FlynnandFlynn1992),thedino-flagellate Oxyrrhis (Flynn and Fielder 1989),andthediatomNitzschia(Jacksonet al.1992).

PigmentsA few algae are used as sources of pig-

mentsinfishfeeds.Haematococcusisusedtoproduceastaxanthin,which isresponsibleforthepinkcolourofthefleshofsalmon.Spirulinaisusedasasourceofothercarotenoidsthatfishessuchasornamentalkoicanconvert toastaxanthin and other brightly coloured pig-ments. Dunaliella produces large amounts ofbeta-carotene.

LipidsIn addition to its high content of high-

quality protein, fishmeal provides lipids richin ‘PUFAs’, or polyunsaturated omega-3 andomega-6 fatty acids. These are the ‘fish oil’lipidsthathavebecomehighlyprizedfortheircontributiontogoodcardiovascularhealth inhumans.But it isnotalwaysappreciatedthatalgaeatthebaseoftheaquaticfoodchaininfactoriginatethese‘fishoil’ fattyacids.Thesedesirable algal fatty acids are passed up thefoodchaintofish,andtheyareindeedessen-tialnutrientsformanyfish.

Algae have been recognised as anobvious alternative source of these ‘fishoil’ fatty acids for use in fish feeds (Milleret al. 2008), especially eicosapentaenoic

acid (EPA), docosahexaenoic acid (DHA),and arachidonic acid (ARA). There is asubstantial literature devoted to analysisof the PUFA content of microalgae, par-ticularlythoseusedinaquaculture,becausethey have long been recognised as thebest source of these essential nutrients

for production of zooplankton necessaryforthefirstfeedingoflarvalfish,aswellasfilter-feedingshellfish.

Many shellfish producers are awarethe sterolprofileof feed lipids isofcriti-cal importance, but much less attentionhas been paid to the importance of the

Macroalgae (seaweeds) of many kinds can form extensive stands with high biomass density

10 | InternatIOnal AquAFeed | September-October 2012 September-October 2012 | InternatIOnal AquAFeed | 11

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sterol profile of fish feeds. Aside fromalterations in thenormal sterolprofileofthe fish, thepossibleendocrineeffectsofplant phytosterols in fish feeds (e.g. soyphytohormones) have yet to be thor-oughlyinvestigated(PickovaandMørkøre2007).

Use of algae in aquacultureMany different algae already play a vital

role in aquaculture. It is widely known thatthe addition of microalgae to larval fish

culture tanks confers a number of benefits,suchaspreventingbumpingagainstthewallsofthetanks(BattagleneandCobcroft2007),enhancing predation on zooplankton (Rochaet al.2008),enhancingthenutritionalvalueofzooplankton (Van Der Meeren et al. 2007),aswellas improving larvaldigestive(Cahuet al.1998)andimmune(Spolaoreaet al.2006)functions.

Furthermore, it has also been shownthat larvae of some fishes benefit greatlyby direct ingestion of microalgae (Reitanet al. 1997). One study has even shownthatthat livezooplanktoncouldbeelimi-natedfromthelarvaldietofRedDrumifmicroalgaewere fed alongwith a formu-lated microparticulate diet (Lazo et al.).

It is not surprising that the biochemicalcompositions of certain marine micro-algae are well-matched to the nutritionalrequirements some marine fish. Larvalfeedsareprobablydeservingof themostattentionineffortstodiscoverhowalgaecan best be used in fish feeds, becausemicroalgae are a natural component ofthe diet of many larval fish, either con-sumed directly or acquired from the gutcontents of prey species such as rotifersandcopepods.Existingprotocolsthatuse

microalgae to improve the PUFA profileof live prey (Table 1) demonstrate howeffectively an algal feed can enhance thenutritionalvalueoftheselivefeeds.

Use of algae in formulated fish feeds

Variousspeciesofmacroalgaeandmicro-algae have been incorporated into fish feedformulations to assess their nutritional value,andmanyhavebeenshowntobebeneficial:ChlorellaorScenedesmus fedtoTilapia(Tartielet al. 2008);Chlorella fed to Korean rockfish(Baiet al. 2001);Undaria orAscophyllum fedtoSeaBream(Yoneet al.1986);Ascophyllum,Porphyra,Spirulina,orUlva fed toSeaBream(Mustafa and Nakagawa 1995); Gracilaria or

Ulva fed to European Sea Bass (Valenteet al. 2006); Ulva fed to Striped Mullet(Wassefet al. 2001);Ulva orPterocladia fed to Gilthead Sea Bream (Wassef et al.2005);Porphyra,oraNannochloropsis-IsochrysiscombinationfedtoAtlanticCod(Walkeret al.2009,2010).Unfortunately,it has rarely been possible to determinethe particular nutritional factors respon-sible for these beneficial effects, eitherbecausenoattemptwasmadetodoso,orpoordesignofthestudy.

Forexample,inoneofthefewstudiesthathasfocusedontheeffectsofsubsti-tutingalgalproteinforglutenprotein,thecontrol and all the test diets containedcaseinplusaddedmethionineand lysine,no analysis of the algal protein wasprovided,andthealgalprotein(abiofuelprocess by-product) contained very highlevels of aluminium and iron (Husseinet al. 2012). More and better-designedstudiesarenecessarybeforewewillhave

agoodunderstandingofhowalgaecanbestbeusedinfishfeeds.

Choosing the right algaeOften the algae chosen for fish feeding

studies appear tohavebeen selected largelyfor convenience, because they are low-costand commercially available. For example,microalgae such as Spirulina, Chlorella andDunaliella canbeproducedbylow-costopen-pond technologies and are marketed as drypowders, and their nutritional profiles are

well-documented.Macroalgaesuchasthe‘kelps’ Laminaria, Undaria, and Durvillea,and the brown rockweed Ascophyllum,occur in dense stands that can be har-vestedeconomically,andtheyhavealonghistoryofuseassourcesofiodine,assoilamendments,andanimalfeedadditivestosupplytraceelements.

In recent years there has been greatinterest in the potential of algae as abiofuel feedstock, and it has often beenproposedthattheproteinportionremain-ingafterlipidextractionmightbeauseful

input foranimal feeds(e.g.Chenet al.2010).However,thealgaechosenforbiofuelproduc-tionmaynotbeoptimalforuseasafeedinput,andtheeconomicpressureforthelowest-costmethods of fuel production is likely to resultin protein residues with contamination thatmakesthemunfitforuseasfeed(e.g.Husseinet al.2012).

Bycontrast,thehigh-valuemicroalgaethatareusedinshellfishandfinfishhatcheriesaregenerallyproduced in closed culture systems to excludecontaminating organisms, and they cannot bedriedbeforeusewithoutadverselyaffectingtheirnutritionalandphysicalproperties,greatlyreduc-ingtheirvalueasfeeds.Inevitablytheirproductioncostsarehigher,buttheirexceptionalnutritionalvaluejustifiestheextraexpense.Table2presents

table 2: Because these algae are produced using continuous-harvest technology that maintains exponential growth, their protein and lipid contents are comparable to those provided by fish feeds.

(Dry Weight)nannochloropsis

oculatatetraselmis sp. Pavlova sp. Isochrysis

(t-Iso)thalassiosira weissflogii

Protein 52% 55% 52% 47% 52%

Carbohydrate 16% 18% 23% 24% 23%

lipid 17% 14% 20% 17% 14%

Various species of microalgae are used as aquaculture feeds, depending on the cell size and nutritional profile needed for particular applications

12 | InternatIOnal AquAFeed | September-October 2012

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September-October 2012 | InternatIOnal AquAFeed | 13

typical nutritional profiles of algae produced byReedMaricultureInc.

Justas itwouldbesenseless toarbitrarilysubstitute one conventional crop plant foranother (e.g. potatoes for soybeans) whenformulating a feed, the particular attributesof each alga must be carefully considered.Inaddition to theprotein/aminoacidprofile,lipid/PUFA/sterolprofile,andpigmentcontent,thereareimportantadditionalconsiderations.

The type and quantity of extracellularpolysaccharides,whichareveryabundantincer-tainalgae,caninterferewithnutrientabsorption,orconverselybeusefulbindingagentsinformingfeed pellets. The thick cell walls of microalgaesuchasChlorellacanpreventabsorptionofthenutritional valueof the cell contents. Inhibitorycompounds such as the phenolics producedby some kelps, and brominated compoundsproduced by red algae such as Laurencia, canrenderanalgawithanexcellentnutritionalanaly-sisunsuitableforuseina feed. Depending ongrowth and process-ing conditions, algaecan contain high con-centrations of traceelements that may bedetrimental.

Fur ther carefulstudy of the prop-

er ties of numer-ous algae will benecessary in ordertooptimallyexploitthe great potentialoffered by thisdiverse group oforganisms. But it isalready apparentthat algae will playan important partin the effor t tomove the formula-tion of fish feed“down the foodchain” to a moresustainablefuture.■

Referencesavailableonrequest

More inforMation:Eric C. Henry PhD, Reed Mariculture Inc.Tel: +1 408 426 5456Fax: +1 408 377 3498Email: eric@reedmariculture.comWebsite: www.reedmariculture.com

12 | InternatIOnal AquAFeed | September-October 2012 September-October 2012 | InternatIOnal AquAFeed | 13

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Volume 15 I s sue 5 2 012

the international magazine for the aquaculture feed industry

The use of algae in fish feeds as alternatives to fishmeal

Gustor Aqua and Ecobiol Aqua:– enhancing digestion in a different manner

Fishmeal & fish oil– and its role in sustainable

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