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Journal of Applied Phycology 9: 393–401, 1997. 393 c 1997 Kluwer Academic Publishers. Printed in Belgium. Microalgae for aquaculture: Opportunities and constraints Michael A. Borowitzka Algae Research Laboratory, School of Biological Sciences, Murdoch University, Murdoch, WA 6150, Australia Received 14 October 1997; accepted 18 October 1997 Key words: aquaculture, pastes, Isochrysis, Tetraselmis, Chaetoceros, Thalassiosira, Nannochloropsis, Pavlova, Skeletonema, culture systems Introduction The aquaculture of macro- and micro-algae is a valu- able global industry. Macroalgae are farmed for their hydrocolloids as well as for food (Abbott, 1996; Bixler, 1996), and microalgae are cultured commercially for use as health food and as a source of valuable chemi- cals such as betacarotene (Belay et al., 1994; Borow- itzka, 1994). Microalgae are also an important food source and feed additive in the commercial rearing of many aquatic animals, especially the larvae and spat of bivalve molluscs, penaeid prawn larvae and live food organisms such as rotifers which, in turn, are used to rear the larvae of marine finfish and crustaceans. The importance of algae in aquaculture is not surprising as algae are the natural food source of these animals. Although several alternatives for algae exist such as yeasts and microencapsulated feeds (Jones et al., 1987; Nell, 1993; Heras et al., 1994; Nell et al., 1996), live algae are still the best and the preferred food source. The decline in fish stocks and in the catch from ‘wild’ fisheries in recent years has lead to an ever increasing focus on aquaculture. The increased impor- tance of aquaculture is well illustrated by the shrimp industry. The world shrimp supply increased from 1925 10 3 t in 1984 to 3080 10 3 t in 1994, an increase of 60% (Ling et al., 1997). The bulk of this increase was in cultured shrimp, which increased 420% in the same period to a total of 921 10 3 t in 1994 which represents 29.9% of the total harvest. With increasing aquaculture of animal species there is an increasing need for suitable microalgae in the production of these animals. This paper will review the main problems and constraints faced by aquaculturalists in algal produc- tion and will consider the main advances being made to improve algal supply for aquaculture. Table 1. Microalgal species commonly used in aquaculture and the animals to which they are usually fed. Species Molluscs Crustaceans Rotifers Isochrysis galbana (T-iso) Chaetoceros muelleri Chaetoceros calcitrans Skeletonema costatum Thalassiosira pseudodonana Tetraselmis spp. Nannochloropsis spp. Pavlova lutheri Nitzschia and Navicula spp. 1 1 Used in the culture of abalone Species There are two main sources of algal species used in aquaculture. These are: (1) natural populations of phy- toplankton, either as they are found in nature or from cultures enriched by adding nutrients (e.g. New, 1990); and (2) unialgal cultures. Unialgal cultures are essential when a high quality feed source with known nutrition- al properties is required. Bacteria-free algal cultures also reduce the risk of introducing unwanted pathogens into the animal cultures which may result in mortali- ty of some of the animals cultured. Table 1 lists the main species used around the world. Live microal- gae also inhibit bacterial growth (Austin & Day, 1990; Austin et al., 1992; Mezrioui et al., 1994) and this is an added advantage they have over artificial feeds such as microencapsulated feeds. In recent years extensive studies have been under- taken to determine the nutritional requirements of the target species and the biochemical composition of algae which possibly can be used as a food source (e.g. Volkman et al., 1981, 1989, 1991, 1993; Brown et al.,

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Journal of Applied Phycology9: 393–401, 1997. 393c 1997Kluwer Academic Publishers. Printed in Belgium.

Microalgae for aquaculture: Opportunities and constraints

Michael A. BorowitzkaAlgae Research Laboratory, School of Biological Sciences, Murdoch University, Murdoch, WA 6150, Australia

Received 14 October 1997; accepted 18 October 1997

Key words:aquaculture, pastes,Isochrysis, Tetraselmis, Chaetoceros, Thalassiosira, Nannochloropsis, Pavlova,Skeletonema, culture systems

Introduction

The aquaculture of macro- and micro-algae is a valu-able global industry. Macroalgae are farmed for theirhydrocolloids as well as for food (Abbott,1996; Bixler,1996), and microalgae are cultured commercially foruse as health food and as a source of valuable chemi-cals such as betacarotene (Belay et al., 1994; Borow-itzka, 1994). Microalgae are also an important foodsource and feed additive in the commercial rearing ofmany aquatic animals, especially the larvae and spat ofbivalve molluscs, penaeid prawn larvae and live foodorganisms such as rotifers which, in turn, are used torear the larvae of marine finfish and crustaceans. Theimportance of algae in aquaculture is not surprisingas algae are the natural food source of these animals.Although several alternatives for algae exist such asyeasts and microencapsulated feeds (Jones et al., 1987;Nell, 1993; Heras et al., 1994; Nell et al., 1996), livealgae are still the best and the preferred food source.

The decline in fish stocks and in the catch from‘wild’ fisheries in recent years has lead to an everincreasing focus on aquaculture. The increased impor-tance of aquaculture is well illustrated by the shrimpindustry. The world shrimp supply increased from1925�103 t in 1984 to 3080�103 t in 1994, an increaseof 60% (Ling et al., 1997). The bulk of this increasewas in cultured shrimp, which increased 420% in thesame period to a total of 921� 103 t in 1994 whichrepresents 29.9% of the total harvest. With increasingaquaculture of animal species there is an increasingneed for suitable microalgae in the production of theseanimals. This paper will review the main problems andconstraints faced by aquaculturalists in algal produc-tion and will consider the main advances being madeto improve algal supply for aquaculture.

Table 1. Microalgal species commonly used in aquaculture and theanimals to which they are usually fed.

Species Molluscs Crustaceans Rotifers

Isochrysis galbana(T-iso) �

Chaetoceros muelleri �

Chaetoceros calcitrans � �

Skeletonema costatum � �

Thalassiosira pseudodonana � �

Tetraselmisspp. �

Nannochloropsisspp. �

Pavlova lutheri �

Nitzschia and Naviculaspp. �1

1 Used in the culture of abalone

Species

There are two main sources of algal species used inaquaculture. These are: (1) natural populations of phy-toplankton, either as they are found in nature or fromcultures enriched by adding nutrients (e.g. New, 1990);and (2) unialgal cultures.Unialgal cultures are essentialwhen a high quality feed source with known nutrition-al properties is required. Bacteria-free algal culturesalso reduce the risk of introducingunwanted pathogensinto the animal cultures which may result in mortali-ty of some of the animals cultured. Table 1 lists themain species used around the world. Live microal-gae also inhibit bacterial growth (Austin & Day, 1990;Austin et al., 1992; Mezrioui et al., 1994) and this isan added advantage they have over artificial feeds suchas microencapsulated feeds.

In recent years extensive studies have been under-taken to determine the nutritional requirements of thetarget species and the biochemical composition ofalgae which possibly can be used as a food source (e.g.Volkman et al., 1981, 1989, 1991, 1993; Brown et al.,

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1989, 1993; Brown, 1991; Brown & Jeffrey, 1992;Brown & Miller, 1992; Dunstan et al., 1992, 1994;de Roeck-Holtzhauer et al., 1993; Brown & Farmer,1994) and these studies provide an excellent data-basefor the selection of algal species for use in aquaculture.However, an understanding of the biochemical com-position is not enough, data are also required on theability of the target animal to feed on the algae, on thedigestibilit of the algae and on the nutritional require-ments of the animal species being cultured. As well asthis we need data on whether the algal species can becultured reliably and cost-effectively on a large scale.The list of algae shown in Table 1 is quite small whencompared with the diversity of natural phytoplanktonand it is clear that continued research will provide awider range of species with improved nutritional prop-erties and possibly better suited for large-scale culturein some parts of the world. For example several recentstudies have identified algal species especially suitedfor tropical aquaculture (Shamsudin, 1992; Renaud &Parry, 1994; Renaud et al., 1994) and high-lipid con-taining strains ofTetraselmiswhich enhance the growthof oyster larvae (Wikfors et al., 1995, 1996).

Constraints on algae production for aquaculture

The main constraint on microbial production for aqua-culture is the cost. For example, a survey of Australianhatcheries conducted by us shows that they estimatethat, on average, 30–40% (max. 70%) of hatcherycosts can be attributed to algal culture. The best USestimate gives a cost of greater than $US 50 kg�1 ofdry algal biomass (Fulks & Main, 1991) for a large,specialised oyster hatchery. However, for many hatch-eries, especially smaller hatcheries, this cost is likely tobe much higher. For example, Coutteau and Sorgeloos(1992) in their world-wide survey of bivalve hatcheriesgives costs of up to $US 300–400 kg�1 dry weightof microalgae, and a more recent international surveyconducted by us give costs of up to $US 600 kg�1

for algae production, with the highest costs in smallhatcheries.

This cost is extremely high when compared withthe costs of other commercial large-scale algal produc-ers. The production costs of algae such asSpirulina,Dunaliella andChlorella are of the order of $US 15–20 kg�1 dry algae (Borowitzka, 1991; Tanticharoen etal., 1993). Why then is the cost of microalgae produc-tion for aquaculture so much higher? The answer tothis question lies in several factors:

– The algal species cultured for aquaculture donot grow in highly selective environments as doDunaliella, SpirulinaandChlorella, and are there-fore generally cultured in closed systems ratherthan in open ponds or raceways.

– The climate where the algae are grown is often notoptimal for growth (too cold, too hot, too muchrain etc.) and the algae have to be grown indoorswith artificial lighting and temperature control thusincreasing energy costs. Artificial lighting alsoresults in lower yields as the cultures are gener-ally light-limited.

– Algal culture requires expertise often not found inthe hatchery/farm and is often regarded as a diver-sion of resources resulting in major problems whencultures ‘crash’. This reduced reliability increasescosts.

– The algae are grown mainly in batch culture whichincreases the labour required and the capital costsof the facilities.

– The culture systems used (carboys, large bags, tow-er reactors, tanks etc. (Fox, 1983; De Pauw &Persoone, 1988; Fulks & Main, 1991; O’Meley& Daintith, 1993)) are inefficient, leading to lowproductivities and less reliable cultures. These sys-tems are also not suitable for computer control orautomation, thus increasing labour costs.

– The cost of producing algal biomass is strong-ly affected by economies of scale (Borowitzka,1992a; Coutteau & Sorgeloos, 1992). The algalrequirements of most hatcheries are small whencompared to the scale of commercialDunaliella,Spirulina and Chlorella culture operations, thussignificantly increasing the unit cost of the algae.

Opportunities

An international workshop on microalgal culture foraquaculture (Fulks & Main, 1991) ranked the prima-ry costs associated with microalgal production in theorder of: labour, supplies and chemicals, facilities andenergy. The potential solutions to the cost of labourwere seen as:(1) computer control/automation,(2) streamlining of scale-up,(3) reduction of the number of culture units,(4) cryopreservation of stock cultures,(5) continuous culture,(6) use of pre-mixed nutrients.

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These solutions however are only a part of the equationand they ignore the wide experience of commercialalgae growers. In particular they ignore the potentialbenefits of using better culture systems and of the use oflarger algae culture facilities.This is partially due to thefact that most aquaculturalists perceive algal culture asan in-house activity and have little experience in large-scale algal culture.

The solution to the high costs of algal culture andthe associated problems with culture stability, lies inhaving dedicated algal production units which can useefficient culture techniques, have appropriately trainedstaff, a Total Quality Management programme, andwhich can achieve economies of scale, thus providinghatcheries with a cheaper, reliable and high qualitysource of algae.

New culture systems

It is necessary to improve the large-scale systems used.Present culture methods used in hatcheries for the pro-duction of the required microalgae rely mainly on bagor tank culture (up to 500 L per bag) and pond cul-ture (up to 10,000 L) (cf. Costa-Pierce, 1982; Lee &Tamaru, 1993; Liao et al., 1993). Algal productivityin these culture systems is low and they are knownto be unreliable and require very careful management(Sato, 1991). The bag and pond culture systems usedrepresent very primitive technology. In the last decade,major advances have been made in the large-scale cul-ture of microalgae, not only in open systems, but also inclosed bioreactors (Tredici & Materassi, 1992; Chau-mont, 1993; Borowitzka, 1996) and the aquacultureindustry has yet to adopt these new technologies.

In order to be able to produce ‘clean’ unialgal cul-tures closed culture systems are essential. Of the var-ious types of closed bioreactor systems available, thetubular photobioreactor seems to be the most reliable,efficient and cost effective. Simple types of tubularreactors were already proposed for aquaculture sometime ago (e.g. Canzonier & Brunetti, 1976) and aroundthe world several research groups are working on dif-ferent designs (e.g. Chaumont et al., 1988; Tredici& Materassi, 1992; Pulz, 1994; Borowitzka, 1996;Hu et al., 1996). The helical tubular photobioreactordesigned by Biotechna Ltd (the BiocoilTM – Robin-son et al., 1988) so far has proven to be the mosteffective and long-term laboratory and pilot-scale stud-ies in large outdoor Biocoils with several microal-gae (Tetraselmis, Isochrysis, Chaetoceros, Pavlova,

Nannochloropsis, Spirulina, Chlorellaetc.) have beencarried out in the UK and Australia (Chrismadha &Borowitzka, 1994; Borowitzka, 1996; Watanabe &Hall, 1996). This system not only provides a con-trolled, contamination-free environment, but it can beused for continuous culture at much higher cell den-sities than can be achieved with traditional systems.The higher cell densities are mainly a result of beingable to work outdoors using natural sunlight. The abil-ity to operate a reliable continuous culture system notonly reduces production costs but provides an algalbiomass of consistent quality. The Biocoil can also besemi-automated with computer control thus reducingthe amount of labour required.

Another closed photobioreactor system whichlooks promising, but which has not yet been tried withalgal species used in aquaculture are flat panels (Tredici& Materassi, 1992; Pulz et al., 1995; Hu et al., 1996).The economics of scale-up for these systems remain tobe evaluated.

A distinct advantage of an advanced closed cul-ture system such as the Biocoil is that growth condi-tions can be controlled and optimised to optimise thegrowth rate and biochemical composition of the algae.Lee and Low (1991) have reported net biomass produc-tivities of 3.64 g L�1 d�1 for Chlorella pyrenoidosain a 1.2-cm diameter tubular reactor in Singapore, andMolina Grima et al. (1996) have reported productivi-ties of 2.7 g L�1 d�1 for Phaeodactylum tricornutumin a 3.0-cm diameter tubular reactor in Almeira, Spain.We have achieved sustainable productivities of 1.2 gL�1 d�1 and> 1:0 g L�1 d�1 with Tetraselmis chuiiand Isochrysis galbana(strain T-iso) respectively in700 L pilot-scale Biocoils with 2.4 cm diameter tub-ing, located outdoors in Perth, Australia. These highproductivities can be attributed to the high incidentirradiance at these sites, the ability to culture the algaeat optimum temperatures and optimal turbulence con-ditions within the bioreactors. The lower productivitiesof the latter two algae can be attributed to the fact thatthey are both flagellates which are more delicate thanChlorellaandPhaeodactylum. As the algae have to becirculated within the bioreactor some sort of pumpingsystem is required. Some alternatives are centrifugalpumps, diaphragm pumps, lobe pumps or airlifts. Thelatter appears to cause the least cell damage to fragilespecies.

Not only can high productivities be achieved, butthe controlled conditions in these bioreactors permitthe production of algal biomass of high nutritional val-ue. Although the exact nutritional requirements of the

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animal species cultured is not completely known, fac-tors such as lipid, protein and vitamin content as well asfatty acid composition are very important (e.g. Kovenet al., 1992; He & Lawrence, 1993; Cahu et al., 1994;Kanazawa & Koshio, 1994; Millican & Helm, 1994).Well mixed, closed culture systems, preferably operat-ed in continuous or semi-continuous mode provide themeans to manipulate and thus optimise the biochemi-cal composition of the algal cells. For example, Chris-madha and Borowitzka (1994) have used variations incell density and irradiance to maximise the content ofthe long-chain polyunsaturated fatty acid, eicosapen-taenoic acid, in the diatomPhaeodactylum tricornutumgrown in semi-continuous culture in a Biocoil. Nutri-ents, light, pH and temperature and growth stage allaffect the biochemical composition of algal cells (e.g.Fabregas et al., 1986; Renaud et al., 1991; Thompsonet al., 1992a,b; Dunstan et al., 1993) and these can bereliably controlled in such a culture system.

An alternative to culture in photobioreactors is het-erotrophic culture which can be cheaper than photoau-totrophic (Gladue & Maxey, 1994).Tetraselmis, forexample, grows well heterotrophically, however theheterotrophically grown cells contain significantly lesslipid than those grown in the light and the proportionof the long-chain polyunsaturated fatty acids in theselipids is furthermore markedly reduced (Day & Tsava-los, 1996). In heterotrophically-grown diatoms on theother hand the cell lipid content was higher than in cellsgrown in the light (Tan & Johns, 1996). However, in allbut one species (Nitzschia laevis) the content of eicos-apentaenoic acid was greater in the light grown cellsthan in the dark grown cells. The range of microalgalspecies which can be grown heterotrophically is quitelarge (Neilson & Lewin, 1974; Hellebust & Lewin,1977) and at least some of these do show a high lipidand PUFA content (Barclay et al., 1994; Gladue &Maxey, 1994). It remains to be seen whether they aresuitable as a feed in aquaculture.

Large-scale algal culture also requires an efficientand cheap harvesting method which is compatible withthe final application of the algae. At present hatcheriesthat concentrate algae use centrifugation to harvest thealgae. Centrifugation is very expensive (cf. Mohn,1988; Borowitzka, 1992a) and damages algal cells,and alternative methods such as flocculation, flotationor enhanced gravity settling need to be evaluated. Forexample, Millamena et al. (1990) found that floccu-lation with alum and lime could be used to concen-trate Chaetoceros calcitrans, Skeletonema costatumand Tetraselmis chuii, but not Isochrysissp. When

Table 2. Ranking of the requirements for algalconcentrates by hatcheries, based on a survey ofAustralian hatcheries. The hatcheries were askedto rank each requirement on a scale of 1 (littleinterest) to 10 (extremely desirable)

Rank

Range Mean

Nutritional value 5� 10 (8.79)

Consistency of supply 5� 10 (8.79)

Management/production

advantages offered 2� 10 (8.31)

Nutritional consistency 1� 10 (8.00)

Product to be alive 1� 10 (7.79)

Supporting research 0� 10 (7.86)

Shelf life 0� 10 (7.64)

Product range 1� 10 (6.43)

sun-dried and ground to 60�m these algae could beused to rear zoea and mysis ofPanaeus monodon. Theflocculated algae could also be frozen at�5 �C andused later as inocula for fresh cultures.

The culture of microalgae for the nutrition ofjuvenile abalone presents a special problem. Abalonerequire algae such as the diatomsNitzschiaandNav-icula which grow on surfaces (Uki & Kikuchi, 1979;Ebert & Houk, 1984; Knauer et al., 1996). These algaecannot be grown efficiently in the more conventionalsystems used for the culture of planktonic microalgaeand are grown on plates or on brushes. With increas-ing interest in commercial abalone culture there is anurgent need for some efficient large-scale culture sys-tems for these algae.

Algae concentrates

A major affecting the production costs of algae is thesize of the culture facility. However, the majority ofhatcheries world-wide are relatively small. It wouldtherefore be advantageous to have dedicated large-scale algal production facilities supplying a numberof hatcheries with their algal requirements. The majorbarrier to the implementation of such dedicated large-scale algal culture facilities is the need to concentrateand preserve the algal biomass so that it can be shippedto the hatcheries for use.

Table 2 shows the results of part of a survey of Aus-tralian hatcheries where the respondents were asked torank the important features of a concentrated microal-gal product on a scale of 1 (little interest) to 10

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(extremely desirable). Not surprisingly, the hatcheriesrated nutritional value as most important, closely fol-lowed by consistency of supply.

Several ways of preserving concentrated algal bio-mass have been studied and these include dried bio-mass, frozen biomass and algal pastes or slurries. Theuse of dried or frozen algal biomass has been stud-ied for many years. For example, Hidu and Ukeles(1962) used freeze-dried algae to feed the larvae of theclam,Mercenaria mercenaria, and frozenSkeletonema(Mock & Murphy, 1970; Mock, 1972) andTetraselmis(AQUACOP, 1977) have been used in penaeid prawnculture. However, Brown (1972) found that frozen andfreeze-driedSkeletonemaandThalassiosirawere notas good as live diatoms as feed forPenaeus aztecus.Sun-driedChaetocerosandTetraselmishave also beenused successfully to feed peneid larvae (Millamena etal., 1990). Spray-dried heterotrophically grown algaehave been available at various times (e.g. Cell Sys-tems Ltd (UK) sold spray-driedTetraselmis suecicaandCyclotella crypticafor about $170 kg�1). Beiden-bach et al. (1990) showed that as much as 75% of livealgae could be replaced by spray-driedTetraselmisinthe culture ofP. vannamei. However these algae aregenerally nutritionally inadequate and their use hascaused problems with fouling of the water (Laing etal., 1990; Laing & Verdugo, 1991; Numaguchi & Nell,1991; Laing & Millican, 1992; Curatolo et al., 1993).

Wet algal concentrates (pastes or slurries) appear tobe a much better alternative, and hatcheries in Canadaand the USA produce limited quantities of these at var-ious times. Algal concentrates have been used success-fully in a number of research facilities and hatcheries(Watson et al., 1986; Nell & O’Connor, 1991; O’Con-nor & Nell, 1992). Some algae such asTetraselmiscan be stored as pastes for very long periods (Montainiet al., 1995), but long-term storage while maintain-ing the nutritional quality of the alga has not yet beenachieved for most species. Further work is essentialtherefore to extend the storage life of the algal concen-trates and to develop appropriate methods of supplyingthese concentrates to the target species. The storage life(defined as the maximum time the paste/slurry can bekept and still retain a nutritional value equivalent to‘fresh’ algae) ranges from about 1 week to 4–5 weeks,depending upon the species of alga. Wet pastes seemto be nutritionally better than then dried algae in partsince they appear to maintain their original compo-sition better. For example, Brown (1995) found thata wet paste ofC. calcitransstored at 4�C lost only29% of its ascorbic acid content compared to algae

dried at 60�C overnight which lost> 94%. Freeze-dried C. calcitransalso maintained its ascorbic acidcontent in storage; however> 85% of the ascorbicacid was lost from the cells on resuspension. Similardegradation of cell contents, especially vitamins andcarotenoids, upon freeze-drying and drum drying havebeen observed with other algae such asScenedesmusandDunaliella (Venkataraman & Becker, 1985; Ben-Amotz & Avron, 1989). These results may explainwhy frozen and dried algae are of lower nutritionalvalue than fresh algae (Laing et al., 1990).

Algal concentrates are not only a source of feed,but they have other potential advantages. Chemical andmicrobial loads associated with direct feeding of algalcultures have been found deleterious to some mollusc(Watson et al., 1986) and crustacean (Zein-Eldin inGriffith et al., 1973) larvae. Exclusion of growth medi-um via the use of algal concentrates may thereforeexplain reports of enhanced larval growth and survivalof some species when fed such concentrates (Nell &O’Connor, 1991). Accordingly, wider use of concen-trates could facilitate production of species for whichefficient output of consistently high quality postlarvaeor juveniles has thus far proven elusive. Such speciesinclude the commercial scallop,Pecten fumatus(Heas-man, pers. comm.); the Jumbo tiger prawn,Penaeusmonodon; the Sydney rock oyster,Saccostrea commer-cialis (Nell et al., 1991) and the silverlip pearl oyster,Pinctada maxima(R. Rose, pers. comm.).

The availability of low cost algal concentrateswould also allow the blending of these concentratesto produce nutritionally superior feeds. Not surpris-ingly, unialgal diets are generally not as nutritionallyadvantageous as mixed algal (or algae and yeast) diets(Epifanio, 1979; Gallardo et al., 1995). Although manyhatcheries do produce mixed diets, the scope for this islimited due to the cost of maintaining a range of algalspecies.

Other opportunities

Microalgae are not only essential food sources, butmay also play a role in enhancing the quality of the ani-mal species cultured. For example, salmonids requirethe addition of carotenoids, especially astaxanthin, totheir diet to achieve the flesh colour required of a highquality product. In the past synthetic carotenoids havebeen used; however consumers now appear to havea preference for ‘naturally’ pigmented fish. The bestnatural sources of astaxanthin are the green flagel-

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late, Haematococcus pluvialis, and the yeast,Phaffiarhodozyma(Borowitzka, 1992b; Johnson & Schroed-er, 1995).Haematococcusin particular has a high con-tent of astaxanthin, and this alga has been the focus ofintense research in the last decade as a source of naturalastaxanthin and some commercial product has recentlybecome available. Feeding studies have shown that it isa very effective pigmenter of salmonids (Sommer et al.,1991b; Choubert & Heinrich, 1993). Further improve-ments in commercial culture technology resulting in acheaper product suitable for widespread application inaquaculture can be expected.

Other algae can also be used for the pigmentation offish and shellfish. For exampleSpirulinacan be used topigment shrimp (Liao, WL et al., 1993) andDunaliel-la salina can be used to pigment other crustaceans(Sommer et al., 1991a).Spirulina is also a commoncomponent of the feed for ornamental fish such as Koicarp, as it enhances pigmentation. Algal carotenoidsmay also function as a growth factor (Dall, 1995) andthis may lead to another new application for algae inaquaculture diets.

Conclusions

The increase in aquaculture and the move towards moreintensive aquaculture means an ever increasing demandfor microalgae. Although alternatives such as microen-capsulated feeds are being developed they are unlikelyto replace the need for live algae. The present highcost and variable quality of algae being produced sig-nificantly affects the profitability of many aquacultureoperations. In order to improve yields and reduce costsongoing research and development is required on thediscovery of new and better species of microalgae, oncheaper and more reliable algal culture systems such asthe Biocoil-type tubular photobioreactor, and on waysto concentrate and preserve the algal biomass. A keyfeature of this is the need to achieve economics of scaleby having large, dedicated microalgal production facil-ities rather than the small in-house algal culture facil-ities characteristic of the aquaculture industry today.Not only can a large dedicated algal culture facilityproduce algae cheaper, but it can also ensure that ahigh quality standard is maintained. Further opportu-nities for improving the economics of aquaculture liein applying the experience of very large commercialproducers of algae such asChlorella, SpirulinaandDunaliella to microalgae production for aquaculture.

Acknowledgements

Many people have contributed directly and indirectlyto the development of the ideas presented in this paper.In particular Drs Mike Heasman, Wayno O’Connorand John Nell have contributed to my understandingof the functions and needs of hatcheries, and Drs Les-ley Borowitzka, Avigad Vonshak, Otto Pulz, AmosRichmond, Mario Tredici, Phang Siew Moi and JohnBenemann have provided for often lively discussionson large-scale algal culture. Thanks also go to theoperators of hatcheries and aquaculture facilities whopatiently explained their operations. Part of this workwas supported by a grant from the Fisheries Researchand Development Corporation.

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