1. September | October 2012
The use of algae in fish feeds as alternatives
to fishmeal
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2. FEATURE
The use of algae in fish feeds
as alternatives to fishmeal
by Eric C. Henry PhD, Research Scientist, Reed Mariculture Inc., USA
F
ishmeal is very extensively used from consideration. This reflects the very methionine, threonine, and tryptophan (Li
in feeds for fish as well as other early evolutionary divergence of different algal et al. 2009), whereas analyses of the amino
animals. A recent global survey groups in the history of life on earth. Only one acid content of numerous algae have
estimated aquaculture consumption of the many algal groups, the Green Algae, found that although there is significant
of fishmeal at 3724 thousand tonnes in produced a line of descent that eventually variation, they generally contain all the
2006 (Tacon and Metian 2008). Now it is gave rise to all the land plants. Therefore it can essential amino acids. For example, surveys
becoming increasingly evident that such con- be difficult to make meaningful generalisations of 19 tropical seaweeds (Lourenço et al.
tinued exploitation of this natural resource about the nutritional value of this extremely 2002) and 34 edible seaweed products
will ultimately become both environmentally diverse group of organisms; rather it is neces- (Dawczynski et al. 2007) found that all
and economically unsustainable. sary to consider the particular qualities of species analysed contained all the essential
specific algae. amino acids, and these findings are consist-
Any satisfactory alternative feed ingre- ent with other seaweed analyses (Rosell
dients must be able to supply compara- Protein and amino acids and Srivastava 1985, Wong and Peter
ble nutritional value at competitive cost. Fishmeal is so widely used in feeds 2000, Ortiz et al. 2006).
Conventional land-based crops, especially largely thanks to its substantial content Analyses of microalgae have found similar
grains and oilseeds, have been favoured of high-quality proteins, containing all the high contents of essential amino acids, as
alternatives due to their low costs, and have essential amino acids. A critical shortcom- exemplified by a comprehensive study of
proved successful for some applications ing of the crop plant proteins commonly 40 species of microalgae from seven algal
when they were used as substitutes for used in fish feeds is that they are deficient classes that found that, “All species had similar
a portion of the fishmeal. But even when in certain amino acids such as lysine, amino acid composition, and were rich in the
these plant-based substitutes essential amino acids” (Brown
can support good growth they et al. 1997).
table 1: nutritional profiles of rotifers enriched using optimized protocols
can cause significant changes in based on culture using reed Mariculture rotiGrow Plus® and enriched with
the nutritional quality of the fish n-rich® feeds Taurine
produced. One often-overlooked
n-rich® feed type High Pro® Pl Plus® Ultra Pl®
nutrient is the non-protein
Why algae? Moderate sulphonic acid taurine, which
The reader may wonder why PUFa; overnight extreme is sometimes lumped with
algae, including both macroalgae applications overnight or 2-6 hr DHa 2 hr amino acids in discussions
gut-load enrichment enrichment
(‘seaweeds’) and microalgae (e.g. of nutrition. Taurine is usu-
maintenance
phytoplankton), and which are ally an essential nutrient for
popularly thought of as ‘plants’, Composition of Biomass carnivorous animals, including
would be good candidates to some fish, but it is not found
serve as alternatives to fishmeal lipid (Dry wt. % of Biomass) 35% 44% 66% in any land plants. However,
in fish feeds. One fundamental DHa (% of lipids) 37% 41% 44% although taurine has been
consideration is that algae are much less often investigat-
the base of the aquatic food ePa 5% 2% 0.5% ed than amino acids, it has
chains that produce the food been reported in significant
ara 1.0% 1.0% 1.2%
resources that fish are adapt- quantities in macroalgae such
ed to consume. But often it is total PUFas 45% 45% 48% as Laminaria, Undaria, and
not appreciated that the bio- Porphyra (Dawczynski et al.
Protein 38% 32% 18%
chemical diversity among differ- 2007, Murata and Nakazoe
ent algae can be vastly greater Carbohydrate 19% 15% 7% 2001) as well as certain
than among land plants, even microalgae, for example the
when ‘Blue-Green Algae’ (e.g. ash 8% 9% 10% green flagellate Tetraselmis
Spirulina), more properly called Dry weight Biomass 9% 9% 9% (Al-Amoudia and Flynn
Cyanobacteria, are excluded 1989), the red unicellular alga
10 | InternatIOnal AquAFeed | September-October 2012

3. FEATURE
Porphyridium (Flynn and Flynn 1992), the dino- Macroalgae (seaweeds) of many kinds can form
flagellate Oxyrrhis (Flynn and Fielder 1989), extensive stands with high biomass density
and the diatom Nitzschia (Jackson et al. 1992).
Pigments
A few algae are used as sources of pig-
ments in fish feeds. Haematococcus is used to
produce astaxanthin, which is responsible for
the pink colour of the flesh of salmon. Spirulina
is used as a source of other carotenoids that
fishes such as ornamental koi can convert to
astaxanthin and other brightly coloured pig-
ments. Dunaliella produces large amounts of
beta-carotene.
Lipids
In addition to its high content of high-
quality protein, fishmeal provides lipids rich
in ‘PUFAs’, or polyunsaturated omega-3 and
omega-6 fatty acids. These are the ‘fish oil’
lipids that have become highly prized for their
contribution to good cardiovascular health in
humans. But it is not always appreciated that
algae at the base of the aquatic food chain in
fact originate these ‘fish oil’ fatty acids. These
desirable algal fatty acids are passed up the acid (EPA), docosahexaenoic acid (DHA), for production of zooplankton necessary
food chain to fish, and they are indeed essen- and arachidonic acid (ARA). There is a for the first feeding of larval fish, as well as
tial nutrients for many fish. substantial literature devoted to analysis filter-feeding shellfish.
Algae have been recognised as an of the PUFA content of microalgae, par- Many shellfish producers are aware
obvious alternative source of these ‘fish ticularly those used in aquaculture, because the sterol profile of feed lipids is of criti-
oil’ fatty acids for use in fish feeds (Miller they have long been recognised as the cal importance, but much less attention
et al. 2008), especially eicosapentaenoic best source of these essential nutrients has been paid to the importance of the
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September-October 2012 | InternatIOnal AquAFeed | 11

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6. FEATURE
Various species of microalgae are used as Ulva fed to European Sea Bass (Valente
aquaculture feeds, depending on the cell size and et al. 2006); Ulva fed to Striped Mullet
nutritional profile needed for particular applications (Wassef et al. 2001); Ulva or Pterocladia
fed to Gilthead Sea Bream (Wassef et
al. 2005); Porphyra, or a Nannochloropsis-
Isochrysis combination fed to Atlantic Cod
(Walker et al. 2009, 2010). Unfortunately,
it has rarely been possible to determine
the particular nutritional factors respon-
sible for these beneficial effects, either
because no attempt was made to do so,
or poor design of the study.
For example, in one of the few studies
that has focused on the effects of substi-
tuting algal protein for gluten protein, the
control and all the test diets contained
casein plus added methionine and lysine,
no analysis of the algal protein was
provided, and the algal protein (a biofuel
process by-product) contained very high
levels of aluminium and iron (Hussein
et al. 2012). More and better-designed
studies are necessary before we will have
sterol profile of fish feeds. Aside from It is not surprising that the biochemical a good understanding of how algae can best
alterations in the normal sterol profile of compositions of certain marine micro- be used in fish feeds.
the fish, the possible endocrine effects of algae are well-matched to the nutritional
plant phytosterols in fish feeds (e.g. soy requirements some marine fish. Larval Choosing the right algae
phytohormones) have yet to be thor- feeds are probably deserving of the most Often the algae chosen for fish feeding
oughly investigated (Pickova and Mørkøre attention in efforts to discover how algae studies appear to have been selected largely
2007). can best be used in fish feeds, because for convenience, because they are low-cost
microalgae are a natural component of and commercially available. For example,
Use of algae in aquaculture the diet of many larval fish, either con- microalgae such as Spirulina, Chlorella and
Many different algae already play a vital sumed directly or acquired from the gut Dunaliella can be produced by low-cost open-
role in aquaculture. It is widely known that contents of prey species such as rotifers pond technologies and are marketed as dry
the addition of microalgae to larval fish and copepods. Existing protocols that use powders, and their nutritional profiles are
well-documented. Macroalgae such as the
‘kelps’ Laminaria, Undaria, and Durvillea,
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. and the brown rockweed Ascophyllum,
occur in dense stands that can be har-
nannochloropsis tetraselmis sp. Pavlova sp. Isochrysis thalassiosira vested economically, and they have a long
(Dry Weight) oculata (t-Iso) weissflogii
history of use as sources of iodine, as soil
amendments, and animal feed additives to
supply trace elements.
Protein 52% 55% 52% 47% 52%
In recent years there has been great
Carbohydrate 16% 18% 23% 24% 23% interest in the potential of algae as a
biofuel feedstock, and it has often been
lipid 17% 14% 20% 17% 14%
proposed that the protein portion remain-
ing after lipid extraction might be a useful
culture tanks confers a number of benefits, microalgae to improve the PUFA profile input for animal feeds (e.g. Chen et al. 2010).
such as preventing bumping against the walls of live prey (Table 1) demonstrate how However, the algae chosen for biofuel produc-
of the tanks (Battaglene and Cobcroft 2007), effectively an algal feed can enhance the tion may not be optimal for use as a feed input,
enhancing predation on zooplankton (Rocha nutritional value of these live feeds. and the economic pressure for the lowest-cost
et al. 2008), enhancing the nutritional value of methods of fuel production is likely to result
zooplankton (Van Der Meeren et al. 2007), Use of algae in in protein residues with contamination that
as well as improving larval digestive (Cahu et formulated fish feeds makes them unfit for use as feed (e.g. Hussein
al. 1998) and immune (Spolaorea et al. 2006) Various species of macroalgae and micro- et al. 2012).
functions. algae have been incorporated into fish feed By contrast, the high-value microalgae that are
Furthermore, it has also been shown formulations to assess their nutritional value, used in shellfish and finfish hatcheries are generally
that larvae of some fishes benefit greatly and many have been shown to be beneficial: produced in closed culture systems to exclude
by direct ingestion of microalgae (Reitan Chlorella or Scenedesmus fed to Tilapia (Tartiel contaminating organisms, and they cannot be
et al. 1997). One study has even shown et al. 2008); Chlorella fed to Korean rockfish dried before use without adversely affecting their
that that live zooplankton could be elimi- (Bai et al. 2001); Undaria or Ascophyllum fed nutritional and physical properties, greatly reduc-
nated from the larval diet of Red Drum if to Sea Bream (Yone et al. 1986); Ascophyllum, ing their value as feeds. Inevitably their production
microalgae were fed along with a formu- Porphyra, Spirulina, or Ulva fed to Sea Bream costs are higher, but their exceptional nutritional
lated microparticulate diet (Lazo et al.). (Mustafa and Nakagawa 1995); Gracilaria or value justifies the extra expense. Table 2 presents
12 | InternatIOnal AquAFeed | September-October 2012

7. FEATURE
take your
production to the
TOP of the
aquafOOd chain.
Many leading aquafeed manufacturers in the
industry count on Extru-Tech to engineer
the perfect aquafeed production solution.
Industry leading equipment and engineered
production advantages will give you the
upper hand over the competition. Could
typical nutritional profiles of algae produced by er ties of numer- you use a cost effective improvement in
Reed Mariculture Inc. ous algae will be performance and finished product quality?
Just as it would be senseless to arbitrarily necessary in order
substitute one conventional crop plant for to optimally exploit Contact one of the aquafeed Consultants
another (e.g. potatoes for soybeans) when the great potential at extru-tech today at 785-284-2153.
formulating a feed, the particular attributes offered by this
of each alga must be carefully considered. diverse group of
In addition to the protein/amino acid profile, organisms. But it is
lipid/PUFA/sterol profile, and pigment content, already apparent
there are important additional considerations. that algae will play
The type and quantity of extracellular an impor tant part
polysaccharides, which are very abundant in cer- in the effor t to
tain algae, can interfere with nutrient absorption, move the formula-
or conversely be useful binding agents in forming tion of fish feed
feed pellets. The thick cell walls of microalgae “down the food
such as Chlorella can prevent absorption of the chain” to a more
nutritional value of the cell contents. Inhibitory sustainable future.
compounds such as the phenolics produced ■
by some kelps, and brominated compounds
References available
produced by red algae such as Laurencia, can on request
render an alga with an excellent nutritional analy-
sis unsuitable for use in
a feed. Depending on
growth and process- Corporate offiCe
ing conditions, algae More inforMation: P.O. Box 8 • 100 Airport Road
can contain high con- Eric C. Henry PhD, Reed Mariculture Inc. Sabetha, KS 66534, USA
centrations of trace Tel: +1 408 426 5456 Phone: 785-284-2153
®
Fax: +1 408 377 3498 Fax: 785-284-3143
elements that may be Email: eric@reedmariculture.com extru-techinc@extru-techinc.com
detrimental. Website: www.reedmariculture.com www.extru-techinc.com
Fur ther careful
study of the prop-
September-October 2012 | InternatIOnal AquAFeed | 13
ET-221A.indd 1 1/20/12 1:57 PM

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