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.

1. September | October 2013
The potential of microalgae meals in
compound feeds for aquaculture
The International magazine for the aquaculture feed industry
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
INCORPORATING
f ish farming technolog y

2. Innovations for a better world.
Bühler AG, Feed & Biomass, CH-9240 Uzwil, Switzerland, T +41 71 955 11 11, F +41 71 955 28 96
fu.buz@buhlergroup.com, www.buhlergroup.com
Fatten up your bottom line. Bühler high-performance animal and aqua feed production
systems are used by leading companies around the world. These producers know they
can rely not just on the technology itself, but also on the support that accompanies it. A
service combining local presence with global expertise both lowers feed mill operating
costs and increases capacity utilization. To find out more, visit www.buhlergroup.com

3. I
ntensive production of mainly car-
nivorous 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.
Algae overview
Marine algae are distributed from the
polar regions to tropical seas in nutrient rich
and poor environments. Algae are photoau-
totrophs and are characterised by their lack
of roots, leaves and presence of chlorophyll a.
They range in size from microscopic individual
cells called microalgae to seaweeds that can
be greater than 30 m in length (Qin 2012).
Marine microalgae are the dominant
primary producers in aquatic systems and
account for a similar level of carbon fixation as
terrestrial plants (40-50%) but represent only
1 percent of the planetary photosynthetic
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
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
Figure 1: Percentages (dry weight basis) of protein, lipid and carbohydrate in
microalgae. The range of values is shown by range bars (Brown 1997)
14 | InternatIOnal AquAFeed | September-October 2013
FEATURE

5. biomass (Stephenson 2011). Microalgae are
sometimes directly consumed by humans as
health supplements due to this high nutritional
value and abundance (Dallaire 2007) but this
is relatively rare.
As carnivorous fish ingest algae as a food
source (Nakagawa 1997) there has been a
move to utilise them for fish feed. Currently
30 percent of the world algal production is
used for animal feed (Becker 2007) but the
use in aquaculture is mainly for larval fish,
molluscs and crustaceans (FAO 2009a). As
mentioned above, the fishmeal and oil use in
aquaculture is unsustainable and algae have
the potential to reduce this dependence. This
is due to the algae being photosynthetic so
they have the ability to turn the sun’s huge
amount of energy, 120,000 TW of radiation,
into protein, lipids and nutrients. More energy
from the sun hits the surface of the earth
in one hour than the energy used in one
year and this is a huge amount of untapped,
sustainable energy can be exploited by algae.
This is a relatively new area of research but
has many positive aspects that give it a large
amount of potential for future use.
Microalgae
The term ‘microalgae’ is often used to
refer specifically to eukaryotic organisms, both
from freshwater and marine environments but
can include prokaryotes such as cyanobacteria
(Stephenson 2011). Microalgal production
has received some attention recently due to
its potential use as a biofuel (Slocomb 2012),
use in animal feed, human consumption and
recombinant protein technology (Becker,
2007; Potvin and Zhang 2010; Williams and
Laurens, 2010). This has resulted in a huge
amount of knowledge and research into
microalgae and
resulted in reviews
being published
about specific sub-
jects such as genetic
engineering of algae
(Qin 2012), poten-
tial use as biofuel
(Demirbas 2011)
and novel methods
to measure such
important com-
ponents such as
protein (Slocomb
2012).
This interest and
knowledge in the
area has allowed
aquaculture to
essentially piggy back
the research being
performed by the
biodiesel industry
and even act syner-
gistically with it by
consuming the by-
products produced
(Ju 2012). Currently
microalgae have
been used in aqua-
culture as food
additives, fishmeal
and oil replace-
ment, colouring of
salmonids, inducing
biological activities
and increasing the
nutritional value of
zooplankton which
are fed to fish lar-
vae and fry (Dallaire
2007).
Although the
biodiesel industry
has been conduct-
ing a large amount
of research, this
has mainly been
focused towards
species that have
high lipid contents
whereas species in
aquaculture must
be of appropriate
size for ingestion
and be read-
ily digested. They
must also have
rapid growth rates,
be able to be cul-
tured on a mass
scale, be robust
enough to cope
with fluctuations
table 2: oil contents of some microalgae
(Demirbas 2007)
Microalgae oil content
(wt% of dry
basis)
Botryococcus braunii 25-75
Chlorella sp. 28-32
Crypthecodinium cohnii 20
Cylindrotheca sp. 16-37
Dunaliella primolectra 23
Isochrysis sp. 25-33
Monallanthus salina >20
nannochloris sp. 20-35
nannochlorosis sp. 31-68
neochloris oleoabundans 35-54
nitzschia sp. 45-47
Phaeodactyhum tricornutum 20-30
Schizochytrium sp. 50-77
tetraselmis sueica 15-23
September-October 2013 | InternatIOnal AquAFeed | 15
FEATURE

6. REAL
BREWERS’YEAST
“Made inGermany”
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.
Leiber GmbH · Hafenstraße 24, 49565 Bramsche, Germany · Tel +49 (0) 5461 9303-0 · Fax +49 (0) 5461 9303-28 · www.leibergmbh.de · info@leibergmbh.de
THE SPECIAL WORLD OF
LEIBER YEAST...
www.leibergmbh.de

7. in temperature, light and nutrients and
have a good nutrient composition (Brown
2002).
Varying nutritional values
The nutritional value of any algal species
depends on its cell size, digestibility, produc-
tion of toxic compounds and biochemi-
cal composition. This, along with differences
among species and method of production,
explains the variability in the amount of
protein, lipids and carbohydrates, which are
12-35 percent, 7.2-23 percent, and 4.6-23
percent respectively (FAO 2009a) (Figure 1).
This level of fluctuation can be influenced by
the culture conditions (Brown et al., 1997) but
rapid growth and high lipid production can be
achieved by stressing the culture.
Protein
Most of the figures published in the litera-
ture on the concentration of algal proteins are
based on estimations of crude protein and
as other constituents of microalgae such as
nucleic acids, amines, glucosamides and cell
wall materials which contain nitrogen; this can
result in an overestimation of the true protein
content (Becker 2007).
The non-protein nitrogen can be up to 12
percent in Scenedesmus obliquus, 11.5 percent
in Spirulina and 6 percent in Dunaliella. Even
with this overestimation the nutritional value
of the algae is high with the average qual-
ity being equal, sometimes even superior, to
conventional plant proteins (Becker 2007)
(Table 1).
The amino acid composition of the
protein is similar between species and is
relatively unaffected by the growth phase
and light conditions (Brown et al., 1993a,
b). Aspartate and
glutamate occur in
the highest concen-
trations (7.1-12.9%)
whereas cysteine,
methionine, tryp-
tophan and histidine
occur in the lowest
concentrations (0.4-
3.2%) with other
amino acids ranging
from (3.2-13.5%)
(Brown 1997).
Lipids
The lipids in micro-
algal cells have roles as
both energy storage
molecules and in the forma-
tion of biological membranes
and can be as high as 70
percent dry weight in some
marine species (Stephenson
2011) (Table 2). Under rapid
growth conditions these lipid
levels can drop to 14-30 per-
cent dry weight, which is a
level more appropriate for
aquaculture. These lipids are
composed of polyunsaturated
fatty acids such as docosa-
hexaenoic acid (DHA), eicos-
apentaenoic acid (EPA) and
arachidonic acid (AA) (Brown
2002) and in high concen-
trations; most species have
percentages of EPA from 7-34
percent (Brown 2002) (Figure
2).
These fatty acids are highly sought after
and as they currently cannot be synthesised
in a laboratory and are usually obtained
through fish oil and are a limiting factor in
vegetable oils such as palm, soybean and
rapeseed oil use in aquaculture. The fatty
acid composition is associated with light
intensity, culture media, temperature and
pH. Appropriate measures and control, along
with the suitable selection of a species, is
necessary to produce algae with the desired
lipid level and composition.
Vitamins
Microalgae also contain vitamins which can
be beneficial to the health of the consumer but
vary greatly between species (Brown 2002).
This variation is greatest for ascorbic acid
(Vitamin C), which varies from 1-16mg g dry
weight (Brown & Miller, 1992), but other vita-
mins typically show a 2-4 x difference between
species (Brown et al., 1999) (Figure 3).
Despite the variation in vitamin C all the
species would provide an adequate supply to
cultured animals which are reported to only
require 0.03-0.2 mg g-1 of the vitamin in their diet
(Durve and Lovell, 1982). However every species
of algae had low concentrations of at least one
vitamin (De Roeck-Holtzhauer et al., 1991) so a
careful selection of a mixed algal diet would be
necessary to provide all the vitamins to cultured
animals feeding directly on microalgae.
Algae in aquaculture
The use of algae as an additive in aqua-
culture has received a lot of attention due
to the positive effect it has on weight gain,
increased triglyceride and protein deposi-
tion in muscle, improved resistance to
disease, decreased nitrogen output into
the environment, increased fish digestibility,
physiological activity, starvation tolerance
and carcass quality (Becker, 2004; Fleurence
2012). Li (2009) showed that the addition
of dried microalgae in the diet, albeit at low
concentrations 1.0-1.5 percent, resulted in
increased weight gain of the channel catfish
(Ictalurus punctatus) along with improv-
ing the feed efficiency ratio and levels of
poly-unsaturated fatty acids. Ganuza (2008)
showed that algal oil can be an alternative
source of DHA (docosahexaenoic acid) to
fish oil in gilthead seabream (Sparus aurata)
microdiets although it did not allow for the
complete substitution of fisheries products
due to the low EPA (eicosapentaenoic acid)
levels in the species of algae used.
These were at relatively low-level inclu-
sions; at greater levels it can have a detri-
mental effect. At 12.5 percent inclusion algae
caused reduced growth performances in rain-
bow trout and at 25 percent and 50 percent
this substitution of fish feed caused nutritional
deficiencies that led to decreased growth,
feed efficiency and body lipids (Dallaire 2007).
Levels of algal inclusion of 15 percent
and 30 percent also reduced feed intake and
growth rate in Atlantic cod (Walker 2011).
As Atlantic cod are known to have a robust
digestive system it was suggested that this was
due to reduced palatability which could be an
issue for algal use in aquaculture.
High levels of inclusion does not cause
such negative effects in all species raised in
aquaculture, 50 percent replacement did
not have a negative effect on shrimp (Ju
2012), but is generally experienced among
finfish.
Figure 2: Average percentage compositions of the long-
chain PUFAs docosahexaenoic acid (DHA; 226n-3),
eicosapentaenoic acid (EPA; 20:5n-) and arachidonic acid
(20;4n-6) of microalgae commonly used in aquaculture.
Data compiled from over 40 species from laboratory of
CSIRO Marine Research.
Figure 3: Concentrations of different vitamins in
microalgae in µg g-1. Graph adapted from Brown
2002 with data collected from Seguineau et al.,
1996 and Brown et al., 1999
16 | InternatIOnal AquAFeed | September-October 2013
FEATURE

8. Algae production
The production of algae, in particular
microalgae, is a rapidly developing industry
due to the biofuel research that is currently
taking place. The annual world production of
all species is estimated to be 10,000 t year-1
(Richmond, 2004) with the main limit to pro-
duction currently being the cost. Production
costs are currently range from US$4-300 per
kg dry weight (FAO 2009a) depending on
the type of production method employed
(Table 3).
There has been a shift away from typical
systems such as outdoor ponds and raceways
to large-scale photobioreactors which have a
much higher surface area to volume ratio and
could potentially reduce the production cost
(Brown 2002). These photobioreactors could
yield 19,000 - 57,000 litres of microalgal oil per
acre per year, which is over 200 times the yield
from the best performing vegetable oils (Chisti
2007), and reduce the cost of algal oil from
$1.81 to $1.40 per litre (Demirbas 2011).
However, for algal oil to be competitive
with petrodiesel, it should be less than $0.48
per litre. This is achievable through economies
of scale (Demirbas 2011) and would make it a
cheap and sustainable oil for the aquaculture
industry. There are also other developments
such as increasing the specific activity of the
enzyme RUBISCO which would increase
yields, transgenic studies, increasing the pro-
portion of photo protective pigments which
would improve the light-dependant reactions
and selecting for algae with small antennas
which is fundamental to achieving high yields
in biomass dense cultures (Stephenson 2011).
This research is essential as the production
costs of microalgae are still too high to
compete with traditional protein sources for
aquaculture (Becker 2007).
Benefits and obstacles
Algae have a great potential for use in
sustainable aquaculture as they are not only a
source of protein, lipids and have other nutri-
tional qualities but they are phototrophic so
produce these directly from sunlight. Producing
100 tons of algal biomass also fixes roughly
183 tons of carbon dioxide which has obvious
implications in this period of climate change.
The production does not always require
freshwater, compete for fertile land and are
not nutritionally imbalanced with regard to
the amino acid content like soybean.
There are still some obstacles such as the
powder-like consistency of the dried biomass
and applications to feed manufacture, the
production costs and pests and pathogens
that will effect large scale algal cultivation
sustainability (Hannon et al., 2010), which is an
area that little is known about.
There still needs to be many feeding trials
as the majority of research has focused on
improving the nutritional value of rotifers
and not as algae as a potential replacement
of fishmeal and fish oil. There is also interest
into storing algal pastes which have extended
shelf life (2-8 weeks) or the use of defatted
microalgae meal from the biodiesel industry.
The use of algae in aquaculture is a promis-
ing and young area of research and when
compared to agriculture, which has increased
crop productivity by 138 percent in a 50 year
period, it demonstrates the great potential that
algae has.
References available on request
September-October 2013 | InternatIOnal AquAFeed | 17
FEATURE
Naturally ahead
MYC OFIX
Myco
toxin Ri
sk
M
a
n a g e M
ent
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

9. www.aquafeed.co.uk
LINKS
• See the full issue
• Visit the International Aquafeed website
• Contact the International Aquafeed Team
• Subscribe to International Aquafeed
The potential of
microalgae meals
– in compound feeds for aquaculture
Understanding ammonia
in aquaculture ponds
Volume 16 Issue 5 2013 - sePTemBeR | oCToBeR
INCORPORATING
fIsh fARmING TeChNOlOGy
EXPERT TOPIC
– Salmon
AquaNor event review
Thisdigitalre-printispartoftheSeptember|October2013editionofInternational
Aquafeed magazine.
Content from the magazine is available to view free-of-charge, both as a full
online magazine on our website, and as an archive of individual features on
the docstoc website.
Please click here to view our other publications on www.docstoc.com.
To purchase a paper copy of the magazine, or to subscribe to the paper
edition please contact our Circulation and Subscriptions Manager on the link
above.
INFORMATION FOR ADVERTISERS - CLICK HERE