The potential of microalgae meals in compound feeds for aquaculture by Perendale


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                     September | October 2013
        The potential of microalgae meals in
         compound feeds for aquaculture

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 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

        ntensive	 production	 of	 mainly	 car-              totrophs	 and	 are	 characterised	 by	 their	 lack	          Marine	 microalgae	 are	 the	 dominant	
        nivorous	 fish	 has	 resulted	 in	 fish	 feeds	     of	roots,	leaves	and	presence	of	chlorophyll	a.	          primary	 producers	 in	 aquatic	 systems	 and	
        containing	 high	 levels	 of	 fishmeal	 and	        They	range	in	size	from	microscopic	individual	           account	for	a	similar	level	of	carbon	fixation	as	
        fish	 oil,	 with	 Europe	 requiring	 around	        cells	 called	 microalgae	 to	 seaweeds	 that	 can	       terrestrial	plants	(40-50%)	but	represent	only	
 1.9	 million	 tonnes	 a	 year.	Although	 this	 use	        be	greater	than	30	m	in	length	(Qin	2012).	               1	 percent	 of	 the	 planetary	 photosynthetic	
 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	

 Algae overview
    Marine	 algae	 are	 distributed	 from	 the	
                                                                       Figure 1: Percentages (dry weight basis) of protein, lipid and carbohydrate in
 polar	 regions	 to	 tropical	 seas	 in	 nutrient	 rich	                     microalgae. The range of values is shown by range bars (Brown 1997)
 and	 poor	 environments.	 Algae	 are	 photoau-

table 1: amino acid profile of different algae as compared with conventional protien sources and the WHo/Fao (1973) reference pattern (g per 100
                 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

                                                    14 | InternatIOnal AquAFeed | September-October 2013

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

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

                                                 16 | InternatIOnal AquAFeed | September-October 2013

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

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