FATTY ACID METABOLISM OF BIVALVES RG Ackman

43 Pages·2001·1.16 MB·English

FATTY ACID MKTABOLISN OF BIVALVES
R. G. Ackma n
Fisheries Research 6 Technology Laboratory
Technical University of Nova Scotia
P.O. Box 1000
Halifax, Nova Scotia 83J 2x4 Canada
ABSTRACT
well-fed, mature, marineb ivalves in their normal mil ieu possess
20-25'a triglyceride in their lipids. This triglyceride servesa s a
temporar y store f or dietary and surplus fatty acids, although some
saturated and monoethylenic fatty acids may be modified to suit
tri glyceride structural needs~ Thus 16:1 ci7.p lentiful,i n marine
phytoplankters, is of ten extendetdo 18:lu 7~ Thep hospholipidas re
formefdr omf atty acidso f the triglyceridea cid pool, whichin the wild
usually includes amplep reformed2 0:5a3a nd2 2:6~3,b ut only minor
amountos f 18:2~6a nd 18:3~3a re found i.n either of these lipid classes,
In f our out of f iv e a vrea gedlo ts of marni.e phytoplan kter fatty acids
the ratio of v6 to ~3 acidsw asv eryc loset o 1:5 . Phospholipidosf two
out of three oyster species Crassostreav irginica andC rassostrea
~ii~ash! ads imila~r 6 to ~3r atioso f 1r4a nda third Ostreae duli.sh ad
a ratioo f 1:1.5,w hereains threeo ther bivalves peciesth e ratios were
markeddlyi f ferent Arcticai slandica1 :16;M ytiluse dulis 1:14;P ectan
mamxi us1 ;2 0.! Nore informatioonn bothi ndividuaplh osphpoild' sa nd
s pec i es i s needed, espec i ally to clari f y the role of
non-mheytl en e-interrupteddie noci f atty acid s in biv alven utr i tion and
lipi d biochemistry.
KEYWORmDoSl:lu sc,b i valve, lipid, fatty acid, tri g lycerideg
phospholi pid,
I NTRODUCTIOK
The biv alves, wit h the exceptioonf terrified scallops,
essen ti al ly in one locat i ona ndin thiss ituationh aveh adto adapt
theirc ellulafru nctiotnos u tilize thef atty acidasv ailablpe,r »«ily
those der i ved di rect ly fromp hytoplanktersT. hen utritional
bacteriaa ndo f their fattya cidsi s noti ncludeidn this stud~y
also beenn ecessartyo exclu de "dissolvedf"a tty acids Fe vir e r 1 796 i
Stewar1t 979;E rhardet t al. 1980G; outxa ndS aliot 1980!a ndt hose
"particulate" matter Erhardt et al. 1980G; outxa ndS aliot
i nlcu dni g thosem erelya bsorbeodn i norgnaic patri cl es B acre Z ona
358
Atwooi d9 7!9 . Theg eneraflu nctionadl holeosf lipids 5n molluschsa s
recently been reviewed by Hosk<n (cid:1)978!.
showsth at in termso f exogenofuatst y acids,b ivalvesa re
with a mx' ture of about2 0-40p ercents aturateadc ids,! 0 -20
perc an t mon o et hylenic acids,a nd2 0-40p ercenpt olyunsaturaatecdid s,
including C>0a nd C22h ighly unsa tur a ted f at ty acidsw hicha re more
commlyo na ss ocia ted wit h marni e anim als ~ Thesea ver agesa pproxmi atet o
f atty acidc ompositioofn s omoef thef oodm xi turesf ountdo support
goodg rowth Qf juvenil es of the Europeaony ster(cid:31) Otsre ae dulsi ! Helm
t9/7- Walne 1979!. A review of the literature strongly suggs ts that
importanceo f pre-f ormedl ong-chain, highly-unsaturatefda tty acids
bivalve nutri tion has been underestimated.
Percentages w/w! of Selected Fatty Acids Averagedfr om Indi-
vidual Analyses of Total Phytoplankter Lipids
Ackman Waldocka nd Chua nd Volkman Langdona nd
Fatty
et al. Nascimento Dupuy et al. Waldock
acid
(cid:1)970! (cid:1)979! (cid:1)980! (cid:1)981! (cid:1)981!e
14:0 6.8 3.5 10.3 17.3 6.1
16:0 22.3 11.7 26.2 17.6 21.4
18:0 2.2 2.1 0.8 1.3
Total 30.3 17.4 38.6 35.7 28.8
16:1 16.9 5.9 10. 4 2.2 10. 5
18:1 4.1 10-5 13. 1 10. 4 11. 8
20:1 0.3 0.6 0.4 1.0
Total 21.3 17.0 23.9 12.6 23.3
18 -.2 a(cid:14) 3.4 2.4 4.0 5.7 4.3
1.8 3td3 7.9 8.3 3.5 6.1 13. 8
18 ~ 4+3 6.4 4.7 2.3 13.6 2.5
20: 4' 2.4 0.1 2.0 0.5
20 ' 4u3 0.1 0.7 0.2 0.2
20:5+3 10.7 6.8 4.6 7.2
22:4~6 ND 0.2
22: 5M 0.2 3.1 0.5 0.4
22: 5Q(cid:11) 0.1 0.5 0.2 0.1
22: 6 d3 4.9 11.5 1.6 9.7 2.6
Total 36. 1 38.3 18.9 39.8 31.5
Total M 6.0 5.8 6 5 5.7 5.2
Total u3 30.1 32.5 12. 4 34. 1 26.3
Twelve species selected from data of Ackman ett al. (cid:1)968! for inclusion
in Ackman et al. (cid:1)970! .
Three species.
Five species including data for «o «o« the~ ] aboratory o ~ - Joseph
KM'MFSOC,A hAa,r leSst.oCn-,! - wainsc ludaet1 d0 .71.,3 a nd
Fou r coccolxthophorzds; xn three, 18:5v3 was
3.3W.
Three species.
3S9
Growth studies involving fatty' acids and Juvenile bivalves have
tended to b simple and to ignore most pri.nciples of animal nutrition,
Al 1 species fed are usually selected, f rom those known to be
Algal spec es
assimilated by bivalves, on the basis of radical di f ferences in fatt
acid compos i tion e.g. Watanabe and Ackman 1974; Langdon ard paid
19S1 ! ~ Under these ci rcumst ances any gr owth di f f e r ence s
a ttributed to the presence or absence of one fat ty acid pr gr oup f
fatty acids, while the ef fects of proteins, carbohydrates, sterols et
are usually i gnored. Nevertheless, i t seems that ocr tai n f atty
could be important positive growth factors Epifanio 1979! To put
role of the dietary fatty acids into perspective, one must consider th
availabi li ty assimilation, di s tribution, and bi ochem' ca 1 modi f i ti o
of phytoplankter fatty acids as food for bivalves.
ln this brief review an attempt will be made to cover these points,
but factors other than fatty acids must necessarily be lef t for other
authors .
INFLUENCE OP LIPID CLASSES
In bivalves, as in other animals, lipids serve as functional
components in cells and membranes, but an energy reserve function
less likely than in higher animals Allen 1976!. Thus to appreciate the
fate of dietary fatty acids in the bivalve it is not suf ficient to just
look at total fatty acids, but it. is first necessary to consider the
lipid, recovery methods and the type of lipid recovered. Up to the
1960' s mos t fatty acid comparisons were based on total extracted
'lipid . This someti.mesi. ncludede xtracts from dried samples in which
the polyunsaturated acids had oxidized. Simple extraction w'th diethyl
ether was also commona, lthough this tended to extract mostly neutral
lipids and to result in poor recovery of the phospholipids, important in
cell membranes tructure and functions. The biphasic solvent extraction
methodd escribed by Bligh and Dyer '19 59! el imi nated lipid extraction
and recovery problems, but total lipid recoveryd id not necessarily
clarif y the f unction of fatty acids, For exampleC erma et a 1. (cid:1)970!
exami ned the fat.ty acids of total lipids of 12 shellfish from the
Adriatic Seaw ith considerablec are but without contributing mucht o our
understanding of fatty acid metabilism in molluscs'
Also, despi te the f act that di fferences in the fatty acids of
neutral" lipids i.e, triglycerides! and "polar" lipids i.e. mostly
phospholipidws!e rer ealized by progressives cientists, the lipid class
separationsw ere laborious and little had been done by the time
thoroughr eviev of molluscl ipids by Voogt (cid:1)972!, or even for the
reviewb y Hoskin. Gardnearn dR iley (cid:1)972! were, howevera,m ong
first to clarify the role of the two basic lipid classesi n molluscs,
andt o note that becausoe f the varyingp roportionso f triglyceride and
phospholipide,a chw ith a different fatty acid compositiona,n alyseso f
bivalve total fatty acids can convey only a limi ted amounot f
informatioonn f atty acida ssimilatioann df unction.B eforper oceeding
to discuss the lipid class data of Tables II and III in detail
worthl ookingb riefly at the role of thesec lassesin bivalves~
In most animals, depot fats usually triglycerides!
morphologicallrye cognizablee ntities, althougshm alla mounts
triglycerideasr e alsof oundin cell membranelns .b ivalveso bviouasn d
360
W
0 I'I
0
CIn
III Ijl
gj Cl C 4.
II
U 'V N
cd VI
0n 'U Ct
CI n4V
tn Ul
rt
K ljf
O '0 N
jC Cl
III
W Cl
W U
N
9
W 0 rrt
0
tt Irt0 0
nn
II
0 Qt rn 0
0 U NON
C
III Crtt .n
JJ '5
Ict 0 C n0l
nI Itt I
~rC 0 n4l Zmnn
4II IA 0c Cl tn
3I 0 CVCt C. tV Ctl
N
0 4 4
III
0 II
0
C
0
ILI 0 N Z I 0
C al
nt~ CIP O
4 CI ~
0 uIC Zr10
cI! 0 Rl
M '0 nl a
Cj 0 0 Z 00
CO 0
0 4n j
'0 4' Irt o cD
II + g0 Z tlt 0 C3I Cl
ILI a
I nn rt CDC l IA N t rn
C4l I
nnW 0 g ttt 0 N ID
rc
IP
W CD
0 tj! nP JI IP
vt 0 N 0 cn0 O
0ILt VCIC N Cl V
nVVIl PtC C
V!
rl trt 0 N N 92D H
cIIDj rIIII ClI IP~ I rt Cnt tt Kt Ct CD 0CtcV CI!t 4 Ct
ICj Cl
j: jtlm nt
cjj C nl
tjI III V 6C l
6 CC 0 N 0 rl CD0 H tnc rl
@0m rt tcj IC 0X z
CQ cII 4
LI nt
nl
0 6 N + N 0 Ct 0 0
a.
0
rt nt C D
a r Cl IP V
000 3 3 333 3 3 nntl 4tCP l 'C4t tC
Vnl tD El 0N 0N 0 0 nl fl V C
361
4 aua uI
A z
~ rA N N
8 4P
0 W u
~ ~ I ~ I I ~ ~
0 an
gw CJ'N ar Nr 0 O 0
p 5J ' I
th 'U Oora ~NO r D
W gr
0 0 Omw 4m 5 (cid:5) 0N
0, 0 I 0
5
4
cp II '40 u
Pl H r 5' an(cid:5)1t
~ I I
NO(cid:5)urN warl
U
I Nut N (cid:5) InN
w Nu r0 < a I I Nf n~
M D
5 H 0 0 0 N 1 9 4 0,
g u
Iv u J
l5 (cid:5) '5
'WWO UW O 5 Our&N 044,(cid:5)~ 4 . 40C0tN n N0
'tl
Dl H Ct O ~ ut N ~+W ~ -
0 u(cid:5) I Nru~~oa 4400~
0
5I 4 0
tLI ul5t Dl (cid:5) W 92W5 M ru n 4' PI]
O n~ 4' O (cid:5) O OO O~
0 '5 4
4(cid:5)(cid:4) CD5 (cid:4) an an
u I 0 CO 4 ngogo
IO C4
4 th 0 N DD (cid:5) t anr c!hl Nr (cid:5)
'4
0 fn W an0 A O W N
I 0 4
uu '0
Ie 4 4 cu Ctf n 0 ~ ID 5 r-
4 0,, 0 0 3
I I/I 4NH+4&
~ 4 4
a aa
CA 4 O D4t
Ig5 0 'HIO U " Oul(cid:5) 5 0 5ta5 (cid:5)O DuWr N4 D'Ra&u0l N
gl
P (cid:0) I n W 0 0 ul (cid:5) aflu a] 0
e 6 0+P<rupON00! I A
'U u 4 (cid:5)
4 0
I
U an 0 (cid:5) 0 H 0 ru w an 34C t
I au
0
cl u
Da 0
~ ~ ~ A A ~ ~ 5
ORO
4 5
0 I0 Ct N
W 0 (cid:5) 5 n N 0 4 fa
'3 4 'ri '0005,gaAgQA A an 4II (cid:5)
4 0 0k Ct I0 0
4 5
5 D n(cid:5)&wour (cid:5) 45 (cid:5) 0
Q Q IJ 4 O Pt ua0 0 H ut 0 O 0 IC
5C 0n '~ I 40
g
0C 4 0 Cl
0 O RRO AAAg 't0D ut 4Dl
V 0 ur 0 04404 C 444
4 Ct l5
8 ID Q g
4l5
w n DM C to
OH9NNua OO N A 0
rv
D na n '(cid:5)0
333 CRjg
N
(cid:5)
tu ut ut I 0 rl 0 N N N fu
NN 'NNN fu 4 Xt
362
discrete depot f at deposits do not occur, although f at globules have
been repor ted i n mantl e vescicu lar cells of Crassostrevai r inica
'" " "' 'r ' "
margni and go~adw asp res.enats trig lycerdi e Allena ndC onley
1982.! Otherwise, i t is usually reported Barbera nd Blake 1981! that
is stored, at least temporari ly, in the digestive di.verticula of
icr exampl in the euh-nntarticl impet.N acelle ~pateenrta l
uariensis simpson 1982!. It is believed that in bivalves such as
Ice la nd sca 1 lop Chlamys is landica Sundet and Vahl 1981!< the
At 1 a nt i c tie ep (cid:20) s e a s ca 1 l op Placopectan magell anicus Robinsone t al.
1981!, or the scallop Chlamys hericia Vassallo 1973!, as well as in C.
Al len and Conley 1982!, modest reserves of lipid are transferred
the gonad at matu ra ti on cf Barber and Blake 1 981! . In the Japanese
pri ckl y sca 1,lo p Chlamysn i pponenssi the li pi d content wet weight! of
visceral organs was 4.6%, while that of the remai.ning sof t parts vas
on1y 1 . 5th Hayashi. and ramada 1 973!. It has been rePor ted f or a variety
pf other types of mari ne shel lf ish that viscera 1 lipids are invariably
least twice the percentage found in the remaining parts of the animal
body Koch' 1975! ~
post questions on the proportions of different lipid classes in the
var ouuss oorr ganasn . of bi va 1 ves remain unanswered, but Allen and Conley
]982! showed that in contrast to the approximately 50:10:40 proportions
off pihos sp hoo lipipd; sterol: triglyceride in C. gigas mantle, the gi.ll and
adductor muse le both had proportions of approximately 80:12:8 ~ The
dd ig est tivev e diverticula differed from both with proportions of 78l7:13,
Langdon a n d 'W a ldocok c (cid:1)981 ! f ound that starved, hatchery-reared and
dextri n-fed C. gigas spat had high proportions of phospho lipid relative
to triglyceride Table Il! . Ratios of up to 8 1 vere observed, and it
' s possible that the low le ve ls of tri 9 lyceride indicated a poor
nutr i tiona1 s tate Sww ief t et al. 1980!. With most of the other diets
d i th C. i as spat Table I I ! the ratio of phosphhoo l li. p id. d toto
triglyceride approached the value of 1:1 which was also repor e n
1 i d C virgini ca adults Watanabe and Ackman
but well (cid:20) fed O. edu s an
i d ti i.s landi.ca Ackman et ale 1974! and Hesodesma
1974!, in w ld Arct ca s
mactr oi des De Horeno et a 1 1976! and also in several of the speci.es
studied by Gardner and Riley (cid:1)972!.
d that triglycerides have consistent fatty acid
I t can be ass ume a
the bivalve body, but. the distribution o a y
patterns throughout . e
acids in the phospholipids may dependo n tthhee ff uunnctci ti oonn aassssocoiacteiad ted wwith
the orga~, or on the re a
hos holi ids, respectively phosphatidylethanolamine and
phosphatidylcholine. Gi.ven these possibbi ill tiees,s , it is not surprising to
find conf l'cting reports on fatty aciidd ccoormn possitions of organs. Thus
Hayashi and yamada (cid:1)973! r.epor r tte ed d mmi nni .mmaa 1 f atty aci d di f f erences
whereas Kochi (cid:1)975! working with several species foun a v
fatty acids differed in consistent pa tteerns f rom those of muscle 1 p s.
Moreover, if phospholipids are thee "viv ta1" membrane component, as s
curious to find a wide variation in the leve 1s.
total saturated fatty acids in this class of l p s a
dif ferent species.
e of the lipi.d and fatty acid
Despi te our incomplete knowledge o
t common bivalves, an overall piiccttuurer e ccaann be
biochemistry of even the mos c
obtained by considering the different basi ti c typess o of faatty acids i.n
detail.
363
SATURATED ACIDS
The saturated fatty acids found in bivalves always include
branchedmhain fatty acids which can be classified i.nto two groups
groupi s madeu p of the three major isoprenoid fatty acids, especiaLLy
4,8,12-trimethyltri decanoic acid derived from the degradation of phytol
Ackman et al. 1971! ~ The second group consists of the iso and anteiso
fatty acids, predominantClyL 5a ndC L7, with someis o Cl6 and Cl8 f atty
aci de. The branched-chain fatty acids of the second group can b
accumulated in marine invertebrates from bacterial lipids Hayashi
Takagi 1977! but are also rormal minor metaboli tes i.n most animals a(cid:30)d
can. be derived from amino acid precursors which are freely available i(cid:30)
marine molluscs Ivanovici et al ~ 1981!. Although of biochemical
interest and possibly key elements in understanding the role of bacteria
in bi valve nutri tion, branched-chainf atty acids are not reported by
many authors and therefore will not be discussed in this review.
Table I shows that 16: 0 palmitic acid! is freely available in
algal diets, and is usually accompanied by approximately half as
14;0 myristic acid! ~ Some workers also report 12;0 lauric
1 (cid:20) 5%i but I t i. s obvious that it and 18:0 stearic acid! are minor
components of most algal lipids. Zt is probable that 14:0 and 16:0 are
equally well assimi. lated by bi valves, but they are also synthes' zed
novo, or e longa ted as required, by most animals Sprecher and James
1979! ~ It is not surprising that bi.valve lipids Table II! contain
20-50% saturated acids. since this is true of most marine animal li.pids
Ackman 1980!, and 16r0 is invariably the major saturated fatty acid at
all evolutionary and trophic levels.
Te t ra s el mi s e u ec I ca and Dunaliel la ter tiolecta were employedb y
l.angdon and Waldock (cid:1)981 ! in a feeding study with juvenile C. gigas,
The total saturated fatty acids (cid:1)4:0 + 16:0 + 18:0 only! i.n the algae
were respectively 32.4 and 18 ~ 6%. Despi.t e this nearly two-fold
difference, the total saturated fatty acids in the phospholipid fract'on
from lipids of juveniles fed on T. suecica and D. tertiolecta were very
similar at 20.9 and 19.0%r espectively Table I I ! . The corresponding
triglycerides of the samej uveniles had respective total saturated fatty
acids of 27.2 and 29,2%. Although the totals for saturated fatty acids
of phospholipid and triglyceride lipid classes dif fer, the similarity
within each lipi d class support s the view that bivalve fatty acid
compositions tend to be species-oriented rather than diet-oriented
(cid:1)4atanabe and Ackman 1974!.
UNSATURATED ACIDS
Both monoteh y lenic and saturated fatty acids mayb e assimilated
from the diet or biosynthesizedd e novo by mosta nimals Ackmane t al ~
1980! Thed esaturatiopnr ocessin animalso perateso n the carbons
the4 9,510p ositioncso untefrdo mth ec arboxyglr oup S prechaenr d~ ames
1979!. Accordinglyd,i rect desaturationo f readily avai.lables aturated
acidsl eads to the conversio1n6s:~ 9, h10-161: palmitoleci acid! and
18:O~> 9 h, 1810-18;1 oleic acid!, but if chain elongation fromC :o C
takese s plaacet henD 9,4 10-16;1~41411, 2-18.1. It is preferabletoL 6 o 18
shorthanndo tatiofno r describinugn saturatfeadtt y acidsb ased
numbeorf carbona tomsf romt he ethylenicb ondc losest to the methylor~
end of the cchhaia inn the ~ methyl groupc arbon countsa s 1 ! Thus
364
2C~ 18: 1~7 clearly indicates the process of ch i
o c a n e ongation with
retention of > structure'
amount of 92 6:1p rovided by the algae Table I! in the wild
appears to be of the same or der of magnit ude as I n the mollusc
triglycerides Table ZI! . Host algal 16:1 isw 7i n structure,b ut algal
18: 1h d9o r 18:1~7f or a mixture hackmaent al ~ 1968!. Table
that 16:1du7in bivalves, whichc ould be of either exogenouOsY
endogenouosr igin, dominatest he 16 : 1 isomers except in tri gl yceri des
f rom C. gigas spat reared on T. suecica. In the sterol es ters of a.
the leve ls of 16 : 1 ~7 are approx' mately equa1 to the levels of
9. The latter appears to be associatedw ith the higher proportions
pf 1 8:1 d sf9f ound i n S terOl eSt erS than i n the f atty aci dS of other lipid
classes. Overall the data in Table II indicates that in bivalves total
is more important in the triglyceride f raction than in the
phospholipid fraction.
In feedi.ng experiments with juveni.le C. gigas, Langdon and Waldock
(cid:1)981 ! found that the 16: 1n7 isomer, which was present in high levels
(cid:2)5.8%,! i n Pavlova lutheri, appeared in the spat triglycerides at a
Of Only 4't Of the tOtal fatty acidS, with 16; ldd9 also present only
trace amounts Table 1V! . However the level of 18:1~7 in the
triglyce rides of the Pavlova fed spat was conspicuously elevated to
14. 7w, indicating that alga 1 16: 1u7 had been partially deposited
unchanged in the. tri glyceri des and parti ally elongated to 18 f 1~7. With
ei ther T. sueci ca or D. tertiolecta as di etary sources of f at ty acids,
the 18 1 Q9 isomer was abundant in both the algae and in the C. fLiias
spat triglycerides. It is remarkable, as shown in Table IV, that. 1B:1c7
was expectedly important in the phospholipids of the juveniles reared on
the latter two algae, as well as i n those reared on P. lutheri. It is
also apparent that in all. cases chain elongation of 18: 1~7 to 20: lm7
took place i.n the j uveni les. High levels of 20:1~7 have also been
reported for other hi valve species Table II! .
Most animals synthesize triglycerides with a particular pattern of
fatty acids attached to the glycerol molecule Brockerhoff 1966!, but it
is unknownw hether this also occurs in bi valves. Brockerhoff (cid:1)966! has
indicated that f or the monoethylenic f atty acids, the chain length may
be important in det erminin g the position on the glycerol moleculea t
which a pa rticu lar f atty acid is attached. Bi vai ves have considerable
flexibility in their biochemical pathwaysf or lipid synthesis Zandeee t
al. 19BO!, and it may be moree conomical in terms of energye xpenditure
to change exogenous1 6;1 7 to 1S;1 7 than to synthesize 18F 19 de novo.
There inay also be different fatty acid pools at different steps in the
lipid assembly process.
The fatty acids of phospholipidss howa pproximatel.tyh e same1 8:1
isomer ratios as the correspondingt riglycerides Tables II and IV!,
indicating that in most bivalvest he 18:1a cidsa re probabldyr awnfr om
samef atty acid pool. Waldocakn dN ascimen(cid:1)9to7 9! foundt hat the
18'-1du9t o 18:1+7 ratio of 13:1 in Chaetocerosc alcitrans was slightly
altered to fg:1 in the phospholipidos f C. gigasl arvae,a ndt he ch~in
extension process then resulted in the radicallf dif eren proper
1 ~9 4 and 6.4% f or 20: 1fa9 and 20: 1~7 erroneouslyp ublisheda s
percentagesfo r' 19:0 and 20:1 +9!. Thee mphasoinse longatioonf
monoethylenic ~7 isomers Table IV!, especial1ly fo rf or the 1B: 1~20 f 1 step,
probably has implications in the forrmation of the non-
365
met hy le ne (cid:20) i nte r rup ted di enoic acids NNlDs see below! because the
NIXDs are dominated by ~7 structures.
Comparison of Weight Percentages of the 1mportant
Table ZV
Monoethylenic Fatty Acids in Total Lipids of pavlova
Tetraselmis suecica and Dunaliella tertiolecta with Trig]ycer
ide and phosptolipid Fatty acids of Experimentally Fed crass
ostrea pic~as Spat from Langdon and Waldock 1981!
P. lutheri T. suecica O. tertiolecta
16: I+9 algae! 1.8 0.6
spat triglyceride trace 2.0 0.3
spat pho sphol ip id tracea 0.4 0.7
18. Ia9 al gae! 3,3 22.7 6.6
spat triglyceride 2.4 24.6 13. 1
spat phospholipid 2.2a 3.8 3.2
20: 1>11/ld9 algae! (cid:2).85!b
spat t r ig lyce ride 6.5 5.6 0.9
spat phospholipid 2.6 3.7 1.5
16:1>7 algae! 25.8 2.0 3.6
spat. triglyceride 4.0 trace 2.2
spat phospholipid 2.2a 1.0 1.2
18:Ia7 algae! 2a5 trace Oa4
spat triglyceride 14.7 trace 0.3
spat phospholipid 7 3.4 10. 0
20: 1>7 algae! (cid:2).85!
spat triglyceride 2.6 6,9 1.8
spat phospholipid 5.7 4.5 4.1
Total lipid (cid:2)9iL triglyceride, 71'8 phospholipid! as phospholipid data
not given.
Total 20:l.
POLYUNSATURATED ACIDS
Ter res rial. herbi vorous animalss ubsist almost exclusively on a
diet of plants rich in CI~ fatty aci ds. There has therefore been
i ntenis v e study i n animalso f the chain elongation of 18:2 6 li nolei =
acid! to 20:4a6 arachidonica cid!, and of 18:3+3 linolenic acid! to
20:5 ~3 and 22:6~3 Holma1n9 81!, Althoughm anyw idely-studiedg ree~
algae,f or examplCeh lorellas p., are commornilcyh i.n C, f at ty
Ackman 1981 !! , bbivivalvesa re exposeidn the wild to a wl8i.ders pectrumo f
fatty acidsf romo thert yp s of phytoplankteinrsc luding preformed2 0:5
~and 22:6 ~3 TableJ .! Unfor tunate ly the pioneeringst udieso n
biochemstir y of polyunsaturatefadt ty acids i.n molluscsw erec ari.edo «
wi th the land ss~~aial il CCepean emoralisb y Vand er Horst, OudejansV, oogte
Zandeaen do thers loc. cite !; convenientslyu mmarizbeyd H oskin(cid:1)9 78!
and Zandee et all.. 33998080.! This terrestrial snail feeds on vegetation
366
rich in C18 acids and necessarily the experime t I k
n a wor on fatty acid
ba sed on radi oacti ve ly la bell d 18:2'
e: and 1S: 3~3
the snails. It wasf ound that a proport' f bo h
ropor ion o both these
f at ty acids was elongated to morhe ighlyu nsaturated'
fatty acids~ However, par t wasd epoi ste d wit hout alteration
also catabolized for energy.
the f i rst decades of this century a distinguished scientist
that scientif ic research could cease, since everything which
discovered had been discovered. Somethingo f the samea ttitude
r ept into mari ne invertebrate f at ty acid biochemistry in the 1 970s' .
< llowing the work with C. nemoralis scientists expected to explain all
nutri tiona1 studies wi -h f atty acids and molluscs sole ly in terms of
8 C>O C2> desaturation/chain elongation process. Recent
phytop lank ton f atty acids studies Table I! suggest on the contrary,
natural bivalve populations can receive all necessary 20: 5M, 22! 5
22:6u3 from their normal diet. Since 18:2w6 and 16:3~3 do not
accumulate in proportion to availability the surplus may simply be
uti ] ized f or energy. As the evidence f or these views is largely
circumstantial i t must be gone into with some detai.l .
case in poi nt is the rearing hy Landon and Waldock (cid:1)981! of
juveni le C. gi gas on D. tertiolecta, which had S~ B t 1S:2 6 and 31.1%
. 3~3, but no 20 5~3 or 22: 6~3. Despi te a high lipid content in the
a lga, growth was poor unti 1 a supplement of 22 6~3 was fed.
Supplemental tri olein had no ef feet at similar levels. In a simi lar
f eedi ng wi th T. sueci.ca, which had 7 ~7 % 20 5~3 but no 22: 6~3, greater
growth occurred than with D. tertiolecta plus 22:6D, and adding 22:6~3
to the T. suecica fed spat resulted in very little extra growth. These
experi ments suggest that chain elongation of 92 82: ~ 6 or 18:3 ~3 is not
sufficient for maximum growth, and tha either 20:5s3 or 22:6e3 is
"essenti al" for growth. In higher animals some interconversion of these
two fatty acids occurs, and it is probable that mixtures of 20: 5>3 and
22:6~3 are optimal for bivalves.
The ten algal polyethylenic fatty acids of Table I do not include
somet hat are potential intermediates in elongation and desaturation of
fatty acids, Thus 1S;3<6, 20:2A and 20: 3~3 are omitted simply because
they do not f igure prominently in hiv alve analyse.s S(cid:31) imilar ly, of the
ten bivalve polyethyleni.fca tty acids shownin Table III, only two(cid:2)0 : S
u3a nd 22: 64 3 ! are quanti tatively important, andt he qualitative and
quanti ta tive sign if icance of the others seems to dde pend on the
experiment and/or analytical group.
It is nowr ecognizedth at in mammatlhse rei s often competitionfo r
elongation/desaturation enzymesb etween 18: 2~~66 aannd 18: 3~3 f at ty aci.ds
and the i.r homolo gues Hol man 1979! . For exampel e aa ~6 and then a 45
desaturase are required for the conversions 11BB:: 22u+66 ~ 20- .4w6 a nd 1S: 3<3
~2o5: ~3~ Probablyt he respectiveen zymeasr e identical. Thef atty
acids of phospholi pi ds can presumablyb e der i vive ed dif necessary, directly
andu nchangefdro, mt he poolo f fatty acidss tored ast ri 1 cerides.I n
g y
e is a virtual absence of
of the cases compared in Table I II t.here
he tri I ce rides. This may
1S-'4<3 in the phospholipids relative to the ~g y
enz s and phospholipds as
f rom the se le ctive association of enzyme
"ly one of these enzymes,t he a 5 desatuarases e,iis s reeqquired to convert
commo~ a t the 2-pos i ti.on n
20'-~ ~3, a f atty acid perhaps most commo~a
moderate (cid:1)-6%! proportions of
phospholipids Brockerhoff 1966!~ The moderae
ble III! seem to be higher than
' 4« i n the bi.v a1 vs phospholi pi ds Table
367