Fatty Acid Pattern Differences Among Individuals of Two Estuarine Fishes (Leiostomus xanthurus and Mugil cephalus)

8 Pages·1994·5.7 MB·English

by  Julia S Lytle

GtdfResearchReports,Vol.9.No.1.49-56,1994 ManuscriptreceivedJanuary26,1993;acceptedApril29,1993
FATTYACID PATTERN DIFFERENCES AMONG INDIVIDUALS OFTWO
ESTUARINE FISHES (LEIOSTOMUSXANTHURUS ANDMUGILCEPHALUS)
JULIAS.LYTLEANDTHOMASV.LYTLE
GulfCoast Research Laboratory, P.O. Box 7000, Ocean Springs, Mississippi
39566-7000
ABSTRACT Tenindividualfishoftwoestuarinespecies,spot{Leiostommxanthurus)andstripedmullet(Mugil
cephalus),wereanalyzedforfattyacids. Fishofsimilarsizewereobtainedfromasinglecollectiontominimize
variabilityduetoage, size,location andseason. Analysisofvariance(ANOVA)ofeachfattyacidprovided
statisticallysimilargroups foreach acidthatexistedamongindividualfish. Fattyacidsin thestripedmullet
providedagreaternumb^ofstatisticallysimilargroupsthanthoseinspot,'mdicatinggreatervariabilityamong
individual striped mullet,whichprobablyreflected agreater diversity in thefeedingregimefor this species,
ANOVAresultswithinclassesoffattyacidsofbothspeciesindicatedgreaterdiversityinmonounsaturatedand
polyunsaturatedthansaturatedfattyacids.Eicosapentaenoicacid(EPA)showedmoremdividualvariabilityinboth
speciesthandiddocosahexaenoicacid(DHA). Dietarylipidsandmetabolicneedsofthetwospeciesaredistinct
andmaybethekeyfactorsinexplainingindividualdifferencesobservedinthesetwofishspecies.
Introduction
inlargenumbersfromagivenareainonecatch,andthey
werenumerousenoughtopermitselectionoffishhaving
Naturalpopulationsoffishescontainfattyacidsand little variationinsize. Additionally,thebiology ofspot
other nutritional components that are highly variable. (Gunter,1945;Dawson,1958;Hodsonetal.,1981;Chest-
Stansby(1981)hasaddressedsomesourcesofvariabilityin nut,1983;Sheridanetal.y1984)andstripedmullet(Odom,
fattyacidcompositionoffishoilswithinagivenspecies. 1966; Thompson, 1966) is well established, and both
Other studies have focused on individual species and speciesarefoundabundantlyinlocalcoastalestuaries.
variationswithrespecttoage(HayashiandTal^gi,1978), Spotisadominantbottomfishandisconsideredtofeed
season (Ueda, 1976; Hayashi and Takagi, 1977. 1978; in schools over sand-mud bottoms on polychaeies,
Gallagheretah, 1989),size(Gallagheretal., 1984)and harpacticoidcopepods,bivalvesandpossiblysomedetritus
geographical location(Addison et «/., 1973; Whyteand (HildebrandandSchroeder,1928;Darnell,1958;Hodson
BoutiUier.1991),buthavenotaddressedvariationsamong etal.,1981). Spothasafairlysmallmouthandpossesses
individualsofthesespecies.Assessingimportanceofthese gillrakersthatpermitretentionofsmallfoodparticlesand
variables isdependentuponappraisal ofindividual vari- preventingestionofrelativelylargefooditemssuchasfish,
ability,sinceinherentbiochemicaldifferencesexistfrom shrimp and crabs (Darnell, 1958; Hodson et al., 1981;
fishtofishevenwhenal!othervariablesareminimized. It Chesmut, 1983;Sheridanetal.,1984).
wasessentialthatspecimensbecarefullyselectedoftwo Ontheotherhand,thestripedmulletbeginsitslifeby
speciesofcoastalGulffinfisheswhichdifferedlittleinsize, eatingplanktonicplantsandanimals,butitchangesitsdiet
development stage, weight or location of catch. This toincludeabroadrangeofdetritusandplantmaterialasit
selectionpermittedspecificexaminationofthosefluctua- develops(Moore,1974).Itfiller-feedsaboveorganicmuds
tionsinindividualfattyacidsthatmayoccurdueonlyto containing microplant material and macroplant detritus
individualdifferences. Byusinganon-randomselection (Odum,1966,1970),anditisgenerallyconsideredtobea
processforsamples,resultscouldnotbeusedtocharacter- broad spectrum herbivore. Occasionally, however, car-
izeoveralltrendsinthetwospecies. However,itwasfelt nivorousfeedinghasbeenobservedinstripedmullet(Bishop
thatresultswoulddefinesomemdividualvariationsthatare andMiglarese,1978),
uniquely characteristic for these two fishes that would Fattyacidsinmarinedietarylipids,whetherplantor
permitinformativeandusefulcomparisonstobemadeand animal, serve as an energy source for metabolism and
thatsuggestionsforthesevariabilitydifferenceswouldbe provide polyunsaturated fatty acids (PUFA) essentialfor
suitable. membranestructureandfunction. Lipidsinmuscletissue
TwospeciesofcoastalGulffinfishes,spotandstriped offishgenerallyreflectthosefattyacidsobtainedfromthe
mullet, were chosen for assessing mdividual variability diet.Sincethesetwospecieshaveawidelydifferentnatural
becausetheymetseveralcriteria. Theyrepresentedfishes diet, they provide an opportunity to examinemdividual
withdiffercnifeedingregimes,theywerecollectedeasily variabilitywithinandbetweenspecies.
49
50 LytleandLytle
Materials and Methods
internal standardmethyl tricosanoate. Quantitativedata
werecorrectedfordifferences indetectorresponses that
Collection weredeterminedthroughanalysisofauthenticstandardsof
eachreportedfattyacid. FAMEweretentativelyidentified
StripedmulletwerecollectedonJanuary21, 1988in bycomparisonwithretentiontimeswiththoseofauthentic
theshallowestuaryofBiloxiBay,Mississippi. Spotwere standards. Verificationofidentificationonselectsamples
collectedonApril 13,1988atShipIsland,abarrierisland wasaccomplishedthroughgaschromatographymassspec-
15milessouthofGultjport,Mississippi,inthenortheastern trometryanalysisconductedbyNationalMarineFisheries
GulfofMexico. Allfish werecollectedby gillnetand Service,CharlestonLaboratory. Concentrationsofindi-
maintainedoniceuntilexamined. Standardlengthswere vidualisomersofPUFAwereseparatelytabulated;separate
measuredandweightsrecorded. Fishofapproximatelythe isomersofmonounsaturates(e.g. 18:1)werenotreported.
samesizewerefilletedandindividualUnplacedseparately
inpolyethylenebags,flushedwithNj,rapidlyfrozenand SampleProtection
storedat*20°C.Averagebodyweightofstripedmulletwas
230g(±12%relativestandarddeviation:RSD)andaverage Several precautions were taken to ensure that no
mm
standardlengthwas221 (±4.5%RSD). Averagebody degradationorotheralterationoflipids occurred during
weightofspotwas 147g(±5.2%RSD),andaveragestan- extraction and saponification. All analytical steps were
mm
dardlengthwas 174 (±3.5%RSD). conducted at ambient temperatures, and samples were
constantlyflushedwithN^topreventoxidation.Further,as
AnalyticalProcedure manystepsaspossiblewereconductedinasingleextraction
mbetoreducelossanddegradationthatoccurswithsample
All solvents used in analysis were HPLC grade or transfer. Allsolventswere flushedwithN^immediately
analyticalreagentgrade. Standardswerepurchasedfrom beforeusetoremovedissolved andtopreventoxidative
NuCheck Prep, Inc. (Elysian, MN). Fillets were degradation. Likewise, samples requiring storage were
homogenized usingaWaringblenderand0.5 galiquots placedinsamplebagswhichwereflushedwithN^before
weighedintoscrew-capped(Teflon-lined)centrifugetubes beingfrozen(-20®C).Inaddition,theantioxidantbutylated
(30ml)andsaponifiedatambienttemperaturewithethanolic hydroxytoluene (BHT) was added in a concentration of
KOHunderNjusingamagneticstirrerforonehour. Care 0.005% (w/v) toextraction solventstopreventoxidative
wasexercisedinthevolumesofsaponifyingmixturesused degradationofunsaturaiedlipids.
tokeepthe waterlevel,derived fromtissue, sufficiently
high to preventtrans-esterification. Solventratios were DataAnalysis
those suggested by Nelson (1966). After dilution with
distilled water, the neutral fraction was extracted with One way analysis of variance (ANOVA) withpost
hexane.Theremainingalkalinesolutionwasacidifiedwith facto95%confidencelevelrangetest(StatisticalGraphics
6NHCI.andfreefattyacidswereextractedwithbenzene. Corporation, 1988)wasusedtocompareindividualfatty
Benzenealiquotswerecombinedandconcentratedusinga acidsaswellascertainparametersd^vedfromfattyacid
rotaryevaporator.Allevaporationswerecloselymonitored dataofindividualfish. Similaritygroupswereestablished
toensurethatdistillationtemperaturesdidnotexceed25®C. ofindividuals foreachvariable which were statistically
Fattyacidswereconvertedtomethylestersusing7%BF^- indistinguishable (p<0.05). In addition, the number of
MeOHbythemethodofMetcalfeetal(1966)modifiedto groups was tallied as a further measure of individual
useambienttemperaturesandaone-hourreactionperiod. variability.
Identificationoffattyacidmethylesters(FANE)was
obtainedby capillary gas chromatography (GC) using a
Perkin-Elmer model Sigma 2000 gas chromatograph
Results
equippedwithflameionizationdetectorandfinedwitha
m mm
3wi0thaX00..2255mfilim.dt.hfiucksneedsssiolifcaDucarpailBloarnydcWolAuXmn(cJo&atWed Figures 1 and 2 depict mean concentration of fatty
Scientific)andoperatedwithasplitratioof100:1. The acidsinthesamplesofindividualspotandstripedmulletas
carricrgas.He.wasmaintainedatiopsi,Oventemperature well as mean % composition of total saturated,
wasprogrammedat90-250‘^Catalinearrateof4°Aninute. monounsaturaiedandPUPA. Figures1and2alsoinclude
DatawasprocessedusingaPerkin-EhnerSigma 10data thestandarddeviationsofthemeansofthetenindividual
system with quantification of ah compounds based on fishandareshownbythedarkbarsinthegraphs. Concen-
individual peak area response by GC compared to the trationsareshowninbothwt%ofthetotalfattyacidsand
FattyAcidVariationsinTwoEstuarineFishes 51
Wt%
/jg/g(1000)
y
Meal SD
Figure1. Leiostomusxanthurus. Distributionoffattyacidsinspot. Emptybarstotheleftrepresentmeanconcentrationsin
wt%oftotalreportedfattyacidsof10individualfish. Barstotherightdepictmeanconcentrationsinpg/g(wettissue). Gray
barsarestandarddeviationscomputedonthemeanofthe10meanvaluesforindividualfish.
t
H ^
Mean SD
Figure2. Mugilcephalm. Distributionoffottyacidsinstripedmullet SeecaptionforFigure1.
1
52 LytleandLytle
inabsoluteconcentrationsofpg/gofwettissue. Absolute encesamonganyofthetenindividualfish.Exceptfor22:
concentrationsareusefulwhenassessingmuscletissuefor in spot, each monounsanirate in both spot and striped
nutritive value, particularly for omega-3 (n-3) content, mulletshowedhighdiversityamongindividualfish(four
since there is an increased interest in possible health tosixsimilaritygroups). Among thePUFA,therewere
benefits (Lands, 1986), while weight percentconcentra- moreANOVAsimilaritygroupsforEPAinbothspotand
tionsareuseful inassessingbiochemical significanceof stripedmulletthanforDHA,indicatingagreaterdiversity
fattyaciddistributions. ofEPA thanDHA inmuscle tissue. In striped mullet,
Tables 1and2containfattyaciddatacomputedona ANOVA treatment of arachidonic (20:4n'6), iinolenic
wt%basisforfattyacidsinmuscletissuefromspotand (18:3n-3) and octadecanoic acid (18:0) each produced
stripedmullet,respectively.Alsoincludedaresununations seven similarity groups, the most diverse fatly acids in
and ratios that are helpful in characteriz'mg fatty acid eitherfish.
profiles in finfish. Superscripts signify the statistically
similargroup(s) thateachindividual fishfallswithinfor FattyAcidClasses
ANOVAtreatmentofeachfattyacidorfattyacidparam-
eptreor.ducAetdtbhyeAeNndOVofAeeaxcahmirnoawtiiosntohfetnhuatmbfaetrlyoafcigd.roups prevaFliegnucreeso1famnondou2nsiandtiucraatteest,hatwibtohthspfoitshehsavsihnogwe4d6%a
Individualsofbothspeciesvariedinfatcontent.Striped monoonsaturated,23%PUFAand31%saturated,ascom-
mulletranged from 1.82-6.38%,whilespotranged from
paredto40%,31%,and29%,respectively,forthesefatty
4.75-8.10%.
acidclassesinstripedmullet. Thesaturatesforbothfishes
werelessdiversethan foreitherthemonounsaturatesor
FattyAcidDistributioninSpotandStripedMullet PUFA, Likewise,theaveragevalueofANOVAsimilarity
groupsforindividualsaturatedfattyacidswaslessthanthat
Fattyacidprofiles(Figures1and2)weresimilarfrom foundforeitheroftheotherfattyacidclassesinbothspot
bodi species, particularly in content of saturated fatty andstripedmullet.
acids. Hexadecanoicacid(16:0)wasdominant,followed Fattyacidsoccurring inconcentrationsabove 1%of
in decreasing order by octadccanoic acid (18:0) and total fatty acids showed a higher degree of individual
tetradecanoicacid(14:0). Theremainingsaturatedacids variabilitythanfattyacidsoccurringinlessthan1%forboth
constimtedlessthanonepercentofthetotalfattyacids. spotandstripedmullet. Theaveragenumberofsimilarity
Thepredominantmonounsaiuraiedacidinbothfishwas groupsforallfattyacidswhoseconcentrationsareabove
16:1. Relativeto16:1,thecontentsof18;1and20:1acids 1%was3.8forspotand5.0forstripedmullet,with2.5and
werehigher in spot than in stripedmullet, whetherex- 4.3groupsforfattyacidscomprisinglessthan 1%.
pressedinwt%orpg/g. ThetwoprincipalPUFAinboth
fishes were eicosapentaenoic acid (EPA, 20:5n-3) and FattyAcidParameters
docosahexaenoicacid(DHA,22:6n-3). Thesen-3PUFA
constituteahigherpercentageofthetotalfatty acidsof Total n-3/n-6 ratio showed little variation among
stripedmullet(23J%)thanthespot(13.5%),althoughin individual spot with ANOVA, separating into only two
absoluteconcentration,thesePUFAareenrichedinspot statisticallysimilargroups.ExcludingindividualspotNo.
(4,530 pg/g) relative to striped mullet (3,120 pg/g). A 1,no di-stinclionoccurredamongindividuals (Table 1).
narrowrange(2.25to2.86%)aswellaslowconcentration Conversely,theseparatesumsofn-3andn-6fattyacidsin
of arachidonic acid (AA, 20;4n-6) was found in spot, spotwereseparatedintofiveandthreesimilaritygroups,
whereasawiderrangeandhigherconcentrations(1.70- respectively. The n-3/n-6ratio also varied less among
7.00%)werefoundinstripedmullet. individualstripedmullet(fourgroups)thantheseparate
totaln-3andtotaln-6fatlyacidparameters(fiveandseven
StatisticalComparisonsofComponentFattyAcids groups,respectively). ANOVAtreatmentappliedtototal
PUFA in both spot and striped mullet produced five
Octadccanoicacid, 18:0,wasthesecondmostdomi- similaritygroups. Inspot,theunsaturated/saturatedand
nantsaturatedfattyacidinbothspotandstripedmullet. In (EPA+DHA)/n-3 parameters produced two and four
spot,nosignificantdifferenceinvalueswasfoundamong ANOVAgroups,butinstripedmullet,itwasfourandsix
anyoftheindividualfish (i.e.only onesimilarity group groups. ANOVA treatment separated the calculated
showninTable 1). Ontheotherhand,therewereseven parametersofstripedmulletintoalargernumberofgroups
statistically similar groups for 18:0 in striped mullet than those ofspot, demonstrating the higherdegree of
(Table2). Minorsaturatedcomponents,20:0 and22:0in individual diversity for component fatty acids in the
stripedmullet(22:0inspot),showednosignificantdiffer- stripedmullet.
1
FattyAodVariationsinTwoEstuarineFishes 53
are to <0 (D cgcicoiO'^-^cMCM^comoj'^cgcoiooi-^
fish. and
^ ^ ^ ^ ^ ^ . 5-s ^ ^ ^ a •. S~J* 4> Ti
individual (p<0.05) CO. ^ ^ ^ ^ ^ ^ CT •£» ZZ- ZZ- ^ ^ 2.
oi (d eg
10
of different I K 8 8 S 5 8 f 5 f I f V % t I % g- g- % I g- f g- ? §
2z3.2S!-^i::.:z.^2222ti22i:i.iS.ei.£i2S.£i2Sl£i‘=>
each 5 3 3
oi eg 'xi o o o o o
from statistically ^
5 ’o 5 A 2 iz- ^ 2 i 5 2
2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2
tissue °§2gsZZg- 2iess25£^ss2sfi*js"^as^«^
not
add.
muscle are
fatty
homogenizedletter feaocrh 2»scd 2$Scd 25in 2;5s 2- 2 2 2 2, 2 2 2- 2 2 2- 2 2 2x®mrce2oMon^Q2oS<i'2dog.s-2H^c®g2O’c>2-o®’^c2-iv'o2i-^
supercript
_ ^ ^
of computed S^I SSi ^ Q2. 2.2g_222^^^2- 2S.22225..g2,2. 2Su2>2S232S^252!252s
same 1*^ $5^ #r^ §a§SiiigiSiS^§2?553Sf85SS
1 analysesthe
groups ^ ^ ^ ^
TABLE replicatesharing 3. Uo 1-. :8C2M sin 2 28^ 2t“s 2I 2Sevi 2MI’ i i^id *^Rd «CO C«M. §lCoM ig«> •e'g: 2r®C«2npc2-oM2^;e2jg-g2M^^2wSg2'c^M^
similarity
rows
fthorere In of ^ a> 28» -^^- -f*ep:- s: .3CM. .8<o. w:^. w_.—. .wca CfMe cd s•— 8<d aid ‘2S-. 2 ^2 ^3Z. h2 ^£i 2 2 2
Entries numbers g 8 g S? p £! a S U> CM CO 5 8 5 5
means
Entarriees deviations. rtefeor 28S8|2^iS2ig^2§S2SSs25s2S§S^2.B.22,g8. 52s-.Ss^CSis2lr'2~f2'§'2''2f"i2'cfm'32£CS"8M 8a2S"u> ''22^CMg"3^i^o^ss3cCJiiM. 3V«'g3c^SJ g38c-Md- ^§
numbers 1 ^
standard
ispnot group gS} (m^O S$CoO i^on9 s(& a i ltOA Og J5OdJ, SjyS^- ^#\t G.CrMA-SCiOl-^S•^5'1-^.C^MSi^SnlCtMS^<.oS!-«CznM-'it^_^-^M=^o
relative
acids
% groups; il^ iiitil5 iio l3 io l'3 l.S l^ il• lm l^l2 f3 l^l3 la ll« l-3
o
Fatty
are ? 2 i i I i II I ? 1 § I ? s i ^ H I 5 2 2 § 3
similarity
xanthurus. parentheses
as
to
in
Leiostomus
Values referred o o o
2 S ^ 22 j2 53 ^ 22 52
:
54 LytleANDLytle
>-(Ou>-^(Otor^coc3r>^u>cij(o-.«-cou>c3r^
are
fish.
and
individual (p<0.05) PeyI. TZ- SjOO.. S«0O^. ww C<>2 !* ^ 2 {5 w S^siassals a2 Ssa
10
of Its I'l5-^ iiHtIv-i, IIIIIIIIIIfsIlil
dilTerent
each 551
from ^
statistically S V* 5S...
^
tissue not !PS. *C> S. n. jg. S<oo ricC:iOSL isoSj r^. <o^ «1^^o.. .0^<>j. uO^j. cSt, r~ CsD )n .g.
muscle acid.
are
letter fatty 5ifg. ai ?fc:,fi g£<x.> 5S. •i.7io> 'Si3' o^5r ^szsi, s^ s^ssrz.ssaSo.s.<>.scjs^sjriso
homogenized each ^^ eg ^CO s5 S 8 s § § s ’-’-^^CO'-WOJOOI-^CtlioS
for
supercript
oanalfyses same computed SSS-. fSa§T S88t ^?2 §3^O ¥^^3. ,8R®w. i2o ^^8 %2CcOj a§5a1S.1*” a oooo-^o'd-o
2
the
TABLE replicatesharing groups a a rf. a 8cd. pSi. 8 S5&'^ aS® SSo'. ^aCO s^^ tips" ^Q5S.5^2go.^^8a8.Sg3*S^.s5V^s«2S|«-P«§sop.'a»y^S.5,i^Q.SJ^CO.55^o
®OJ 5" tt> 2*o ^ g § s b i ^’-’’-''rJSSWojooeocdS-
similarity
three rows ^
for in of 8 8 8 8 .$CO. .8CO. 8VO Soi' 12c.Q- i2u>, p8>. a82^:::::,2.g.88.cU.8.^.3co8-O-
cd2888c>iujoSs
means Entries
numbers
are 288^8®^^ ^siSSsaiVl
to
Entries deviations. refer V3^2S5S 3R CSO C?D S S 3 S S i O®S-^-!af5w&®Sl^i.5asai3Sa
muUet standard numbers ^ 8 ^ 8 O SS' %CQ zi. -S. ^ a a ^ Sa8-'aSSO-<*a25D-^.3hS->a1^Ueoa^>''«sS8-^^i8SC-M*a^?..^^3-"^c3p0ro'
a 8 8 § ^ § 2co<OMM>^-«i4-r«~n'-<-«coM-«ctqZ.—
group
striped
aocifds %relaatrivee groups; .Sto. 2to SC5M| Ias Vai%ia§ga-g%agz5rS. 8rt\3e2jiw. s.S’^-:S.5^-3.Stq, .5^.8Kp. .SCcevDgj.?jCcNMd^. .8aS«>p.SjCt[Oow. p33
Fatty
similarity
parentheses
as
cephalus. to
in
^ £
s i
MugUValues referred PpppO'^'>--.--.-OJCO ^ T*; V! T*: «o to ^ CO a C "T V V o:
FattyAcidVariationsinTwoEstuarineFishes 55
Discussion Saturatedfattyacids,bothindividuallyandasaclass,
areconservative, i.e. are relatively constantandin this
Thepolyunsaturatedfatlyacidsinallfishlipids(both casedemonstratelittlefluctuationinlevelanddistribution
n-3andn-6)arcderivedsolelyfromthediet,butultimately amongindividualsofeitherspotorstripedmullet Onthe
areofplantorigin. Ingeneral,plantssynthesizealloftheir otherhand,themonounsaturales,bothindividuallyandas
fauy acids, and phytoplankton is the basic food in the aclass,exhibitedawidervariationamongtheindividual
aquatic field, 'lliose species tlutt feeddirectly on plant fishforbothspecies. Individualstripedmulletshoweda
material(phytoplanktonandalgae)reflectthoseplantfatty considerable range in 16:1 concentrations; again, this
acids,whilehigherordercarnivoresaccumulaten-3andn- couldbearesultofthebroadspectrumofplantanddetrital
6 PUFA contained in their prey whichhaveprogressed materialinthedietThenarrowerrangeofconcentrations
through the food chain from the original plant source of16:1 amongindividualspotmayreflecttheconsistent
(Sargent.1976;SargeniandWhittle.1981).Redandbrown invertebratediet.
macroalgaefoundinboththenorthernandsouthernhemi- Arachidonicacid,themajorn-6PUFAfoundinboth
spheresarerichinarachidonicacidandEPA(Jamiesonand spotandmullet,wasoneofthemostvariableconstituents
Reid. 1972). Dunstaneiat.(1988)reportedhighconcen- in mullet, producing seven statistically similar groups
trationsofbothEPAandarachidonicacidinfinfisheswho withfourgroupsinspot. Thatvariationprovidesstrong
feedonmacroalgaeintemperateAustralianwaterswhich evidencethatthisn-6PUFAisanon-conservativecompo-
isconsistentwithfindingsofEvansetaL(1986);highlevels nent inboth species. Highproportions as well as high
ofboth fatty acids were also observed with the striped variabilityofarachidonicacidarecharacteristicoftropi-
mulleiinthisstudy.Gibsonetal.il984)reportedfattyacids cal Australian marinefish and shellfish (Gibson, 1983;
in24Australianfinfishes.ofwhichonlythemembersofthe Sincl^, 1983). However, significantlevelshavebeen
mulletfamily(Mugilidae).whiting,turbotandleatheijacket reportedinsomenorthernhemispherefish(KinsellaetaL,
hadhigherEPAconcentrationsdianDHA. Adietcontain- 1977;GunstoneetaL,1978;GibsonetaL,1984;Goochet
ingmacroalgaemayhelpexplaintheelevatedlevelsofboth aL, 1987).
arachidonicacidandEPAinthestripedmullet. Insummary, theresultsofthisstudy,basedupona
Thepronouncedvariabilityinthefattyacidlevelsin small but selective group of fish, indicate that each
individualstripedmulletismostlikelyduetoinclusionof constituentfattyacidaswellasfattyacidclassvariesin
detrital material in thediet, rather than the macroalgae. individualswithinaspeciesofmarinefish,evenwhenall
Organicdetrinisinestuarinewatersandsedimentsiscom- environmentalandphysiologicaleffectsareminimized.
posedprimarilyofsmallamorphousaggregateswhichmay Theextentofindivido^fishvariationdiffersbetweenthe
originatefromseveralsources,includingbenthicmicroalgae, twospeciesthatwerestudied,withstripedmulletshowing
phytoplankton,microbesandaggregatesofdissolvedor- much greater variability in fatty acid composition and
ganiccarbonexcretedorleachedfromplantsandanimals lipidcontentthandidindividualspot. Dietismostlikely
as well as salt marsh plants (Boesch and Tamer, 1984). theprimarycauseofvariations inindividual fish,and a
Organiccarboninestuarine sedimentsisextremelyvari- morediversedietprobablyaccountsfortheaccentuation
able(LytleandLytle,1985)andwouldaccountforthemore inindividualvariabilityinstripedmullet. Itispossible
highly variabledietofstripedmulletwhichisderivedin thatsamplescollectedfromotherlocalesorduringanother
largemeasurefromsedimentaryorganicmatter. seasonwouldhaveshownentirelydifferenttrends. This
Spotfeedalmostexclusivelyoninvertebrates,prima- canonlybeestablishedfrommoredefinitiveinvestigations
rily marinepolychaetesand smallbivalves. Becauseof (m thecompositionoffishdietsunder avariety offish
theirselectivefeedingh^its.theirdietismoreconsistent collectionconditions.
thanthedietofstripedmullet,particularlythosefeedingin
thesameareas. N^'mepolychaeteworms,adietaryitem
ofspotbutnotmullet,containhighconcentrationsofn-3
PUFA with EPA (20:5n-3) concentrations much higher Acknowledgments
DHA
than (22:6n-3)(LytleandLytle. 1990a). Similarly.
EPAconcentrationswerehigherthanDHAconcentrations Theauthors thankConstanciaRamos for technical
inthe individual spot Over90% of40 speciesofGulf assistanceandRobinOverstreet formanuscriptreview.
finfishes analyzed in our laboratory (Lytle and Lytle. The work was supported by NOAA National Marine
1990b)containedhigherconcentrationsofDHAthanEPA FisheriesServiceGrantNo.NA88AA-H-SK018andthe
Spotwasoneoftheexceptions. StateofMississippi.
, .
56 LytleandLytle
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