- Email: [email protected]
Comparison of lipid and fatty acid composition in vendace (Coregonus albula L.) and available plankton feed
Camp. Biochem. Phwiol. Printed in Great B&in
Vol.
103A, No. 1, pp.205-212,
1992
~3~-9629~92 $5.00 + 0.00 Q 1992 Pergamon Press Ltd
COMPARISON OF LIPID AND FATTY ACID COMPOSITION IN VENDACE (COREGONUS ALBULA AND AVAILABLE PLANKTON FEED REINO R. LPIKO,*~
MARJUT RAJASILTA$
and
RAIMO
L.)
HILTUNEN§
*Laboratory
of Food Chemistry, Department of Chemistry and Biochemistry, University of Turku, SF-ZOSOOTurku, Finland. Tel.: (358) 921645701; ftaboratory of Ecology and Morphology, Department of Biology, University of Turku, SF-20500 Turku, Finland; $Department of Pharmaceutics, University of Helsinki, SF-00170 Helsinki, Finland (Received 20 January 1992) Abstract-l. The food of vendace in Lake Pyhijijlrvi (SW Finland) consisted mainly of cladocerans and copepods throughout the sampling period from May to October. 2. The content of triacylglycerols and polar lipids of vendaee flesh, varied seasonally, in accordance with the total lipids. Triacylglycerols dominated in vendace flesh, while these and polar lipids occurred in nearly equal proportions in composite plankton. In vendace gut, the share of polar lipids decreased markedly. 3. Plankton and vendace flesh total lipids were composed of the same fatty acids. Their reiative amounts varied, especially in poiyenoic acids and in the ratio of w-6 and w-3 polyenoics. 4. The fatty acid composition of fish flesh lipids remained fairly similar throughout the whole sampling period with a slight seasonal variation of some fatty acids occurring in plankton total lipids.
INTRODUCTION
Vendace (Coregonus afbula L.) is the most important fish caught professionally in the lakes of Finland. Lake Pyhgjijiirvi, in Sakyla, which is the study area of the present work, is well known for its exceptionally high fish production (mean annual catch over the last 20 years = 63 kg/ha/year; cf. Sarvala et al., 1984). Vendace and whitefish (Coregonus iavaretus ~1.) are the most important species of the fish catch. A typical feature of the vendace population in this lake is that it consists of 0-2-year-old fish. Lipids and fatty acids of vendace flesh and roe of this fake have been studied earlier but only from fish collected during the spawning period in late autumn (Kaitaranta and Linko, 1979; Kaitaranta, 1980). The lipid classes were analysed only from fish roe. Previous studies carried out by e.g. Lasker and Theilacker (1962), Lambertsen and Myklestad (1972), Sargent et al. (1979), Ratnayake and Ackman (1979a,b), Linko et al. (1985) and Muje et al. (1989) have shown that the lipids of the feed organisms are of great importance in the fatty acid composition of fish lipids. The aim of the present work was to compare the lipid and fatty acid composition of vendace flesh with that of composite plankton sampled from lake Pyhajlrvi throughout May and October, which is the main feeding and growth period of vendace in the lake (Hehninen at al., 1990). The composition of plankton species was also monitored.
tTo whom correspondence
should be addressed.
MATERIALS AND METHODS
Study urea The study area of the present work, Lake PyhsjijPrvi in SiikyIl(61 “OS’N:22”2O’E)is a large (area 154 km2), shallow (mean depth 5.4 m) clear water (Secchi disc depth 3-4 m) lake in south-western Finland. The iake is mesotrophic, having a phytoplankton primary production of 4%56g C/m*/year (Jumppanen, 1986) and total herbivorous crustacean production of 5 g C/m’/year (Sarvala er al., 1988). The lake basin is open, having only a few islands. Due to its vast pelagial and shallowness, the water circulation is effective and no thermal stratification is found during summer. Water temperature varies normally between 0 and cry 20°C throughout May and October, the maximum occurring in July. Fish and plankton samples The samptes were collected between May 30 and October 2 in I985 Fish were caught by gifl nets during the night, put on ice immediately after landing and cold-transported to the laboratory within 2 hr. one-kilogram samples of vendace consisting of 15-20 fish were pooled at each sampling time. Fish were filleted and the skins removed. The filleted fish was minced and the meat thoroughly mixed, before taking the samples for the dry weight determinations (A.O.A.C. method No. 43.233) and for the lipid extractions, Plankton was sampled at the same time as vendace hauling a 15Ofim Hensen net at a depth of O-3 m. The sample was brought to the laboratory in cold lake water. It was sieved through a 200 ym filter before analysis in order to eliminate phytoplankton, which is not used as food by vendace in the lake (~elminen et al., 1990). The zoopiankton remaining on the sieve was weighed and after careful mixing of the sample the aliquots were jmm~iateiy taken for dry weight dete~ination (see above) and for lipid extractions. The species composition of zooplankton was dete~ned by counting and identifying 2~300 indi~d~ls from a 205
REINOR.
206
subsample representing the sieved and mixed sample. The percentage of each species in the zooplankton biomass was calculated using values of total organic body carbon @gC) (unpublished data of J. Sarvala; Dept. Biology, University of Turku). In some vendace samples the gut content of half of the fish was pooled and mixed thoroughly for determining its dry matter content (see above) and for the extraction of the lipids. The composition of the food of the fish was examined by mixing the gut contents of the other half of the fish sample (10-I 5 individuals) in ethanol solution and analysing the food items from the subsample as above. The dates of sampling the fish and plankton are shown in the accompanying tables. Lipid fractionations and fatty acid analysis The lipids were extracted from both fish and plankton by the method of Bligh and Dyer (1959). The extracts were concentrated under vacuum and dried under nitrogen. The remaining total lipids were weighed and redissolved in CHCl, and stored under nitrogen at -25°C until analysed. Part of the total fish lipids were resolved into phospholipid and triacylglycerol fractions. Silicic acid column chromatography was applied to separate neutral and phosphoIipids. The absorbent was pretreated as described by Kaitaranta (1980) and the two lipid fractions were eluted from the column according to Rouser er al. (1976). The phospholipid fraction was concentrated and stored as with the total lipids. Triacylglycerols were separated from the total lipids by means of thin-layer chromatography (TLC) using silica gel plates (DC-Alufolien Kieselgel 60, Merck AC Art. 5553): The plates were developed in a mixture of hexane-diethyl ether-acetic acid (85: 15: l.S, by vol.). The resolved triacylglycerol bands were scraped from the plates and extracted successively with a mixture of chloroform and methanol (1: 1 v/v) and methanol. The triacylglycerol fraction was concentrated and stored as with the total lipids. The lipid class determinations were performed from the total lipids of fish flesh, gut content and plankton using quantitative thin-layer chromato~aphy-flame ionization detection (TLC-FID). Lipid classes were separated on Chromarod-S-II rods with a coating of silica gel using a mixture of hexane-diethyl ether-acetic acid (80: 6:0.5, by vol.) as a deveioping solvent. The quantitation was obtained using an Iatroscan TH-10 Analyzer (Iatron Laboratories Inc., Japan) as described in detail by Kaitaranta (1980). The fatty acids of the total lipids, phospholipid and triacylglycerol fractions were converted to their methyl esters according to the method of IUPAC (1979). The purified esters were analysed by glass capillary GLC on a OV-351 column (25 m long and 0.32 mm id.) as described in a previous paper (Kaitaranta and Linko, 1984). RESULTS
The cladoceran species Holopedium gibbet-urn predominated in the zooplankton collected in June (Table 1). Calanoida copepodids and adult (mainly Heterocope appendiculata) and cladocerans Bosmina and Daphnia made up the rest of the zooplankton biomass. In July and early August, the zooplankton consisted primarily of Daphnia species (70-90% of biomass). Later, in autumn, the biomass of cyclopoid copepodids and adults increased, although other copepodids (Eudiaptomus and Heterocope) and cladocerans Chydorus, Daphnia and Bosmina were also abundant. Vendace fed on zooplankton throughout summer. Cyclopoid copepodids and adults were the most important food source at the end of May. In June,
LINKO et
al.
fish fed primarily on Bosmina (90% of the total number of prey taken) but also took some Holopedium (8%) and Daphnia (1%). In July, the food consisted of copepods (75%) and Bosmina (22%), which were again, in August, the most numerous prey (48 and 48% respectively). Dry matter and fat content
The dry matter and total lipid content of vendace flesh, gut content and plankton are shown in Fig. 1. Remarkable changes occurred in the dry weight of the fish flesh during the summer and early autumn. Flesh contained 22% dry matter at the end of May, gradually rising to 25.5% at the beginning of August, maintaining roughly the same level up to early September, after which decreasing rather sharply to 22.1% at the beginning of October. These variations in the dry matter content of fish flesh depend mainly on the lipids, which accumulate into the musculature during the summer and are mobilized before reproduction in October (Fig. 1). The total iipid content of the flesh was highest (4.9% of the fresh weight) at the end of August and lowest (2.1-2.2%) in the late spring (May) and early autumn vetoer) with one exception (27 June; 1.5%). The eqcipment used for the collection of plankton samples enabled the gathering of only small amounts of biomass for the analysis. Thus, it was not possible to determine the dry matter, and even total lipid content, of all samples. However, the results obtained clearly show that the dry weight, as well as the total lipid content, although being at a low level, behaved quite opposite to those in fish samples concerning their dependence on time of year. Thus, there were more dry matter and total lipids in plankton samples collected in spring and autumn than in those collected in the early and middle summer (Fig. 1). The few analyses made at random on the gut content of vendace indicated that the dry matter and total lipid content of the plankton biomass were concentrated 20-30-fold when transported into the gut of fish (Fig. 1). Lipid composition
The average lipid class composition of vendace flesh, gut content and plankton is shown in Table 2. The extracted total lipids were separated with TLCFID into their major lipid fractions, the polar lipids, triacylglycerols and steroh. The polar lipids were not sub-divided further but analysed as one group. The major lipids in vendace flesh are triacylglycerols (66-86%), followed by pofar lipids (12-30%) and sterols (l-4%). The relative proportions of different lipid classes in the fish flesh varied significantly over the S month sampling period. The greatest, and quite opposite, changes were found in the percentage of triacylglycerols and polar lipids. Triacylglycerols accumulated in the musculature as a depot fat from the end of May to the middle of July, but decreased slowly thereafter, being at the same percentage level at the beginning of October as in the late spring. On the other hand, the relative proportions of the polar lipids were highest in fish samples collected in May and in October and lowest in the middle of Juty. However, the total lipid content of the fish flesh increased from May till the
Lipids and fatty acids in vendace and plankton Table I. Composition of zooplankton (% Species
June 21
73 18 4 _
46 I7 2 -
Holopedium Daphnia Bosmina Chydorus Ceriodaphnia Diaphanosoma Polyphems Leptodora Calanoida c&a Cyclopoida c&a CoDeooda nau~l.
W)
_ + + +
Aug. 14 (%)
88 + _ -
71 _
+ -
_ 7
A
w
5
n --_ 0
2
E
I--
;
n -,
JUNE
m.‘\
0. i
_
__--
__--
JULY
__--
,
‘I--ii ____-___
JUNE
JULY
I
2i _ _
the study period
Aug. 20 W) _
Sept. 5 (OhI -
Oct. 2 W)
8 I 4 + 2 _ _
6 2 12 -
9 20 8 _ _ _ _
65 21 +
IO 70 -
35 27 +
_
stage; + = < I %; - = not found.
25
&
-
_ _
+ II -
end of August, after which it declined (Fig. 1). Thus, if the amounts of triacylglycerols and polar lipids are calculated from the fresh weight of the fish flesh, it is observed that the maximum value (3.7%) of the former lipid fraction was not achieved until August and that (1.1%) of the latter fraction at the same time. The zooplankton of Lake PyhgjijBrvicomprised the same lipid fractions as vendace flesh (Table 2). In some plankton samples small amounts of free fatty acids (under 1% of the total lipids) were found. However, there were much more polar lipids in plankton than in fish flesh. The relative amounts of polar lipids and tricylglycerols in plankton were at about the same level, 45-51% and 41-51% respectively, excluding the values of one sample. The content of sterols varied from 2% to 8% of total lipids.
0
in the lake samples during
July 15 (%) _
3+4 -
4
a = adult; c = copepodid
of fresh weight)
June 17 (“/J
207
w-_,
AUG.
k------’
I
SEPT.
I
OCT.
,m“,-¤ AUG.
I
SEPT.
I
OCT.
Fig. 1. Dry matter (A) and total lipid (B) content of vendace flesh (a), gut content (A) and of plankton (B) in Lake Pyhiijiirvi at different times of year. Vertical bars indicate the standard deviation of the samples when ~0.04.
The same three major lipid components as above were also found in the gut content of vendace (Table 2). In comparison to the plankton lipids the percentage share of the polar lipids in the gut content was remarkably lower, which bears out their primary utilization as fishfood. Fatty acid composition
The relative proportions of 30 fatty acids of different lipid extracts, fractions of vendace flesh and of plankton (see above) were determined. Twenty-four of these fatty acids, which constitute over 90-95% of the total fatty acids, are listed in Tables 3-6. In the total lipids of vendace flesh, 10 major fatty acid components were found. These are: myristic (14:0), palmitic (16:0), palmitoleic (16:107) oleic (18:1w9), linoleic (18:2w6), arachidonic (20:4w6), (18 :4w 3), linolenic (18 : 30 3), octadecatetraenoic eicosapentaenoic (20 : 5w 3) and docosahexaenoic (22 :6w 3) acids (Table 3). The share of these acids was over three-quarters of the total fatty acid content. The proportions of the main fatty acid components remained relatively similar throughout the whole 5 month sampling period (Table 3). The fatty acid composition of triacylglycerols, the depot fat of vendace flesh, behaved similarly with that of the total lipids concerning their time dependence (Table 4): moreover, their fatty acid compositions resembled each other. This is explained by the fact that triacylglycerols constitute the major share of vendace total lipids (Table 2). However, triacylglycerols contain distinctly lower amounts of docosahexaenoic acid than the total lipids. It depends on the latter also containing polar lipids rich in docosahexaenoic acid (cf. Table 5). Typical to the fatty acid composition of the polar lipids (phospholipids) of vendace flesh is the abundance of palmitic, docosahexaenoic and eicosapentaenoic acids and the shortage of monoenoic acids (Table 5). Table 6 shows that plankton total lipids are composed of the same fatty acids as those of vendace flesh. However, the relative amounts of the fatty acids differ distinctly between plankton and fish lipids. Thus, in plankton lipids were more myristic, linoleic, arachidonic and eicosapentaenoic acids, but less oleic, and especially docosahexaenoic, acids than in vendace flesh lipids. In the fish flesh docosahexaenoic acid enriches in triacylglycerols and especially in the polar lipid fraction, which suggests that chain elongation and desaturation of eicosapentaenoic acid
208
REINO
R.
LINKO et a/.
occurs in the fish organs. Also the fatty acid composition of the gut content of vendace indicates this kind of lipid metabolism (Table 6). The relative proportions of some fatty acids of plankton lipids fluctuate according to the season (Table 6). Thus, the percentage of myristic and octadecatetraenoic acids decreases gradually from spring to autumn, while that of the paimitoieic acid increases. DISCUSSION
Vendace is a selective planktivore and its diet consists mainly of ciadocerans and copepods, other groups of zooplankton being of minor importance (e.g. Viljanen, 1983). Analyses of gut contents made in the present study showed that the species food was largely the same as that of zooplankton collected for lipid analyses. Clodocerans (Bosmina and Duphniu) and cyciopoid and caianoid copepods (Eudiaptomus) are the preferred prey which make up the bulk of the total amount of food consumed by vendace in Lake Pyhajlrvi (Heiminen et al., 1990). Characteristic seasonal variations occur in the lipid contents of zooplankton and vendace flesh. The lipid content of plankton was highest in May but declined to a rather low level for the summer months. Although the lipid content followed changes in the biomass of copepods to some extent, the changes are hardly caused by differences in plankton composition. For example, Vijverberg and Frank (1976) found no differences in lipid concentrations of copepods and ciadocerans. Zooplankton is dependent on phytoplankton in its energy gain and thus, the lipid content may indicate some changes in primary production. The lipid content rose again at the beginning of autumn, when the share of copepods in the plankton increased. The lipid content of vendace flesh gradually increased during the summer reaching its peak at the end of August and diminishing rapidly thereafter. This is evidently connected with the development of the gonads. In Finland, rapid gonadal development of vendace starts in July-August (Lehtonen, 1981) and spawning begins on average at the end of October (Lind, 1976). Muje et al. (1989) have found the same trend in the total lipid content of the vendace muscle in two different lake types, oligotrophic Lake Suvasvesi and mesotrophic Lake Kaliavesi in eastern Finland. However, the relatively low lipid content of vendace caught from Suvasvesi and Kaliavesi as compared to that from Pyhajarvi in the present work is worthy of note. Lahti (1987) has also obtained low lipid levels in the vendace muscle from Lake Suvasvesi and Lake North-Konnevesi. However, there were differences in the total lipid content between the lakes which are due to limnological and planktonproductive differences in the lakes (Lahti and Lindqvist, 1986). In zooplankton from Lake Pyhaj&i there were only two major lipid classes, triacylglycerols and polar lipids, their relative proportions being nearly equal. The lack of wax esters is important, as it also reflects the lipid and fatty acid composition of vendace flesh. This coincides with the report of Takahashi and Yamada (1976) that in the freshwater milieu there is no organism comparable to
Lipids and fatty acids in vendace and plankton Table 3. The relative proportions Fatty acid --Total saturated Total straight chain 14:o 16:O 18:O Total monoenoic Total o9-series 16:109 18:Iw9 20:Iw9 Total oFseries I6:107 18;lw7 2O:lw7 Total polyenoic Total w6-series 18:2w6 18:3u6 20:206 20:3w6 20:4w6 22:4w6 22:506 Total w 3-series 18:3w3 l8:403 20:3w3 20:4oJ3 to: 503 21:5w3 22: 503 22:6w3 . _
209
of fatty acids of vendace flesh total lioids in Lake Pvhiiiarvi at different times of vear
30 May
4 June
17 June
27 June
I5 July
S Aug.
20 Aug.
5 Sept.
2 Oct.
24.9
25.9
27.5
23.8 6.6 14.0 2.2 16.4 7.2 0.1 6.9 0.4 9.2 6.9 2. i 0.2 51.3 10.5 3.8 0.6 0.4 0.2 3.0 0.5 2.0 40.8 6.0 7.8 0.3 1.8 8.7 0.4 1.9
24.8 8.3 13.4 I.7 16.4 6.2 0.2 5.9 0.3 10.0 7.8 2.0 0.2 50.6 9.3 3.8 0.6 0.3 0.2 2.6 0.3 1.5 41.3 6.8 10.2 0.3 I.8 9.3 0.3 1.5 11.1_
26.5 25.4 7.1 14.5 2.7 17.8 9. I 0.1 8.4 0.6 8.7 6.3 2.2 0.2 49.3 10.1 3.8 0.5 0.4 0.2 2.8 0.5 1.9 39.2 5.8 7.4 0.5 2.4 8.1 0.4 I.9 12.7
26.3 7.6 15.1 2.7 18.6 8.6 ND 8.2 0.4 10.0 7.4 2.5 0.1 49.9 10.7 3.8 0.6 0.4 0.3 3.0 0.5 1.9 39.2 5.7 8.1 0.4 2.0 9.1 0.4 1.9 11.6
27.9 26.7 7.2 15.5 3.1 19.5 10.0 0.1 9.4 0.5 9.5 6.8 2.6 0.1 46.9 10.6 3.7 0.6 0.4 0.3 3.2 0.6 1.6 36.2 5.0 7.2 0.4 1.9 8.2 0.4 1.5 11.7
27.1 25.9 6.8 15.5 2.9 19.2 9.8 0.1 9.2 0.5 9.4 6.8
27.1 27.3 7.1 16.1 3.2 21.5 11.7 0.1 11.0 0.6 9.8 7.0 2.7 0.1 51.4 12.1 4.2 0.6 0.5 0.3 3.6 0.7 2.2 39.3 5.4 7.2 0.4 2.1 8.9 0.4 2.0 12.9
27.8 27.1 6.8 16.3 3.1 20.8 10.4 0.1 9.8 0.5 10.4 6.9 3.4 0. I 52.0 11.7 4.0 0.6 0.4 0.2 3.7 0.6 2.2 40.3 5.3 7.1 0.4 I.9 8.9 0.4 2.1 14.2 0.3
27.6 26.4 6.4 15.9 3.3 19.6 10.4 0.1 9.7 0.6 9.2 6.4 2.7 0.1 54.0 12.9 4.2 0.6 0.4 0.3 4.3 0.7 2.4 41.1 5.1 6.5 0.4 I.9 9.1 0.4 2.5 15.2 0.3
of wax is also water 1986).
However, in the latter the polar lipids dominate over the triacylglycerols and free fatty acids. In vendace flesh the triacylglycerois and polar lipids were the main components. Polar lipids in fish tissues
rob/u3
;:: 47.0 IO.8 3.8 0.6 0.4 0.2 3.3 0.6 1.0 36.2 4.6 7.0 0.4 2.0 8.4 0.4 1.8 11.2
ND not detected.
marine esters. found milieu
copepods with respect to accumulation A similar situation as that in freshwater in the plankton lipids of the brackish of the Baitic Sea (Kaitaranta ef ol.,
Table 4. The relative proportions Fatty acid Total saturated Total straight chain 14:o 16:O 18:O Total monoenoic Total w9-series 16:109 18:109 20: 1~9 Total 0 7-series 16:11x7 I8:107 20: ICI? Total poiyenoic Total d-series 18:2w6 18:3w6 20: 206 20:3w6 20:4w6 22~4~6 22:506 Total w3.series 18:3u3 18:4w3 20: 303 20:4cu3 20: 5~3 21:503 22~503 22:603 ND: not detected.
of fatty acids of vendace flesh t~acyl~y~rois
in Lake Pyh&j;iiirviat different times of year
30 May
4 June
I7 June
27 June
15 July
5 Aug.
20 Aug.
5 Sept.
2 Oct.
27.6 26.2 8.5 13.7 2.5 20.1 8.7 0.2 8.0 0.5 Il.4 8.4 2.5 0.2 44.0 10.1 4.5 0.6 0.4 0.2 2.5 0.3 1.6 33.9 6.6 8.1 0.3 1.7 7.6 0.4 1.7 7.5
28.0 26.9 9.3 13.7 2.0 IQ.4 7.8 0.2 7.3 0.3 11.6 9.2 2.4 ND 46.0 9.2 4.5 0.3 0.3 0.1 2.4 0.3 I .4 36.8 7.2 10.0 0.2 1.6 8.5 0.3 1.5 7.5
26.3 25.2 8.7 13.3 2.1 19.5 9.1 0. I 8.5 0.5 10.4 8.0 2.3 0.1 50.0 9.7 4.4 0.3 0.4 0.2 2.5 0.3 1.6 40.3 7.0 9.7 0.5 2.2 8.7 0.5 2.0 9.7
25.6 24.3 8.2 12.9 2.3 19.2 8.2 0.2 7.7 0.5 11.0 8.2 2.3 0.5 47.4 9.6 4.0 0.7 0.4 0.2 2.7 0.3 1.3 37.8 6.4 9.8 0.4 2.0 9.1 0.4 1.7 8.0
28.1 26.8 9.4 14.1 2.5 20.2 9.6 0.1 9.2 0.5 10.6 8.1 2.4 0.1 43.9 9.4 3.9 0.4 0.4 0.2 2.9 0.3 1.3 34.5 6.0 9.1 0.3 1.8 8.0 0.4 1.6 7.3
28.2 27.0 1.7 15.3 3.1 21.4 10.9 0.1 10.3 0.5 10.5 7.1
27.0 26.2 8.3 14.2 2.6 21.5 11.0 0.1 10.4 OS 10.5 8.0 2.4 0.1 52.6 11.6 4.5 0.7 0.4 0.3 3.4 0.4 1.8 41.0 6.6 9.1 0.6 2.3 9.8 0.5 2.2 9.9
27.3 26.9 8.3 14.6 2.7 21.7 10.9 0.1 10.3 0.5 10.8 7.8 2.9 0.1 51.2 11.6 4.5 0.7 0.4 0.3 3.5 0.4 1.8 39.6 6.3 9.3 0.5 2.0 9.4 0.4 2.0 9.7
27.0 26.2 8.1 14.3 3.1 23.0 11.0 0.2 10.2 0.6 12.0 7.8 4.0 0.2 59.6 13.1 5.2 0.7 0.4 0.4 3.8 0.6 2.0 31.5 6.0 8.0 0.5 2.0 8.7 0.4 2.3 9.6
::: 44.1 10.4 4.1 :1: 0:2 3.1 0.3 1.6 33.7 5.4 1.7 0.4 1.7 8.7 0.4 1.8 8.1
210
REINO R. LINKO et al. Table 5. The relative proportions Pyhlilrvi Fatty acid Total saturated 12:o 14:o 15:o 16:O 18:O Total monoenoic Total w9-series 16:lw9 18:lw9 Total o7-series 16:lw7 18:lw7 Total polyenoic Total wb-series 18:206 18:306 20:2w6 20: 3~6 20:4w6 22:4w6 2215~6 Total w 3-series 18:3w3 18:4w3 20:3w3 20:4w3 20:5w3 21:5w3 22:5w3 22~603
of fatty acids of vendace flesh polar lipids in Lake at different times of year
4 June
17 June
27 June
15 July
5 Aug.
28.3 I.1 3.1 2.7 19.2 2.2 7.0 5.3 I .4 3.9 1.7 0.1 1.6 65.3 10.3 1.5 0.2 0.2 0.2 4.2 0.3 3.7 55.0 2.6 1.9 0.3 1.5 10.3 0.3 I.7 36.4
25.6 ND 2.4 0.4 20.3 2.5 6.8 5.0 1.3 3.7 I.8 0.1 1.7 67.7 10.2 1.6 ND ND ND 4.7 ND 3.9 57.5 2.4 I.3 0.3 I.7 10.2 ND 1.9 39.7
26.7 0.3 2.0 0.4 21.7 2.3 7.7 5.9 1.0 4.9 1.8 0.1 1.7 65.7 12.0 1.3 0.1 0.2 0.2 5.2 0.6 4.4 53.7 1.7 I.2 0.2 1.4 9.9 0.2 2.1 37.0
28.8 0.2 1.7 0.4 24.1 2.4 7.3 5.7 1.0 4.7 2.1 0.1 2.0 63.4 II.6 1.2 0.1 0.2 0.2 5.1 0.4 4.4 51.8 1.3 0.9 0.2 1.0 9.6 ND 1.8 37.0
31.0 ND 1.5 0.3 26.2 3.0 7.3 5.4 0.8 4.6 I .9 ND 1.9 61.5 II.1 1.2 0.1 0.2 0.2 5.1 0.4 3.9 50.4 1.4 1.0 0.3 1.0 9.1 ND 1.6 36.0
ND: not detected.
are mainly composed of phospholipids and function as structural lipid while triacylglycerols are usually considered to be depot fat (Ackman et al. 1980). It is Table 6. The relative proportions
Fatty acid Total saturated Total straight chain 14:o 16:0 18:0 Total monoenoic Total o9-series 16:109 18:109 20:109 Total w7-series 16:lw7 lS:lw7 2O:lw7 Total polyenoic Total w6-series 18:206 18:306 20:2w6 20:3w6 20:406 22~406 22: 5~6 Total o3-series 18:303 18:403 20:303 20:4w3 20:5w3 21:5w3 22:503 22:6w3 ND: not detected.
significant that fatty alcohols and wax esters were not detected in vendace lipids. There were in vendace flesh on average three times more triacylglycerols
of fatty acids in total lipids of composite plankton times of year 30 May
I7 June
30.2 29.8 12.8 13.5 3.0 8.9 3.6 0.1 3.4 0.1 5.3 3.8 1.4 0.1 59.0 16.7 6.7 0.9 0.2 0.2 7.6 0.1 1.0 42.9 6.7 12.8 ND 0.6 18.0 0.4 0.2 4.2
28.6 27.1 11.5 II.9 2.6 12.2 4.2 0.1 3.9 0.2 8.0 6.5 I .4 0.1 48.2 13.4 5.1 0.9 0.1 0.2 6.3 0.1 0.7 34.8 5.1 11.4 ND ND 14.4 0.3 0.3 3.7
Plankton 27 June 20 Aug.
-
34.8 33.3 14.4 14.1 2.9 9.9 3.8 0.1 3.6 0.1 6.1 4.6 1.4 0.1 51.0 15.4 6.8 0.9 ND 0.1 6.8 ND 0.8 35.6 6.2 10.2 ND 0.4 14.7 0.3 0.2 3.6
29.1 28.6 8.1 15.8 4.1 12.9 4.7 0.1 4.4 0.2 8.2 5.1 3.0 0.1 58.0 19.7 6.2 I .o 0.3 0.2 6.5 0.1 5.4 38.3 6.1 6.9 0.1 1.0 12.1 0.2 0.8 II.1
and of vendace gut content in Lake PyhijijBrvi at different
5 Sept.
2 Oct.
27.4 26.9 7.8 14.6 3.5 21.4 4.9 0.2 4.4 0.3 16.5 12.7 3.1 0.1 51.4 15.4 3.9 1.1 0.2 0.3 6.2 0.2 3.5 36.0 5.0 6.0 0.2 1.2 14.8 0.2 0.8 7.8
25.4 25.2 7.1 13.8 2.2 31.1 4.7 0.4 4.1 0.2 26.4 23.5 2.9 ND 43.6 12.6 3.3 3.1 0.1 0.2 3.7 ND 2.2 31.0 3.5 5.0 0.1 0.7 16.0 0.1 0.6 5.0
Vendace gut content I7 June Z 27 June I5 July 30.2 28.9 9.5 14.4 3.3 15.3 7.2 0.1 7.0 0.1 8.1 6.1 1.9 0.1 45.1 10.7 4.4 0.7 ND 0.3 3.6 0.2 1.5 34.4 6.6 6.6 0.6 1.6 9.3 0.4 1.2 8.1
28.4 27.1 9.0 14.1 3.1 17.7 6.4 0.1 6.1 0.2 II.3 7.3 3.9 0.1 45.8 10.8 4.4 0.6 ND 0.2 3.7 0.3 1.6 35.0 5.7 8.9 0.6 1.5 9.6 0.4 1.2 7.1
26.4 25. I 7.7 13.6 2.9 19.0 9.4 0.1 8.9 0.4 9.6 6.8 2.7 0.1 46.4 10.9 3.7 1.3 ND 0.2 3.9 0.3 I.5 35.5 5.6 8.2 0.3 1.8 9.7 0.4 1.4 8.1
211
Lipids and fatty acids in vendace and plankton
than polar lipids. Their content calculated from the fresh weight of fish varied seasonally in accordance with the total lipids. In Baltic herring flesh the seasonal variation of the total lipids coincides with that of depot fat (Link0 et al., 1985). In many other freshwater fish the flesh contains low quantities of triacylglycerols and a relatively high proportion of phospholipids (Kinsella et al., 1978). When the lipid composition of vendace gut content is compared with that of plankton, a marked decrease of polar lipids is found. This points to the activity of phosphohpases in the gut content (Olley and Lovern, 1960) although it has been shown that in fish nonspecific intestinal lipase also hydrolyses triacylglycerols (Cowey and Sargent, 1977). Fifty fatty acid components of vendace flesh lipids were identified earlier by GLC-MS (Kaitaranta and Linko, 1979; Kaitaranta, 1980). Fish were caught from Lake Pyhiijarvi as in the present study, when the proportions of 30 fatty acids from fish and plankton lipids were determined. The data indicate that the vendace flesh total lipids contained about 40% eicosa~ntaenoic and docosahexaenoic acid of the total polyunsaturated acids, which fitted weil into the typical limits, 30-40%, set for freshwater fish polyenoics (Kinsella et al., 1977). Of further interest to human nutrition is the relatively high content of linoleic, linolenic and arachidonic acids in the lipids of vendace, which is also characteristic for freshwater fish (Gruger et al., 1964; Chetty et al., 1989). In addition, the total amount of polyenoic acids in vendace lipids rose to over 50%. The ratio w6/w3 of polyunsaturated acids was 0.3 in vendace total lipids, which coincides with that (0.3-0.4) of freshwater fish. On the other hand, in sea-fish of the northern hemisphere the ratio is 0.1 and in some warm sea water fish the ratio is approaching 0.9 or even above 1, owing to the high amounts of arachidonic acid (Gibson, 1983; Gibson et al., 1984). Vendate lipids contained 20: 1~7 and 20: 109 eicosenoic acid isomers in only very minor proportions and docosenoic acids (22: 1) were not found at all. This can be understood on the basis of the lipid composition of its plankton feed. In this respect, vendace lipids resemble also those of the organisms in freshwater milieu (Kinsella et al., 1977; Ackman er al., 1980). On the contrary, the depot fats of many sea-fish in the northern hemisphere contain fairly large amounts of 20: 109 eicosenoic and 22: lo 11 docosenoic acid isomers, which, plausibly, are derived from their diet (Ratnayake and Ackman, 1979a,bf. These fatty acids have been observed to cause some adverse physiological changes in animal experiments. The relative proportions of fatty acids in vendace flesh lipids remained quite unchanged throughout the summer and early autumn. Moreover, the values coincide well with those found earlier in a very large sample of mature female vendace by Kaitaranta (1980). In the latter study the fatty acid patterns of the lipid fractions from flesh and roe were also found to be similar to each other. These findings confirm the report of Agren et al. (1987), that in vendace muscle tissue the fatty acid spectrum remains unchanged in relation to the reproductive cycle. However, the fatty acid composition of vendace flesh total lipids given by Agren et al, (I 987)
and Muje et al. (1989) deviates greatly from that found in the present study. On the other hand, it resembles the fatty acid pattern of the polar lipids with an abundance of 22 : 6~3 and 16:O acids and shortage of monoenoic acids. The rather low lipid content of vendace from the lakes of eastern Finland reflects also the dominance of poiar lipids in fish flesh (cf. Kin&la et al., 1977, 1978). The fatty acid composition of the total lipids of zooplankton from Lake Pyh~j~~i and also from mesotrophic Lake Kallavesi was rather similar (Muje et al. 1989). The 20503 acid was the major component, but there were also relatively large amounts of 18:303, 18:4w3, 22:603, 18:206 and 20:4w6 acids. The plankton lipids of Lake Suvasvesi contained in addition somewhat more 22 : 6w 3 acid than those mentioned above (Muje et al., 1989). A slight seasonal variation in the proportions of some fatty acids may depend on the fluctuation of water temperature (cf. Farkas, 1979). On the other hand, 20: 503 and 22: 6~03 acids dominated in the lipids of zooplankton collected from the Baltic Sea off the south-west coast of Finland (Kaitaranta et ai., 1986) as their lipids were composed mainly of phospholipids. Nevertheless, some distinguishing features also exist in the fatty acid compositions of small copepods and wax esters containing larger euphausiids and copepods of marine origin (cf. Kaitaranta et a/., 1986). The results of the present study suggest that the alkyl chains of plankton fatty acids are transferred to the vendace flesh lipids without major modifications. However, differences in the relative proportions of some fatty acids between fish flesh and plankton lipids indicate that fish may alter their overall depot fat composition to suit their particular needs. Thus, chain elongation and desaturation of fatty acids may occur in fish organs, which is retlected in the results of anaiyses of the fish gut content. Yu ef al. (1977) suggested that a mechanism exists in fish which regulates and maintains certain levels of body lipid saturation. Acknowledgements-The authors express their sincere thanks to Kirsi Karkinen for technical assistance. This study was supported by a grant from Turun Yliopistosaltio, Finland. REFERENCES Ackman R. G., Sebedio J.-L. and Kovacs M. J. P. (1980) Role of eicosenoic and docosenoic fatty acids in freshwater and marine lipids. Mar. Chem. 9, 157-164. Agren J., Muje P.. Hiinninen O., Herranen J. and Penttill I. (1987) Seasonal variations of lipid fatty acids of boreal freshwater fish species. Camp. Biochem. Physiol. 888, 905-909. Bhgh E. D. and Dyer W. J. (1959) A rapid method of total lipid extraction and purification. Can. J. Biochem. Physiol. 37, 911-917. Chetty N., Reavis S. C., Immelman A. R., Atkinson P. M. and Van As J. G. (1989) Fatty acid comoosition of some South African freshwater fish. Samj 76,‘368-370. Cowey C. 8. and Sargent J. R. (1977) Lipid nutrition in fish. Comp. Eiochem. Physioi. 57B, 269--273. Farkas T. (1979) Adaptation of fatty acid compositions to temperature-a study on planktonic crustaceans. Camp. Biochem. Physiol. MB, 71-76.
212
REIN0
R. I
Gruger E. H. Jr., Nelson R. W. and Stansby M. E. (1964) Fatty acid composition of oils from 21 species of marine fish, freshwater fish and shell fish. J. Am. Oil Chem. Sot. 41, 662-667. Gibson R. A. (1983) Australian fish-An excellent source of both arachidonic acid and omega-3 polyunsaturated fatty acids. Lipids 18, 743-752. Gibson R. A., Kneebone R. and Kneebone G. M. (1984) Comparative levels of arachidonic acid and eicosapentaenoic acid in Malaysian fish. Comp. Biochem. Physiol. 18, 325-328.
Helminen H., Sarvala J. and Hirvonen A. (1990) Growth and food consumption of vendace Coregonus albula (L) in Lake Pyhajarvi, SW Finland: a bioenergetics modelling analysis. Hydrobiologia 200/201, 51 I-522. IUPAC Applied Chemistry Division, Commission on Oils, Fats and Derivatives (1979) Preparation of fatty acid methyl esters. In Standard Methods for the Analysis of Oils, Fats and Deriuatiues, method II D.19, 2.301. pp. 96-102. Pergamon Press, Oxford. Jumppanen K. (1986) Sakyliin Pyhiijarven ainetaseet, veden laatu ja kasviplanktonin perustuotanto v. 1985. Lounais-&omen l-25.
Vesiensuojeluyhdistys
r.y.
julk.
29,
Kaitaranta J. K. (1980) Lipids and fatty acids of a whitefish (Coregonus albula) flesh and roe. J. Sci. Food Agric. 31, 130331308.
Kaitaranta J. K. and Linko R. R. (1979) Fatty acids of a whitefish (Coregonus albula) flesh lipids. J. Sci. Food Agric. 30, 921-926.
Kaitaranta J. K. and Linko R. R. (1984) Fatty acids in the roe lipids of common food fishes. Comp. Biochem. Physiol. 19B, 331-334.
Kaitaranta J. K., Linko R. R. and Vuorela R. (1986) Lipids and fatty acids in plankton from the Finnish coastal waters of the Baltic Sea. Comp. Biochem. Physiol. 85B, 427433.
Kinsella J. E., Shimp J. L., Mai J. and Weihrauch J. (1978) Lipids in fish fillets: changes following cooking by different methods. J. Food Sci. 43, 1669-1674. Kinsella J. E., Shimp J. L. and Weihrauch J. (1977) Fatty acid content and composition of freshwater finfish. J. Am. Oil Chem. Sot. 54, 424429.
Lahti E. (1987) Total lipid and cholesterol contents of liver and muscle in some fish species, especially vendace (Coregonus albula L.) in Finland. Arch. Hydrobiol. 110, 133-142.
Lahti E. and Lindqvist 0. V. (1986) Seasonal and area1 differences in the thyroid histology of the vendace (Coregonus albula L.) in fresh and brackish waters in Finland. Arch. Hydrobiol. 106, 487496.
Lambertsen G. and Myklestad H. (1972) Lipider i Rauate (Calanusfinmarchicus) en viktig naeringskilde for sild og lodde. In Proceedings of 6th Nordic Fat Symposium, GrenH 1971, pp. 83-91. Lasker R. and Theilacker G. H. (1962) The fatty acid composition of the lipids of some Pacific sardine tissues
in relation to ovarian maturation and diet. J. Lipid Res. 3,6&64.
Lehtonen H. (1981) Biology and stock assessment of Coregonids by the Baltic coast of Finland. Finn. Fish. Res. 3, 31-83. Lind E. A. (1976) Riippuvuus Ympiiristiitekijiiistd Ja Lajinsisiiiset Suhteet
Eriiissii Suomen
Muikkupopulaatioissa.
Univ. Oulu, pp. l-109. Linko R. R., Kaitaranta J. K. and Vuorela R. (1985) Comparison of fatty acids in Baltic herring and available plankton feed. Camp. Biochem. Physiol. 82B, 699-705. Muje P., Agren J. J., Lindqvist 0. V. and Hlnninen 0. (1989) Fatty acid composition of vendace (Coregonus albula L.) muscle and its plankton feed. Camp. Biochem. Physiol. 92B, 75-79.
Olley J. and Lovern J. A. (1960) Phospholipid hydrolysis in cod flesh stored at various temperatures. J. Sci. Food Agric. 11, 644-652.
Ratnayake W. N. and Ackman R. G. (1979a) Fatty alcohols in capelin, herring and mackerel oils and muscle lipids. I. Fatty alcohol details linking dietary copepod fat with certain fish depot fats. Lipids 14, 7955803. Ratnayake W. N. and Ackman R. G. (1979b) Fatty alcohols in capelin, herring and mackerel oils and muscle lipids. II. A comparison of fatty acids from wax esters with those of triglycerides. Lipids 14, 804810. Rouser G., Kritchevsky G. and Yamamoto A. (1976) Column chromatographic and associated procedures for separation and determination of phosphatides and glycolipids. In Lipid Chromatographic Analysis (Edited by Marinetti G. V.), pp. 713-776. Marcel Dekker, New York. Sargent J. R., McIntosh R., Baumeister A. and Blaxter J. H. S. (1979) Assimilation of wax esters of marine zooplankton by herring (&pea harengus) and rainbow trout (Sabno gairdnerii). Mar. Biol. 51, 203-207. Sarvala J., Aulio K., Mobi H., Rajasilta M., Salo J. and Vuorinen I. (1984) Factors behind the exceptionally high fish yield in the Lake Pyhajarvi southwestern Finlandhypotheses on the biological regulation of fish production. Aqua Fennica 14, 49-57. Sarvala J., Sainio J., Nevalainen J. and Vuorinen I. (1988) Population dynamic and production of Bosmina coregoni in a mesotrophic lake having high production of planktivorous fish. Verh. Internat. Vereing. Limnol. 23, 2067. Takahashi H. and Yamada M. (1976) Lipid composition of seven species of crustacean plankton. BUN. Jap. Sot. Scient. Fish. 42, 769-776.
Vijverberg J. and Frank Th. H. (1976) The chemical composition and energy contents of copepods and cladocerans in relation to their size. Freshwater Biol. 6, 3333345. Viljanen M. (1983) Food and food selection of cisco (Coregonus albula L.) in a dysoligotrophic lake. Hydrobiology 101, 1299138. Yu T., Sinnhuber R. 0. and Putnam G. 13.(1977) Effect of dietary lipids on fatty acid composition of body lipid in rainbow trout (Sabno gairdneri). Lipids 12, 490499.
Vol.
103A, No. 1, pp.205-212,
1992
~3~-9629~92 $5.00 + 0.00 Q 1992 Pergamon Press Ltd
COMPARISON OF LIPID AND FATTY ACID COMPOSITION IN VENDACE (COREGONUS ALBULA AND AVAILABLE PLANKTON FEED REINO R. LPIKO,*~
MARJUT RAJASILTA$
and
RAIMO
L.)
HILTUNEN§
*Laboratory
of Food Chemistry, Department of Chemistry and Biochemistry, University of Turku, SF-ZOSOOTurku, Finland. Tel.: (358) 921645701; ftaboratory of Ecology and Morphology, Department of Biology, University of Turku, SF-20500 Turku, Finland; $Department of Pharmaceutics, University of Helsinki, SF-00170 Helsinki, Finland (Received 20 January 1992) Abstract-l. The food of vendace in Lake Pyhijijlrvi (SW Finland) consisted mainly of cladocerans and copepods throughout the sampling period from May to October. 2. The content of triacylglycerols and polar lipids of vendaee flesh, varied seasonally, in accordance with the total lipids. Triacylglycerols dominated in vendace flesh, while these and polar lipids occurred in nearly equal proportions in composite plankton. In vendace gut, the share of polar lipids decreased markedly. 3. Plankton and vendace flesh total lipids were composed of the same fatty acids. Their reiative amounts varied, especially in poiyenoic acids and in the ratio of w-6 and w-3 polyenoics. 4. The fatty acid composition of fish flesh lipids remained fairly similar throughout the whole sampling period with a slight seasonal variation of some fatty acids occurring in plankton total lipids.
INTRODUCTION
Vendace (Coregonus afbula L.) is the most important fish caught professionally in the lakes of Finland. Lake Pyhgjijiirvi, in Sakyla, which is the study area of the present work, is well known for its exceptionally high fish production (mean annual catch over the last 20 years = 63 kg/ha/year; cf. Sarvala et al., 1984). Vendace and whitefish (Coregonus iavaretus ~1.) are the most important species of the fish catch. A typical feature of the vendace population in this lake is that it consists of 0-2-year-old fish. Lipids and fatty acids of vendace flesh and roe of this fake have been studied earlier but only from fish collected during the spawning period in late autumn (Kaitaranta and Linko, 1979; Kaitaranta, 1980). The lipid classes were analysed only from fish roe. Previous studies carried out by e.g. Lasker and Theilacker (1962), Lambertsen and Myklestad (1972), Sargent et al. (1979), Ratnayake and Ackman (1979a,b), Linko et al. (1985) and Muje et al. (1989) have shown that the lipids of the feed organisms are of great importance in the fatty acid composition of fish lipids. The aim of the present work was to compare the lipid and fatty acid composition of vendace flesh with that of composite plankton sampled from lake Pyhajlrvi throughout May and October, which is the main feeding and growth period of vendace in the lake (Hehninen at al., 1990). The composition of plankton species was also monitored.
tTo whom correspondence
should be addressed.
MATERIALS AND METHODS
Study urea The study area of the present work, Lake PyhsjijPrvi in SiikyIl(61 “OS’N:22”2O’E)is a large (area 154 km2), shallow (mean depth 5.4 m) clear water (Secchi disc depth 3-4 m) lake in south-western Finland. The iake is mesotrophic, having a phytoplankton primary production of 4%56g C/m*/year (Jumppanen, 1986) and total herbivorous crustacean production of 5 g C/m’/year (Sarvala er al., 1988). The lake basin is open, having only a few islands. Due to its vast pelagial and shallowness, the water circulation is effective and no thermal stratification is found during summer. Water temperature varies normally between 0 and cry 20°C throughout May and October, the maximum occurring in July. Fish and plankton samples The samptes were collected between May 30 and October 2 in I985 Fish were caught by gifl nets during the night, put on ice immediately after landing and cold-transported to the laboratory within 2 hr. one-kilogram samples of vendace consisting of 15-20 fish were pooled at each sampling time. Fish were filleted and the skins removed. The filleted fish was minced and the meat thoroughly mixed, before taking the samples for the dry weight determinations (A.O.A.C. method No. 43.233) and for the lipid extractions, Plankton was sampled at the same time as vendace hauling a 15Ofim Hensen net at a depth of O-3 m. The sample was brought to the laboratory in cold lake water. It was sieved through a 200 ym filter before analysis in order to eliminate phytoplankton, which is not used as food by vendace in the lake (~elminen et al., 1990). The zoopiankton remaining on the sieve was weighed and after careful mixing of the sample the aliquots were jmm~iateiy taken for dry weight dete~ination (see above) and for lipid extractions. The species composition of zooplankton was dete~ned by counting and identifying 2~300 indi~d~ls from a 205
REINOR.
206
subsample representing the sieved and mixed sample. The percentage of each species in the zooplankton biomass was calculated using values of total organic body carbon @gC) (unpublished data of J. Sarvala; Dept. Biology, University of Turku). In some vendace samples the gut content of half of the fish was pooled and mixed thoroughly for determining its dry matter content (see above) and for the extraction of the lipids. The composition of the food of the fish was examined by mixing the gut contents of the other half of the fish sample (10-I 5 individuals) in ethanol solution and analysing the food items from the subsample as above. The dates of sampling the fish and plankton are shown in the accompanying tables. Lipid fractionations and fatty acid analysis The lipids were extracted from both fish and plankton by the method of Bligh and Dyer (1959). The extracts were concentrated under vacuum and dried under nitrogen. The remaining total lipids were weighed and redissolved in CHCl, and stored under nitrogen at -25°C until analysed. Part of the total fish lipids were resolved into phospholipid and triacylglycerol fractions. Silicic acid column chromatography was applied to separate neutral and phosphoIipids. The absorbent was pretreated as described by Kaitaranta (1980) and the two lipid fractions were eluted from the column according to Rouser er al. (1976). The phospholipid fraction was concentrated and stored as with the total lipids. Triacylglycerols were separated from the total lipids by means of thin-layer chromatography (TLC) using silica gel plates (DC-Alufolien Kieselgel 60, Merck AC Art. 5553): The plates were developed in a mixture of hexane-diethyl ether-acetic acid (85: 15: l.S, by vol.). The resolved triacylglycerol bands were scraped from the plates and extracted successively with a mixture of chloroform and methanol (1: 1 v/v) and methanol. The triacylglycerol fraction was concentrated and stored as with the total lipids. The lipid class determinations were performed from the total lipids of fish flesh, gut content and plankton using quantitative thin-layer chromato~aphy-flame ionization detection (TLC-FID). Lipid classes were separated on Chromarod-S-II rods with a coating of silica gel using a mixture of hexane-diethyl ether-acetic acid (80: 6:0.5, by vol.) as a deveioping solvent. The quantitation was obtained using an Iatroscan TH-10 Analyzer (Iatron Laboratories Inc., Japan) as described in detail by Kaitaranta (1980). The fatty acids of the total lipids, phospholipid and triacylglycerol fractions were converted to their methyl esters according to the method of IUPAC (1979). The purified esters were analysed by glass capillary GLC on a OV-351 column (25 m long and 0.32 mm id.) as described in a previous paper (Kaitaranta and Linko, 1984). RESULTS
The cladoceran species Holopedium gibbet-urn predominated in the zooplankton collected in June (Table 1). Calanoida copepodids and adult (mainly Heterocope appendiculata) and cladocerans Bosmina and Daphnia made up the rest of the zooplankton biomass. In July and early August, the zooplankton consisted primarily of Daphnia species (70-90% of biomass). Later, in autumn, the biomass of cyclopoid copepodids and adults increased, although other copepodids (Eudiaptomus and Heterocope) and cladocerans Chydorus, Daphnia and Bosmina were also abundant. Vendace fed on zooplankton throughout summer. Cyclopoid copepodids and adults were the most important food source at the end of May. In June,
LINKO et
al.
fish fed primarily on Bosmina (90% of the total number of prey taken) but also took some Holopedium (8%) and Daphnia (1%). In July, the food consisted of copepods (75%) and Bosmina (22%), which were again, in August, the most numerous prey (48 and 48% respectively). Dry matter and fat content
The dry matter and total lipid content of vendace flesh, gut content and plankton are shown in Fig. 1. Remarkable changes occurred in the dry weight of the fish flesh during the summer and early autumn. Flesh contained 22% dry matter at the end of May, gradually rising to 25.5% at the beginning of August, maintaining roughly the same level up to early September, after which decreasing rather sharply to 22.1% at the beginning of October. These variations in the dry matter content of fish flesh depend mainly on the lipids, which accumulate into the musculature during the summer and are mobilized before reproduction in October (Fig. 1). The total iipid content of the flesh was highest (4.9% of the fresh weight) at the end of August and lowest (2.1-2.2%) in the late spring (May) and early autumn vetoer) with one exception (27 June; 1.5%). The eqcipment used for the collection of plankton samples enabled the gathering of only small amounts of biomass for the analysis. Thus, it was not possible to determine the dry matter, and even total lipid content, of all samples. However, the results obtained clearly show that the dry weight, as well as the total lipid content, although being at a low level, behaved quite opposite to those in fish samples concerning their dependence on time of year. Thus, there were more dry matter and total lipids in plankton samples collected in spring and autumn than in those collected in the early and middle summer (Fig. 1). The few analyses made at random on the gut content of vendace indicated that the dry matter and total lipid content of the plankton biomass were concentrated 20-30-fold when transported into the gut of fish (Fig. 1). Lipid composition
The average lipid class composition of vendace flesh, gut content and plankton is shown in Table 2. The extracted total lipids were separated with TLCFID into their major lipid fractions, the polar lipids, triacylglycerols and steroh. The polar lipids were not sub-divided further but analysed as one group. The major lipids in vendace flesh are triacylglycerols (66-86%), followed by pofar lipids (12-30%) and sterols (l-4%). The relative proportions of different lipid classes in the fish flesh varied significantly over the S month sampling period. The greatest, and quite opposite, changes were found in the percentage of triacylglycerols and polar lipids. Triacylglycerols accumulated in the musculature as a depot fat from the end of May to the middle of July, but decreased slowly thereafter, being at the same percentage level at the beginning of October as in the late spring. On the other hand, the relative proportions of the polar lipids were highest in fish samples collected in May and in October and lowest in the middle of Juty. However, the total lipid content of the fish flesh increased from May till the
Lipids and fatty acids in vendace and plankton Table I. Composition of zooplankton (% Species
June 21
73 18 4 _
46 I7 2 -
Holopedium Daphnia Bosmina Chydorus Ceriodaphnia Diaphanosoma Polyphems Leptodora Calanoida c&a Cyclopoida c&a CoDeooda nau~l.
W)
_ + + +
Aug. 14 (%)
88 + _ -
71 _
+ -
_ 7
A
w
5
n --_ 0
2
E
I--
;
n -,
JUNE
m.‘\
0. i
_
__--
__--
JULY
__--
,
‘I--ii ____-___
JUNE
JULY
I
2i _ _
the study period
Aug. 20 W) _
Sept. 5 (OhI -
Oct. 2 W)
8 I 4 + 2 _ _
6 2 12 -
9 20 8 _ _ _ _
65 21 +
IO 70 -
35 27 +
_
stage; + = < I %; - = not found.
25
&
-
_ _
+ II -
end of August, after which it declined (Fig. 1). Thus, if the amounts of triacylglycerols and polar lipids are calculated from the fresh weight of the fish flesh, it is observed that the maximum value (3.7%) of the former lipid fraction was not achieved until August and that (1.1%) of the latter fraction at the same time. The zooplankton of Lake PyhgjijBrvicomprised the same lipid fractions as vendace flesh (Table 2). In some plankton samples small amounts of free fatty acids (under 1% of the total lipids) were found. However, there were much more polar lipids in plankton than in fish flesh. The relative amounts of polar lipids and tricylglycerols in plankton were at about the same level, 45-51% and 41-51% respectively, excluding the values of one sample. The content of sterols varied from 2% to 8% of total lipids.
0
in the lake samples during
July 15 (%) _
3+4 -
4
a = adult; c = copepodid
of fresh weight)
June 17 (“/J
207
w-_,
AUG.
k------’
I
SEPT.
I
OCT.
,m“,-¤ AUG.
I
SEPT.
I
OCT.
Fig. 1. Dry matter (A) and total lipid (B) content of vendace flesh (a), gut content (A) and of plankton (B) in Lake Pyhiijiirvi at different times of year. Vertical bars indicate the standard deviation of the samples when ~0.04.
The same three major lipid components as above were also found in the gut content of vendace (Table 2). In comparison to the plankton lipids the percentage share of the polar lipids in the gut content was remarkably lower, which bears out their primary utilization as fishfood. Fatty acid composition
The relative proportions of 30 fatty acids of different lipid extracts, fractions of vendace flesh and of plankton (see above) were determined. Twenty-four of these fatty acids, which constitute over 90-95% of the total fatty acids, are listed in Tables 3-6. In the total lipids of vendace flesh, 10 major fatty acid components were found. These are: myristic (14:0), palmitic (16:0), palmitoleic (16:107) oleic (18:1w9), linoleic (18:2w6), arachidonic (20:4w6), (18 :4w 3), linolenic (18 : 30 3), octadecatetraenoic eicosapentaenoic (20 : 5w 3) and docosahexaenoic (22 :6w 3) acids (Table 3). The share of these acids was over three-quarters of the total fatty acid content. The proportions of the main fatty acid components remained relatively similar throughout the whole 5 month sampling period (Table 3). The fatty acid composition of triacylglycerols, the depot fat of vendace flesh, behaved similarly with that of the total lipids concerning their time dependence (Table 4): moreover, their fatty acid compositions resembled each other. This is explained by the fact that triacylglycerols constitute the major share of vendace total lipids (Table 2). However, triacylglycerols contain distinctly lower amounts of docosahexaenoic acid than the total lipids. It depends on the latter also containing polar lipids rich in docosahexaenoic acid (cf. Table 5). Typical to the fatty acid composition of the polar lipids (phospholipids) of vendace flesh is the abundance of palmitic, docosahexaenoic and eicosapentaenoic acids and the shortage of monoenoic acids (Table 5). Table 6 shows that plankton total lipids are composed of the same fatty acids as those of vendace flesh. However, the relative amounts of the fatty acids differ distinctly between plankton and fish lipids. Thus, in plankton lipids were more myristic, linoleic, arachidonic and eicosapentaenoic acids, but less oleic, and especially docosahexaenoic, acids than in vendace flesh lipids. In the fish flesh docosahexaenoic acid enriches in triacylglycerols and especially in the polar lipid fraction, which suggests that chain elongation and desaturation of eicosapentaenoic acid
208
REINO
R.
LINKO et a/.
occurs in the fish organs. Also the fatty acid composition of the gut content of vendace indicates this kind of lipid metabolism (Table 6). The relative proportions of some fatty acids of plankton lipids fluctuate according to the season (Table 6). Thus, the percentage of myristic and octadecatetraenoic acids decreases gradually from spring to autumn, while that of the paimitoieic acid increases. DISCUSSION
Vendace is a selective planktivore and its diet consists mainly of ciadocerans and copepods, other groups of zooplankton being of minor importance (e.g. Viljanen, 1983). Analyses of gut contents made in the present study showed that the species food was largely the same as that of zooplankton collected for lipid analyses. Clodocerans (Bosmina and Duphniu) and cyciopoid and caianoid copepods (Eudiaptomus) are the preferred prey which make up the bulk of the total amount of food consumed by vendace in Lake Pyhajlrvi (Heiminen et al., 1990). Characteristic seasonal variations occur in the lipid contents of zooplankton and vendace flesh. The lipid content of plankton was highest in May but declined to a rather low level for the summer months. Although the lipid content followed changes in the biomass of copepods to some extent, the changes are hardly caused by differences in plankton composition. For example, Vijverberg and Frank (1976) found no differences in lipid concentrations of copepods and ciadocerans. Zooplankton is dependent on phytoplankton in its energy gain and thus, the lipid content may indicate some changes in primary production. The lipid content rose again at the beginning of autumn, when the share of copepods in the plankton increased. The lipid content of vendace flesh gradually increased during the summer reaching its peak at the end of August and diminishing rapidly thereafter. This is evidently connected with the development of the gonads. In Finland, rapid gonadal development of vendace starts in July-August (Lehtonen, 1981) and spawning begins on average at the end of October (Lind, 1976). Muje et al. (1989) have found the same trend in the total lipid content of the vendace muscle in two different lake types, oligotrophic Lake Suvasvesi and mesotrophic Lake Kaliavesi in eastern Finland. However, the relatively low lipid content of vendace caught from Suvasvesi and Kaliavesi as compared to that from Pyhajarvi in the present work is worthy of note. Lahti (1987) has also obtained low lipid levels in the vendace muscle from Lake Suvasvesi and Lake North-Konnevesi. However, there were differences in the total lipid content between the lakes which are due to limnological and planktonproductive differences in the lakes (Lahti and Lindqvist, 1986). In zooplankton from Lake Pyhaj&i there were only two major lipid classes, triacylglycerols and polar lipids, their relative proportions being nearly equal. The lack of wax esters is important, as it also reflects the lipid and fatty acid composition of vendace flesh. This coincides with the report of Takahashi and Yamada (1976) that in the freshwater milieu there is no organism comparable to
Lipids and fatty acids in vendace and plankton Table 3. The relative proportions Fatty acid --Total saturated Total straight chain 14:o 16:O 18:O Total monoenoic Total o9-series 16:109 18:Iw9 20:Iw9 Total oFseries I6:107 18;lw7 2O:lw7 Total polyenoic Total w6-series 18:2w6 18:3u6 20:206 20:3w6 20:4w6 22:4w6 22:506 Total w 3-series 18:3w3 l8:403 20:3w3 20:4oJ3 to: 503 21:5w3 22: 503 22:6w3 . _
209
of fatty acids of vendace flesh total lioids in Lake Pvhiiiarvi at different times of vear
30 May
4 June
17 June
27 June
I5 July
S Aug.
20 Aug.
5 Sept.
2 Oct.
24.9
25.9
27.5
23.8 6.6 14.0 2.2 16.4 7.2 0.1 6.9 0.4 9.2 6.9 2. i 0.2 51.3 10.5 3.8 0.6 0.4 0.2 3.0 0.5 2.0 40.8 6.0 7.8 0.3 1.8 8.7 0.4 1.9
24.8 8.3 13.4 I.7 16.4 6.2 0.2 5.9 0.3 10.0 7.8 2.0 0.2 50.6 9.3 3.8 0.6 0.3 0.2 2.6 0.3 1.5 41.3 6.8 10.2 0.3 I.8 9.3 0.3 1.5 11.1_
26.5 25.4 7.1 14.5 2.7 17.8 9. I 0.1 8.4 0.6 8.7 6.3 2.2 0.2 49.3 10.1 3.8 0.5 0.4 0.2 2.8 0.5 1.9 39.2 5.8 7.4 0.5 2.4 8.1 0.4 I.9 12.7
26.3 7.6 15.1 2.7 18.6 8.6 ND 8.2 0.4 10.0 7.4 2.5 0.1 49.9 10.7 3.8 0.6 0.4 0.3 3.0 0.5 1.9 39.2 5.7 8.1 0.4 2.0 9.1 0.4 1.9 11.6
27.9 26.7 7.2 15.5 3.1 19.5 10.0 0.1 9.4 0.5 9.5 6.8 2.6 0.1 46.9 10.6 3.7 0.6 0.4 0.3 3.2 0.6 1.6 36.2 5.0 7.2 0.4 1.9 8.2 0.4 1.5 11.7
27.1 25.9 6.8 15.5 2.9 19.2 9.8 0.1 9.2 0.5 9.4 6.8
27.1 27.3 7.1 16.1 3.2 21.5 11.7 0.1 11.0 0.6 9.8 7.0 2.7 0.1 51.4 12.1 4.2 0.6 0.5 0.3 3.6 0.7 2.2 39.3 5.4 7.2 0.4 2.1 8.9 0.4 2.0 12.9
27.8 27.1 6.8 16.3 3.1 20.8 10.4 0.1 9.8 0.5 10.4 6.9 3.4 0. I 52.0 11.7 4.0 0.6 0.4 0.2 3.7 0.6 2.2 40.3 5.3 7.1 0.4 I.9 8.9 0.4 2.1 14.2 0.3
27.6 26.4 6.4 15.9 3.3 19.6 10.4 0.1 9.7 0.6 9.2 6.4 2.7 0.1 54.0 12.9 4.2 0.6 0.4 0.3 4.3 0.7 2.4 41.1 5.1 6.5 0.4 I.9 9.1 0.4 2.5 15.2 0.3
of wax is also water 1986).
However, in the latter the polar lipids dominate over the triacylglycerols and free fatty acids. In vendace flesh the triacylglycerois and polar lipids were the main components. Polar lipids in fish tissues
rob/u3
;:: 47.0 IO.8 3.8 0.6 0.4 0.2 3.3 0.6 1.0 36.2 4.6 7.0 0.4 2.0 8.4 0.4 1.8 11.2
ND not detected.
marine esters. found milieu
copepods with respect to accumulation A similar situation as that in freshwater in the plankton lipids of the brackish of the Baitic Sea (Kaitaranta ef ol.,
Table 4. The relative proportions Fatty acid Total saturated Total straight chain 14:o 16:O 18:O Total monoenoic Total w9-series 16:109 18:109 20: 1~9 Total 0 7-series 16:11x7 I8:107 20: ICI? Total poiyenoic Total d-series 18:2w6 18:3w6 20: 206 20:3w6 20:4w6 22~4~6 22:506 Total w3.series 18:3u3 18:4w3 20: 303 20:4cu3 20: 5~3 21:503 22~503 22:603 ND: not detected.
of fatty acids of vendace flesh t~acyl~y~rois
in Lake Pyh&j;iiirviat different times of year
30 May
4 June
I7 June
27 June
15 July
5 Aug.
20 Aug.
5 Sept.
2 Oct.
27.6 26.2 8.5 13.7 2.5 20.1 8.7 0.2 8.0 0.5 Il.4 8.4 2.5 0.2 44.0 10.1 4.5 0.6 0.4 0.2 2.5 0.3 1.6 33.9 6.6 8.1 0.3 1.7 7.6 0.4 1.7 7.5
28.0 26.9 9.3 13.7 2.0 IQ.4 7.8 0.2 7.3 0.3 11.6 9.2 2.4 ND 46.0 9.2 4.5 0.3 0.3 0.1 2.4 0.3 I .4 36.8 7.2 10.0 0.2 1.6 8.5 0.3 1.5 7.5
26.3 25.2 8.7 13.3 2.1 19.5 9.1 0. I 8.5 0.5 10.4 8.0 2.3 0.1 50.0 9.7 4.4 0.3 0.4 0.2 2.5 0.3 1.6 40.3 7.0 9.7 0.5 2.2 8.7 0.5 2.0 9.7
25.6 24.3 8.2 12.9 2.3 19.2 8.2 0.2 7.7 0.5 11.0 8.2 2.3 0.5 47.4 9.6 4.0 0.7 0.4 0.2 2.7 0.3 1.3 37.8 6.4 9.8 0.4 2.0 9.1 0.4 1.7 8.0
28.1 26.8 9.4 14.1 2.5 20.2 9.6 0.1 9.2 0.5 10.6 8.1 2.4 0.1 43.9 9.4 3.9 0.4 0.4 0.2 2.9 0.3 1.3 34.5 6.0 9.1 0.3 1.8 8.0 0.4 1.6 7.3
28.2 27.0 1.7 15.3 3.1 21.4 10.9 0.1 10.3 0.5 10.5 7.1
27.0 26.2 8.3 14.2 2.6 21.5 11.0 0.1 10.4 OS 10.5 8.0 2.4 0.1 52.6 11.6 4.5 0.7 0.4 0.3 3.4 0.4 1.8 41.0 6.6 9.1 0.6 2.3 9.8 0.5 2.2 9.9
27.3 26.9 8.3 14.6 2.7 21.7 10.9 0.1 10.3 0.5 10.8 7.8 2.9 0.1 51.2 11.6 4.5 0.7 0.4 0.3 3.5 0.4 1.8 39.6 6.3 9.3 0.5 2.0 9.4 0.4 2.0 9.7
27.0 26.2 8.1 14.3 3.1 23.0 11.0 0.2 10.2 0.6 12.0 7.8 4.0 0.2 59.6 13.1 5.2 0.7 0.4 0.4 3.8 0.6 2.0 31.5 6.0 8.0 0.5 2.0 8.7 0.4 2.3 9.6
::: 44.1 10.4 4.1 :1: 0:2 3.1 0.3 1.6 33.7 5.4 1.7 0.4 1.7 8.7 0.4 1.8 8.1
210
REINO R. LINKO et al. Table 5. The relative proportions Pyhlilrvi Fatty acid Total saturated 12:o 14:o 15:o 16:O 18:O Total monoenoic Total w9-series 16:lw9 18:lw9 Total o7-series 16:lw7 18:lw7 Total polyenoic Total wb-series 18:206 18:306 20:2w6 20: 3~6 20:4w6 22:4w6 2215~6 Total w 3-series 18:3w3 18:4w3 20:3w3 20:4w3 20:5w3 21:5w3 22:5w3 22~603
of fatty acids of vendace flesh polar lipids in Lake at different times of year
4 June
17 June
27 June
15 July
5 Aug.
28.3 I.1 3.1 2.7 19.2 2.2 7.0 5.3 I .4 3.9 1.7 0.1 1.6 65.3 10.3 1.5 0.2 0.2 0.2 4.2 0.3 3.7 55.0 2.6 1.9 0.3 1.5 10.3 0.3 I.7 36.4
25.6 ND 2.4 0.4 20.3 2.5 6.8 5.0 1.3 3.7 I.8 0.1 1.7 67.7 10.2 1.6 ND ND ND 4.7 ND 3.9 57.5 2.4 I.3 0.3 I.7 10.2 ND 1.9 39.7
26.7 0.3 2.0 0.4 21.7 2.3 7.7 5.9 1.0 4.9 1.8 0.1 1.7 65.7 12.0 1.3 0.1 0.2 0.2 5.2 0.6 4.4 53.7 1.7 I.2 0.2 1.4 9.9 0.2 2.1 37.0
28.8 0.2 1.7 0.4 24.1 2.4 7.3 5.7 1.0 4.7 2.1 0.1 2.0 63.4 II.6 1.2 0.1 0.2 0.2 5.1 0.4 4.4 51.8 1.3 0.9 0.2 1.0 9.6 ND 1.8 37.0
31.0 ND 1.5 0.3 26.2 3.0 7.3 5.4 0.8 4.6 I .9 ND 1.9 61.5 II.1 1.2 0.1 0.2 0.2 5.1 0.4 3.9 50.4 1.4 1.0 0.3 1.0 9.1 ND 1.6 36.0
ND: not detected.
are mainly composed of phospholipids and function as structural lipid while triacylglycerols are usually considered to be depot fat (Ackman et al. 1980). It is Table 6. The relative proportions
Fatty acid Total saturated Total straight chain 14:o 16:0 18:0 Total monoenoic Total o9-series 16:109 18:109 20:109 Total w7-series 16:lw7 lS:lw7 2O:lw7 Total polyenoic Total w6-series 18:206 18:306 20:2w6 20:3w6 20:406 22~406 22: 5~6 Total o3-series 18:303 18:403 20:303 20:4w3 20:5w3 21:5w3 22:503 22:6w3 ND: not detected.
significant that fatty alcohols and wax esters were not detected in vendace lipids. There were in vendace flesh on average three times more triacylglycerols
of fatty acids in total lipids of composite plankton times of year 30 May
I7 June
30.2 29.8 12.8 13.5 3.0 8.9 3.6 0.1 3.4 0.1 5.3 3.8 1.4 0.1 59.0 16.7 6.7 0.9 0.2 0.2 7.6 0.1 1.0 42.9 6.7 12.8 ND 0.6 18.0 0.4 0.2 4.2
28.6 27.1 11.5 II.9 2.6 12.2 4.2 0.1 3.9 0.2 8.0 6.5 I .4 0.1 48.2 13.4 5.1 0.9 0.1 0.2 6.3 0.1 0.7 34.8 5.1 11.4 ND ND 14.4 0.3 0.3 3.7
Plankton 27 June 20 Aug.
-
34.8 33.3 14.4 14.1 2.9 9.9 3.8 0.1 3.6 0.1 6.1 4.6 1.4 0.1 51.0 15.4 6.8 0.9 ND 0.1 6.8 ND 0.8 35.6 6.2 10.2 ND 0.4 14.7 0.3 0.2 3.6
29.1 28.6 8.1 15.8 4.1 12.9 4.7 0.1 4.4 0.2 8.2 5.1 3.0 0.1 58.0 19.7 6.2 I .o 0.3 0.2 6.5 0.1 5.4 38.3 6.1 6.9 0.1 1.0 12.1 0.2 0.8 II.1
and of vendace gut content in Lake PyhijijBrvi at different
5 Sept.
2 Oct.
27.4 26.9 7.8 14.6 3.5 21.4 4.9 0.2 4.4 0.3 16.5 12.7 3.1 0.1 51.4 15.4 3.9 1.1 0.2 0.3 6.2 0.2 3.5 36.0 5.0 6.0 0.2 1.2 14.8 0.2 0.8 7.8
25.4 25.2 7.1 13.8 2.2 31.1 4.7 0.4 4.1 0.2 26.4 23.5 2.9 ND 43.6 12.6 3.3 3.1 0.1 0.2 3.7 ND 2.2 31.0 3.5 5.0 0.1 0.7 16.0 0.1 0.6 5.0
Vendace gut content I7 June Z 27 June I5 July 30.2 28.9 9.5 14.4 3.3 15.3 7.2 0.1 7.0 0.1 8.1 6.1 1.9 0.1 45.1 10.7 4.4 0.7 ND 0.3 3.6 0.2 1.5 34.4 6.6 6.6 0.6 1.6 9.3 0.4 1.2 8.1
28.4 27.1 9.0 14.1 3.1 17.7 6.4 0.1 6.1 0.2 II.3 7.3 3.9 0.1 45.8 10.8 4.4 0.6 ND 0.2 3.7 0.3 1.6 35.0 5.7 8.9 0.6 1.5 9.6 0.4 1.2 7.1
26.4 25. I 7.7 13.6 2.9 19.0 9.4 0.1 8.9 0.4 9.6 6.8 2.7 0.1 46.4 10.9 3.7 1.3 ND 0.2 3.9 0.3 I.5 35.5 5.6 8.2 0.3 1.8 9.7 0.4 1.4 8.1
211
Lipids and fatty acids in vendace and plankton
than polar lipids. Their content calculated from the fresh weight of fish varied seasonally in accordance with the total lipids. In Baltic herring flesh the seasonal variation of the total lipids coincides with that of depot fat (Link0 et al., 1985). In many other freshwater fish the flesh contains low quantities of triacylglycerols and a relatively high proportion of phospholipids (Kinsella et al., 1978). When the lipid composition of vendace gut content is compared with that of plankton, a marked decrease of polar lipids is found. This points to the activity of phosphohpases in the gut content (Olley and Lovern, 1960) although it has been shown that in fish nonspecific intestinal lipase also hydrolyses triacylglycerols (Cowey and Sargent, 1977). Fifty fatty acid components of vendace flesh lipids were identified earlier by GLC-MS (Kaitaranta and Linko, 1979; Kaitaranta, 1980). Fish were caught from Lake Pyhiijarvi as in the present study, when the proportions of 30 fatty acids from fish and plankton lipids were determined. The data indicate that the vendace flesh total lipids contained about 40% eicosa~ntaenoic and docosahexaenoic acid of the total polyunsaturated acids, which fitted weil into the typical limits, 30-40%, set for freshwater fish polyenoics (Kinsella et al., 1977). Of further interest to human nutrition is the relatively high content of linoleic, linolenic and arachidonic acids in the lipids of vendace, which is also characteristic for freshwater fish (Gruger et al., 1964; Chetty et al., 1989). In addition, the total amount of polyenoic acids in vendace lipids rose to over 50%. The ratio w6/w3 of polyunsaturated acids was 0.3 in vendace total lipids, which coincides with that (0.3-0.4) of freshwater fish. On the other hand, in sea-fish of the northern hemisphere the ratio is 0.1 and in some warm sea water fish the ratio is approaching 0.9 or even above 1, owing to the high amounts of arachidonic acid (Gibson, 1983; Gibson et al., 1984). Vendate lipids contained 20: 1~7 and 20: 109 eicosenoic acid isomers in only very minor proportions and docosenoic acids (22: 1) were not found at all. This can be understood on the basis of the lipid composition of its plankton feed. In this respect, vendace lipids resemble also those of the organisms in freshwater milieu (Kinsella et al., 1977; Ackman er al., 1980). On the contrary, the depot fats of many sea-fish in the northern hemisphere contain fairly large amounts of 20: 109 eicosenoic and 22: lo 11 docosenoic acid isomers, which, plausibly, are derived from their diet (Ratnayake and Ackman, 1979a,bf. These fatty acids have been observed to cause some adverse physiological changes in animal experiments. The relative proportions of fatty acids in vendace flesh lipids remained quite unchanged throughout the summer and early autumn. Moreover, the values coincide well with those found earlier in a very large sample of mature female vendace by Kaitaranta (1980). In the latter study the fatty acid patterns of the lipid fractions from flesh and roe were also found to be similar to each other. These findings confirm the report of Agren et al. (1987), that in vendace muscle tissue the fatty acid spectrum remains unchanged in relation to the reproductive cycle. However, the fatty acid composition of vendace flesh total lipids given by Agren et al, (I 987)
and Muje et al. (1989) deviates greatly from that found in the present study. On the other hand, it resembles the fatty acid pattern of the polar lipids with an abundance of 22 : 6~3 and 16:O acids and shortage of monoenoic acids. The rather low lipid content of vendace from the lakes of eastern Finland reflects also the dominance of poiar lipids in fish flesh (cf. Kin&la et al., 1977, 1978). The fatty acid composition of the total lipids of zooplankton from Lake Pyh~j~~i and also from mesotrophic Lake Kallavesi was rather similar (Muje et al. 1989). The 20503 acid was the major component, but there were also relatively large amounts of 18:303, 18:4w3, 22:603, 18:206 and 20:4w6 acids. The plankton lipids of Lake Suvasvesi contained in addition somewhat more 22 : 6w 3 acid than those mentioned above (Muje et al., 1989). A slight seasonal variation in the proportions of some fatty acids may depend on the fluctuation of water temperature (cf. Farkas, 1979). On the other hand, 20: 503 and 22: 6~03 acids dominated in the lipids of zooplankton collected from the Baltic Sea off the south-west coast of Finland (Kaitaranta et ai., 1986) as their lipids were composed mainly of phospholipids. Nevertheless, some distinguishing features also exist in the fatty acid compositions of small copepods and wax esters containing larger euphausiids and copepods of marine origin (cf. Kaitaranta et a/., 1986). The results of the present study suggest that the alkyl chains of plankton fatty acids are transferred to the vendace flesh lipids without major modifications. However, differences in the relative proportions of some fatty acids between fish flesh and plankton lipids indicate that fish may alter their overall depot fat composition to suit their particular needs. Thus, chain elongation and desaturation of fatty acids may occur in fish organs, which is retlected in the results of anaiyses of the fish gut content. Yu ef al. (1977) suggested that a mechanism exists in fish which regulates and maintains certain levels of body lipid saturation. Acknowledgements-The authors express their sincere thanks to Kirsi Karkinen for technical assistance. This study was supported by a grant from Turun Yliopistosaltio, Finland. REFERENCES Ackman R. G., Sebedio J.-L. and Kovacs M. J. P. (1980) Role of eicosenoic and docosenoic fatty acids in freshwater and marine lipids. Mar. Chem. 9, 157-164. Agren J., Muje P.. Hiinninen O., Herranen J. and Penttill I. (1987) Seasonal variations of lipid fatty acids of boreal freshwater fish species. Camp. Biochem. Physiol. 888, 905-909. Bhgh E. D. and Dyer W. J. (1959) A rapid method of total lipid extraction and purification. Can. J. Biochem. Physiol. 37, 911-917. Chetty N., Reavis S. C., Immelman A. R., Atkinson P. M. and Van As J. G. (1989) Fatty acid comoosition of some South African freshwater fish. Samj 76,‘368-370. Cowey C. 8. and Sargent J. R. (1977) Lipid nutrition in fish. Comp. Eiochem. Physioi. 57B, 269--273. Farkas T. (1979) Adaptation of fatty acid compositions to temperature-a study on planktonic crustaceans. Camp. Biochem. Physiol. MB, 71-76.
212
REIN0
R. I
Gruger E. H. Jr., Nelson R. W. and Stansby M. E. (1964) Fatty acid composition of oils from 21 species of marine fish, freshwater fish and shell fish. J. Am. Oil Chem. Sot. 41, 662-667. Gibson R. A. (1983) Australian fish-An excellent source of both arachidonic acid and omega-3 polyunsaturated fatty acids. Lipids 18, 743-752. Gibson R. A., Kneebone R. and Kneebone G. M. (1984) Comparative levels of arachidonic acid and eicosapentaenoic acid in Malaysian fish. Comp. Biochem. Physiol. 18, 325-328.
Helminen H., Sarvala J. and Hirvonen A. (1990) Growth and food consumption of vendace Coregonus albula (L) in Lake Pyhajarvi, SW Finland: a bioenergetics modelling analysis. Hydrobiologia 200/201, 51 I-522. IUPAC Applied Chemistry Division, Commission on Oils, Fats and Derivatives (1979) Preparation of fatty acid methyl esters. In Standard Methods for the Analysis of Oils, Fats and Deriuatiues, method II D.19, 2.301. pp. 96-102. Pergamon Press, Oxford. Jumppanen K. (1986) Sakyliin Pyhiijarven ainetaseet, veden laatu ja kasviplanktonin perustuotanto v. 1985. Lounais-&omen l-25.
Vesiensuojeluyhdistys
r.y.
julk.
29,
Kaitaranta J. K. (1980) Lipids and fatty acids of a whitefish (Coregonus albula) flesh and roe. J. Sci. Food Agric. 31, 130331308.
Kaitaranta J. K. and Linko R. R. (1979) Fatty acids of a whitefish (Coregonus albula) flesh lipids. J. Sci. Food Agric. 30, 921-926.
Kaitaranta J. K. and Linko R. R. (1984) Fatty acids in the roe lipids of common food fishes. Comp. Biochem. Physiol. 19B, 331-334.
Kaitaranta J. K., Linko R. R. and Vuorela R. (1986) Lipids and fatty acids in plankton from the Finnish coastal waters of the Baltic Sea. Comp. Biochem. Physiol. 85B, 427433.
Kinsella J. E., Shimp J. L., Mai J. and Weihrauch J. (1978) Lipids in fish fillets: changes following cooking by different methods. J. Food Sci. 43, 1669-1674. Kinsella J. E., Shimp J. L. and Weihrauch J. (1977) Fatty acid content and composition of freshwater finfish. J. Am. Oil Chem. Sot. 54, 424429.
Lahti E. (1987) Total lipid and cholesterol contents of liver and muscle in some fish species, especially vendace (Coregonus albula L.) in Finland. Arch. Hydrobiol. 110, 133-142.
Lahti E. and Lindqvist 0. V. (1986) Seasonal and area1 differences in the thyroid histology of the vendace (Coregonus albula L.) in fresh and brackish waters in Finland. Arch. Hydrobiol. 106, 487496.
Lambertsen G. and Myklestad H. (1972) Lipider i Rauate (Calanusfinmarchicus) en viktig naeringskilde for sild og lodde. In Proceedings of 6th Nordic Fat Symposium, GrenH 1971, pp. 83-91. Lasker R. and Theilacker G. H. (1962) The fatty acid composition of the lipids of some Pacific sardine tissues
in relation to ovarian maturation and diet. J. Lipid Res. 3,6&64.
Lehtonen H. (1981) Biology and stock assessment of Coregonids by the Baltic coast of Finland. Finn. Fish. Res. 3, 31-83. Lind E. A. (1976) Riippuvuus Ympiiristiitekijiiistd Ja Lajinsisiiiset Suhteet
Eriiissii Suomen
Muikkupopulaatioissa.
Univ. Oulu, pp. l-109. Linko R. R., Kaitaranta J. K. and Vuorela R. (1985) Comparison of fatty acids in Baltic herring and available plankton feed. Camp. Biochem. Physiol. 82B, 699-705. Muje P., Agren J. J., Lindqvist 0. V. and Hlnninen 0. (1989) Fatty acid composition of vendace (Coregonus albula L.) muscle and its plankton feed. Camp. Biochem. Physiol. 92B, 75-79.
Olley J. and Lovern J. A. (1960) Phospholipid hydrolysis in cod flesh stored at various temperatures. J. Sci. Food Agric. 11, 644-652.
Ratnayake W. N. and Ackman R. G. (1979a) Fatty alcohols in capelin, herring and mackerel oils and muscle lipids. I. Fatty alcohol details linking dietary copepod fat with certain fish depot fats. Lipids 14, 7955803. Ratnayake W. N. and Ackman R. G. (1979b) Fatty alcohols in capelin, herring and mackerel oils and muscle lipids. II. A comparison of fatty acids from wax esters with those of triglycerides. Lipids 14, 804810. Rouser G., Kritchevsky G. and Yamamoto A. (1976) Column chromatographic and associated procedures for separation and determination of phosphatides and glycolipids. In Lipid Chromatographic Analysis (Edited by Marinetti G. V.), pp. 713-776. Marcel Dekker, New York. Sargent J. R., McIntosh R., Baumeister A. and Blaxter J. H. S. (1979) Assimilation of wax esters of marine zooplankton by herring (&pea harengus) and rainbow trout (Sabno gairdnerii). Mar. Biol. 51, 203-207. Sarvala J., Aulio K., Mobi H., Rajasilta M., Salo J. and Vuorinen I. (1984) Factors behind the exceptionally high fish yield in the Lake Pyhajarvi southwestern Finlandhypotheses on the biological regulation of fish production. Aqua Fennica 14, 49-57. Sarvala J., Sainio J., Nevalainen J. and Vuorinen I. (1988) Population dynamic and production of Bosmina coregoni in a mesotrophic lake having high production of planktivorous fish. Verh. Internat. Vereing. Limnol. 23, 2067. Takahashi H. and Yamada M. (1976) Lipid composition of seven species of crustacean plankton. BUN. Jap. Sot. Scient. Fish. 42, 769-776.
Vijverberg J. and Frank Th. H. (1976) The chemical composition and energy contents of copepods and cladocerans in relation to their size. Freshwater Biol. 6, 3333345. Viljanen M. (1983) Food and food selection of cisco (Coregonus albula L.) in a dysoligotrophic lake. Hydrobiology 101, 1299138. Yu T., Sinnhuber R. 0. and Putnam G. 13.(1977) Effect of dietary lipids on fatty acid composition of body lipid in rainbow trout (Sabno gairdneri). Lipids 12, 490499.