The proximate and fatty acid composition of some estuarine crustaceans

Estuarine and Coastal Marine Science (1976) 4, 215-224

The Proximate and Fatty Acid Composition of some Estuarine Crustaceans

J. W. Moore” School of Biological Sciences, University of Bath, BAz 7A Y, England Received 3 January 1975 and in revised form 22 May I975

The lipid content of Crangon crangon, Gammarus salinus, Neomysis integer, Praunus flexuosus and Orchestia gammarella collected from the reservoir of the Oldbury power station on the Severn Estuary ranged from 25 to 33% of the dry weight over the course of one year while the corresponding values for ash averaged 1924%. Water accounted for 75-80% of the wet weight except in the case of 0. gammarella (70%). The unusually high lipid values were probably connected with the highly favourable environmental conditions in the reservoir while both the size and reproductive condition of the animals were also important in determining the size of the lipid store. Phospholipids accounted for as much as 33% of the total lipid in C. crangon and for as little as 24% in N. integer and P. flexuosus. The predominant fatty acids in both the neutral and phospholipids of all species were 16 : o, 18 : I, 20 : 5 and 22 : 6.

Introduction Although crustaceans form an integral part of the energy cycle of estuaries (Moore & Moore, 19764 b), the literature dealing with the chemical composition of many of these animals is comparatively restricted. In a number of mysid species, for example, data are based on samples collected at only one time of the year (Linford, 1965; Seguin, 1968), while in the case of several common amphipods and decapods information of even a more general nature is not available. The only exception to the above trend is provided by Neomysis integer (Leach), a species which, through the work of Raymont et al. (1966) Morris (1971, 1973) and Morris et al. (1973), has become well known. The purpose of this paper was therefore to describe changes in the relative amounts of total and phospholipid, water and ash (i.e. proximate analysis) in the most common crustaceans in the Severn Estuary over the course of one year. Some additional data on the fatty acid composition of both the neutral and phospholipids of these animals are also presented.

Materials and methods Representatives of the decapod Crangon crangon (L.) the amphipod Gammarus salinus and the mysids Neomysis integer (Leach) and Praunus jlexuosus (Miiller) were collected with a plankton net (mesh size, 0.8 mm) at monthly intervals during December 1973 and most of 1974 from the intake current of the Oldbury-on-Severn nuclear power station (Lat. 51’39’; Long. 2”34’) as outlined in Moore & Moore (1976a). Additional samples Spooner,

“Present address: Environment Canada, P.O. Box 2310, Yellowknife, Northwest Territories, XOE IHO Canada.

a16

J. W. Mooye

TABLE I. Grouping of the crustaceans according ductive condition for proximate analyses

Crangon crangon (I) 2'0-4.0 (2)4.x-6.0 (3) >6.0,

females in berry

(4) >;e;r;ddn;,males(4)

Gammarus salinus (I)

0’2-0’5

(2) 0.6-1.0 (3) 1.1-1.5

Neomysis integer (I)

0’5-1.0

(2) 1'1-1'5 (3) 1.6-2.0,

males and females

1.6-2.0

to length

(cm), sex and reproOrchestia gammarella

Praunus flexuosus (I)

1’0-1’5

(I)

0'2-0'5 o&1.0

(2) 1.6-2.0

(2)

(3)

(3) 1’1--r’5,

males and fzmales

2’1-2’5,

males and females (4) 1.6-2.0, males and females

(5) >6.0, males

of the semi-terrestrial amphipod O~chestiagammayella (Pallas) were collected at the same time by hand in the immediate vicinity of the power station. All animals were returned immediately to the laboratory and grouped as outlined in Table I with lengths being taken from the tip of the rostrum to the insertion of the telson. After blotting the animals lightly with tissue, their wet weight was determined and they were then dried by sublimation in a LeyboldHeraeus GT 2 type freeze drier. Total lipids in samples of about 5 g in the caseof C. crangon and I g in the other species were extracted by leaving the material overnight in IOO ml chloroform : methanol (2 : I, v : v) foIlon-ed by homogenization of the entire sample for 3 min. The organic solvents were then evaporated using a Buchler Rotary-Evapomix and the lipid extract was dried to constant weight by sublimation. The phospholipid fraction of each species was determined by ashing duplicate lipid aliquots of 1.5 mg with sulphuric and perchloric acids (3 : 2, v : v), estimating the total weight of phosphorus and multiplying the value by 25 (Hunter & Rose, 1972). The fatty acids of both the phospho- and neutral lipids in only the largest size class of each organism were determined as outlined in Moore (1975~). Samples of each species weighing I g (5 g in C. crangon) were ashed at 550 “C for 24 h. The intake of the Oldbury nuclear power station is drawn from a reservoir built out over the intertidal flats and flooded at least 8 h per day during periods of high tide. Bottom deposits in and around the reservoir consist mainly of organically rich sand with few if any macrophytes. The alga1 content of the reservoir water was determined at monthly intervals by filtering one litre of water through a Millipore membrane (0.45 pm) and examining the filtrate at a magnification of 400~. The amount of suspended solids in the reservoir was estimated by drying a Millipore membrane (0.45 pm) to constant weight, filtering 4oo500 ml of water through it, and redrying the membrane and filtrate. The latter material was ashed at 550 “C for 24 h. Water temperatures were taken at midday throughout the study and salinity was occasionally determined.

Results Environmental conditions Water temperatures increased from about 7 “C during the winter months to 19~~19-5 “C by August, falling to approximately 8 “C by the end of the study (November). Salinity of the reservoir water usually averaged about 25x0 at high tide while the corresponding value at low tide, when the reservoir was completely isolated from the estuary, was 16x,. The most common microscopic algae in the reservoir regardless of season were diatoms and cyanophytes. The standing crop of these plants was always low with maximum and minimum

Fatty acids in estuarine crustaceans

217

values of IOOO and IOO cells/litre occurring in the summer and winter, respectively. On the other hand, the dry weight of suspended solids was always high, seldom falling below I g/litre. The organic content of this material fluctuated between 4 and 180/ of the total dry weight. Proximate analyses Crangon crangon. With the exception of large non-berried females during the summer, length and sex did not affect the water content of representatives of Crangon crangon measuring more than 4.0 cm. The greatest amount of water in these animals, representing from 77*8-80*5% of the wet weight, occurred during the winter with values subsequently decreasing more or less continuously to 75.5~76.0% by the summer and autumn (Figure I). The only departure from the above trend occurred during April when a value of approxiimately 73% was recorded. Seasonal changes in the total lipid content of these animals followed virtually the opposite pattern with maximum and minimum values, representing 28 and 22% of the dry weight, occurring in the summer and winter, respectively. Ash levels fluctuated without any apparent seasonal pattern between 18.8 and 21.8% of the dry weight. Although the water content of non-berried females was higher than that outlined above (79-84s) and that of total lipid correspondingly lower, the seasonal pattern of variation of these two components remained similar to that described earlier. Ash values were almost unchanged, fluctuating only slightly about the mean of 20%. Seasonal variations in the proximate composition of Crangon shorter than 4.0 cm were identical to those outlined

water

Isoy-----o+

70 L I LIpId

2o I---vJ-c

I I I I I I I I I I I Feb June act oec APr Aug Figure I. Percentage change in the water, lipid and ash content of Crangon crangon longer than qo cm collected monthly from the Severn Estuary. 0

218

J. W. Moore

above. However, there was more water in these animals (79.5-83-o%) and less lipid (19-c24*5%), with the amount of ash remaining unchanged. Between 80 and 90% of the Crangon contained large amounts of food (mainly plant material) in their stomachs irrespective of time of year, size, sex or reproductive condition. The dry weight of the stomach contents, expressed as a percentage of the dry weight of these animals, varied from approximately 5*o”h (S.E. = fo.so%) in individuals shorter than 4.0 cm to 3.6% (LE. = f0*55~/~) in those greater than 6.0 cm again regardless of season. Gammarus salinus. No distinct pattern of season change was observed in the water content of representatives of Gammarus sahus, with values fluctuating between 77.1 and 79.7% of the wet weight regardless of the size of the animal. Similarly, the total lipid content, representing from 30.1 to 33.9% of the dry weight, varied without a consistent trend. As in the case of Crangon crangon, ash remained relatively constant at about 24+0~/~of the dry weight (range, 23.3-25.4%). Over 95% of the animals, irrespective of month or size, contained food (almost exclusively detritus) in their gut. The dry weight of this material, determined only for individuals longer than 1.0 cm and expressed as a percentage of the dry body weight, averaged 5.1 y. (S.E. = &I.o%). Neomysis integer, Praunus flexuosus. Neomysis integer was captured in only small quantities during the fall and early winter and thus chemical analyses were not conducted at this time. Water levels of Neomysis regardless of sex, length or time of year remained relatively constant, averaging about 79.4% of th e wet weight (range 77.9-80.1 Oh). Similarly, lipid values ranged from only 21.4 to 23.9% of the dry body weight with ash remaining steady at 20'2-

Feb.

Apr.

JIJW

Aug

03

Figure 2. Percentage change in the water, lipid and ash content gammarella collected monthly from the Severn Estuary.

of Orchestia

Fatty acids in estuarine crustaceans

219

20.9%. Almost all the animals invariably contained food in their gut and, although a gravimetric estimate of the amount of this material was not made, it appeared that the entire gut was filled to near capacity. As with Neomysis, PraunusJEexuosus occurred abundantly only during the warmer months. This animal invariably contained less water than N. integer averaging about 76.2% of the wet weight irrespective of length, sex or season and once again the range of values was small (74.3-77.8) %. Lipid 1evels were virtually identical to those of Neomysis with an average of 23.9 ‘A (range 21.5-24.7 ‘A) but ash remained considerably lower (average 14.8 %; range I 3 ‘3-15.7 %). The gut of almost all these animals always appeared to be filled to near capacity. Orchestia gammarella. The water content of the semi-terrestrial Orchestiu gammarekz regardless of sex or length showed little consistent pattern of seasonal change (Figure 2). Values were considerably lower than those of the other species and fluctuated between 69 and 72 ‘A but, on one occasion, in the middle of May, rose to 76 %. Lipid values on the other hand averaged about 25 ‘A during the winter months falling to approximately 22.9 ‘A between July and September. As with the aquatic species, ash levels remained relatively steady with a mean value of 20%. There appeared to be very little material in the gut of Orchestia during the year and, although an estimate of weight was not made, the ingested material occupied only about IO ‘A by volume of the entire gut. However, as easily digested animals such as protozoa could have formed the main bulk of the diet, these data do not necessarily imply that the animals were limited in their feeding. Phospholipid

and fatty

acid analyses

The amount of phospholipid in each species, expressed as a percentage by weight of the total lipid, remained virtually unchanged throughout the study. Crangon crangon usually contained the greatest amount of this substance with values ranging from 30 to 33% irrespective of size, sex or reproductive condition. The second largest amounts occurred in Orchestia gammarella (q-32.5oj,), f o11owed by Gammarus salinus (27-29.5;/0) and Neomysis integer and Praunus jexuosus (both 24-27’5 %). During both March and August, the predominant fatty acid in the phospholipids of representatives of Crangon crangon measuring more than 6.0 cm in length was 18 : I, accounting for between 26 and 28% of the total fatty acid complement (Table 2). It was TABLE 2. Fatty acid composition, expressed as percentage molar concentration, of the phospholipids of Crarzgon crangon, Gammarus salinus, Neomysis integer, Praunus jlexuosus and Orchestia gammarella at different times of the year

Fatty acid

Crangon March August

‘4

: 0

6.2

7'5

15

:o

0’3

0’4

16 : o 16 : I 16 : 2

21.8

22'9

10.3

18

3’2 26.2 0’9 0.6

II’2 0’4 2.9 27.8

:o

I8 : I 18 : 2 18

: 3

20 : 5 22

: 6

Unidentified

0'5

15.2

II.7 3’1

Gammarus March August 4’3 0’0 23’7 9’5 0’3 4’5 25'0

0'2

2'1

O’S 16.3

o-5 19.2

9’3 0.6

8.0

2.9

3’9 0’3

25’1 8.4 0.3 3’9 24’7 I’7

Neomysis rlugust

Praunus August

4’3 0.6 26.1 9’2

3’9 0’0

0’1

2’3 20.6 I’1

1’0

0.8

X7.4 9’0 4’3

21’3 13’1 0’5

25'1

6.9 0.4 3.6 23’4 0.6 1’7 ‘9’3 14-2 0’9

Orchestia MarchAugust

8.2

6.5

0’4 26.3 9” 3’1

O’S 27.0 7’7

4’3 16.9 I.9 0.9 16-3 IO.9 1.7

4’9 21.6 1’1 0’5 13.4 “‘3 3’5

2'0

J. W. Moore

220

followed, in order of descending importance, by 16 : o (22-23%), 20 : 5 (IS-16%), 16 : I I %) and 22 : 6 (9-12%). Although much the same pattern was observed for representatives of Gammarus salines greater than 1.0 cm in length, this was not the case with Neomysis integer, Praunus jkxuosus and Orchestia gammerella measuring more than I ‘0, I ‘5 and 1.0 cm, respectively. Thus, 16 : o was most important representing between 25 and 27% of the fatty acids with the corresponding values for 18 : I ranging from 17 to 23%. The third most important fatty acid in these three species was invariably 20 : 5 (13-21%) but, in contrast rather than 16 : I (7-9%). to Crangcm and Gammarw, was followed by 22 : 6 (II-14%) In the case of C. crangon, G. sahus and 0. gammarella, no clear change in the proportions of the different fatty acids was usually observed between the two sampling dates (March and August). In the latter species, however, 18 : I rose sharply from 17 to 22% as water temperatures increased. As only a few representatives of Neomysis integer and Praunus jexuosus were collected during the colder periods, seasonal changes in the fatty acids composition of these species were not determined. During both March and August, the predominant fatty acids in the neutral lipids of Crangon crangon were similar to those of the phospholipids with the exception that both 20 : 5 and 22 : 6 occurred more commonly in the former group of lipids (Table 3). A similar but more marked pattern was observed in the case of Gammarus salinus regardless of season with 20 : 5 becoming the second most important fatty acid accounting for 22-25% of the total, followed by 16 : o and 22 : 6. The fatty acid complement of the neutral lipids of Neomysis, Praunw and Orchestia was more or less similar to that outlined for Gammarus and, in the caseof the latter species, no change was observed in the proportions of the different fatty acids over the course of the two sampling periods. (ID-I

Discussion An interesting feature of this investigation is the high lipid values, i.e. 21-33% of the dry weight, recorded for Crangon, Gammarus, Neomysis and Praunus. In comparison to these levels the lipid content of Neomysis integer collected from the Southampton area of England, for example, seldom exceeded 15% (Raymont et al., 1966) while Linford (1965) and Seguin (1968) showed that the corresponding levels in several other estuarine mysids ranged from 9 to 13%. Similarly, decapods are usually reported to contain less than 3% lipid (expressed as a percentage of wet weight) compared with a value of approximately 6.5% in the case of TABLE 3. Fatty acid composition, expressed as percentage molar concentration, of the neutral lipids of Crangon crangon, Gammaw salinus, Neomysis integer, Praunus .flexuosus and Orchestia pammarella at different times of the year Fatty acid :o :o :o : I :z :o 18 : I

14 15 16 16 16 18

18:2 18 : 3 20 :5 22 :6

Unidentified

Crangon March August

Gammmus March August

4’5 0.6 19’9 7’3 0‘0

3.8 1.1 18.3 7’9 0’0

4.5 0.5 19’3 8.7 0’1

2'5 26-8

4'8 25'0 2'0 1'3 19.0 14'1 2'7

3'9 22.4 2.3 I'2 21.3 '4'3

I’S 1-0

17'9 13'7 4'3

I’5

6.2 0.4 17.2 10.2 0.4 3'8 20.4 2'1

1.r 19'4 14.3 4'5

Neomysis

August 6.9 0.5 21.3 4’5 4’3

4’2 14’7 I’5 0’5 25’3 9.8 6.5

Praunus

August 5’3 0'2 23.2 5'1 2.3 4'9 20.7 2'0

1’1 22'1 11'4 "7

Orchestia March August 5’9 0’0 19’3 9’7 I‘0 5.3 19.0 I'1

0’9 19.7 14'1 4'0

7’0 0.3 19.8 7’8 0.7 4.8 x6.7 1’9 1.4 20.8 15'7 3"

Fatty acids in estuarine crustaceans

221

Crangon crangon (Konosu et al., 1958; Raymont et al., 1967; A&man & Eaton, 1967; Dabrowski et al., 1969). Although data on the proximate composition of amphipods are relatively scarce, several papers have given the caloric content of this group of animals. Thus, assuming a value of 9500 Cal/g for lipid and 4200 Cal/g for protein and carbohydrate (Prosser & Brown, 1961), the energy content of Gammarus salinus in the present study varied from about 4800 to 5000 Cal/g dry weight. In contrast, Brawn et al. (1968) and Davis & Warren (1968) reported values of approximately 3800 and 4200 Cal/g, respectively, for other species of amphipods. In an attempt to explain these high lipid values, additional collections of Crangon and Gammarus were made during April and May 1975 at Minehead, which is situated on the Bristol Channel approximately 80 km downstream from Oldbury. Further samples of Crangon were collected at Berkeley, which is located about 7 km upstream from Oldbury, during the same time period. Although it also would have been desirable to take samples of Neomysis and Praunus, very few of these animals were available in either locality. At Minehead, the lipid content of female Crangon measuring more than 4.0 cm in length averaged I I ~8% while at Berkeley the corresponding figure was I 5‘5 %, values which are considerably less than those recorded from Oldbury. Similarly, in the case of Gammarus collected from Minehead, lipid represented only 15-70/O of the dry weight of the animal. Since these values correspond to those reported for other crustacean populations, as outlined in the preceding paragraph, it appears that unusually favourable environmental conditions exist in the vicinity of the Oldbury power station for Crangon and Gammarus and also possibly for Neomysis and Praunus. One important factor contributing to the favourable environment at Oldbury is possibly related to the fact that, since the reservoir holds a large number of animals at low tide, these organisms fail to expend the energy involved in moving with the tides. In addition, the relatively small daily variation in the salinity of the reservoir together with the increase in temperature associated with the heated effluent of the power station, apparently favours most species (Moore, 1975b). For example, a general improvement in the growth rate, an extension of the breeding season and a reduction in the minimum size at maturity was observed for many animals living near the power station. It is also important to note that virtually all of the animals at Oldbury contained large amounts of food in their gut regardless of season.This latter feature is presumably related to the fact that the unusually high turbidity levels in the estuary allow the animals to remain active during the day when they would otherwise normally be buried in the sediments and presumably restricted in their feeding (Moore, 1975b). In addition, since Neomysis and Praunus are largely filter feeders, the large amount of suspended solids in the estuary undoubtedly provides an abundant supply of food for these animals. As pointed out earlier, data on the proximate composition of amphipods are scarce but, by transforming the values obtained for Orchestiu in this study into their caloric equivalents, comparisons may be made with other species. In this context, the caloric equivalent for Orchestiu ranged from 4200 to 4500 Cal/g. These values are considerably lower than those obtained for Gammarus from the reservoir and lie close to the range often reported for amphipods. The average water content of Crangon, Gammarus, Neomysis and Praunus ranged from 76 to 79% of the wet weight, values which are almost identical to those reported for the same and/or comparable species in other areas (Raymont et al., 1966, 1967; Driver et al., 1974; Mauchline & Fisher, 1969; Tyler, 1973). Similarly, although Orchestiugammareh contained only about 70% water, many other semi-terrestrial invertebrates exhibit comparatively low levels (e.g. Pillay & Nair, 1973). Ash in Neomysis was much higher than the values reported

t

by Raymont et al. (1964) for the same species. This would imply that the remaining fraction of Neomysis used in the present study, i.e. protein, carbohydrate and chitin, accounted for only 58% of the dry weight, thus contrasting with the data of Raymont et al. (1964, 1966) which showed that these components represented over 80% in the same species. The ash content of Gammarus and Orchestia fell within the range normally reported for amphipods (Omori, 1969; Driver et aE., 1974) and the values recorded for Crangon are typical of many other decapods (e.g. Raymont et al., 1969). The proximate composition of G. salinus, N. integer, P. flexuosus and 0. gammarella remained constant as the animals increased in size. Many authors, on the other hand, have shown that the amount of water falls while that of lipid rises as the animal grows, with Linford (1965), for example, demonstrating a 60% increase in the proportion of lipid in female representatives of Neomysis integer weighing between 20 and 50 mg. Changes in the ash content of crustaceans with size are only poorly documented but, as most of this material would be tied up in the exoskeleton, it seems likely that small individuals would contain comparatively more ash than larger specimens, reflecting the surface area/body volume ratio. Although some variation existed and with the exception of non-berried females, the proportion of lipid in Crangon crangon increased gradually during the summer and fall. Similar changes have been observed for a number of other animals including decapods (Tyler, I&, euphausiids (Mauchline & Fisher, 1969)~ copepods (Marshall & Orr, 1955) and teleosts (Love, 1970) and are usually correlated with food supply. In the present study, the gut contents of Crangon, consisting mainly of detritus and a few animal fragments, weighed approximately the same throughout the year and thus changes in the amount of available food probably had little to do with lipid fluctuations. Presumably the absorption efficiency of Crangon, which would undoubtedly be temperature dependent, had undergone a considerable increase during the spring and the possibility of significant variation in the quality of the food cannot be overlooked. Lipid levels remained high into October even though water temperatures had decreased implying only slight utilization of this energy reserve. Female Crangon which were not in berry showed a depression in lipid levels during the summer. Presumably, these animals had recently spawned (Lloyd & Yonge, 1947), resulting in a loss of the substantial amounts of lipid occurring in their eggs, a pattern noted for other species (Mauchline & Fisher, 1969). In the context of the influence of reproduction on proximate composition, it should be noted that developing eggs in females occasionally cause a rise in the total lipid content of the animal (Littlepage, 1964), a feature which was not observed in this study. Gammarus salinus showed no change in the proportion of lipid throughout the year, a feature undoubtedly related to the fact that the gut always appeared to be full. It is surprising, however, that no drop was observed in females during the reproductive period, thus indicating only a comparatively small amount of lipid in this species is tied up in the eggs. Since the lipid levels of Gammarus remained constant throughout the year, it appears that this animal does not undergo any period of prolonged starvation in the Severn Estuary, as suggested for several other species of crustaceans in other areas (e.g. Mauchline & Fisher, 1969). Neomysis integer and Praunus flexuosus also showed no change in the percentage of lipid during the warmer months, a pattern previously demonstrated by Raymont et al. (1966) for the former species. Both of these mysids are largely filter feeders and thus have, in the Severn, an unusually large supply of food reflected in the amount of suspended solids. It is interesting to note, however, that Morris (1971) recorded a sharp decrease in the amount of lipid in N. integer during the summer. However, this author did not sort the animals

Fatty acids in estuarine crustaceans

223

according to sex or size and thus the possibility exists that these factors contributed significantly to the fluctuations. In contrast to Crangon, the percentage of lipid in Orchestiu gammarella appears to have dropped during the summer. Unfortunately, as it was difficult to obtain an accurate assessment of the gut contents of this species, it is impossible to correlate this change with food levels. If, however, no significant difference existed in the nutritional status of the animal throughout the year, as was the case for all the other species, the fall in lipid probably indicates that the animal was under metabolic stress, possibly due to high atmospheric temperatures. The level of phospholipids in all five of the species investigated in this study remained relatively low compared to other populations, with Ackman & Eaton (1967) and Brockerhoff et al. (1964) reporting values of 47 and 54% for the decapod Pandalus and mixed zooplankton, respectively. As phospholipids are used largely for structural rather than nutritional purposes (Love, 1970), it seems that these low values reflect the unusually high total lipid levels. The predominant fatty acids in the neutral lipids of the five species, i.e. 16 : o, 18 : I, 20 : 5, 22 : 6, were similar to those described for the total lipids of most other marine Crustacea (Mauchline & Fisher, 1969; Farkas & Herodek, 1964; Lewis, 1962). The fatty acid spectrum of Neomysis integer was similar to that described by Morris (1971) for the same species but differed considerably from that reported by Raymont et al. (1968). Although the degree of unsaturation in crustacean lipids usually increases as the temperature drops (Farkas & Herodek, 1964; Jeffries, 1970)~ this pattern was only poorly defined in the case of C. crangon, G. salinus and 0. gammarella, the only species for which summer and winter samples were collected. As pointed out by Love (1970) the degree of shift is largely dependent on the difference in temperature between the seasons which, in this study, was no more than I I “C. The fatty acids in the phospholipids of the five species, although exhibiting some variation, were generally similar to those occurring in the neutral lipids. In contrast, several authors, e.g. Ackman & Eaton (1967); Yadava et al. (1973), suggested that these two fatty acid complements are normally different but this feature would undoubtedly depend on both the species involved and environmental conditions.

References Ackman, R. G. & Eaton, C. A. 1967 Fatty acid composition of the decapod shrimp, Pandalus borea& in relation to that of the euphausiid, Meganyctiphanes norvegica. Journal of the Fisheries Research Board of Canada ~4~467-47 I. Brawn, V. M., Peer, D. L. & Bentley, R. J. 1968 Caloric content of the standing crop of benthic and epibenthic invertebrates of St. Margaret’s Bay, Nova Scotia. Journal of the Fisheries Research Board of Canada 25, 1803-1811. Brockerhoff, H., Yurkowski, M., Hoyle, R. J. & A&man, R. G. 1964 Fatty acid distribution in lipids of the Fisheries Research Board of Canada 21, I 379-1384. of marine plankton. ~ou7nal Dabrowski, T., Kolakowski, E. & Karnicka, B. 1969 Chemical composition of shrimp flesh (Parapenaeus spp.) and its nutritive value. Journal of the Fisheries Research Board of Canada 26, 29692974. Davis, G. E. & Warren, C. E. 1968 Estimation of food consumption rates. In Methods for Assessmentof Fish Production in Fresh Waters (Ricker, W. E., ed.). IBP Handbook No. 3. Blackwell, Oxford. Driver, E. A., Sugden, L. G. & Kovach, R. J. 1974 Calorific, chemical and physical values of potential duck foods. Freshwater Biology 4, 281-292. Farkas, T. & Herodek, S. 1964 The effect of environmental temperature on the fatty acid composition of crustacean plankton. Journal of Lipid Research 5,369-373. Hunter, K. & Rose, A. H. 1972 Lipid composition of Saccharomyces cerevisiae as influenced by growth temperature. Biochimica et Biophysics Acta 260, 639-653. Jefferies, H. P. 1970 Seasonal composition of temperate plankton communities: fatty acids. Limnalogy and Oceanography 15,419-426. Konosu, S., Katori, S., Akiyama, T. & Mori, T. 1958 Amino acid composition of crustacean muscle proteins. Bulletin of theJapanese Society of Scientific Fisheries 24, 300-304.

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