Chemical composition of dietary species of marine unicellular algae and rotifers with emphasis on fatty acids

The lipid profiles of a few species of marine unicellular algae and yeast were studied with emphasis on fatty acids as part of a search for the nutritional value of plankton to the diet of marine fish larvae commonly used in marine hatcheries. The general proximate chemistry of rotifers was closely related to the proximate chemistry of the diet organism, exhibiting a higher content of protein and carbohydrate and a lower content of lipid. Major lipids in all algae, yeast and rotifers comprised mono-, di- and tri-glycerides and polar lipids. The algae Chaetoceros gracilis Schutt, Isochrysis galbana Parke and their respective algaefed rotifers exhibited higher amounts of neutral lipids, consisting mainly of cyclic and branched polyunsaturated components. Fatty acid composition of the algae was species-specific, with the highest ratio of polyethylenic to saturated and monoethylenic acid in I. galbana and Phaeodactylum tricornutum Bohlin, and the highest content (15%) of n-3 highly unsaturated fatty acids in Nannochloropsis salina and P. tricornutum. A closely mirrored distribution of the fatty acids, but with a lower amount of n-3 highly unsaturated fatty acids, was present in the respective algae-fed rotifers. Comparison of the fatty acid spectrum of Artemia sp. and Euterpina acutifrons grown in the laboratory on I. galbana with zooplankton samples of E. acutifrons and Oitona nana collected from the sea showed a higher concentration of docosahexaenoic acid (22:6 n-3) in the naturally collected sample. The results indicate that the efficacy of the food algae C. gracilis and I. galbana in increasing the survival of fish larvae in marine hatcheries is not obvious on the sole basis of fatty acid composition.     

Increased docosahexaenoic acid levels in total and polar lipid of European sea bass (Dicentrarchus labrax) postlarvae fed vegetable or animal phospholipids

A 6-week feeding trial was conducted with 44-d-old European sea bass (Dicentrarchus labrax L.) in order to examine the effect of various dietary phospholipid (PL) sources on the incorporation of n-3 highly unsaturated fatty acids (HUFA) in tissue lipids. From weaning onwards the fish received diets prepared by coating different lipid fractions (7.5% diet) on an extruded basal diet (92.5% diet). The two PL-free control diets contained 0.5 and 2% of an emulsifier blend, respectively. Seven other diets contained 2% PL, differing by their purity and origin (vegetable or animal). All diets were rendered isolipidic by the addition of hydrogenated coconut oil. Feeding the PL-supplemented diets, except the diet containing hydrolyzed soybean PL (lyso PL), resulted in a higher survival and a 10 to 30% better growth as compared to the PL-free diets. No difference according to the PL origin was observed. The sea bass final lipid content increased with increasing body weight. Also the lipid class composition of the fish was clearly correlated with the final weight gain. Total neutral lipid increased from 51% of total lipid (initial fish) to 76% for fish fed the PL-free diets, and up to 88% for fish fed the sunflower PL. Weaning the fish on the experimental diets induced important changes in their fatty acid profiles characterized by a decrease in 18:3n-3, 20:5n-3 and 20:4n-6 and an increase in saturated fatty acids and 22:6n-3 (DHA). According to the fatty acid composition of both total and polar lipid, the weaned fish could be divided into three groups reflecting the dietary fatty acids: a group fed the vegetable PL, a group fed the animal PL and a PL-deprived group. An effect of dietary PL on the incorporation of dietary n-3 HUFA, more particularly DHA, was noticed. For a similar supply of DHA through the neutral lipids in the diet, fish fed PL-supplemented diets (except for the lyso PL diet) had 10 to 25% higher DHA levels in total and polar lipid than PL-deprived fish. This PL effect was already clear at the end of the weaning and was not related to the presence of n-3 HUFA in the PL source, as suspected in a previous study when feeding egg yolk PL. A better incorporation of DHA was not obtained by replacing the PL by an emulsifier or by lyso PL with higher emulsifying properties. Present results confirm a role of dietary PL in the absorption of dietary neutral lipids, by a mechanism other than emulsification. Received: 27 May 1997 / Accepted: 30 June 1997     

Changes in lipids during the development of Calanus finmarchicus s.l. from Copepodid I to adult

The total lipid and wax ester content as well as the fatty acid and alcohol composition of all copepodid stages and adults of Calanus finmarchicus s.l. were investigated at different locations in the North Sea in 1983 and 1984. Total lipid and the wax ester proportion increased exponentially until Copepodid V. The females were sometimes lower in lipids than the Stage V. The wax ester proportion reached about 90% of total lipids in males and Copepodid V and up to 40% in Copepodid I. The major fatty acids were 16:0, 20:5, and 22:6 and the major fatty alcohols were 16:0, 20:1 and 22:1. At one station the 18:4 acid became one of the dominant acids, because of a Phaeocystis sp. bloom, indicating that the fatty acids of the diet are incorporated mostly unchanged into the lipids of the copepods. The other main fatty acids 20:1 and 22:1 are probably synthesized de novo, serving as precursors for the principal alcohols 20:1 and 22:1. Their levels decreased in the younger stages due to increases in 16:0 alcohol. The fatty alcohol-forming enzyme seems to be specific for saturated and monounsaturated acids, which may be synthesized de novo or derived from diet.     

Membrane lipids of red muscle mitochondria from land-locked and sea-run Arctic char, Salvelinus alpinus

Although laboratory studies of the effects of temperature, salinity, and diet on biological membranes of fish indicate substantial alterations in phospholipid and fatty acid composition to maintain functional properties, there are few parallel studies of wild populations. We, therefore, examined the red muscle, mitochondrial phospholipids and phospholipid fatty acids in two fish populations differing in their environmental temperature, salinity, and diet. Sea-run and freshwater (land-locked) Arctic char (Salvelinus alpinus L.) were collected from Igloolik Island, Northwest Territories, Canada, in the summer of 1991. Several differences between the phospholipids of these fish, and those reported for red muscle mitochondria in other fish species, included a higher cardiolipin content and a higher proportion of short-chain monoenes, especially 16:1. In congruence with previous studies of changes in cardiolipin fatty acids in other species of cold-acclimated fish, the fatty acid content of cardiolipin of both Arctic char groups was more saturated and less polyunsaturated than in warm-acclimated fish. Other aspects of the lipid composition of these membranes were not consistent with laboratory studies of cold-acclimated fish. For example, the fatty acids comprising phosphatidylethanolamine and phosphatidylcholine were more saturated than would be predicted based on laboratory studies of cold-acclimated fish. Some of these differences may be attributable to differences in the proportions of dietary n3 and n6 fatty acids in freshwater and marine environments. A strategy common to both groups of Arctic char is the maintenance of a similar relationship between phospholipid fatty acid chain length and degree of unsaturation in both Arctic char populations in spite of differences in diet and thermal regimes. The observed differences in membrane composition between land-locked and sea-run fish presumably act to maintain mitochondrial function in these different environments. Received: 27 May 1997 / Accepted: 12 June 1997     

Fatty-acid composition of ovulated eggs from wild and cultured turbot (Scophthalmus maximus) in relation to yolk and oil globule lipids

The fatty-acid composition of lipids from ovulated eggs of wild and cultured turbot was investigated in order to estimate the nutritional requirements during embryonic and early larval development. Lipid comprised 13.8±0.5% (n=5) and 13.2±0.7% (n=7) of the egg dry weight in wild and cultured turbot, respectively. Polyunsaturated fatty acids (PUFA) of the (n-3) series accounted for 39% of total fatty acids in total lipid of both wild and cultured fish. The predominant (n-3) FUFA was docosahexaenoic acid (22:6 n-3), which also was the most abundant fatty acid in turbot eggs and comprised 24 and 23% of the total egg fatty acids in wild and cultured fish, respectively. Phospholipids, triacylglycerols and cholesterol-wax esters of turbot eggs all exhibited a specific fatty-acid profile distinctly different from that of total lipid. The general pattern of the fatty-acid distribution in lipids of eggs from wild and cultured turbot was similar, but the relative amount of 18:2(n-6) was considerably higher and 20:1(n-9) slightly higher in cultured fish. These differences were extended to all lipid classes and probably reflect the dietary intake of certain vegetable and marine fish oils. Calculations based on light microscopical studies showed that 55 to 60% of the total lipids in cultured turbot eggs are confined to the oil globule. The size of the oil globule remained constant during embryogenesis, and a reduction in size occurred first after hatching and mainly after yolk depletion. This implies that the total amount of lipids utilised during the embryonic development is considerably less than the total lipids present in ovulated turbot eggs. Comparison of the fatty-acid composition of total lipids from eggs and vitellogenin of wild turbot reveals that egg lipids contained a lower level of saturated and a higher level of monounsaturated fatty acids. Eggs also contained wax esters, which were not detected in vitellogenin, suggesting that vitellogenin is not the only source of lipids for turbot eggs.     

Lipid storage and composition in tropical surgeonfishes (Teleostei: Acanthuridae)

The lipid composition of tropical marine reef fishes is poorly known, despite their use as food by local human populations and recent interest in health-related benefits of fish lipids. We examined the composition of lipids from epaxial muscle, liver, and two storage sites [mesenteries surrounding the gut (intraperitoneal fat, IPFs) and retroperitoneal fat bodies (FBs) posterior to the peritoneal cavity] in three species of surgeonfishes from Ishigaki Island, Japan: Naso lituratus (Bloch and Schneider, 1801), Acanthurus lineatus (Linnaeus, 1758), and A. bariene (Lesson, 1830). Triacylglycerols dominated all samples of neutral lipid and constituted ≥ 99% of FBs and IPFs. Polar lipids generally contained large fractions of phosphatidylethanolamine and phosphatidylcholine. Quantified fatty acids ranged in length from C₁₄ to C₂₄. C₁₆ fatty acids prevailed (>35% of neutral fatty acids, >23% of polar fatty acids), although C₁₈ (>16 and >14%, respectively) and C₂₀ acids (>8 and >19%, respectively) were also common. Saturated fatty acids, dominated by palmitic acid (16:0), comprised 38.7 to 50.7% of acids from neutral lipids and 30.8 to 41.1% from polar lipids. The most common monounsaturated acids were 18:1n9 and 20:1n9. Polyunsaturated acids were prevalent in polar lipids (especially 20:4n6, 20:5n3, 22:2n3, 22:5n3, 22:5n6 and 22:6n3). Common polyunsaturated acids of neutral lipids were 18:2n6, 18:4n3, several n-3 and n-6 C₂₀ acids, 22:2n3 and 22:5n3. IPF and FB were almost identical across species, and lipids of fat bodies (IPFs, FBs) were more similar to those of muscle than those of liver for all three species. The FBs appear to constitute an accessory storage site, which overcomes constraints on lipid storage imposed by a small, inflexible abdominal cavity that contains both viscera and consistently voluminous gut contents. Fatty acid signatures indicate that largely overlooked epiphytic or epilithic diatoms contribute significantly to lipid acquisition. The combination of large quantities of both saturated and n-3 and other polyunsaturated fatty acids in surgeonfishes, in contrast to low saturates and high polyunsaturated acids in lipids of commercially important cool-water fishes, suggests that a study of dietary effects of fish lipids on human inhabitants of the tropics may be instructive insofar as human health and nutrition are concerned. Received: 16 March 1998 / Accepted: 6 August 1998     

Effect of lipid emulsions on production and fatty acid composition of eggs of the scallop<Emphasis Type="Italic"> Argopecten purpuratus</Emphasis>

The impact of supplementing lipid emulsions rich in eicosapentaenoic acid (EmEPA), docosahexaenoic acid (EmDHA) or saturated fatty acids (EmCOCO) to a standard algal diet [3:1 mixture of Isochrysis galbana (T-iso) and Chaetoceros neogracile, St-diet] on Argopecten purpuratus broodstock was evaluated. Broodstock fecundity was compared as well as the egg quality in terms of lipid content, fatty acid composition and lipid class distribution. Fecundity was defined as the number of eggs released in the spawning process, since spawning was virtually complete. Results indicated that the total lipid content of the eggs of A. purpuratus was diet independent. A greater energy reserve was spent on a larger number of oocytes and not on bigger sized oocytes with a higher lipid content. The lipids supplied through the emulsions were at least partially allocated to the eggs, demonstrating that the fatty acid composition of the eggs could be manipulated, especially the neutral lipid fraction. Levels of EPA changed more rapidly than DHA levels, supporting the observation that they fulfilled an energetic and structural role, respectively. The St-diet supplemented with 50%EmCOCO resulted in a significantly higher fecundity compared to the algal diet supplemented with 25%EmEPA+25%EmDHA and the non-supplemented algal diet. It would seem that saturated fatty acids (SAFA) were more easily or preferentially incorporated in the female gonads of A. purpuratus. The relative content of SAFA and 18:2( n-6) in these eggs rose significantly. The relative content of the highly unsaturated fatty acids, EPA and DHA, on the other hand was substantially lower in the neutral lipid fraction, but hardly affected in the polar lipid fraction. It appeared that the maintenance of an adequate DHA/EPA ratio (approximately 1.2) was more important than the absolute levels of the two fatty acids, as long as a threshold value was reached.     

An experimental study of the effect of diet on the fatty acid profiles of the European Cuttlefish (<Emphasis Type="Italic">Sepia officinalis</Emphasis>)

Fatty acid analysis is an alternative dietary investigation tool that complements the more traditional techniques of stomach content and faecal analysis that are often subject to a wide range of biases. In applying fatty acid analysis to ecosystem studies, it is important to have an understanding of the effect diet has on the fatty acid profile of the predator. A feeding experiment, using crustacean and fish as prey for the European cuttlefish Sepia officinalis, was conducted to evaluate the effect of prey fatty acids on the fatty acid profile of this marine predator. Cuttlefish were fed on a fish diet for the first 29 days, and then changed to a crustacean diet for a further 28 days. Another group of cuttlefish was fed on a crustacean diet for the first 29 days, and then changed to a fish diet for a further 28 days. An analysis of the cuttlefish digestive gland showed that the fatty acid profile reflected that of the prey, with cuttlefish on a crustacean diet being clearly distinguishable from the cuttlefish on a fish diet. Cuttlefish fed on a fish diet for 29 days prior to the switch in diet were comparatively higher in 16:0, AA, 20:1ω9, DPA6, DHA, 22:4ω6 and DPA3 than those fed on crustaceans. Cuttlefish fed on a crustacean diet for 29 days prior to the switch in diet were comparatively higher in 17:1ω8, 18:1ω9, 18:2ω6, 18:1ω7, EPA and 20:2ω6 than those fed on fish. Following a change in diet, the fatty acid profile of the cuttlefish digestive gland reflected that of the new diet within 14 days. The results confirm that the fatty acid profile of the cuttlefish digestive gland clearly reflects the profile of its recent diet. It also shows that the digestive gland may not be an organ that accumulates dietary lipids for long-term storage, but rather is an organ where lipids are rapidly being turned over and potentially excreted.     

Lipid class and fatty acid composition of brain lipids from Atlantic herring (Clupea harengus) at different stages of development

Little is known about the changes in composition of brain lipids and fatty acids at different stages of development in fish. Wild Atlantic herring (Clupea harengus L.) were collected from Loch Linnhe and the Firth of Clyde, Scotland, from August 1990 to March 1991. Lipid class and fatty acid compositions of brain lipids were studied at four different stages of development: larvae at the end of the yolk sac stage, two juvenile stages and sexually mature adults. The total lipid content in brains increased during development, and larval brains contained higher proportions of neutral lipids and lower proportions of polar lipids than the brains of juvenile or adult herring. Increased proportions of polar lipids in juvenile and adult herring brains were mainly due to increased percentages of phosphatidylcholine (PC), phosphatidylethanolamine (PE), cerebrosides and sulphatides. The increase in the proportions of the glycolipid classes suggested increasing levels of myelination with development. In total lipids, saturated fatty acids generally decreased and monounsaturated fatty acids and dimethyl acetals (derived from PE-plasmalogen) increased from larvae to adults. However, the proportions of polyunsaturated fatty acids in individual phosphoglycerides were generally highest in juvenile stages, due mainly to increased 22:6n-3, and were lowest in adult fish. Relatively high percentages of 24:1 isomers were found in all the phosphoglycerides, but primarily PC, and these increased during development from larvae to adult. Fatty acids were distributed between individual phosphoglycerides with a characteristic pattern that did not change with development, although the relative amounts of individual fatty acids were altered. The variations and roles of the different lipid components of herring brain are discussed with respect to lipid compositions and functions in brains of other fishes and vertebrates.     

Toxicity of cypermethrin on total lipids and free fatty acids in liver,muscle, kidney and ovary of Clarias batrachus (L) and recovery response

Alterations in the levels of lipid metabolites, total lipids and free fatty acids, were studied in physiologically important tissues viz; liver, muscle, kidney and ovary of a freshwater edible fish Clarias batrachus. The fish was exposed to sublethal concentration (1/3 of LC50 value for 96?h) of a synthetic pyrethroid insecticide, cypermethrin for 1, 5 and 10 days. After 10 days of exposure, fish were released into fresh water and total lipids and free fatty acids were determined at intervals of 1, 5 and 10 days to assess fish recovery response after cessation of cypermethrin exposure. Fish showed an increased rate of lipogenesis in liver, muscle, kidney and ovary during the exposure period followed by a decrease after transfer of fish into fresh water. There was also an elevation in liver and kidney free fatty acids contents, while the muscle and ovary free fatty acid contents were reduced during exposure period. The alterations in free fatty acids were restored to near normal values after 10 days of cessation of exposure.     

Trophic ecology of Rimicaris exoculata : a combined lipid abundance/stable isotope approach

The alvinocaridid shrimp Rimicaris exoculata is an abundant component of the biota of Mid-Atlantic Ridge hydrothermal vents. To determine the nutritional strategy of this organism, we analysed the molecular abundance and carbon isotopic composition of its phospholipid fatty acids. High abundances of n-7 fatty acids (>40% total fatty acids) were observed in R. exoculata muscle tissues, in bacterial epibionts scraped from its gill bailers, and from the bacterially infested metal sulphides that the shrimp ingest. The phospholipid fatty acid abundance data indicates that the bacteria in the sulphides are closely related to the bacterial epibiota inhabiting the shrimp gill bailers, carapace and other body parts. Compound specific δ¹³C analyses of the phospholipid fatty acids gave average values of −12‰ for the epibiont bacteria and −21‰ for the sulphide bacteria. This difference may be largely due to the expression of different forms of RuBisCO (Forms I and II) which fractionate against ¹³C to different extents. Carbon limitation within the shrimp epibiont population may be an additional factor. The δ¹³C values (mean = −13‰) of the saturated and monounsaturated fatty acids isolated from the muscle tissues of R. exoculata were very close to those of the epibionts, indicating that the predominant source of dietary carbon for the shrimp is their epibionts, with a lesser contribution from free-living bacteria. The δ¹³C values (−26‰) of shrimp cholesterol were much more negative than those of the fatty acids, and this cholesterol is likely to have derived from the oceanic photic zone. Received: 26 June 1997 / Accepted: 6 November 1998     

Fatty acids of the female horseshoe crab Xiphosura (Limulus) polyphemus

The fatty acid composition of 9 different tissues and organs of the female horseshoe crab Xiphosura (Limulus) polyphemus — one of the very few recent representatives of the ancient arthropod class Merostomata — was investigated in reference to the distribution of fatty acids through the marine food web. Fatty acid spectra, in which polyunsaturated fatty acids are predominant, especially eicosapentaenoic acid (20:5 3), revealed features characteristic of marine lipids. However, rather large quantities of monoenoic fatty acids also occur in all organs. In the saturated fatty acid fractions, the high content of branched-chain components is worth noticing, particularly in the gills and the carapace (35%); in all probability, the high amount of the branched-chain fatty acids is associated with their protective function in surface lipids. Isoprenoid fatty acids such as pristanic and phytanic acid were absent.     

Fatty acid evidence for the importance of myctophid fishes in the diet of king penguins, Aptenodytes patagonicus

We tested the usefulness of the fatty acid signature-method in investigating the diet of seabirds in conjunction with the conventional technique of stomach-content analysis. We compared the fatty acid composition of subcutaneous white adipose tissue (SWAT) of king penguin chicks (Aptenodytes patagonicus) during fattening periods to that of total lipids from their food. In both spring and autumn, the fatty acid composition of chick SWAT was identical to that of the dietary lipids. Because the diet of adult king penguins feeding for self-maintenance (i.e. not for their chicks) was essentially unknown, we subsequently analysed their SWAT fatty acid patterns after premolting and prebreeding foraging trips (during which they build up large energy reserves). The fatty acid composition of SWAT from adults was identical to that of chick adipose tissue and food. King penguin diet and SWAT were characterized by high levels of very long-chain mono-unsaturated fatty acids (20 to 24 carbon atoms, 16 to 23% by mass) and (n-3) poly-unsaturated fatty acids (19 to 27%); these consisted mainly of 20:1n-9 (5 to 8%) and 22:1n-11 (5 to 8%), and 22:6n-3 (10 to 13%) and 20:5n-3 (3 to 9%), respectively. Prey items identified from chick stomach contents indicated that the bulk of the food was oceanic myctophid fishes, mainly Electrona carlbergi, Krefftichthys anderssoni and Protomyctophum tenisoni. The fatty acid composition of four other species of myctophid fishes was similar to that of penguin diet and SWAT, but markedly different from that measured for a squid species and that reported for crustaceans. These findings indicate that adult king penguins prey on myctophid fish not only to feed their chicks but also for their own nutrition. The fatty acid signature-technique is therefore a reliable method to gain information on the food and feeding ecology of seabirds when more conventional techniques are of limited value. Such information is important to the understanding of trophic relationships between key species of the ecosystems, and also to provide insight into the nature of avian adaptations to the marine environment. Received: 11 December 1997 / Accepted: 25 July 1998     

Lipids of some Caribbean and Red Sea corals: total lipid,wax esters,triglycerides and fatty acids

The Caribbean reef-building corals Porites porites (Pallas) and Montastrea annularis (Ellis and Solander) and the Red Sea corals Pocillopora verrucosa (Ellis and Solander), Stylophora pistillata (Esper) and Goniastrea retiformis (Lamark) were analysed for total lipid, wax ester and triglyceride content, and fatty acid composition. M. annularis contained about 32% of dry weight as total lipid, whereas much lower values of between 11 and 17% were recorded for the other four species. It is concluded that there is greater variation in coral total lipid than hitherto thought. The total lipid contained a substantial proportion of wax ester (22 to 49%) and triglyceride (18 to 37%). The storage lipids (wax esters and triglycerides) accounted for between 6 and 20% of the dry weight and between 46 and 73% of the total lipid. Variation in lipid content between species could not be attributed to geographical location, but the low values for total lipid in Red Sea corals may in part be due to environmental factors as these samples were collected in winter. All corals analysed contained high levels of saturated fatty acids, the most abundant fatty acids being 16:0, 18:0 and 18:1n-9. Marked differences were observed in polyunsaturated fatty acid (PUFA) content between species, with comparatively low levels of 10 and 11% of fatty acids being recorded in M. annularis and G. retiformis, respectively. The values for the other species ranged between 21 and 37%. Fatty acid composition may vary according to the proportions of fatty acids obtained from diet, algal photosynthesis and synthesis by the animal tissues.     

Lipid synthesis from acetate by the in vitro incubated ovaries of the penaeid shrimp Penaeus semisulcatus

The present research was aimed at studying the synthesis of lipids from ¹⁴C-acetate in vitro by ovarian tissue in relation to oogenesis and at examining the binding of newly synthesized lipids to ovarian proteins. Lipid synthesis gradually increased during oogenesis. Fifty percent of the newly synthesized lipids was phosphatidyl choline; triacylglycerols reached 30 to 35%; diacylglycerol was a relatively important component of the synthesized neutral lipids in immature ovaries. Cholesterol was not synthesized. Only saturated (73%) and monounsaturated (26%) fatty acids were labeled. Polyunsaturated fatty acids were not synthesized. Bound lipids in developing ovaries were associated mainly with vitellin. Lipids were bound also to two other proteins in immature ovaries. Binding of lipids to vitellin was observed at the commencement of vitellogenesis. Up to a third of the newly synthesized lipids was bound to vitellin, with triacylglycerols and phosphatidyl choline as the main bound lipids. Peneaus semisulcatus individuals examined in the present study were collected in Haifa Bay, Israel during the years 1990 to 1992.     

Studies on the nutrition of marine flatfish. The effect of dietary fatty acids on the tissue fatty-acids of the plaice Pleuronectes platessa

The ratios of polyunsaturated fatty acids in the lipids of hatchery-reared plaice [Pleuronectes platessa (L.)] maintained on a diet containing corn oil and freeze-dried cod muscle accurately reflect ratios of polyunsaturated fatty acids in the diet. Such plaice have much greater levels of triglycerides in both their livers and extrahepatic tissues than wild plaice of comparable size; the total amount of 22:6 3 acid in triglycerides of the two groups is, however, very similar. Transfer of experimental plaice to a fat-free diet caused a marked depletion of triglycerides from both livers and extrahepatic tissues with almost all fatty acids being reduced in amount. Addition of 12:0 and 14:0 ethyl esters (4% of each) to the fat-free diet caused some accumulation of triglycerides in extrahepatic tissues. Further addition of 18:2 6 and 18:3 3 acids (both at levels of 0.4%) to the diet caused an accumulation of triglycerides in the liver. These triglycerides had increased levels of saturated and monounsaturated fatty acids up to C 18 but the levels of higher polyunsaturated fatty acids were not inereased. There was relatively little change in the fatty acids of phospholipids throughout these experimental dietary regimes. The levels of phospholipids were constant and very similar to those of wild plaice. The results indicate: (1) plaice fed a diet relatively low in 22:6 3 acid may accumulate relatively large amounts of triglyceride in order to store adequate amounts of 22:6 3 acid; (2) plaice are capable of synthesising saturated and mono-unsaturated fatty acids up to C 18 in the presence of dietary 12:0 and 14:0 acids; (3) 18:2 6 and 18:3 3 acids in the diet do not undergo chain elongation and further desaturation in plaice with the dietary regimes we used.     

Variation in lipid classes during the molting cycle of the prawn Penaeus japonicus

The variation in the concentration and fatty acid composition of lipid classes during the molting cycle of the prawn Penaeus japonicus was investigated. The lipid concentration of the whole body reached a maximum at mid-premolt (Stage D₂) and then decreased to low level at late premolt (Stage D_3–4). The accumulation of lipids during the premolt period seemed to be attributable to the increase of both polar and neutral lipids. The increase of neutral lipids at Stage D₂ was derived from not only triglycerides but also free sterols and free fatty acids. Regarding the fatty acid composition of every lipid class, a marked variation occurred mainly at the intermolt (Stage C). In this stage, the polar lipids were rich in monoenoic acids such as 18:1 and poor in polyenoic acids such as 20:53 and 22:63. The triglycerides were rich in polyenoic acids at Stage C, but poor in monoenoic acids such as 16:1 and 18:1. The steryl esters contained large amounts of saturated acids such as 16:0 and 18:0 throughout the molting cycle, however the level of polyenoic acids increased at Stage C.     

Trophodynamics and seasonal cycle of the copepod Pseudocalanus acuspes in the Central Baltic Sea (Bornholm Basin): evidence from lipid composition

Seasonal lipid dynamics of the copepod Pseudocalanus acuspes were studied in the Bornholm Basin (Central Baltic Sea) on a monthly basis from March 2002 until March 2003 and were interpreted in light of life cycle strategies and diet selection. The individual total lipid content of females ranged from 0.9 to 1.8 μg, with relative wax ester content reaching a significant maximum in May (44% of total lipids) and minimum (17% of total lipids) in April and November. Significant changes in size, lipid content, lipid classes and fatty acid composition of structural as well as storage lipids suggested five characteristic seasonal phases that were induced by different feeding histories and environmental conditions. Storage lipids were characterized by 18:1(n−9) as major component, which ranged between 44% of total fatty acids in June and 23% in February. The strong coherence between 18:1(n−9) in the seston lipids and the occurrence of ciliates emphasized the importance of ciliates in the diet of P. acuspes. As indicated by changes in the amounts of fatty acid markers, other food sources varied over the year, suggesting an opportunistic feeding behavior. The spring period was characterized by an increase in typical diatom and dinoflagellate markers, whereas other sources, potentially cyanobacteria, became more important during summer. The life cycle strategy is discussed with respect to extant adaptations to high latitudinal habitats.     

Characterizing the resident, fermentative microbial consortium in the hindgut of the temperate-zone herbivorous fish, Hermosilla azurea (Teleostei: Kyphosidae)

The zebraperch, Hermosilla azurea Jenkins and Evermann, a warm-temperate marine fish species with a strictly macroalgal diet, has a relatively long digestive tract with an enlarged hindgut and an associated blind caecum (HC). In zebraperch sampled off Santa Catalina Island, California (33°19′42′′N; 118°18′37′′W) in years 1995 through 2001, direct cell counts, gut epithelium assessment of bacterial attachment, and short-chain fatty acid (SCFA) analyses verified that the zebraperch HC possesses a dense and morphologically diverse, fermentative microbiota. Bacterial cell counts and morphological diversity were significantly higher in HC contents compared to anterior gut regions, suggesting that microbial populations were growing along the digestive tract. Similarly, electron micrographs of the HC epithelium revealed attached microbes, further supporting the possibility that these organisms constitute resident microbiota. Five different SCFAs were detected in all three regions of the digestive tract, but levels were up to three times greater in HC contents. Acetate was consistently the prevailing SCFA in all gut regions. Sequence analysis of bacterial 16S rDNA was used to identify predominant bacterial groups in HC contents. Of the seven main bacterial types identified, Enterovibrio spp. were the dominant bacteria in HC contents followed by species of Bacteroides,Faecalibacterium, and Desulfovibrio. Taken together, our findings show that the zebraperch HC harbors a consortium of microbes that appears to assist in the breakdown of algal polysaccharides in the herbivorous diet of the fish.     

Lipid composition of<Emphasis Type="Italic"> Symphodus ocellatus</Emphasis> (Perciforme: Labridae) in the north-western Mediterranean: influence of two different biotopes

The lipid content and fatty acid composition of the small common wrasse Symphodus ocellatus was analysed within two populations located in very different biotopes on the French shore: a Caulerpa taxifolia meadow located in Cap Martin and a Posidonia oceanica bed located in Villefranche. Polar lipids represented 82–90% of the total lipid in adult female livers, gonads and in eggs. Cholesterol in gonads and eggs and triacylglycerols in livers were the dominant neutral lipids. Differences in lipid classes were found in livers between the two populations, but not in their gonads and eggs. Moreover, a quantitative difference in total lipid content was evident. Young fish living on the C. taxifolia meadow in winter had 21% less lipid than those living on the P. oceanica bed. The populations of S. ocellatus showed differences between triacylglycerol versus phospholipid fatty acid compositions and between gonad versus liver fatty acid compositions. Moreover, a significant difference was found between both populations in their liver triacylglycerol fatty acid compositions, suggesting a difference in diet. Gut content analysis supported this hypothesis as it showed important differences in the ingested preys between the two populations in January (planktonic vs. benthic, frequency of isopods) and in June (frequency of gastropods). Thus, we found that the fish populations from Villefranche and Cap Martin showed significant differences in body lipids due to different nutritional habits.Communicated by S.A. Poulet, Roscoff