Lipid compositions,water contents,swimbladder morphologies and buoyancies of nineteen species of midwater fishes (18 myctophids and 1 neoscopelid)

Lipid compositions, water contents, swimbladder morphologies and specific gravities were studied for 19 species of oceanic midwater fishes, chiefly myctophids (lanternfishes) collected offshore from Oregon and California from 1975–1979. Three groups of species were recognizable. The first group had bodies low in both lipid and water content; they were denser than seawater, regardless of swimbladder morphology, which varied from absent through non-inflated to inflated. The second group had bodies low in lipid but high in water content; they were neutrally buoyant, evidently because of their high content of water, although their swimbladders were never inflated. The majority of the members of the aforementioned groups contained higher proportions of triglycerides than wax esters. The third group had bodies with high lipid but low water content; those with high triglyceride content had swimbladders ranging from non-inflated to (less commonly) inflated, were denser than seawater, and the lipid percentage of their body weights varied both with size and season, indicating that triglycerides function mainly as an energy store. The adults of species in the third group with a higher content of wax esters than triglycerides lacked inflated swimbladders, were neutrally buoyant, and the lipid percentage of their body weights was relatively constant with size and season, indicating that wax esters permit these fishes to attain neutral buoyancy in seawater.     

Lipid composition of twenty-two species of Antarctic midwater zooplankton and fish

Total lipids, hydrocarbons, wax esters, triacylglycerols, and phospholipids were determined for 22 major biomass species of zooplankton and fish in an Antarctic mesopelagic community that were collected in 1982 and 1983. Lipid levels were similar to levels in more temperate mesopelagic species. Total lipid concentration was depth related, with all lipid-rich species being collected at depths greater than 230 m. Wax ester content in copepods (60 to 70% of the total lipid) was generally higher than in subtropical species. Lipids indicated three predator-prey relationships (Parandania boecki-Atolla wyvillei, Thysanoessa macrura-Calanoides acutus andEurythenes gryllus-Atolla wyvillei). These were confirmed by gut content analyses. The mesopelagic fishBathylagus antarcticus, Pleuragramma antarcticum, andProtomyctophum bolini stored most lipid intramuscularly, whereasElectrona antarctica andGymnoscopelus nicholsi contained extensive stores in subcutaneous lipid sacs. The intramuscular lipids inP. antarcticum and the subcutaneous lipid sacs ofE. antarctica were primarily wax esters, possibly used for increased buoyancy or long-term energy storage. Unlike the odd-carbon preference of aliphatic hydrocarbons which typifies terrestrial plants and temperate marine organisms, even-carbon chain-length paraffins predominate in 80% of the Antarctic species analyzed. Although the source of these even-carbon n-alkanes cannot be determined from our data, their dominance in the species analyzed suggests that an unusual biochemical pathway may be responsible for their synthesis in this ecosystem.     

The occurrence of wax esters in crustaceans from the North-east Atlantic Ocean

The lipids of 2 species and 1 group of copepods, 4 species of euphausiids, 2 species of mysids, and 6 species of decapods, taken from different depths in the North-eastern Atlantic Ocean and Western Mediterranean Sea, have been analysed specifically for their wax ester content. The mid-water animals living below 500 m contained large amounts of wax ester (30 to 80% total lipid), while those animals living in the upper 600 to 700 m or on the sea floor had only small wax ester fractions (5 to 10% total lipid). It is suggested that the wax esters are laid down by those animals living in areas of low food density, where energy conservation is important, partly to achieve a more neutral buoyancy. In addition, it would appear that wax esters can function as energy reserves.     

Wax-ester metabolism in the orange roughyHoplostethus atlanticus (Beryciformes: Trachichthyidae)

Freshly caught orange roughy (Hoplostethus atlanticus) obtained at the edge of the Chatham Rise, east of the South Island of New Zealand, in June 1988, were used to investigate tissue-specific lipid synthesis and to obtain blood for plasma lipoprotein analysis. Tissue slices prepared from an intraneurocranial fat deposit, pieces of skull (neurocranium), swimbladder and liver were incubated with radioactive acetate, palmitate and oleate, and the labelled lipids extracted and analysed. All four tissues could incorporate acetate label into fatty acids which were themselves incorporated into triacylglycerols and phospholipids although not into wax esters, the most abundant lipid class in these tissues. Exogenous palmitate and oleate were also incorporated into more complex lipids, with the label from oleate (but not palmitate) being found in wax esters as well as triacylglycerols and phospholipids. The distribution of the label in the wax esters showed that some reduction of the fatty acid to fatty alcohol had occurred. The only exception to this pattern was the swimbladder, which incorporated small amounts of palmitate-label into both the fatty acid and fatty alcohol portions of the wax esters. Lipoproteins were isolated from serum by centrifugation. All lipoprotein classes contained phospholipid, cholesterol, triacylglycerol, cholesteryl esters and wax esters. A very low-density lipoprotein class also contained large amounts of unesterified fatty acids, which are possibly artefacts resulting from storage of the samples. Significant quantities of-3 fatty acids were also found in the serum lipids.     

The composition and biosynthesis of lipids in Thysanoessa raschi from the Clyde Estuary,Scotland

The lipid composition and biosynthesising activity of Thysanoessa raschi collected from the Clyde Estuary, Scotland, in May 1981 were examined. Triacylglycerols were the major lipid class present, although 16.7% of the total lipid were wax esters in which phytol was the dominant fatty alcohol. The thoracic contents (hepatopancreas) of the krill were capable of biosynthesising lipids in vitro from various labelled substrates. Radioactivity from [1-¹⁴C] palmitic acid was incorporated into lipids in the order phospholipids>triacylglycerols>wax esters; the bulk of the radioactivity was present in all cases in the fatty acyl moieties of the lipids. [U-¹⁴C] glucose labelled lipids in the order phospholipids>triacylglycerols>free fatty acids> was esters; in the first two lipids the radioactivity was mainly in the glycerol moieties, whereas in was esters it was solely in the fatty acyl moieties. The extent of labelling of these lipids from [U-¹⁴C] alanine was less than that from [U-¹⁴C] glucose, but the pattern of labelling was generally similar. More than 90% of the radioactivity incorporated into total lipid from ³H₂O was present in free fatty acids from which it was calculated that the hepatopancreas of T. raschi can synthesise 2.5 g of fatty acid per hour at 15°C. This value is approximately three times lower than that previously determined for T. inermis from Balsfjorden, northern Norway. The results are discussed in terms of the sources of the dietary lipids of krill and the role of endogenous biosynthesis in contributing to its lipid reserves.     

Lipid composition and partitioning of deepwater chondrichthyans: inferences of feeding ecology and distribution

The composition of lipids and fatty acids was determined for the livers, muscle, pancreas, kidney and stomach fluids of deepwater chondrichthyan species (including 11 squaliformes, 3 chimaeriformes, 1 hexanchiforme and 3 carcharhiniformes) caught as bycatch from continental waters off south-eastern Australia. The lipid class, fatty acid and fatty alcohol composition differed markedly in each tissue and in each species. The lipid and fatty acid composition of large, lipid-rich (38–70% wet weight, ww) livers demonstrated the multifunctional role of this organ in: lipid distribution, storage and biosynthesis, and buoyancy regulation. In the liver, the importance of certain lipids (including squalene, diacylglyceryl ethers, triacylglycerols and to a lesser extent wax esters) as mediators of buoyancy varied according to lifestyle and habitat. Less variability was observed in the muscle profiles, characterized by low lipid content (<1.0% ww) and high relative levels of polar lipids (>70%). The lipid and fatty acid profiles of the kidney and pancreas showed the highest intraspecific variability, suggesting these organs also have complex roles in lipid storage and metabolism. Overall intra- and interspecific differences in the tissue fatty acid profiles could be related to differences in a number of factors including phylogeny, habitat (depth), buoyancy regulation and diet and presumably also reflect different ecological roles. The lipid and fatty acid profiles are the first published for Rhinochimaera pacifica, Chimaera lignaria and Figaro boardmani and the first to demonstrate interspecific variation in lipid profiles of various tissues of deepwater chondrichthyans. The application of multivariate analysis to lipid class and fatty acid tissue profiles in chondrichthyans inferred dietary differences and metabolic preferences between species and habitats. These results have important implications for the future use of fatty acids as dietary tracers in chondrichthyan research.     

Occurrence of inflated swimbladders in five species of lanternfishes (family Myctophidae) from waters off southern California

The swimbladders of three species of myctophid fishes (Symbolophorus californiensis, Tarletonbeania crenularis and Diaphus theta, collected in the Southern California Bight between 1963 and 1978), previously observed to have both inflated and noninflated swimbladders as adults, were examined to determine if the swimbladders either vary in their inflation on a diel basis or cease to be inflated and possibly become nonfunctional in some individuals. The swimbladders of two lanternfishes reported to lack inflated swimbladders as adults (Lampanyctus regalis and L. ritteri) were included in the study for comparison. Only the swimbladder of L. regalis did not increase in size with increasing fish size. In the remaining four species, both the lengths and volumes of noninflated swimbladders were positively correlated with fish standard length (SL). Although the swimbladder continued to increase in size, inflated swimbladders were not found in L. ritteri>2 mm SL. Inflated and noninflated swimbladders occurred in overlapping size ranges of S. californiensis, T. crenularis, and D. theta. Only 11% of the D. theta swimbladders were inflated, and the occurrence of inflated swimbladders dit not differ significantly with day vs night capture or fish size. Although the frequency of occurrence of inflated swimbladders decreased significantly in larger S. californiensis, both S. californiensis and T. crenularis caught at the surface at night with a neuston net had significantly higher proportions of inflated swimbladders than did those collected below the surface with either daytime or night-time trawls. The swimbladder does not appear to become nonfunctional in either species. Rather than maintaining either constant volumes or constant masses of gas in their swimbladders during their vertical migrations, both species may inflate their swimbladders only while in the surface waters at night, and have noninflated swimbladders while at other depths of their vertical ranges.     

Chemical composition of midwater fishes as a function of depth of occurrence off the Hawaiian Islands: Food availability as a selective factor?

The variation with depth in water, lipid, protein, carbon and nitrogen contents (% wet weight) of 42 species of midwater fishes, collected in November 1976 off the west coast of Oahu in the Hawaiian Archipelago, was measured. The Hawaiian fishes show significant relationships between these components and depth of occurrence. The slopes of these relationships are not significantly different from those reported for midwater fishes from off California, USA. However, the fishes from Hawaii have significantly lower lipid levels and higher protein levels than do the species from off California. The deep-living Hawaiian species (500 m and deeper) have significantly lower lipid (% wet weight), but there is no significant difference in protein (% wet weight). The difference in lipid contents at all depths appears to be an evolved characteristic, with the greater lipid levels off California being selected for by greater spatial and temporal variation in the food supply for these fishes off the California coast than off Hawaii. The higher protein contents in the shallow-living Hawaiian fishes appear to reflect greater muscle power selected for in these fishes by the greater water clarity, and therefore greater reactive distances, in the surface layers off Hawaii. These conclusions support the general hypothesis that the lower protein contents of bathypelagic fishes are not directly selected by food limitation at depth, but rather result from the relaxation of selection for rapid-swimming abilities at greater depths due to the great reduction at greater depths in the distance over which visual predator-prey interactions can take place. The lower lipid levels in the deeper-living species are apparently made possible by the reduced metabolic rates of these species which reduces their need for energy stores.     

Lipogenesis in the arctic euphausiid Thysanoessa inermis

Biosynthesis of lipids by Thysanoessa inermis collected from Balsfjorden, northern Norway, in May 1980, was examined in vitro. The highest concentration of lipid within the krill was in the hepatopancreas, and this organ was the most active in esterifying free fatty acids into wax esters. The hepatopancreas (i.e., thoracic contents) incorporated (¹⁴C) glucose, (¹⁴C) alanine and ³H₂O into wax esters, with the fatty alcohol moieties being labelled more than the fatty acids. (¹⁴C) fatty acid was incorporated preferentially into the fatty acid moieties of wax esters, this incorporation being markedly stimulated by free fatty alcohol. It is concluded that the fatty alcohols of wax esters are preferentially biosynthesized de novo from dietary protein and carbohydrates, whereas the fatty acids derive preferentially from dietary lipid. On the basis of ³H incorporated from ³H₂O, the hepatopancreas in a 50 mg II-group (2 yr old) individual of T. inermis is capable of biosynthesizing de novo, approximately 0.1 mg of lipid (as fatty acids) per day at 5°C.     

Effect of light on the total lipid content and storage lipids of the symbiotic sea anemoneAnemonia viridis

In order to examine the effect of light level on the storage lipids of the symbiotic sea anemoneAnemonia virudis (Forskäl), anemones were exposed to three experimental light regimes of 10, 100 and 300 E m^-2s^-1. Anemones were fed once a week. After 30 d there were no significant differences in the total lipid levels between anemones at any of the light intensities. However, after 60 d lipids had increased in proportion to light level in both the animal-tissue and zooxanthellae compartments. The higher levels of total lipid were in part due to increases in storage lipid (wax esters and triglycerides). Wax ester levels increased in the animal tissues but remained constant in the zooxanthellae, whereas triglycerides increased in both compartments. In contrast to fed anemones, starved anemones which were maintained at 300 E m^-2s^-1 for 30 or 60 d did not show a statistically significant change in lipid levels at 60 d, although a slight increase in the lipid level was observed. However, there was a significant increase in the storage lipids, which suggested that the non-storage phospholipids and structural lipids had declined as a result of cellular catabolism. The composition of the wax esters and triglycerides of both fed and starved anemones was analysed and compositional changes were observed at higher light intensities.     

Ecological investigations on the zooplankton community in balsfjorden,northern Norway: Lipids and fatty acids in Meganyctiphanes norvegica,Thysanoessa raschi and T. inermis during mid-winter

Total lipid of Meganyctiphanes norvegica (M. Sars) contained 53% triacylglycerols and traces of wax esters, that of Thysanoessa raschi (M. Sars) contained 44% triacylglycerols and 10% wax esters and that of T. inermis (Krøyer) contained 28% triacylglycerols and 40% wax esters. The triacylglycerols of M. norvegica were relatively rich in 20:1 and 22:1 fatty acids and its traces of wax esters resembled those of calanoid copepods. The triacylglycerols of both Thysanoessa species were deficient in 20:1 and 22:1 fatty acids but were richer in 16:1(n-7) and 18:1 (n-7) acids than those of M. norvegica. The wax esters of T. raschi contained phytol as almost the only fatty alcohol and were rich in 16:0 and 18:1 (n-9) fatty acids. The wax esters of T. inermis contained mainly 16:0 and 14:0 fatty alcohols with lesser amounts of phytol and their dominant fatty acid was 18:1, especially the (n-9) isomer. The triacylglycerols of T. inermis had 18:4 (n-3) as the major polyunsaturated fatty acid. From these and other aspects of fatty acid and fatty alcohol analyses it is concluded that a major foodstuff of M. norvegica in Balsfjorden is wax ester-rich calanoid copepods. T. raschi and especially T. inermis are concluded to have much more preference for phytoplanktonic food. Results are discussed in terms of current knowledge of the lipid chemistry of krill in the northern and southern hemispheres.     

On the lipid biochemistry of polar copepods: compositional differences in the Antarctic calanoids Euchaeta antarctica and Euchirella rostromagna

During austral summer of 1985 different developmental stages (CIII, CIV, CV, females, males) of the Antarctic copepod Euchaeta antarctica and females of Euchirella rostromagna were collected in the southeastern Weddell Sea to determine their lipid contents and compositions. For E. antarctica the analyses revealed a strong ontogenetic accumulation of lipids towards the older copepodids with highest lipid contents in late CV stages and adults. The females of E. rostromagna had moderate lipid levels. The most striking difference between these two species concerns their lipid class compositions. E. antarctica deposited predominantly wax esters, whereas in E. rostromagna the major lipid class consisted of triacylglycerols, an unusual storage lipid in polar marine copepods. Principal fatty acids in E. antarctica were the monounsaturates 18:1(n-9) and 16:1(n-7), especially in the lipid-rich stages, while the polyunsaturated fatty acids 20:5(n-3) and 22:6(n-3), usually membrane lipids, dominated in the lipid-poor stages. The wax ester moieties in E. antarctica consisted almost entirely of 14:0 and 16:0 fatty alcohols. Major components in E. rostromagna were the fatty acids 18:1(n-9), 16:0, 20:5(n-3) and 22:6(n-3). The potential of fatty acids and alcohols as typical trophic markers is rendered largely insignificant in the two species due to catabolic processes.     

Biosynthesis of lipds in zooplankton from Saanich Inlet,British Columbia,Canada

Lipid analyses were carried out on various species of zooplankton captured in Saanich Inlet, British Columbia, Canada, during September, 1972. The amphipod Cyphocaris challengeri had the highest level of lipid, consisting mainly of wax esters. The copepod Calanus pacificus had moderate amounts of lipid, with triglyceride as the major neutral lipid. The euphausiid Thysanoessa raschii contained mainly triglyceride in its moderate levels of neutral lipid, while wax esters and, to a lesser extent, triglycerides were present in the very small levels of neutral lipid in the chaetognath Sagitta elegans. The major fatty alcohols in wax esters of both Cyphocaris challengeri and Calanus pacificus were 20:1 and 22:1, although notable differences were found in the major fatty acids. Biosynthetic studies showed that phospholipids were labelled faster than neutral lipids in all species with both (U-¹⁴C) glucose and (1-¹⁴C) palmitic acid as precursors. Only species containing significant amounts of wax esters in their neutral lipids incorporated substantial amounts of radio-activity from (1-¹⁴C) palmitic acid into wax esters in (i) living animals, (ii) preparations containing fragments of tissue, (iii) cell-free systems. All species incorporated added fatty alcohols into wax esters in preparations containing tissue fragments and in cell-free preparations. Both the fatty acid and fatty alcohols of the wax esters of both Calanus pacificus and S. elegans were labelled from (1-¹⁴C) palmitic acid, consistent with de novo biosynthesis of the esters. (1-¹⁴C) hexadecanol was incorporated into wax esters almost entirely in the fatty alcohol moiety. It is concluded that all species examined formed was esters when presented with preformed fatty alcohols, but only those species that had wax esters as a major component of the neutral lipids were capable of de novo biosynthesis of the lipids.     

Complex patterns of change in the macrobenthos of a large sandbank following dredging

The impact of dredging operations on the marine benthos of a large, subtropical, sublittoral sandbank (Middle Banks, Moreton Bay, Queensland, Australia) was investigated during July and August 1982. Statistical comparisons (ANOVA) of species richness, total abundance, Shannon diversity and Shannon equitability were made with extensive predredging data base. Both the dredged and adjacent areas were investigated. Changes in sediments and the distribution and deposition rates of the dredge plumes were also examined. There were significant decreases (P0.025) in the species richness (from 33.0 to 16.6 mean number of species per site), total abundance (from 117.9 to 47.6 mean number of individuals per site) and Shannon diversity (from 4.03 to 3.22 mean diversity per site) within the dredged area. There were significant increases (P0.01) in species richness (from 31.2 to 67.9 mean number of species per site) and total abundance (from 177.7 to 752 mean number of individuals per site) in adjacent benthic areas. The distribution and the predicted deposition rates of the sediment plume correlated precisely with the area of enhancement (P<0.05). The potential causal relationship between deposition and faunal enhancement is discussed. We suggest that the enhanced effect is probably a response of the benthic biota to an increase in available resources.     

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.     

Compositional topography of melon and spermaceti organ lipids in the pygmy sperm whale Kogia breviceps: Implications for echolocation

The forehead of the pygmy sperm whale Kogia breviceps contains a large melon of fatty tissue in front of a small, fat-filled, cornucopia-shaped spermaceti organ. This unique anatomical structure may possibly play an acoustical role in the whale's echolocation system, similar to the fatty melon sound lens postulated for dolphins. To better understand its function, we have studied the compositional topography of the K. breviceps melon and spermaceti organ lipids. The fatty head tissues of an adult K. breviceps were serially sectioned into 9 transverse slices. Appropriate tissue samples were cut from every other slice, and analyzed for % lipid and lipid class composition. Wax esters and triglycerides were the only major lipids present; their average carbon number in each sample was determined by gas-liquid chromatography (GLC). Our topographical analyses of K. breviceps melon indicate 3 regions of distinctive lipid composition: a fat-poor melon exterior, an outer melon of medium fat content having % triglyceride>% wax ester, and a fat-rich inner melon having % wax ester>% triclyceride. The spermaceti organ contains a fat-rich core of very high wax-ester content (84 to 99%), surrounded by a fat-poor case. Average carbon numbers of both wax esters and triglycerides were lowest in the inner melon and the spermaceti organ. At the rear of the spermaceti organ lies the museau de singe, an apparent sound generator. The lipid topography data plus anatomical and acoustical considerations suggest that the K. breviceps melon/spermaceti organ system may function as an acoustical transducer, directing and refracting sound waves from this source for the purpose of echolocation.     

Variation in the lipid content of wild-caught females of the marine shrimpPenaeus kerathurus during sexual maturation

Changes in total lipids, lipid classes and their fatty acid contents were studied in the ovaries and midgut glands ofPenaeus kerathurus Forskäl females during sexual maturation. The shrimp were captured in the Gulf of Cádiz (southwest Spain) in 1990. The lipid content and fatty acids, in relative terms, increased during ovarian development. The greatest changes occurred between Maturation Stages III and IV. Ovarian lipids were dominated by polar classes, whereas in the midgut gland the major classes were triacylglycerols and sterol esters. The amounts of major fatty acids in ovaries (16:0, 16:1n-7, 18:1n-9, 18:1n-7, 20:5n-3 and 22:6n-3) increased with increasing maturity, but declined slightly between Stages III and IV. The total polar lipid content of the midgut was 5.7% (by dry weight) and its fatty acid composition remained constant during the whole study period. Total lipid content of the midgut gland showed an upward trend during sexual maturation, except between Stages II and III, when a slight decrease was observed. Predominant fatty acids in the midgut gland (16:1n-7, 20:5n-3 and 22:6n-3) displayed a noteworthy decline between Stages II and III, corresponding with the marked increase in total lipid fatty acid content in the ovaries during the same period.     

Ontogenetic and seasonal changes in lipid and fatty acid/alcohol compositions of the dominant Antarctic copepods Calanus propinquus,Calanoides acutus and Rhincalanus gigas

Lipid compositions of the dominant Antarctic copepods Calanoides acutus, Rhincalanus gigas and Calanus propinquus from the Weddell Sea have been investigated in great detail. Copepods were collected during summer in 1985 and late spring/early winter in 1986. The analyses revealed specific adaptations in the lipid biochemistry of these species which result in very different lipid components. The various copepodite stages of C. acutus synthesize wax esters with long-chain monounsaturated moieties and especially the alcohols consisted mainly of 20:1(n-9) and 22:1(n-11). R. gigas also generates wax esters, but with moieties of shorter chain length. The fatty alcohols consisted mainly of 14:0 and 16:0 components, while the major fatty acids were 20:5, 18:4 and 22:6, of which 18:4 probably originated from dietary input. In contrast, C. propinquus accumulates triacylglycerols, a very unusual depot lipid in polar calanoid copepods. Major fatty acids in C. propinquus were the long-chain monounsaturates 22:1(n-9) and 22:1(n-11), which may comprise up to 50% of total fatty acids. In C. acutus and C. propinquus there was a clear increase of long-chain fatty acids with increasing developmental stage. In contrast, the fatty acid and alcohol composition of the R. gigas copepodite stages were characterized by the dominance of the polyunsaturated fatty acids as well as high amounts of the monounsaturates 18:1(n-9) and 16:1(n-7). There was a considerable decrease of the dietary fatty acid 18:4(n-3) towards the older stages during summer; in late winter/early spring 18:4 was only detected in very low amounts. This tendency was also found in the other two species, but was less pronounced. In all three species dry weight and lipid content increased exponentially from younger to older stages. The highest portion of wax esters, or of triacylglycerols in C. propinquus, was found in the adults. Dry weight and lipid content were generally higher during summer. In late winter/early spring the variability was more pronounced and lipid-rich specimens showed a selective retention of long-chain monounsaturated fatty acids, whereas in lipid-poor specimens these fatty acids were very much depleted.     

Wax ester biosynthesis by midwater marine animals

Lipid is a major energy reserve in many aquatic animals, and wax esters are the principal type of lipid present in most pelagic marine invertebrates and teleost fishes from deep water or near-surface cold waters. It has been suggested that these wax esters are biosynthesized by only a few organisms, and are then transferred along the food web to the fishes and marine mammals. We found that accessible mesopelagic myctophid (Lampanyctus ritteri, Stenobrachius leucopsarus and Triphoturus mexicanus) and gonostomatid (Cyclothone atraria and Gonodtoma gracile) fishes and crustaceans (Gaussia princeps, Calanus helgolandicus, Acanthephyra quadrispinosa and Sergestes prehensilis) biosynthesize wax esters from acetate, longchain alcohol or fatty acid precursors, in vivo or in vitro. In the latter experiments, organ tissues (hepatopancreas and gut) are more active than muscle, although, overall, fish muscle is probably a major site of wax ester biosynthesis in the species studied. Therefore, wax esters are not persistent dietary survivors in the food web of the oceanic midwaters; rather, most invertebrates and fishes in this environment make wax esters, modifying ingested fats to their own characteristic patterns.     

Acute toxicities of eleven metals to early life-history stages of the yellow crab Cancer anthonyi

We report findings from the first laboratory experiments to assess toxicities of metals found in drilling muds to embryos and prezoeae of a brachyuran crab. Embryos of Cancer anthonyi are brooded externally on the abdomen of female crabs; thus, embryos may be continuously exposed to pollutants contained in sediments of contaminated benthic habitats. Lethal concentrations of metals to embryos after 7 d exposures were: iron and barium (sulfate), 1 000 mg l^–1; barium (chloride), 100 mg l^–1; aluminum and nickel, 10 mg l^–1; copper and lead, l mg l^–1; cadmium, chromium VI and manganese, 0.01 mg l^–1; mercury, 0.001 mg l^–1. All metals effectively retarded embryos from hatching at concentrations equal or lower to those causing mortality, except for cadmium. Particularly impressive was iron, which suppressed hatching at l to 10 mg l^–1, concentrations previously found non-deleterious to marine organisms and 100 times more dilute than concentrations causing significant embryo mortality. The effects of metals on embryos increased as a function of exposure duration. Embryo mortality was delayed for at least 120 h at concentrations 1.0 mg l^–1, with the exception of mercury. Lethal concentrations established at 96 h were meaningless for crab embryos, because acute toxic thresholds were not attained by that time. Larval survivorship to chromium VI, copper, and zinc increased following exposure of embryos to these metals at low concentrations (1.0 mg l^–1), suggesting induction of biochemical pathways for products which bind or metabolize metals. Identical exposures of embryos to lead failed to enhance subsequent larval survivorship, showing that inductions may be metal-specific. We suggest that exposures of brachyuran embryos at field sites and the success of their subsequent hatching in the laboratory may be a means of assessing environmental contamination otherwise difficult to monitor.