Effect of the addition of polyunsaturated fatty acids to the diet on the growth and fecundity ofDaphnia galeata

1. The importance of long-chain polyunsaturated fatty acids (PUFAs), in particular eicosapentaenoic acid (EPA), for the growth and development of Daphnia galeata (Sars) was tested using food types differing in PUFA and EPA contents.
2. Life history experiments of D. galeata fed with the cryptophyceans Rhodomonas lacustris (Pascher & Ruttner) and Cryptomonas pyrenoidifera (Gentler), and the green alga Scenedesmus acutus (Meyen), showed that both cryptophycean species were higher in quality than S. acutus.
3. Since the cryptomonads contained significant amounts of EPA while no EPA could be detected in Scenedesmus , tests were performed to ascertain whether EPA was responsible for the differences in food quality. Feeding daphnids a mixed diet of Scenedesmus and emulsion particles that were rich in EPA and DHA, resulted in a significant improvement in the intrinsic population growth rate. The initial difference in food quality between Scenedesmus and the cryptomonads was completely compensated for by addition of emulsion to the Scenedesmus food.
4. From the observed stimulatory effect of the addition PUFA to the daphnid diet, this study concludes that the presence of such long-chain PUFA improves food quality for daphnids.     

Influence of biochemical,mineral and morphological features of natural food on tropical cladocerans

Five laboratory experiments were performed to evaluate the effect of supplements of fatty acids and a green alga on the individual growth and reproduction of three species of tropical cladocerans Ceriodaphnia richardi, Daphnia ambigua, and D. gessneri feeding on natural seston from the Brazilian Lake Monte Alegre. Cohorts of newborns from cultivated females were submitted to one of the following treatments: (1) Natural seston, (2) Natural seston + microcapsules of EPA and DHA or linoleic and linolenic fatty acids, (3) Natural seston + oil-free microcapsules, and (4) Natural seston + green alga Scenedesmus spinosus (1 mg C l⁻¹). Particulate organic carbon, algal carbon, C:P ratios of seston and green alga, polyunsaturated fatty acids (PUFA) content of seston and cladocerans, as well as phytoplankton composition, size, and shape were measured. The addition of fatty acids to seston did not significantly enhance growth and reproduction of the cladocerans, suggesting that sestonic PUFA content is sufficient for promoting cladoceran development, even in the cool–dry season when the fatty acids used in the experiments were 5–10 times lower in the seston than in the warm–wet season. Despite high C:P molar ratios in most experiments, there was only one indication of growth limitation by P. Reproduction was more affected than individual growth on some occasions by food quantity (energy) caused apparently by algal size, morphology, and digestion resistance. Energy availability, which is affected by algae morphological characteristics, seems to prevail over PUFA and P in controlling growth and reproduction of cladocerans in tropical Lake Monte Alegre.     

Is the fatty acid composition of Daphnia galeata determined by the fatty acid composition of the ingested diet?

1. The fatty acid (FA) composition of Daphnia galeata and their algal food was analysed and showed many similarities, however, some significant differences were also found in the relative abundance of the FA C16 : 4ω3 and docosahexaenoic acid (DHA). Their relative abundances were much lower in daphnids than in their algal diet.
2. When daphnids were fed three distinct emulsion particles with DHA : eicosapentaenoic acid (EPA) ratios of c. 0.7, 2 and 4, the final DHA : EPA ratio in the daphnids always favoured EPA. The increase of the food DHA : EPA ratio resulted in a minor increase of DHA (to c. 2%). Feeding the animals on emulsion particles with increasing ratios of DHA : EPA, caused a minor ( c. 2%) increase of DHA level but EPA levels remained high ( c. 10%).
3. When labelled with [¹⁴C]linoleic acid and [¹⁴C]linolenic acid daphnids showed low conversion of both essential FA into C20 polyunsaturated fatty acids (PUFAs). This low conversion activity might explain the importance of C20 PUFAs as dietary compounds in the food of Daphnia.
4. The results indicate the insignificance of DHA and C16 : 4ω3 for daphnids. As EPA can be derived from C18 : 3ω3 it is not strictly essential, although it might be a significant factor in food quality for Daphnia.     

Temperature affects the limitation of Daphnia magna by eicosapentaenoic acid,and the fatty acid composition of body tissue and eggs

1. Poikilothermic animals incorporate more polyunsaturated fatty acids (PUFAs) into their cellular membranes as temperature declines, suggesting an increased sensitivity to PUFA limitation in cool conditions. To test this we raised Daphnia magna at different temperatures and investigated the effect of varying dietary PUFA on life history parameters (i.e. growth, reproduction) and the PUFA composition of body tissue and eggs. 2. Upon a PUFA‐rich diet (Cryptomonas sp.) females showed higher concentrations of several ω3 PUFAs in their body tissue at 15 °C than at 20 °C and 25 °C, indicating a greater structural requirement for ω3 PUFAs at low temperature. Their eggs had an equal but higher concentration of ω3 PUFAs than their body tissue. 3. In a life history experiment at 15 and 20 °C we supplemented a diet of a PUFA‐free cyanobacterium with the ω3 PUFA eicosapentaenoic acid (EPA). The growth of D. magna was more strongly EPA limited at low temperature. A greater requirement for structural EPA at 15 °C was indicated by a steeper increase in somatic EPA content with dietary EPA compared to 20 °C. 4. At 20 °C the development of eggs to successful hatching was high when EPA was supplied to the mothers. At 15 °C the hatching success was generally poor, despite of a higher maternal provision of EPA to eggs, compared to that at 20 °C, suggesting that EPA alone was insufficient for proper neonatal development at the low temperature. The growth of offspring from mothers raised at 20 °C without EPA supplementation was very low, indicating that the negative effects of EPA deficiency can be carried on to the next generation. 5. The fatty acid composition of Daphnia sp. in published field studies shows increasing proportions of saturated fatty acids with increasing environmental temperature, whereas ω3 PUFAs and EPA show no clear pattern, suggesting that variations in dietary PUFA may mask temperature‐dependent adjustments in ω3 PUFA concentrations of cladocerans in nature.     

Growth Responses of Tropical Cladocerans to Seston from Lake Monte Alegre (Brazil) Supplemented with Phosphorus, Fatty Acids, a Green Algae and a Cyanobacterium

The cladocerans Ceriodaphnia richardi, Daphnia ambigua, D. gessneri and Moina micrura were used to access food quality of Lake Monte Alegre’s seston. Experiments were carried out in summer and autumn as growth assays with lake seston only (control) and seston supplemented with phosphate, fatty acids or Synechococcus, and Scenedesmus. In summer, high C:P ratios in seston suggested strong phosphorus limitation, however, contrary to the expectations of stoichiometric theory, the addition of phosphate to seston did not improve cladoceran growth. Addition of PUFA increased growth rates and clutch size of D. gessneri, suggesting a possible deficiency in essential fatty acids in summer. Addition of Scenedesmus increased significantly growth rates of the cladocerans D. gessneri and C. cornuta, suggesting energy limitation in summer. In autumn, C:P ratios were lower than in summer, but still above the threshold ratio for Daphnia. At this time, addition of phosphate increased significantly growth rates of Daphnia suggesting strong P limitation, especially in D. gessneri. However, energy limitation was still important in autumn, as suggested by a further increase in growth rates in +Syn and +Sce treatments. Energy limitation was especially strong for Moina micrura, which is a fast-growing species, with high P content. Algal digestion resistance is a plausible hypothesis for energy limitation, since carbon concentrations in both seasons were above incipient limiting levels. These results show that the seston C:P ratio was not a consistent predictor of cladoceran P limitation and that factors other than P and energy limitation seem to be also important, such as PUFA or other biochemical factors. An erratum to this article is available at .     

UV radiation and phosphorus interact to influence the biochemical composition of phytoplankton

1. Numerous laboratory studies have shown that food quality is suboptimal for zooplankton growth. However, little is known about how food quality is affected by the interaction of potential global change factors in natural conditions. Using field enclosures in a high altitude Spanish lake, seston was exposed to increasing phosphorus (P) concentrations in the absence and presence of UV radiation (UVR) to test the hypothesis that interactions between these factors affected the biochemical and stoichiometric composition of seston in ways not easily predicted from studies of single factors. 2. Phosphorus enrichment increased the content of total fatty acids (TFA), ω3‐polyunsaturated fatty acids (ω3‐PUFA) and chlorophyll‐a : carbon (Chl‐a : C) and C : N ratios in seston. The pronounced increase in ω3‐PUFA was largely explained by the enhancement of 18:3n‐3 (α‐linolenic acid). In contrast, P‐enrichment lowered the content of highly unsaturated fatty acids (HUFA), the HUFA : PUFA ratio and, at high P loads, seston C : P ratio. Although phytoplankton assemblages dominated by Chlorophytes were not rich in HUFA, seston in the control had substantially higher 20:4n‐6 (arachidonic acid, ARA) content (79% of HUFA) than did P‐enriched enclosures. 3. The UVR increased the content of ω3‐PUFA and TFA in seston at the two ends of the trophic gradient generated at ambient and high concentrations of P, but decreased seston C : P and HUFA at all points on this gradient. ARA was not detected in the presence of UVR. 4. The interaction between P and UVR was significant for seston HUFA and C : P ratios, indicating that the effect of UVR in reducing HUFA (decreased food quality) and C : P ratios (enhanced food quality) was most pronounced at the low nutrient concentrations characteristic of oligotrophic conditions and disappeared as P increased. Therefore, any future increase in UVR fluxes will probably affect most strongly the food quality of algae inhabiting oligotrophic pristine waters although, at least in the Mediterranean region, these effects could be offset by greater deposition of P from the atmosphere.     

Preface

Recent studies on food quality for zooplankton have developed two new hypotheses, the importance of the dietary carbon to phosphorus (C : P) ratio and of certain ‘essential’ fatty acids. These new hypotheses, the controversies they have provoked and the general lack of field studies prompted us to organize a workshop. Thus, the first international Plankton Ecology Group (PEG) workshop on The Role of Food Quality for Zooplankton was held from 17 to 21 March 1996 at the Centre of Limnology in Nieuwersluis, the Netherlands. The main objectives were to take stock of the state-of-the-art in food quality research, to address the factors that determine food quality, and to integrate the available information into a coherent and consistent view of food quality for the zooplankton. In contrast to most PEG meetings, we restricted the meeting to about 35 participants. However, international participation was broader than usual and included colleagues from North America and Asia, as well as Europe. The workshop’s organizers, Ramesh Gulati, a senior scientist, and Paul M. M. Weers, a post-doc at the Centre Of Limnology, approached potential speakers, in some cases suggesting topics for presentation. Each of five sessions was introduced with a review paper or a modelling paper.This special volume of Freshwater Biology contains twenty-six papers, including a summary by R. Gulati & B. DeMott. This paper briefly describes the findings of the workshop, and discusses them in light of the literature, discussions at the workshop and written comments from participants. Each of the workshop papers was peer reviewed, usually by two but in some cases by three referees. We learned that fatty acids and phosphorus are not mutually exclusive alternatives; the content of polyunsaturated acids of certain algae, especially eicosapentaenoic acid (EPA), is markedly affected by the algal P content. Thus, elemental limitation and fatty acid limitation may have additive or interacting effects. Although further research might modify this view, the accumulating evidence for P limitation seems stronger than for fatty acids limitation. However, despite laboratory studies that have clarified the potential mechanisms of food quality, the paucity of field studies prevents a consensus on the importance of specific mechanisms in nature. We also learned much from aquaculture studies, which have developed techniques for enriching zooplankton food with fatty acids and essential nutrients. We believe that the workshop proceedings will both contribute to our understanding and stimulate further research on food quality for zooplankton. Lastly, we take cognizance that cyanobacterial toxins are an important area of food quality research, which for practical reasons, did not receive our attention. Several presentations, however, revealed that cyanobacteria are also potentially poor food due to both higher C:P ratios and lower fatty acid content than many other algal species.Paul Weers’ efforts in organizing the workshop were very helpful. We acknowledge the facilities, funds and encouragement provided by staff and administration of the Centre of Limnology. We are also grateful to the participants for their cooperation and to the reviewers, many of whom were workshop participants.RAMESH D. GULATI BILL DE MOTT     

两种水华藻——球形棕囊藻和铜绿微囊藻的脂肪酸组成特征与水华形成机制

浮游植物所含的不饱和脂肪酸是测定其作为食物质量的指标,并在浮游植物向浮游动物及其它动物能量转化过程中起着关键的作用,必需不饱和脂肪酸的缺乏有利于水华的形成。球形棕囊藻(Phaeocystis globosa)和铜绿微囊藻(Microcystis aeruginosa)分别是常见的海洋和淡水水华藻类,该文分析了它们在不同生长期的脂肪酸组成,探讨了这两种藻类的脂肪酸组成特征。球形棕囊藻和铜绿微囊藻的脂肪酸碳链长为14~20个碳原子,脂肪酸种类组成都比较简单,以饱和脂肪酸为主,未检测到二十碳五烯酸(Eicosapentaenoic acid,EPA)和二十二碳六烯酸 (Docosahexaenoic acid,DHA)等动物的必需脂肪酸。球形棕囊藻的总脂肪酸含量在247.294~735.44 μg·g^-1干重之间,在对数期和延滞期含量最高的脂肪酸分别是C14:0和C16:0;而两株铜绿微囊藻的总脂肪酸在1 405.095~6 087.617μg·g^-1干重之间,以C16:0含量最高。两株铜绿微囊藻的脂肪酸含量在对数期和延滞期差异明显(p<0.05),但球形棕囊藻的脂肪酸含量在不同生长期差别不大。由于缺乏必需脂肪酸EPA和DHA,球形棕囊藻和铜绿微囊藻不能为高营养级的生物提供必需的不饱和脂肪酸,不是浮游动物等生物的良好食物。因此球形棕囊藻和铜绿微囊藻作为浮游动物的食物质量较低,浮游动物对它们的捕食压力也较小,可能是这两种藻容易暴发水华的重要原因。     

Accumulation of polyunsaturated fatty acids by cladocerans: effects of taxonomy,temperature and food

1. Zooplankton are important in transferring dietary nutrients, including polyunsaturated fatty acids (PUFA), up through aquatic food webs. 2. We tested the hypothesis that the taxonomic composition of zooplankton affects the retention and subsequent transfer of PUFA from upwards through the food web. Using laboratory experiments, we investigated dietary PUFA accumulation and bioconversion capacities of six cladoceran species (Ceriodaphnia sp., Daphnia longispina, Daphnia magna, Daphnia pulex, Scapholeberis mucronata and Simocephalus vetulus) fed on two diets (Scenedesmus obliquus and Cryptomonas sp.) that differed in their PUFA profiles. We performed experiments at two different temperatures (14 and 20 °C) to assess the role of temperature in the trophic transfer of PUFA. 3. There was little variation in the concentrations of PUFA in these cladocerans which were controlled by dietary PUFA supply. Moreover, as expected, the concentrations of PUFA in all cladoceran species were higher at low temperature. 4. However, even if the composition of PUFA in the cladoceran species generally corresponded to that in their diet, preferential accumulation of some PUFA was recorded in all these taxa. When fed on a highly unsaturated fatty acid‐deficient diet, all the cladocerans showed some ability to convert C18‐PUFA into arachidonic acid and eicosapentaenoic acid. Interspecific variation in the ability to accumulate and bioconvert PUFA in cladocerans was more pronounced at low temperature (14 °C) for both diets. 5. Our results strongly suggest that in heterogeneous habitats with food partitioning between co‐existing cladocerans, foraging behaviour may affect the transfer of PUFA more strongly than interspecific variation in accumulating and/or bioconverting dietary PUFA.     

Essential fatty acids and phosphorus in seston from lakes with contrasting terrestrial dissolved organic carbon content

1. It is often assumed that lakes highly influenced by terrestrial organic matter (TOM) have low zooplankton food quality because of elemental and/or biochemical deficiencies of the major particulate organic carbon pools. We used the biochemical [polyunsaturated fatty acids, especially eicosapentaenoic acid (EPA) – 20:5ω3] and elemental (C : P ratio) composition of particulate matter (PM) as qualitative measures of potential zooplankton food in two categories of lakes of similar primary productivity, but with contrasting TOM influence (clear water versus humic lakes). 2. C : P ratios (atomic ratio) in PM were similar between lake categories and were above 400. The concentration (μg L⁻¹) and relative content (μg mg C⁻¹) of EPA, as well as the particulate organic carbon concentration, were higher in the humic lakes than in the clear‐water lakes. 3. Our results show high fatty acid quality of PM in the humic lakes. The differences in the biochemical quality of the potential zooplankton food between lake categories can be attributed to the differences in their phytoplankton communities. 4. High biochemical quality of the food can result in high efficiency of energy transfer in the food chain and stimulate production at higher trophic levels, assuming that zooplankton are able to ingest and digest the resource available.     

Fatty acid retention under temporally heterogeneous dietary intake in a cladoceran

Omega‐3 (ω3) and ‐6 (ω6) polyunsaturated fatty acids (PUFA) are essential for all aquatic animals, but their dietary availability can be highly heterogeneous in space and time. The way consumers retain PUFA across such heterogeneous feeding conditions remains poorly understood. In a series of feeding experiments, we investigated how retention efficiencies (i.e. amount in consumer biomass/amount ingested) of PUFA and bulk carbon responded to heterogeneous PUFA intake in Daphnia magna. Heterogeneous PUFA intake was achieved by exposing D. magna to algal diets of different PUFA content and composition for specific time periods. The retention efficiency of carbon did not change among dietary treatments. At shorter exposure to PUFA‐rich diet, retention efficiencies of most PUFA were 2–3 times higher than that of bulk carbon, clearly indicating PUFA bioaccumulation in D. magna. Increasing exposure to PUFA‐rich diet caused exponential decrease of retention efficiencies for most PUFA. However, D. magna receiving more PUFA were richer in these compounds despite lower retention efficiency. Eicosapentaenoic (20:5ω3) and arachidonic acid (20:4ω6) and their precursors were always supplied in the same proportions (3.6:1), but the 20:5ω3/20:4ω6 ratio in D. magna (an important measure of nutritional quality for consumers) increased with exposure time to these PUFA from 2.2:1 to 3.8:1, thus eventually matching the diet. Our results suggest that D. magna is an efficient gatherer, accumulator, and repository of PUFA under low/fragmented dietary availability. However, at higher availabilities, PUFA are not always bioaccumulated in D. magna. Hence, the efficiency of PUFA transfer by daphnids in food webs may depend on temporal PUFA availability and its range of variation. Finally, we show that heterogeneity in PUFA intake may also affect higher trophic levels by influencing nutritionally critical PUFA ratios of zooplankton.     

Differences in dietary and plasma fatty acids between wild and captive populations of a rare reptile, the tuatara (Sphenodon punctatus)

Tuatara (Sphenodon) are rare reptiles endemic to New Zealand. Wild tuatara on Stephens Island (study population) prey on insects as well as the eggs and chicks of a small nesting seabird, the fairy prion (Pachyptila turtur). Tuatara in captivity (zoos) are fed diets containing different insects and lacking seabirds. We compared the fatty acid composition of major dietary items and plasma of wild and captive tuatara. Fairy prions (eaten by tuatara in the wild) were rich in C20 and C22 polyunsaturated fatty acids (PUFA), especially the n-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). In contrast, items from the diet of captive tuatara contained no C20 and C22 PUFA and were higher in medium-chain and less unsaturated fatty acids. Plasma from wild tuatara was higher in n-3 PUFA [including alpha-linoleic acid (C18:3n-3), EPA and DHA], and generally lower in oleic acid (C18:1) and palmitic acid (C16:0), than plasma from captive tuatara in the various fractions (phospholipid, triacylglycerol, cholesterol ester and free fatty acids). Plasma from wild adult tuatara showed strong seasonal variation in fatty acid composition, reflecting seasonal consumption of fairy prions. Differences in the composition of diets and plasma between wild and captive tuatara may have consequences for growth and reproduction in captivity. Accepted: 3 August 1998     

Effects of essential fatty acids and N and P-limited algae on the growth rate of tropical cladocerans

SUMMARY 1. In this study, the effects of nutrient (N and P) deficiency and the importance of essential polyunsaturated fatty acids (PUFA) [eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)] to tropical cladocerans, growth and reproduction were determined in a growth bioassay.
2. The animals were fed N/P-sufficient, N-deficient and P-deficient algae, and also N and P-deficient algae supplemented with fish oil emulsions rich in EPA and DHA.
3. Cladocerans showed different responses to nutrient-deficient algae and also to supplements of fish oil emulsions. Moina micrura was most sensitive to P-deficient alga and, surprisingly, grew better and produced more eggs in N-deficient alga than in N/P sufficient alga. Ceriodaphnia cornuta was less sensitive, growing well in both N and P-deficient algae. This species, however, had a lower clutch size in N-deficient alga. On the other hand, Daphnia gessneri was the most sensitive to mineral limitation, showing decreased growth and clutch size in both nutrient-deficient algae.
4. The PUFA supplements to nutrient-deficient algae increased growth rates only for M. micrura and C. cornuta , suggesting that these fatty acids are important food requirements for these species.     

Biotic invasions can alter nutritional composition of zooplankton communities

Ecologists and ecosystem managers often base their understanding of trophic dynamics on consumer and resource biomass. However, the factors that alter the relative nutritional value of resources are often poorly understood, despite their potential to decouple trophic interactions. Recent population declines in pelagic fishes of the upper San Francisco Estuary were not accompanied by an equivalent decrease in zooplankton biomass, which are the main resource for the fish and their larvae. It was hypothesized that changes in zooplankton nutritional conditions following the establishment of invasive species caused food‐quality related limitations for these higher‐order consumers. Using stable isotopes, elemental stoichiometry and fatty acid analyses for all dominant invasive and native zooplankton taxa and seston, we characterized the plankton community structure in the estuary and demonstrated taxon‐specific differences in their nutritional value. We then quantified the temporal dynamics in meso‐zooplankton proportions of docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), polyunsaturated fatty acids (PUFA), and ratio of n3:n6 fatty acids. We found temporal increase in the community‐level DHA, n3 to n6 fatty acid ratio, decrease in the community‐level EPA and PUFA in the brackish water region, but no change in the bulk PUFA proportions in the freshwater region of the estuary. These changes were caused mainly by declines of native cladocerans that are rich in EPA and by an increase in the dominance of invasive taxa with high DHA concentrations, similar to that of native taxa. Although we showed temporal shifts in individual fatty acid classes, the proportion of the essential fatty acids remained relatively high, suggesting that nutritional prey availability for fish remained unchanged with the shift in species composition. We argue that the nutritional content of resource communities should be considered when analyzing the long‐term trophic dynamics and designing effective management and restoration strategies.     

Light,nutrients and the fatty acid composition of stream periphyton

1. While the balance of light and nutrients is known to influence the food quality of herbivores by altering algal phosphorus and nitrogen content, the combined effects of light and nutrients on fatty acid synthesis in freshwater periphyton are relatively unknown. In this study, we manipulated light and phosphorus concentration in large, flow‐through experimental streams to examine their effects on both elemental stoichiometry and fatty acid content in periphyton. 2. Two levels of phosphorus (4 and 80 μg L^?1) and three of light (17, 40, 110 μmol photons m^?2 s^?1) were applied in a factorial design in two separate experiments. Diatoms dominated periphyton communities in both experiments, comprising >95% of algal biovolume. Periphyton growth in the streams was simultaneously affected by both resources, even at low rates of supply. 3. Periphyton C/P and C/N ratios increased with light augmentation and decreased with phosphorus enrichment, and consistent with the light : nutrient hypothesis (LNH). Light effects were strongest in streams with low phosphorus concentrations. 4. Periphyton fatty acids reflected the dominance of diatoms : palmitic (16 : 0), palmitoleic (16 : 1ω7) and eicosapentanoic (20 : 5ω3) were the principal saturated (SAFA), monounsaturated (MUFA) and polyunsaturated fatty acids (PUFA), respectively. Linoleic (18 : 2ω6) and linolenic (18 : 3ω3) acids, characteristic of chlorophytes and cyanophytes, were rare, comprising <2% of total fatty acids. 5. Periphyton fatty acid profiles were highly sensitive to light and phosphorus. The proportion of fatty acids comprised by SAFA and MUFA increased with light augmentation and decreased with phosphorus enrichment, whereas PUFA decreased with light and increased with phosphorus. Light effects on fatty acid composition were strongest in phosphorus‐poor streams. PUFA declined with increasing light/phosphorus ratios in the streams, whereas ‘energy’ fatty acids (16 : 0 and 16 : 1) increased. The ratio of SAFA/PUFA was strongly and positively correlated with C/P and C/N ratios. SAFA and MUFA, normalised to dry mass, increased two‐ to threefold with increasing light, while PUFA normalised to dry mass was not significantly affected by light. 6. Similarities in the responses of fatty acids and elemental stoichiometry to light and phosphorus treatments suggested that they were influenced by a common mechanism. Both components of food quality appeared to be sensitive to light‐regulated rates of carbon fixation which, when coupled with insufficient supplies of phosphorus, caused diatom cells to store surplus carbon in SAFA, MUFA and other carbon‐rich compounds that diluted both essential fatty acids and mineral nutrients.     

Seasonal variation in fatty acid composition of silver pomfrets,Pampus argenteus (Euphrasen), in Kuwait waters

Proximate and fatty acid composition of wild silver pomfrets, Pampus argenteus, were studied in Kuwait waters for a period of 1 year (November 2007–October 2008) to see whether there were any seasonal compositional differences between males and females. Ten adults (five males, five females) were sampled each month during (i) Pre‐spawning (March–May), (ii) Spawning (June–August), (iii) Post‐spawning (September–November), and (iv) Winter (December–February). Both sexes had significantly (P < 0.05) higher whole body moisture and lower crude protein and lipid contents in winter compared to the respective males and females sampled in other seasons. However, females had significantly higher (9.1%) lipid content during the pre‐spawning season than females in other seasons (7.0–8.2%). The most abundant fatty acid in whole body lipid in both sexes was C16 followed by C18:1n‐9, which accounted for about 31–35% and 22–24% of total lipids, respectively. Males in the pre‐spawning and spawning seasons had significantly higher total monosaturated fatty acids (MUFA) than males and females in post‐spawning and winter. Males had significantly higher total polyunsaturated fatty acids (PUFA) during post‐spawning seasons than females in pre‐spawning and winter seasons. However, there were no significant differences (P > 0.05) in total saturated fatty acids (SFA), PUFA, EPA (eicosapentaenoic acid), DHA (docosahexaenoic acid) or n‐3/n‐6 ratios between respective males and females in different seasons. Livers in males had significantly (P < 0.05) higher MUFA, SFA, PUFA, EPA and DHA than respective females in all months during the spawning season. Female gonads had significantly (P < 0.05) higher MUFA and PUFA but lower SFA content than males in different months during the spawning season. In contrast to the liver, the gonad DHA content and n‐3/n‐6 ratios in females were significantly higher than in males. The gonads from both sexes contained more than double the amount of EPA present in liver; in the case of DHA this was more than three‐fold higher in female gonads, but not in males. Thus, the presence of higher proportions of PUFA, EPA and DHA in gonads, particularly in eggs of silver pomfret, indicates their need for these fatty acids, which may be used as a guideline for dietary essential n‐3 fatty acid requirements for feed formulation of this species. A higher content of DHA in eggs also indicates the higher requirement for DHA in the broodstock diet of silver pomfret.     

Effect of frozen storage on fatty acid composition of the different tissues of four scombrid and one dussumeriid species

In the current study, the effect of frozen storage at ?18°C was evaluated on fatty acid composition of different body parts (liver, muscle tissue, and viscera) of narrow‐barred Spanish mackerel (Scomberomorus commerson, Lacépède, 1800), longtail tuna (Thunnus tonggol, Bleeker, 1851), kawakawa (Euthynnus affinis, Cantor, 1849), king mackerel (Scomberomorus guttatus, Bloch & Schneider, 1801), and rainbow sardine (Dussumieria acuta, Valenciennes, 1847) caught in the Persian Gulf. Changes in saturated fatty acids (SFAs), monounsaturated fatty acids (MUFAs), polyunsaturated fatty acids (PUFAs), eicosapentaenoic acid plus docosahexaenoic acid/palmitic acid (EPA+DHA/C16), ω3 PUFA/ω6 PUFA (ω3/ω6), and polyunsaturated fatty acids/saturated fatty acids (PUFA/SFA) were investigated during a 6‐month period. A decrease in unsaturated fatty acids, particularly PUFAs (60–100%) as well as ω3/ω6, EPA+DHA/C16 (polyene index) and PUFA/SFA ratios, indicated a decrease in the nutritional values of the samples.     

Vallisneria natans detritus supports Daphnia magna somatic growth and reproduction under addition of periphyton

Submerged macrophytes are regarded as being hardly assimilated by zooplankton for their lack of essential nutrients such as polyunsaturated fatty acids (PUFAs) thus serve as poor quality food, contrary to field stable isotopic investigations with observed macrophyte carbon contributions to zooplankton. However, periphyton growing on them produces the PUFAs and is thus a nutrient supplement. We hypothesize that with this supplement, zooplankton can be supported by macrophyte carbon. To test this hypothesis, we fed zooplankton with (1) ¹³C enriched Vallisneria natans detritus, (2) periphyton and (3) a mix of the two. We compared growth and reproduction of zooplankton under these three food treatments and calculated zooplankton assimilation of macrophyte carbon when fed a mixed diet, using a stable isotope-mixing model. The fatty acid profile of the two carbon resources was also analyzed. Our results demonstrate that Daphnia magna can grow and reproduce well, and use V. natans carbon when a supplement of periphyton is available.

     

Seasonal correlations of elemental and ω3 PUFA composition of seston and dominant phytoplankton species in a eutrophic Siberian Reservoir

The elemental and fatty acid composition of seston was studied for 3 years, from May to October, in a small Reservoir. Under comparatively low C:P ratio, multivariate canonical analysis revealed no straightforward simple correlations between phosphorus and single ω3 PUFA species, but complex significant interaction between elemental composition (stoichiometry) of seston and total sestonic ω3 PUFA as a whole. Since sestonic C, P and N were found to originate mostly from phytoplankton, the contents of particulate elements and PUFA were attributed to single species in periods of their pronounced dominance. Phytoplankton species of genera of Stephanodiscus, Peridinium, Gomphosphaeria, Planktothrix and Anabaena in periods of their pronounced dominance had relatively constant species-specific elemental and PUFA composition. Phytoplankton species significantly differed in their elemental and PUFA composition, as well as in ratios of C:N, N:P, PUFA:P and partly C:P that indicate food quality for zooplankton. Hence, there were no phytoplankton species of clearly high or low nutritional value. All of phytoplankters, or at least detritus, that originated from them, may meet specific elemental and biochemical requirements of specific groups of zooplankton. Dividing phytoplankton on basis of their elemental and biochemical composition, i.e., nutrition quality, into large taxa (cyanobacteria, diatoms, etc.) appeared to be too coarse for assessing nutritional value for zooplankton.