Improving estimates of trophic shift (Δδtrophic) for diet reconstruction studies using enzyme activities

For diet reconstruction studies using stable isotopes, accurate estimates of trophic shift (Δδ_trophic) are necessary to get reliable results. Several factors have been identified which affect the trophic shift. The goal of the present experiment was to test whether measurements of the activities of enzymes could improve the accuracy of estimation of trophic shift in fish. Forty-eight Nile tilapia (Oreochromis niloticus) were fed under controlled conditions with two diets differing in their protein content (21 and 41%) each at four different levels (4, 8, 12 and 16 g kg^? 0.8 d^? 1). At the end of the feeding experiment, proximate composition, whole body δ¹³C and δ¹⁵N as well as the activities of enzymes involved in anabolism and catabolism were measured. Step-wise regression specified contributing variables for Δδ¹⁵N (malic enzyme, aspartate aminotransferase and protein content) and Δδ¹³C_{lipid-free material} (aspartate aminotransferase and protein content). Explained variation by using the significant main effects was about 70% for Δδ¹⁵N and Δδ¹³C_{lipid-free material}, respectively. The results of the present study indicate that enzyme activities are suitable indicators to improve estimates of trophic shift.     

Isotopic discrimination between food and blood and feathers of captive penguins: implications for dietary studies in the wild

Using measurements of naturally occurring stable isotopes to reconstruct diets or source of feeding requires quantifying isotopic discrimination factors or the relationships between isotope ratios in food and in consumer tissues. Diet-tissue discrimination factors of carbon ((13)C/(12)C, or delta (13)C) and nitrogen ((15)N/(14)N, or delta (15)N) isotopes in whole blood and feathers, representing noninvasive sampling techniques, were examined using three species of captive penguins (king Aptenodytes patagonicus, gentoo Pygoscelis papua, and rockhopper Eudyptes chrysocome penguins) fed known diets. King and rockhopper penguins raised on a constant diet of herring and capelin, respectively, had tissues enriched in (15)N compared to fish, with discrimination factors being higher in feathers than in blood. These data, together with previous works, allowed us to calculate average discrimination factors for (15)N between whole lipid-free prey and blood and feathers of piscivorous birds; they amount to +2.7 per thousand and +4.2 per thousand, respectively. Both fish species were segregated by their delta (13)C and delta (15)N values, and importantly, lipid-free fish muscle tissue was consistently depleted in (13)C and enriched in (15)N compared to whole lipid-free fish. This finding has important implications because previous studies usually base dietary reconstructions on muscle of prey rather than on whole prey items consumed by the predator. We tested the effect of these differences using mass balance calculations to the quantification of food sources of gentoo penguins that had a mixed diet. Modeling indicated correct estimates when using the isotopic signature of whole fish (muscle) and the discrimination factors between whole fish (muscle) and penguin blood. Conversely, the use of isotopic signatures of muscle together with discrimination factors between whole fish and blood (or the reverse) leads to spurious estimates in food proportions. Consequently, great care must be taken in the choice of isotopic discrimination factors to apply to wild species for which no controlled experiments on captive individuals have been done. Finally, our results also indicate that there is no need to remove lipids before isotopic analysis of avian blood.     

Dietary protein source affects lipid metabolism in the European seabass (Dicentrarchus labrax)

The study was undertaken to evaluate the effects of dietary protein sources on lipogenesis and fat deposition in a marine teleost, the European seabass (Dicentrarchus labrax). Four isonitrogenous (crude protein (CP, Nx6.25), 44% DM) and isoenergetic (22-23 kJ/g DM) diets were formulated to contain one of the following as the major protein source: fish meal (FM), one of two soy protein concentrates (SPC) and corn gluten meal (CGM). Apparent digestibility coefficients of the diets and raw ingredients, as well as soluble nitrogen (ammonia and urea) and phosphorus excretion were measured. Growth rates of seabass fed plant protein-based diets were significantly lower than those fed fish meal based diet. The protein utilisation was strongly correlated to the dietary essential amino acids index. Measurements of N excretion (ammonia and urea nitrogen) confirmed these data. Daily fat gain at the whole body level ranged between 1.1 to 1.7 g/kg BW, with the highest values being recorded in fish fed the fish meal based diet. Levels of plasma triglycerides and cholesterol were lower in fish fed soy protein diets than in those fed the diet solely based on fish meal. Soy protein rich diets decreased the activities of selected hepatic lipogenic enzymes (glucose 6-phosphate dehydrogenase, malic enzyme, ATP-citrate lysase, acetylcoenzyme A carboxylase and fatty acid synthetase). Highest lipogenic enzyme activities where found in fish fed the fish meal diet, except for fatty acid synthetase which was increased in seabass fed the corn-gluten meal based diets. Overall data suggest that dietary protein sources affects fat deposition and the lipogenic potential in European seabass.     

Suppression of hepatic fatty acid synthase by feeding alpha-linolenic acid rich perilla oil lowers plasma triacylglycerol level in rats

This study was performed to determine the effects of dietary perilla oil, a n-3 alpha-linolenic acid (ALA) source, on hepatic lipogenesis as a possible mechanism of lowering triacylglycerol (TG) levels. Male Sprague-Dawley rats were trained for a 3-hour feeding protocol and fed one of five semipurified diets as follows: 1% (w/w) corn oil control diet, or one of four diets supplemented with 10% each of beef tallow, corn oil, perilla oil, and fish oil. Two separate experiments were performed to compare the effects of feeding periods, 4 weeks and 4 days. Hepatic and plasma TG levels were decreased in rats fed perilla oil and fish oil diets, compared with corn oil and beef tallow diets. The activities of hepatic lipogenic enzymes such as fatty acid synthase (FAS), glucose-6-phosphate dehydrogenase, and malic enzyme were suppressed in the fish oil, perilla oil, and corn oil-fed groups, and the effect was the most significant in the fish oil-fed group. Also, the activities of glycolytic enzymes, glucokinase, and L-pyruvate kinase showed the similar trend as that of lipogenic enzymes. The activity of FAS, the key regulatory enzyme in lipogenesis, was positively correlated with hepatic and plasma TG levels and reduced significantly in the perilla oil-fed group compared with corn oil-fed group. In addition, the FAS activity was negatively correlated with the hepatic microsomal content of EPA and DHA. In conclusion, suppression of FAS plays a significant role in the hypolipidemic effects observed in rats fed ALA rich perilla oil and these effects were associated with the increase of hepatic microsomal EPA and DHA contents.     

Effects of elemental composition on the incorporation of dietary nitrogen and carbon isotopic signatures in an omnivorous songbird

The use of stable isotopes to infer diet requires quantifying the relationship between diet and tissues and, in particular, knowing of how quickly isotopes turnover in different tissues and how isotopic concentrations of different food components change (discriminate) when incorporated into consumer tissues. We used feeding trials with wild-caught yellow-rumped warblers (Dendroica coronata) to determine delta15N and delta13C turnover rates for blood, delta15N and delta13C diet-tissue discrimination factors, and diet-tissue relationships for blood and feathers. After 3 weeks on a common diet, 36 warblers were assigned to one of four diets differing in the relative proportion of fruit and insects. Plasma half-life estimates ranged from 0.4 to 0.7 days for delta13C and from 0.5 to 1.7 days for delta15N . Half-life did not differ among diets. Whole blood half-life for delta13C ranged from 3.9 to 6.1 days. Yellow-rumped warbler tissues were enriched relative to diet by 1.7-3.6% for nitrogen isotopes and by -1.2 to 4.3% for carbon isotopes, depending on tissue and diet. Consistent with previous studies, feathers were the most enriched and whole blood and plasma were the least enriched or, in the case of carbon, slightly depleted relative to diet. In general, tissues were more enriched relative to diet for birds on diets with high percentages of insects. For all tissues, carbon and nitrogen isotope discrimination factors increased with carbon and nitrogen concentrations of diets. The isotopic signature of plasma increased linearly with the sum of the isotopic signature of the diet and the discrimination factor. Because the isotopic signature of tissues depends on both elemental concentration and isotopic signature of the diet, attempts to reconstruct diet from stable isotope signatures require use of mixing models that incorporate elemental concentration.     

Insights into fish host-parasite trophic relationships revealed by stable isotope analysis

Trophic relationships between 10 species of fish host and their associated nematode, cestode, and copepod parasites were investigated using stable isotopes of carbon and nitrogen. Nematodes and cestodes were consistently depleted in 15N with respect to their host, and such fractionation patterns are unlike those conventionally observed between consumers and their diets. Species of copepod parasite were sometimes depleted and sometimes enriched in 15N with respect to fish hosts, and this confirms earlier reports that the nature and magnitude of ectoparasite-host fractionations can vary. Significant differences in delta15N and delta13C were observed among fish tissues, and the isotopic signature of parasites did not always closely correspond to that of the tissue with which the parasite was found most closely associated, or on which the parasite was thought to be feeding. Several possible explanations are considered for such discrepancies, including selective feeding on specific amino acids or lipids, migration of the parasite among different fish tissues, changes in the metabolism of the parasite associated with life history and migration between different host animals.     

Stable Isotope Trophic Shifts in White-Tailed Deer

Abstract Differences between diet and tissue isotope values known as trophic shifts (Δδ¹³C and Δδ¹⁵N) occur during digestion and assimilation of consumed food. Consideration of trophic shifts is essential when using stable isotopes for dietary reconstruction but has received little attention for cervids. Therefore, our purpose was to determine C and N trophic shifts in tissues of captive white-tailed deer (Odocoileus virginianus) fed corn and alfalfa in known amounts over a 4-month period. Antler has also received limited consideration for use in dietary reconstruction, thus, we analyzed tissue to expose variation among locations along the main beam and between antler components. We collected antler, hair, red blood cells (RBCs), and serum at the end of the feeding trial and analyzed them to determine C (δ¹³C) and N (δ¹⁵N) isotope values. Trophic shifts occurred between diet and all tissues for both isotopes with mean Δδ¹³C = 1.19 ± 2.23% and Δδ¹⁵N = 4.93 ± 0.74%. Antler trophic shifts were greater than those in all other tissues for δ¹³C, whereas antler and RBCs shared similar trophic enrichment over diet but differed from hair and serum for Δδ¹⁵N. Trophic shift values were significantly related to diet in hair and serum for δ¹³C and antler and RBCs for Δδ¹⁵N. Isotope values for antler core and periphery plus antler locations along the main beam did not vary. Antler collagen significantly varied from whole antler for δ¹³C but not δ¹⁵N. Our findings provide mean trophic shift values by tissue that can be used for dietary reconstruction in the study and management of cervids.     

Stable isotope variability in tissues of the Eurasian perch Perca fluviatilis

Stable isotope analysis is frequently used as a complementary method of dietary analysis, to describe trophic relationships and assess food-web structure. These studies allow a precise determination, based on the calculation of a diet-tissue fractionation factor. The fractionation factor, determined for whole organisms or specific tissues, may vary substantially in natura. In the present study, delta13C and delta15N were assessed in lipid-free tissues (spleen, liver, viscera, scales, gills, spine, white muscle, brain) and in available energy reserves (proteins, glycogen, lipids) of Eurasian perch (Perca fluviatilis) reared under controlled conditions and fed for 4 months with the same artificial diet. Some discrepancies in delta15N and delta13C data were observed among tissues, respectively up to 3.43 per thousand and 2.54 per thousand for delta15N and delta13C. The 15N signature in organs depends on their metabolic activity. Despite a significant delta13C enrichment from feed to tissues, the lipids in spine, liver and viscera exhibit a certain stability.     

Comparative studies on lipogenic enzyme activities in brown adipose tissue and liver of the rat during starvation-refeeding transition and cold exposure

1. The effect of starvation-refeeding transition and cold exposure on the activity of lipogenic enzymes in brown adipose tissue (BAT) and liver from rats was compared. 2. Starvation caused a decrease of lipogenic enzyme activities in BAT and liver. 3. Refeeding of the animals with a high carbohydrate diet caused an increase of lipogenic enzymes in these tissues. 4. Cold exposure (4 degrees C for 30 days) led to the increase of BAT enzyme activities to the values observed in rats fed a high carbohydrate diet. 5. Under the same conditions the activity of hepatic lipogenic enzymes also increased but never reached the values observed in the liver of rats fed with a high carbohydrate diet. 6. Therefore BAT and liver lipogenic enzymes showed, in general, a similar pattern of variation under identical nutritional conditions, but substantial differences between these two organs occurred as far as the response to cold exposure was concerned. 7. The experiments also revealed that in the control animals BAT displayed a higher lipogenic potential than the liver.     

Effect of normal and waxy maize starch on growth, food utilization and hepatic glucose metabolism in European sea bass (Dicentrarchus labrax) juveniles

We determined the effect of dietary starch on growth performance and feed utilization in European sea bass juveniles. Data on the dietary regulation of key hepatic enzymes of the glycolytic, gluconeogenic, lipogenic and amino acid metabolic pathways (hexokinase, HK; glucokinase, GK; pyruvate kinase, PK; fructose-1,6-bisphosphatase, FBPase; glucose-6-phosphatase, G6Pase; glucose-6-phosphate dehydrogenase, G6PD; alanine aminotransferase, ALAT; aspartate aminotransferase, ASAT and glutamate dehydrogenase, GDH) were also measured. Five isonitrogenous (48% crude protein) and isolipidic (14% crude lipids) diets were formulated to contain 10% normal starch (diet NS10), 10% waxy starch (diet WS10), 20% normal starch (diet NS20), 20% waxy starch (diet WS20) or no starch (control diet). Another diet was formulated with no carbohydrate, and contained 68% crude protein and 14% crude lipids (diet HP). Each experimental diet was fed to triplicate groups of 30 fish (initial weight: 23.3 g) on an equivalent feeding scheme for 12 weeks. The best growth performance and feed efficiency were achieved with fish fed the HP diet. Neither the level nor the nature of starch had measurable effects on growth performance of sea bass juveniles. Digestibility of starch was higher with waxy starch and decreased with increasing levels of starch in the diet. Whole-body composition and plasma metabolites, mainly glycemia, were not affected by the level and nature of the dietary starch. Data on enzyme activities suggest that dietary carbohydrates significantly improve protein utilization associated with increased glycolytic enzyme activities (GK and PK), as well as decreased gluconeogenic (FBPase) and amino acid catabolic (GDH) enzyme activities. The nature of dietary carbohydrates tested had little influence on performance criteria.     

Variability in the trophic position of larval fish in a coastal pelagic ecosystem based on stable isotope analysis

We used stable isotopes of carbon (C) and nitrogen (N) to investigatethe trophic position of six species of larval fish in the pelagicecosystem of coastal Newfoundland. Isotope profiles from phytoplankton,net plankton and macrozooplankton were consistent with previousstudies. All species of larval fish showed a length-dependentshift in ¹³C that indicates a move to a pelagic diet from thecombined pelagic and demersal eating habits of the adult spawners.The trophic position of four larval fish species (American plaice,yellowtail flounder, cunner, radiated shanny) was consistentwith them feeding primarily on copepods, as expected from stomachcontent analysis. The ¹⁵N-based trophic position of larval witchflounder and capelin indicates that they feed significantlyon phytoplankton and heterotrophic protists from the microbialloop, respectively; this evidence contrasts with stomach contentanalysis. Although links between larval fish and the microbialloop are not considered as common as is the link with crustaceanzooplankton, this and other studies challenge the long-heldbelief that marine fish larvae feed effectively exclusivelyon copepods.     

Stable isotopes document seasonal changes in trophic niches and winter foraging individual specialization in diving predators from the Southern Ocean

1. Climatic variation outside the breeding season affects fluctuations in population numbers of seabirds and marine mammals. A challenge in identifying the underlying biological mechanisms is the lack of information on their foraging strategies during winter, when individuals migrate far from their breeding grounds. 2. We investigated the temporal variability in resource partitioning within the guild of five sympatric Subantarctic penguins and fur seals from Crozet Islands. The stable isotopic ratios of carbon (delta(13)C) and nitrogen (delta(15)N) for whole blood were measured for penguins and fur seals, as were the isotopic ratios for penguin nails and food. Animals were sampled at two periods, during breeding in summer and at their arrival in the colonies in spring (hereafter winter, since the temporal integration of blood amounting to several months). 3. In summer, delta(13)C and delta(15)N for blood samples defined three foraging areas and two trophic levels, respectively, characterizing four nonoverlapping trophic niches. King penguins and female Antarctic and Subantarctic fur seals are myctophid eaters foraging in distinct water masses, while both macaroni and rockhopper penguins had identical isotopic signatures indicating feeding on crustaceans near the archipelago. 4. Isotopic ratios were almost identical in summer and winter suggesting no major changes in the species niches, and hence, in the trophic structure of the guild during the nonbreeding period. A seasonal difference, however, was the larger variances in delta(13)C (and also to a lesser extent in delta(15)N) values in winter, thus verifying our hypothesis that trophic niches widen when individuals are no longer central place foragers. 5. Winter isotopic ratios of macaroni penguins and male Antarctic fur seals had large variances, indicating individual foraging specializations. The range of delta(13)C and delta(15)N values of male fur seals showed, respectively, that they dispersed over a wide latitudinal gradient (from Antarctica to north of the archipelago) and fed on different prey (crustaceans and fish). 6. By comparing summer and winter isotopic ratios and examining the summer diet, we highlight the feeding habits of marine predators that were not previously addressed. The findings have a number of implications for understanding the functioning of the pelagic ecosystem and on the demography of these species.     

Effects of food quality on tissue-specific isotope ratios in the mussel <Emphasis Type="Italic">Perna perna</Emphasis>

Investigations into trophic ecology and aquatic food web resolution are increasingly accomplished through stable isotope analysis. The incorporation of dietary and metabolic changes over time results in variations in isotope signatures and turnover rates of producers and consumers at tissue, individual, population and species levels. Consequently, the elucidation of trophic relationships in aquatic systems depends on establishing standard isotope values and tissue turnover rates for the level in question. This study investigated the effect of diet and food quality on isotopic signatures of four mussel tissues: adductor muscle, gonad, gill and mantle tissue from the brown mussel Perna perna. In the laboratory, mussels were fed one of the two isotopically distinct diets for 3 months. Although not all results were significant, overall δ¹³C ratios in adductor, mantle and gill tissues gradually approached food source signatures in both diets. PERMANOVA analyses revealed significant changes over time in tissue δ¹³C (mantle and gill) with both diets and in δ¹⁵N (all tissues) and C:N ratios (mantle and gill) for one diet only. The percentage of replaced carbon isotopes were calculated for the 3 month period and differed among tissues and between diets. The tissue with the highest and lowest amount of replaced isotopes over 81 days were mantle tissue on the kelp diet (33.89%) and adductor tissue on the fish food diet (4.14%), respectively. Percentages could not be calculated for any tissue in either diet for δ¹⁵N due to the lack of significant change in tissue nitrogen. Fractionation patterns in tissues for both diets can be linked to nutritional stress, suggesting that consumer isotopic signatures are strongly dependent on food quality, which can significantly affect the degree of isotopic enrichment within a trophic level.     

Digestive enzymes and metabolic profile of Pseudoplatystoma corruscans (Teleostei: Siluriformes) in response to diet composition

Digestive enzyme responsiveness to feeding and associated adjustments of metabolism can be used to derive nutritionally effective diet formulations. Juvenile pintado (Pseudoplatystoma corruscans) were fed different diets. After feeding, fish were killed and blood, liver and white muscle were collected to evaluate metabolites. Stomach along with anterior, middle and posterior intestine were sampled for enzyme analysis. Non-specific protease, trypsin, chymotrypsin, amylase and lipase were assayed. Crude protein (CP) did not induce proteolytic activity; highest protease activities were observed in the stomach. Amylase was higher in the stomach in fish feeding on diets containing 13-25% starch. Lipase activity was observed along the gastrointestinal tract, with the highest activities observed in the middle section. The metabolic profile of white muscle was not affected by CP. In contrast, some plasma and liver metabolites were altered concomitant with changes in the digestive enzymes. Amino acid catabolism was increased. Digestion in pintado was responsive to cornstarch, reflected in intermediary metabolism; proteolytic activities of the digestive tract seem to be sufficient to deal with large amounts of dietary protein. As a result, we are able to recommend a balance between protein and energetic compounds, such as lipids and carbohydrates, in the diet to optimize fish growth.     

Stable isotopes, beaks and predators: a new tool to study the trophic ecology of cephalopods, including giant and colossal squids

Cephalopods play a key role in the marine environment but knowledge of their feeding habits is limited by lack of data. Here, we have developed a new tool to investigate their feeding ecology by combining the use of their predators as biological samplers together with measurements of the stable isotopic signature of their beaks. Cephalopod beaks are chitinous hard structures that resist digestion and the stable isotope ratios of carbon (delta13C) and nitrogen (delta15N) are indicators of the foraging areas and trophic levels of consumers, respectively. First, a comparison of delta13C and delta15N values of different tissues from the same individuals showed that beaks were slightly enriched in 13C but highly impoverished in 15N compared with lipid-free muscle tissues. Second, beaks from the same species showed a progressive increase in their delta15N values with increasing size, which is in agreement with a dietary shift from lower to higher trophic levels during cephalopod growth. In the same way, there was an increase in the delta15N signature of various parts of the same lower beaks in the order rostrum, lateral walls and wings, which reflects the progressive growth and chitinization of the beaks in parallel with dietary changes. Third, we investigated the trophic structure of a cephalopod community for the first time. Values of delta15N indicate that cephalopods living in slope waters of the subantarctic Kerguelen Islands (n=18 species) encompass almost three distinct trophic levels, with a continuum of two levels between crustacean- and fish-eaters and a distinct higher trophic level occupied by the colossal squid Mesonychoteuthis hamiltoni. delta13C values demonstrated that cephalopods grow in three different marine ecosystems, with 16 species living and developing in Kerguelen waters and two species migrating from either Antarctica (Slosarczykovia circumantarctica) or the subtropics (the giant squid Architeuthis dux). The stable isotopic signature of beaks accumulated in predators' stomachs therefore revealed new trophic relationships and migration patterns and is a powerful tool to investigate the role of the poorly known cephalopods in the marine environment.     

Feeding level and individual metabolic rate affect δ13C and δ15N values in carp: implications for food web studies

Stable isotope analyses are often used to calculate relative contributions of multiple food sources in an animals diet. One prerequisite for a precise calculation is the determination of the diet-tissue fractionation factor. Isotopic ratios in animals are not only affected by the composition of the diet, but also by the amount of food consumed. Previous findings regarding the latter point are controversial. As stable isotope analyses have often been used to investigate aquatic food webs, an experiment with carp (Cyprinus carpio L.) was carried out to test the influence of the feeding level and individual metabolic rate on ¹³C and ¹⁵N values of the whole body. After an initial phase, 49 carp were assigned randomly to four groups and fed the same diet at different levels for 8 weeks. For 15 fish, the energy budget was determined by indirect calorimetry. Feed and individual fish were analysed for their proximate composition, gross energy content and ¹³C and ¹⁵N values. ¹³C and ¹⁵N values differed significantly at different feeding levels. While ¹³C values of the lipids and ¹⁵N values decreased with increasing feeding rate, ¹³C values of the lipid-free matter showed a non-linear pattern. Data obtained from fish held in the respirometric system revealed a relationship between ¹³C values and the percentage retention of metabolizable energy. Our results show that reconstructing the diets of fish from the isotopic ratios when the feeding level and individual metabolic rates are unknown would introduce an error into the data used for back-calculation of up to 1 for both ¹³C and ¹⁵N values and may have substantial effects on the results of calculated diets. As other workers have pointed out, the development and application of stable isotopes to nutritional ecology studies is a field in its infancy and gives rise to erroneous, misleading results without nutritional, physiological and ecological knowledge.     

不同时期北部湾日本带鱼营养生态位差异

基于2008—2009年和2018年对北部湾日本带鱼的采样,通过测定碳氮稳定同位素,计算其营养级、营养生态位等指标,对比分析10年前后日本带鱼营养生态位的差异,探究其生态适应能力的变动。结果表明: 2个时期北部湾日本带鱼碳稳定同位素(δ¹³C)值差异明显,2018年δ¹³C值范围变窄,平均值变小,推测日本带鱼食物来源由偏中上层向偏中下层水域转变;氮稳定同位素(δ¹⁵N)值的范围和平均值基本保持不变,营养级范围和平均值(3.38和3.43)变化不明显,说明近10年来北部湾日本带鱼在生态系统中的营养层次比较稳定。日本带鱼δ¹³C值与肛长相关性不显著,δ¹⁵N则为极显著正相关性。在营养生态位方面,2018年的生态位指标均出现不同程度的下降,下降幅度的范围为1.1%~32.1%;生态位总面积和核心生态位面积分别由20.20和4.68缩小至14.20和3.18,说明北部湾日本带鱼的营养生态位发生了显著变化,对资源利用能力和环境适应能力下降。推测,10年来北部湾日本带鱼的营养级变化不明显,但由于食物来源发生变化,营养来源多样性下降,营养生态位变小。     

Muscle delta13C change in Nile tilapia (Oreochromis niloticus) fingerlings fed on C3-or C4-cycle plants grain-based diets

The effects of grain-based diets from C3 or C4-cycle plants on muscle delta(13)C change process in Nile tilapia (Oreochromis niloticus) fingerlings were investigated. Two groups of sex reversal males Nile tilapia fingerlings were fed with isoproteic (32.0% DP) and isocaloric (3200 kcal DE/kg) diets, differing from each other by their delta(13)C. Muscle samples were collected and the carbon isotopic composition was measured. For C4 diet, the formula for the muscle delta(13)C change related to the intake time of a new diet was delta(13)C=-14.88-9.21e(-0.0209t) and the half-life (T) of the muscle carbon was 33.2 days. For C3 diet, the formula was delta(13)C=-25.43+8.59e(-0.0533t) with T=13 days. The C3 diet was considered more appropriate based on its palatability and consequent larger food intake than the C4 diet, resulting in an increased muscle delta(13)C change rate. However, for future studies, would be necessary to mix both the C3 and C4 feedstuffs to formulate diets nutritionally appropriated, with contrasting stable isotopes signatures. Tissue delta(13)C change rate is therefore indicated as a promising tool to better understand the biotic and abiotic factors that influence nutrients utilization from the diet and animal growth.     

Influence of dietary non-essential amino acid profile on growth performance and amino acid metabolism of Nile tilapia, Oreochromis niloticus (L.)

The quality of dietary protein is an important factor influencing the growth performance of fish. To evaluate the quality of protein, the variables commonly studied are the composition of the essential amino acids, the digestibility and the protein use efficiency. The goal of the present experiment was to test the effect of the dietary non-essential amino acid composition on the growth of Nile tilapia (Oreochromis niloticus). The fish were fed three purified diets differing only in their non-essential amino acid composition. The influence of the experimental diets on the growth performance, on the activity of enzymes involved in the amino acid metabolism, aspartate aminotransferase (ASAT) and alanine aminotransferase (ALAT), and on whole body delta(15)N values was investigated. Body mass, lipid, protein and energy gain differed significantly between the feeding groups. The activity of ASAT in the whole liver was significantly higher in fish with a positive protein balance compared to fish which lost protein. Whole body delta(15)N values of fish were negatively correlated with their body mass gain. Despite the poor utilisation of synthetic amino acids, the experiment indicates the importance of the dietary non-essential amino acid composition for the growth performance of fish. The study reveals the possibility to trace the utilisation of synthetic amino acids by determining the isotopic composition of dietary amino acids and tissues or whole bodies of animals.