Abel, Hansjörg

[["dc.bibliographiccitation.firstpage","90"],["dc.bibliographiccitation.issue","2"],["dc.bibliographiccitation.journal","The Science of Nature"],["dc.bibliographiccitation.lastpage","93"],["dc.bibliographiccitation.volume","91"],["dc.contributor.author","Gaye-Siessegger, Julia"],["dc.contributor.author","Focken, Ulfert"],["dc.contributor.author","Abel, Hansjoerg"],["dc.contributor.author","Becker, K."],["dc.date.accessioned","2018-11-07T10:51:31Z"],["dc.date.available","2018-11-07T10:51:31Z"],["dc.date.issued","2004"],["dc.description.abstract","Although stable isotope ratios in animals have often been used as indicators of the trophic level and for the back-calculation of diets, few experiments have been done under standardized laboratory conditions to investigate factors influencing delta(15)N and delta(13)C values. An experiment using Nile tilapia [Oreochromis niloticus (L.)] was therefore carried out to test the effect of different dietary protein contents (35.4, 42.3, and 50.9%) on delta(15)N and delta(13)C values of the whole tilapia. The fish were fed the isoenergetic and isolipidic semi-synthetic diets at a relatively low level. delta(15)N and delta(13)C values of the lipid-free body did not differ between the fish fed the diets with different protein contents, but the trophic shift for N and C isotopes decreased with increasing protein accretion in the individual fish, for N from 6.5parts per thousand to 4parts per thousand and for C in the lipid-free body from 4parts per thousand to 2.5parts per thousand. This is the first study showing the strong influence of the individual protein balance to the degree to which the isotopic signature of dietary protein was modified in tissue protein of fish. The extrapolation of the trophic level or the reconstruction of the diet of an animal from stable isotope ratios without knowledge of the individual physiological condition and the feeding rate may lead to erroneous results."],["dc.identifier.doi","10.1007/s00114-003-0496-2"],["dc.identifier.isi","000189206300006"],["dc.identifier.pmid","14991147"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/48911"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Springer"],["dc.relation.issn","0028-1042"],["dc.title","Individual protein balance strongly influences delta N-15 and delta C-13 values in Nile tilapia, Oreochromis niloticus"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","71"],["dc.bibliographiccitation.issue","1"],["dc.bibliographiccitation.journal","COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY A-MOLECULAR & INTEGRATIVE PHYSIOLOGY"],["dc.bibliographiccitation.lastpage","77"],["dc.bibliographiccitation.volume","146"],["dc.contributor.author","Gaye-Siessegger, Julia"],["dc.contributor.author","Focken, Ulfert"],["dc.contributor.author","Abel, Hansjoerg"],["dc.contributor.author","Becker, K."],["dc.date.accessioned","2018-11-07T11:06:18Z"],["dc.date.available","2018-11-07T11:06:18Z"],["dc.date.issued","2007"],["dc.description.abstract","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 (Oreochronds 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. (c) 2006 Elsevier Inc. All rights reserved."],["dc.identifier.doi","10.1016/j.cbpa.2006.09.025"],["dc.identifier.isi","000244583100007"],["dc.identifier.pmid","17157045"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/52273"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Elsevier Science Inc"],["dc.relation.issn","1095-6433"],["dc.title","Influence of dietary non-essential amino acid profile on growth performance and amino acid metabolism of Nile tilapia, Oreochromis niloticus (L.)"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","117"],["dc.bibliographiccitation.issue","1"],["dc.bibliographiccitation.journal","COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY A-MOLECULAR & INTEGRATIVE PHYSIOLOGY"],["dc.bibliographiccitation.lastpage","124"],["dc.bibliographiccitation.volume","140"],["dc.contributor.author","Gaye-Siessegger, Julia"],["dc.contributor.author","Focken, Ulfert"],["dc.contributor.author","Abel, Hansjoerg"],["dc.contributor.author","Becker, K."],["dc.date.accessioned","2018-11-07T08:36:30Z"],["dc.date.available","2018-11-07T08:36:30Z"],["dc.date.issued","2005"],["dc.description.abstract","To test whether the measurement of selected enzyme activities could be used to estimate more precisely the trophic shift of C isotopes, Nile tilapia (Oreochromis niloticus) were fed semi-synthetic diets differing in their lipid contents (1.7%, 5.0%, 10.8% and 20.0%). The diets were formulated to contain the same amount of nitrogen and metabolizable energy and were made from casein, wheat starch, corn germ oil supplemented with vitamins, minerals and L-arginine. The influence of the different diets on the activity of two lipogenic enzymes, ATP-citrate lyase and malic enzyme, on delta(13)C values in the whole fish, the liver and their correlation was investigated. There was a strong positive correlation between delta(13)C values in the lipids of whole fish and those of their livers. The activities of lipogenic enzymes increased significantly with increasing trophic shift of C isotopes (Deltadelta(13)C(dict-fish) values) in the lipids. If the relationship between trophic shift and enzyme activity can be confirmed in situations where feed quantity and quality are not known, the determination of enzyme activities would enable better estimates of the trophic shift to be made thus significantly improving back-calculation of diets from stable isotope data. (C) 2004 Elsevier Inc. All rights reserved."],["dc.identifier.doi","10.1016/j.cbpb.2004.11.011"],["dc.identifier.isi","000226964400013"],["dc.identifier.pmid","15664320"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/18324"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Elsevier Science Inc"],["dc.relation.issn","1095-6433"],["dc.title","Improving estimates of trophic shift in Nile tilapia, Oreochromis niloticus (L.), using measurements of lipogenic enzyme activities in the liver"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","90"],["dc.bibliographiccitation.issue","1"],["dc.bibliographiccitation.journal","Journal of Fish Biology"],["dc.bibliographiccitation.lastpage","100"],["dc.bibliographiccitation.volume","71"],["dc.contributor.author","Gaye-Siessegger, Julia"],["dc.contributor.author","Focken, Ulfert"],["dc.contributor.author","Abel, Hansjoerg"],["dc.contributor.author","Becker, K."],["dc.date.accessioned","2018-11-07T11:01:03Z"],["dc.date.available","2018-11-07T11:01:03Z"],["dc.date.issued","2007"],["dc.description.abstract","The influence of different feeding levels below and slightly above maintenance on whole body delta C-13 and delta N-15 values of Nile tilapia Oreochromis niloticus was examined. The energy budget of each fish was determined by indirect calorimetry. The delta C-13 values of the lipid-free material of Nile tilapia fed below and slightly above maintenance level did not differ between the feeding groups, but the delta C-13 values in the lipids and the delta N-15 values of the lipid-free material showed small but significant differences. Those fish with a negative lipid retention had significantly higher delta C-13 values in the lipid fraction compared to fish that synthesized fatty acids. There was a significant negative correlation between the amount of energy metabolized by the fish and both the delta C-13 values in the lipids and the delta N-15 values of the lipid-free material. Fasting and feeding below the maintenance level may influence the isotopic composition of animals and should therefore be considered in ecological and nutritional studies. (c) 2007 The Authors Journal compilation. (c) 2007 The Fisheries Society of the British Isles."],["dc.identifier.doi","10.1111/j.1095-8649.2007.01469.x"],["dc.identifier.isi","000247441800006"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/51068"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Blackwell Publishing"],["dc.relation.issn","0022-1112"],["dc.title","Starvation and low feeding levels result in an enrichment of C-13 in lipids and N-15 in protein of Nile tilapia Oreochromis niloticus L."],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","175"],["dc.bibliographiccitation.issue","2"],["dc.bibliographiccitation.journal","Oecologia"],["dc.bibliographiccitation.lastpage","183"],["dc.bibliographiccitation.volume","138"],["dc.contributor.author","Gaye-Siessegger, Julia"],["dc.contributor.author","Focken, Ulfert"],["dc.contributor.author","Muetzel, S."],["dc.contributor.author","Abel, Hansjoerg"],["dc.contributor.author","Becker, K."],["dc.date.accessioned","2018-11-07T10:52:59Z"],["dc.date.available","2018-11-07T10:52:59Z"],["dc.date.issued","2004"],["dc.description.abstract","Stable isotope analyses are often used to calculate relative contributions of multiple food sources in an animal's 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 delta(13)C and delta(15)N 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 delta(13)C and delta(15)N values. delta(13)C and delta(15)N values differed significantly at different feeding levels. While delta(13)C values of the lipids and delta(15)N values decreased with increasing feeding rate, delta(13)C values of the lipid-free matter showed a non-linear pattern. Data obtained from fish held in the respirometric system revealed a relationship between delta(13)C 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 1parts per thousand for both delta(13)C and delta(15)N 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."],["dc.identifier.doi","10.1007/s00442-003-1429-7"],["dc.identifier.isi","000188244300003"],["dc.identifier.pmid","14608500"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/49244"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Springer"],["dc.relation.issn","0029-8549"],["dc.title","Feeding level and individual metabolic rate affect delta C-13 and delta N-15 values in carp: implications for food web studies"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","181"],["dc.bibliographiccitation.issue","3"],["dc.bibliographiccitation.journal","Isotopes in Environmental and Health Studies"],["dc.bibliographiccitation.lastpage","190"],["dc.bibliographiccitation.volume","40"],["dc.contributor.author","Gaye-Siessegger, Julia"],["dc.contributor.author","Focken, Ulfert"],["dc.contributor.author","Abel, Hansjoerg"],["dc.contributor.author","Becker, K."],["dc.date.accessioned","2018-11-07T10:45:59Z"],["dc.date.available","2018-11-07T10:45:59Z"],["dc.date.issued","2004"],["dc.description.abstract","The use of stable isotope techniques for the reconstruction of diets has increased over the last decade. However, isotopic ratios in an animal are not only affected by the composition of the feed, but also by the amount of feed consumed. An uncertainty of up to 1 parts per thousand for both delta(13)C and delta(15)N values has been observed when the feeding level is unknown. This may have substantial effects on the results of back-calculation. As the feeding level of animals is unknown in nature, an additional indicator for their nutritional status is needed. High feeding levels and a consequent surfeit of dietary energy lead to the synthesis of lipids. In order to test whether the level of lipogenesis could be used as an indicator, Nile tilapia ( Oreochromis niloticus ) were fed four isonitrogenous and isoenergetic wheat-based semi-synthetic diets with different lipid contents (2.0 %, 4.5 %, 9.5 % and 13.3 %) for eight weeks. Body composition, gross energy content and delta(13)C values in the lipids and the lipid-free material were determined in diets and fish bodies. The livers of three fish per feeding group were assayed for the activity of two lipogenic enzymes, ATP-citrate lyase and malic enzyme. There was a strong negative correlation between delta(13)C values in the lipids of the individual fish and the apparent lipid conversion. The activities of lipogenic enzymes decreased with rising lipid content in the diet. The delta(13)C values in the lipids decreased significantly with increasing specific activity for both enzymes. In this experiment where lipogenesis was influenced by the composition of the diet, it was possible to determine the exact value for the trophic shift in relation to the enzyme activities. Further experiments to investigate the use of enzyme activities in situations where the feeding level of an animal is unknown are recommended."],["dc.identifier.doi","10.1080/10256010410001726897"],["dc.identifier.isi","000223534400003"],["dc.identifier.pmid","15370281"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/47638"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Taylor & Francis Ltd"],["dc.publisher.place","Abingdon"],["dc.relation.conference","26th Annual Meeting of the German-Association-for-Stable-Isotope-Research"],["dc.relation.eventlocation","Cologne, GERMANY"],["dc.relation.issn","1025-6016"],["dc.title","Dietary lipid content influences the activity of lipogenic enzymes in the liver and on whole body delta C-13 values of Nile tilapia, Oreochromis niloticus (L.)"],["dc.type","conference_paper"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","125"],["dc.bibliographiccitation.issue","2"],["dc.bibliographiccitation.journal","Isotopes in Environmental and Health Studies"],["dc.bibliographiccitation.lastpage","134"],["dc.bibliographiccitation.volume","39"],["dc.contributor.author","Gaye-Siessegger, Julia"],["dc.contributor.author","Focken, Ulfert"],["dc.contributor.author","Abel, Hansjoerg"],["dc.contributor.author","Becker, K."],["dc.date.accessioned","2018-11-07T10:38:38Z"],["dc.date.available","2018-11-07T10:38:38Z"],["dc.date.issued","2003"],["dc.description.abstract","Many scientists use naturally occurring stable isotopes to reconstruct the diets of animals. However, isotopic ratios may be affected not only by the composition of the diet but also by the amount of food consumed. Thus, an experiment using tilapia (Oreochromis niloticus) was carried out to test the influence of feeding level on delta(13)C and delta(15)N of fish given a semi-synthetic wheat gluten/wheat starch based diet. In addition, the effect of diet quality was tested by comparing tilapia given this feed with tilapia fed a fish meal/wheat meal based diet. Forty-four tilapia were reared individually. After a prefeeding phase, fish were randomly assigned to five groups, four on the semi-synthetic diet at different feeding levels and one group on the fish meal/wheat meal based diet fed at the. equivalent of the highest level of the semi-synthetic diet. The experiment lasted eight weeks. Proximate composition, gross energy content and delta(13)C and delta(15)N values were determined in feed and fish, for delta(13)C separately in the lipids and the lipid-free matter. delta(13)C in the lipids and the lipid-free matter and delta(15)N of tilapia fed the semi-synthetic diet decreased significantly with increasing feeding rate. The absolute values of the trophic shift in fish fed the semi-synthetic wheat based diet were significantly higher than in fish fed the fish meal/wheat meal based diet. The different delta(13)C and delta(15)N values in tilapia fed the same diet at different feeding levels and the influence of feed quality on the trophic shift add to the uncertainty involved in the use of stable isotopes in ecological research."],["dc.identifier.doi","10.1080/1025601031000113556"],["dc.identifier.isi","000183568200005"],["dc.identifier.pmid","12872804"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/45853"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Taylor & Francis Ltd"],["dc.publisher.place","Abingdon"],["dc.relation.conference","23rd Annual Meeting of the German-Association-for-Stable-Isotope-Research"],["dc.relation.eventlocation","WARNEMUNDE, GERMANY"],["dc.relation.issn","1025-6016"],["dc.title","Feeding level and diet quality influence trophic shift of C and N isotopes in Nile tilapia (Oreochromis niloticus (L.))"],["dc.type","conference_paper"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","129"],["dc.bibliographiccitation.issue","2"],["dc.bibliographiccitation.journal","Isotopes in Environmental and Health Studies"],["dc.bibliographiccitation.lastpage","141"],["dc.bibliographiccitation.volume","43"],["dc.contributor.author","Gaye-Siessegger, Julia"],["dc.contributor.author","Focken, Ulfert"],["dc.contributor.author","Abel, Hansjoerg"],["dc.contributor.author","Becker, Klaus"],["dc.date.accessioned","2018-11-07T11:06:44Z"],["dc.date.available","2018-11-07T11:06:44Z"],["dc.date.issued","2007"],["dc.description.abstract","The aim of this study was (1) to assess the effects of dietary protein content and feeding level on trophic shifts of C and N isotopes (Delta delta C-13(tissue-diet) and Delta delta N-15(tissue-diet)) and (2) to test whether the measurement of the activities of two enzymes involved in the metabolism of amino acids could improve the accuracy of estimation of the trophic shifts of C and N isotopes. For this, 36 Nile tilapia (Oreochromis niloticus) were kept under controlled conditions for 8 weeks and fed at three different levels (2, 4 and 8 g kg(-0.8) d(-1)) with three diets differing in their protein content only (20, 29 and 39 %). For each fish, food to fish body trophic shifts of C and N isotopes were measured as well as the hepatic activities of aspartate aminotransferase (ASAT) and glutamate dehydrogenase (GDH). The feeding level affected the activities of ASAT and GDH as well as the trophic shifts of C and N isotopes significantly but the dietary protein content had no significant effect except on the specific activity of ASAT. Fish fed at the lowest level had significantly higher trophic shifts of C and N isotopes than fish fed at higher levels. The trophic shifts were significantly lower in fish with a high protein utilisation. Values of the 'goodness-of-fit' for linear regressions between enzyme activities and trophic shifts were low. Thus, activities of ASAT and GDH are not suitable for predicting estimates of trophic shifts in situations where the amount of food consumed or the dietary protein content is not known. In further studies, activities of enzymes involved in the metabolism of amino acids combined with measurements of the activities of other enzymes should be used to try and improve the accuracy of estimates of trophic shifts."],["dc.identifier.doi","10.1080/10256010701360405"],["dc.identifier.isi","000248115300005"],["dc.identifier.pmid","17558750"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/52388"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Taylor & Francis Ltd"],["dc.relation.issn","1025-6016"],["dc.title","Dietary back-calculation using stable isotopes: can activities of enzymes involved in amino acid metabolism be used to improve estimates of trophic shifts in fish?"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]