Rainbow trout are an important salmonid species whose poor utilization of dietary carbohydrates spurred research investigating molecular and physiological components of its glucoregulation. Among the environmental factors described to exert robust changes in glucose metabolism in rainbow trout, nutrition and social stress are among the most studied: Diets exceeding 20% of carbohydrates and chronic social stress induce hyperglycemia in adult and juvenile rainbow trout, respectively. Common to both responses is a contribution of hepatic de novo gluconeogenesis, which has been described to evade repression in response to high dietary carbohydrate content and to be stimulated in subordinate rainbow trout. Compared to previous studies investigating the regulation of hepatic gluconeogenesis at the molecular level, the recent publication of the annotated rainbow trout genome has opened novel possibilities to investigate paralogue-specific and posttranscriptional regulation of gluconeogenesis. In this thesis, I identify and describe the regulation of the novel phosphoenolpyruvate carboxykinase paralogue pck2b in rainbow trout and identify specific miRNA candidates predicted to contribute to gene paralogue-specific regulation of gluconeogenesis in nutritional and social contexts using small RNA next generation sequencing, real-time RT-PCR and in silico target prediction approaches. In nutritional and social status experiments, in silico predicted targets of differentially expressed hepatic miRNAs are enriched for gluconeogenesis regulation, suggesting a posttranscriptional component in regulating gluconeogenic transcript abundance. Differentially expressed hepatic miRNAs in both experiments comprise evolutionarily conserved and teleost-specific miRNAs, and are indicative of both environmental factor-specific and common regulation of gluconeogenesis transcripts in rainbow trout liver. Together this work provides novel comparative insight into hepatic miRNA-dependent glucoregulation and identifies several specific candidate miRNAs for future functional validation in hepatic glucoregulation in rainbow trout.

In the heart, unidirectional blood flow depends on proper heart valve function. As, in mammals, regulatory mechanisms of early heart valve and bone development are shown to contribute to adult heart valve pathologies, we used the animal model zebrafish (ZF, Danio rerio) to investigate the microarchitecture and differentiation of cardiac valve interstitial cells in the transition from juvenile (35 days) to end of adult breeding (2.5 years) stages. Of note, light microscopy and immunohistochemistry revealed major differences in ZF heart valve microarchitecture when compared with adult mice. We demonstrate evidence for rather chondrogenic features of valvular interstitial cells by histological staining and immunodetection of SOX-9, aggrecan, and type 2a1 collagen. Collagen depositions are enriched in a thin layer at the atrial aspect of atrioventricular valves and the ventricular aspect of bulboventricular valves, respectively. At the ultrastructural level, the collagen fibrils are lacking obvious periodicity and orientation throughout the entire valve. (J Histochem Cytochem 67:361–373, 2019)

Trophic downgrading of ecosystems necessitates a functional understanding of trophic cascades. Identifying the presence of cascades, and the mechanisms through which they occur, is particularly important for seagrass meadows, which are among the most threatened ecosystems on Earth. Shark Bay, Western Australia provides a model system to investigate the potential importance of top-down effects in a relatively pristine seagrass ecosystem. The role of megagrazers in the Shark Bay system has been previously investigated, but the role of macrograzers (i.e., teleosts), and their importance relative to megagrazers, remains unknown. The objective of my dissertation was to elucidate the importance of teleost macrograzers in transmitting top-down effects in seagrass ecosystems. Seagrasses and macroalgae were the main food of the abundant teleost Pelates octolineatus, but stable isotopic values suggested that algae may contribute a larger portion of assimilated food than suggested by gut contents. Pelates octolineatus is at risk from numerous predators, with pied cormorants (Phalacrocorax varius) taking the majority of tethered P. octolineatus. Using a combination of fish trapping and unbaited underwater video surveillance, I found that the relative abundance of P. octolineatus was greater in interior areas of seagrass banks during the cold season, and that the mean length of P. octolineatus was greater in these areas compared to along edges of banks. Finally, I used seagrass transplants and exclosure experiments to determine the relative effect of megagrazers and macrograzers on the establishment and persistence of three species of seagrasses in interior microhabitats. Teleost grazing had the largest impact on seagrass species with the highest nutrient content, and these impacts were primarily observed during the warm season. My findings are consistent with predictions of a behaviorally-mediated trophic cascade initiated by tiger sharks (Galeocerdo cuvier) and transmitted through herbivorous fishes and their predators.

In seawater, drinking is a fundamental part of the osmoregulatory strategy for teleost fish, and presents a unique challenge. The intestine has an established role in osmoregulation, and its ability to effectively absorb fluid from imbibed seawater is crucial to compensating for water losses to the surrounding hyperosmotic environment. Alongside solute-linked water transport (driven by NaCl cotransport), intestinal bicarbonate (HCO3-) secretion also benefits fluid absorption directly (via apical Cl-/HCO3- exchange), and indirectly through the formation of calcium carbonate (CaCO3) thus removing the osmotic influence of Ca2+ within the gut fluid. For the European flounder (Platichthys flesus), elevated luminal Ca2+ has proven to be a specific, potent stimulator of HCO3- secretion both in vitro and in vivo where these actions are presumably modulated by an extracellular Ca2+-sensing receptor (CaR). The focus of this work was to learn more about how intestinal HCO3- secretion is regulated, the role of Ca2+, and more specifically the CaR. To achieve this, in vitro ‘gut sac’ experiments investigated how luminal Ca2+ influenced HCO3- secretion, and associated ion and fluid transport. Contrary to expectation, increasing Ca2+ from 5 to 20 mM did not stimulate HCO3- secretion. In an attempt to elucidate the role of CaCO3 precipitation in fluid absorption, and further explore the physiological implications of HCO3- secretion, the intestine was perfused in vivo with salines containing varying concentrations of Ca2+ (10, 40 and 90 mM). The production and secretion of HCO3-, in addition to CaCO3 formation increased accordingly with Ca2+, and was associated with a dramatic 25 % rise in the fraction of fluid absorbed by the gut. Additional in vitro experiments, utilising the Ussing chamber, helped establish some of the characteristics of intestinal HCO3- secretion by the euryhaline killifish (Fundulus heteroclitus), but was unresponsive to elevated mucosal Ca2+. Further attempts to potentiate the activity of the CaR, and application of the receptor agonists gadolinium (Gd3+) and neomycin, failed to produce responses consistent with the effect of Ca2+ observed previously, either in vitro or in vivo. With no evidence supporting a direct role for an extracellular, intestinal CaR in HCO3- secretion it was argued that secretion would be principally regulated by two factors, the ability of the epithelia to generate high levels of intracellular HCO3- and the rate of CaCO3 formation.

Machos adultos de P. lineatus tiveram suas gônadas processadas de acordo com as rotinas de microscopia de luz e microscopia eletrônica de transmissão. Para a cultura de células, os testículos foram digeridos enzimaticamente, a suspensão testicular foi separada por gradiente descontínuo com Percoll seguido pelo plaqueamento diferencial por adesão e as células foram cultivadas. Foi realizado o método de enriquecimento das espermatogônias por citometria de fluxo. Os testículos apresentam as regiões anterior, média e posterior com distribuição semelhante dos tipos de células, e o diâmetro nuclear das células germinativas diminui significativamente durante a espermatogênese. As espermatogônias cultivadas por 15 dias com meio para proliferação celular resultaram em grandes aglomerados celulares que foram caracterizados com o anti-Vasa, anti-GFRa1 e anti-OCT4. As culturas que receberam o meio para diferenciação celular mostraram processo de proliferação lento das espermatogônias primárias comparado com a cultura que teve o meio indicado para proliferação celular. / Adult males of P. lineatus had their gonads used according routines of light microscopy and transmission electron microscopy. For cell culture, the testes were enzymatically digested; testicular suspension was separated by discontinuous gradient with Percoll followed by adhesion differential plating and the cells were cultured. The enrichment of the spermatogonia was carried by flow cytometry. The testes present three regions with similar distribution of cell types, and nuclear diameter of germ cells decreases significantly during spermatogenesis. The spermatogonia cultured for 15 days with medium for cell proliferation, resulted in large cell agglomerates which were characterized with the antibodies anti-Vasa, anti-GFRa1 and anti-anti-OCT4. The cultures that receiving medium for cell differentiation showed slow proliferation process of primary spermatogonia compared to cell culture medium suggestive for cell differentiation.

Após a reprodução de Astyanax altiparanae, foram obtidas larvas e juvenis da espécie, os quais foram coletados desde a eclosão até 120 dias após a eclosão (dpe). Por meio de métodos histoquímicos e imuno-histoquímica foram detectadas a neuro (NH) e adeno-hipófise (AH). Nas 3 regiões da AH, rostral (RPD) e proximal (PPD) pars distalis, e pars intermedia (PI), foram encontrados 8 tipos celulares produtores de hormônios, sendo, na RPD, as células produtoras de ACTH e PRL; na PPD, GTH (FSH e LH), GH e TSH; e na PI, MSH e SL. As prolactínicas foram as primeiras células identificadas com 1 dpe no início da formação da glândula. A NH foi diferenciada com 3 dpe junto com as células produtoras de ACTH, MSH, TSH e FSH. A identificação das células produtoras de LH, SL e GH ocorreu com 5 dpe. Com 20 dpe houve um grande aumento da hipófise e o aparecimento do pedúnculo. Com 60 dpe a hipófise apresentou-se semelhante à observada nos adultos. Os resultados desta pesquisa colaboram para o conhecimento do eixo hipotálamo-hipófise-gônada em teleósteos sul-americanos. / After reproduction of A. altiparanae, was made larvae and juveniles of this specie, were collected from zero to 120 days post hatching (dph). By histochemical and immunohistochemical techniques were detected neuro (NH) and adenohypophysis (AH). In 3 regions of AH, rostral (RPD), proximal (PPD) pars distalis and in pars intermedia (PI), eight producing hormones cell types are distinguished, being, in the RPD, ACTH and PRL producing cells; in PPD, GTH (FSH and LH), GH and TSH; and in the PI, MSH and SL. The first cells identified were prolactins at 1dph, in the beginning of the formation of the gland. NH differentiated at 3dph along with identification of ACTH, MSH, TSH and FSH producing cells. The identification of LH, SL and GH producing cells was possible at 5dph. At 20dph, there was a large increase in the pituitary, and it was observed the presence of the pituitary stalk. At 60 dph the pituitary showed a similar morphology to that observed in adults. The results of this research collaborate to knowledge of the hypothalamic-pituitary-gonadal axis in South American teleosts.

Made available in DSpace on 2014-06-11T19:27:58Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-07-20Bitstream added on 2014-06-13T18:56:54Z : No. of bitstreams: 1 claudiano_gs_me_jabo.pdf: 778732 bytes, checksum: c2e3587b8838e9676707fe996742c881 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Neste trabalho, investigou-se a cinética das alterações vasculares e celulares na aerocistite, induzida pela inoculação da Aeromonas hydrophila inativada em Piaractus mesopotamicus e inibição da atividade enzimática da fosfolipase A2 e ciclooxigenase na inflamação aguda. Para tanto, foram utilizadas a indometacina, meloxicam e a dexametasona, aplicados por via parenteral, 30 minutos antes do estímulo lesivo. As alterações de permeabilidade vascular foram avaliadas nos tempos de 30, 90, 120, 180 e 240 minutos pós-estímulo, observando-se que o máximo da exsudação plasmática ocorre com 180 MPE. O pré-tratamento com indometacina ou meloxicam, neste tempo, inibiu significativamente o aumento de permeabilidade vascular e a dexametasona apresentou um bloqueio mais precoce e efetivo do que os outros AINES, inibindo nos tempos de 120 e 180 MPE. O exsudato celular inflamatório foi avaliado seis, 24 e 48 horas após estímulo, verificando-se que a inoculação da bactéria causou aumento progressivo do acúmulo de células, atingindo o máximo após 24 HPE, sendo maior que nos outros grupos estudados. Neste tempo, verificou-se que todas as drogas testadas foram efetivas para a redução significativa do acúmulo celular. A contagem diferencial das células presentes no foco inflamado demonstrou predomínio de linfócitos e trombócitos, seguida de macrófagos e granulócitos, com acúmulo mais tardio destas últimas. O pré-tratamento com indometacina e dexametasona causou bloqueio no acúmulo de todas as células identificadas. Os resultados demonstraram que, entre as diferentes doses de cada droga testada, não foram observadas diferenças significativas. As avaliações sugeriram que os eicosanoides, assim como acontece em mamíferos, participam ativamente dos fenômenos vasculares e têm papel relevante na quimiotaxia de leucócitos / In this teaching we investigated the kinetics of vascular and cellular changes in aerocistite induced by inoculation of inactivated Aeromonas hydrophila in Piaractus mesopotamicus and pharmacological effect of the enzymatic activity of phospholipase A2 and cyclooxygenase in acute inflammation. To this end, we used indomethacin, meloxicam and dexamethasone, applied intraparenteral 30 minutes before stimulation harmful. Changes in vascular permeability were evaluated in 30, 90, 120, 180 and 240 minutes post-stimulation, we observed that the maximum plasma exudation occurs with 180 MPE and pretreatment with indomethacin or meloxicam at this time significantly inhibited the increase vascular permeability and dexamethasone had a lock early and effective than other NSAIDs inhibited at 120 and 180MPE. The cellular inflammatory exudate was assessed with six, 24 and 48 hours after stimulation, verifying that the bacteria caused a progressive increase in accumulation of cells, peaking at 24 HPE, higher than the other groups analyzed, and this time all tested drugs were effective in significantly reducing the buildup. The differential count of cells present in the exudate showed a predominance of lymphocytes and thrombocytes, and granulocyte macrophage followed with a later accumulation of the latter. Pretreatment with indomethacin and dexamethasone caused a blockage in the migration of all cells evaluated. The results showed that among the different doses of each drug tested was not observed any significant difference. Analysis of those exposed, suggest that eicosanoids, with in mammals, participate actively in the vascular phenomena and has important role in chemotaxis of leukocytes in acute inflammatory process induced by A. hydrophila in pacu

Submitted by Luciana Sebin (lusebin@ufscar.br) on 2016-09-12T18:16:09Z No. of bitstreams: 1 TeseNSS.pdf: 3636561 bytes, checksum: af079696a221c11c574fe705355778f8 (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-09-13T18:23:49Z (GMT) No. of bitstreams: 1 TeseNSS.pdf: 3636561 bytes, checksum: af079696a221c11c574fe705355778f8 (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-09-13T18:23:56Z (GMT) No. of bitstreams: 1 TeseNSS.pdf: 3636561 bytes, checksum: af079696a221c11c574fe705355778f8 (MD5) / Made available in DSpace on 2016-09-13T18:24:03Z (GMT). No. of bitstreams: 1 TeseNSS.pdf: 3636561 bytes, checksum: af079696a221c11c574fe705355778f8 (MD5) Previous issue date: 2015-08-24 / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / The increase of fish production in intensive systems involves the use of antimicrobians in the treatment of diseases caused by bacteria. Therefore, the aim of this study was to evaluate acute toxicity (CL50; 48h) of the antimicrobial azithromycin (AZT) for fingerlings of tilapia (Oreochromis niloticus), the effects on young tilapia, after chronic exposure (14 days) via hematological analysis, morphology gills, liver and kidneys and antioxidant system responses in the liver, and to determine the efficacy of control of Aeromonas hydrophila via hematological analysis and innate immune response, in addition to the morphological effects gills, kidneys and liver and antioxidant system responses in the liver. The acute toxicity (LC50; 48h) of the AZT to tilapia was > 100 mg L-1 being th AZT classified as practically non-toxic. After chronic exposure, there was an increase in hematocrit (Hct), hemoglobin concentration (Hb) and in the mean corpuscular volume of erythrocytes (MCV) and no change in the other variables of the red series was observed. The leukocytes increased after exposure to 100 mg L-1 AZT. Histological changes in gills suggest defense response against irritant agent and indicate normal structure and function of the organ; in the kidney no changes was observed and in the liver changes were classified as moderate to severe. In the efficacy trial, the offering of medicated food with AZT (100 and 125 mg kg-1) to animals infected with A. hydrophila was efficient and all of the treated animals survived; of the untreated animals 22% came to death. The Hct decreased and the hematimetric indices mean corpuscular hemoglobin and mean corpuscular hemoglobin concentration increased, the percentage of lymphocytes decreased and the percentage of neutrophil increased in untreated infected animals, but were unchanged in animals treated with AZT. No change occurred in innate immunity assessed by the activity of lysozyme, complement system and leukocytes respiratory burst activity. Gills showed no changes that could interfere in the organ function, in the liver changes were classified from mild to moderate and didn´t occurred alterations in the kidneys. Animals treated with AZT showed no adverse effects related to defense cells and the innate immune activity. The drug also caused no changes in antioxidant defense enzymes in the animals' liver after chronic exposure and did not generate oxidative stress. After challenge with A. hydrophila occurred an increased in the activity of catalase, glutathione peroxidase, glutathione transferase and glutathione level in the liver of animals treated with AZT and the glutathione level decreased in the infected group and untreated. These responses suggest that infection caused by A. hydrophila can induce an increased production of ROS and, consequently, stimulated responses of the antioxidant defenses. These responses were effective to prevent the occurrence of oxidative stress. / O aumento da produção de peixes em sistema intensivo implica no uso de antimicrobianos em tratamento de doenças causadas por bactérias. Dessa forma, o objetivo deste estudo foi avaliar toxicidade aguda (CL50;48h) do antimicrobiano azitromicina (AZT) para alevinos de tilápia (Oreochromis niloticus). Os seus efeitos em jovens de tilápia, após exposição crônica (14 dias), pela análise hematológica, morfologia de brânquias, fígado e rins e respostas do sistema antioxidante no fígado, assim como a determinação da eficácia sobre Aeromonas hydrophila, pela análise hematológica e resposta imune inata, além dos efeitos morfológicos em brânquias, fígado e rins e respostas do sistema antioxidante no fígado. A toxicidade aguda (CL50;48h) da AZT para tilápia foi > 100 mg L-1 sendo classificada como praticamente não tóxico. Após exposição crônica, ocorreu aumento do hematócrito (Hct), concentração de hemoglobina (Hb), e no volume corpuscular médio dos eritrócitos (VCM) sem alterações nas demais variáveis da série vermelha. Os leucócitos aumentaram após exposição a 100 mg L-1 de AZT. As alterações histológicas nas brânquias sugerem resposta de defesa contra agente irritante e indicou estrutura e função normal do órgão; nos rins não ocorreu alterações e no fígado foram classificadas como moderadas a severas. No ensaio de eficácia, com ração medicada com AZT (100 e 125 mg kg-1) aos animais infectados com A. hydrophila se mostrou eficiente, e todos os animais tratados sobreviveram. A mortalidade no grupo não tratado foi de 22 %. O hematócrito diminuiu e os índices hematimétricos, hemoglobina corpuscular média e a concentração de hemoglobina corpuscular média aumentaram. A porcentagem de linfócitos diminuiu e a de neutrófilos aumentou nos animais infectados não-tratados, mas sem alteração nos animais tratados. Não ocorreu alteração na imunidade inata, avaliada pela atividade da lisozima, sistema complemento e “burst” respiratório dos leucócitos. As brânquias não apresentaram alterações que interferissem na função do órgão. No fígado as alterações foram classificadas de leves a moderadas, sem alteração nos rins. Animais tratados com AZT não apresentaram efeitos adversos relacionados às células de defesa e atividade imune inata. O fármaco também não causou alterações nas enzimas de defesa antioxidantes no fígado dos animais após exposição crônica, sem estresse oxidativo. Após desafio com A. hydrophila ocorreu aumento da atividade da catalase, glutationa peroxidase, glutationa transferase e nível de glutationa no fígado dos animais tratados com AZT e o nível de glutationa diminuiu no grupo infectado e não tratado. Estas respostas sugerem que a infecção causada pela A. hydrophila pode induzir o aumento da produção de espécies reativas de oxigênio e, consequentemente, estimulou as respostas das defesas antioxidantes. Essas respostas foram eficientes para evitar a ocorrência de estresse oxidativo. / FAPESP: 2011/21552-6

Resumo: Neste trabalho, investigou-se a cinética das alterações vasculares e celulares na aerocistite, induzida pela inoculação da Aeromonas hydrophila inativada em Piaractus mesopotamicus e inibição da atividade enzimática da fosfolipase A2 e ciclooxigenase na inflamação aguda. Para tanto, foram utilizadas a indometacina, meloxicam e a dexametasona, aplicados por via parenteral, 30 minutos antes do estímulo lesivo. As alterações de permeabilidade vascular foram avaliadas nos tempos de 30, 90, 120, 180 e 240 minutos pós-estímulo, observando-se que o máximo da exsudação plasmática ocorre com 180 MPE. O pré-tratamento com indometacina ou meloxicam, neste tempo, inibiu significativamente o aumento de permeabilidade vascular e a dexametasona apresentou um bloqueio mais precoce e efetivo do que os outros AINES, inibindo nos tempos de 120 e 180 MPE. O exsudato celular inflamatório foi avaliado seis, 24 e 48 horas após estímulo, verificando-se que a inoculação da bactéria causou aumento progressivo do acúmulo de células, atingindo o máximo após 24 HPE, sendo maior que nos outros grupos estudados. Neste tempo, verificou-se que todas as drogas testadas foram efetivas para a redução significativa do acúmulo celular. A contagem diferencial das células presentes no foco inflamado demonstrou predomínio de linfócitos e trombócitos, seguida de macrófagos e granulócitos, com acúmulo mais tardio destas últimas. O pré-tratamento com indometacina e dexametasona causou bloqueio no acúmulo de todas as células identificadas. Os resultados demonstraram que, entre as diferentes doses de cada droga testada, não foram observadas diferenças significativas. As avaliações sugeriram que os eicosanoides, assim como acontece em mamíferos, participam ativamente dos fenômenos vasculares e têm papel relevante na quimiotaxia de leucócitos / Abstract: In this teaching we investigated the kinetics of vascular and cellular changes in aerocistite induced by inoculation of inactivated Aeromonas hydrophila in Piaractus mesopotamicus and pharmacological effect of the enzymatic activity of phospholipase A2 and cyclooxygenase in acute inflammation. To this end, we used indomethacin, meloxicam and dexamethasone, applied intraparenteral 30 minutes before stimulation harmful. Changes in vascular permeability were evaluated in 30, 90, 120, 180 and 240 minutes post-stimulation, we observed that the maximum plasma exudation occurs with 180 MPE and pretreatment with indomethacin or meloxicam at this time significantly inhibited the increase vascular permeability and dexamethasone had a lock early and effective than other NSAIDs inhibited at 120 and 180MPE. The cellular inflammatory exudate was assessed with six, 24 and 48 hours after stimulation, verifying that the bacteria caused a progressive increase in accumulation of cells, peaking at 24 HPE, higher than the other groups analyzed, and this time all tested drugs were effective in significantly reducing the buildup. The differential count of cells present in the exudate showed a predominance of lymphocytes and thrombocytes, and granulocyte macrophage followed with a later accumulation of the latter. Pretreatment with indomethacin and dexamethasone caused a blockage in the migration of all cells evaluated. The results showed that among the different doses of each drug tested was not observed any significant difference. Analysis of those exposed, suggest that eicosanoids, with in mammals, participate actively in the vascular phenomena and has important role in chemotaxis of leukocytes in acute inflammatory process induced by A. hydrophila in pacu / Orientador: Flávio Ruas de Moraes / Coorientador: Marco Antonio de Andrade Belo / Banca: Rogério Salvador / Banca: Marileda Bonafim Carvalho / Mestre

The deep-sea is the largest habitat on earth, containing over 90 percent of the world’s oceans and home to over 20,000 species. Deep-sea ecosystems are increasingly impacted by human activities including fishing and oil extraction. To understand potential impacts on deep-sea food webs, it is crucial to gather baseline data in these systems. I quantified the trophic interactions of three groups of deep-water animals across a range of trophic levels living in the northern and eastern Gulf of Mexico using stable isotope analysis. First, I propose methods for correcting δ15N values for the presence of nitrogenous metabolic waste products (e.g., urea) in muscle tissue using chemical extractions and/or species-specific mathematical normalizations. Significant differences in δ15N, %N, and C:N values as a result of extractions were observed in eight of ten shark and all three hagfish species. The δ15N values increased, but shifts in %N and C:N values were not unidirectional. Mathematical normalizations for δ15N values were successfully created for four shark and two hagfish species. I then describe the trophic interactions of three consumer assemblages. Carbon isotopic values indicate a heavy reliance on allochthonous nutrient inputs from surface waters. Nitrogen isotopic values reveal somewhat atypical taxa as top predators in the deep sea. Shark, teleost, and invertebrate species across a wide range of body sizes are feeding at a similar trophic level. This apparent lack of size structuring could be the result of a high degree of opportunistic scavenging or perhaps feeding at many trophic levels simultaneously in an oligotrophic system. There was a high degree of isotopic niche overlap among species within each consumer assemblage, perhaps the result of limited nutrient resources in the deep-sea. In general, individuals from the northern sampling stations displayed higher δ13C and δ15N values than those from the eastern sites. With the exception of a few species, there were no strong relationships between body size and isotopic values. The present study is among the first characterizations of the trophic structure of deep-sea organisms in the Gulf of Mexico and establishes system baselines for future studies describing deep-water systems and investigating anthropogenic impacts.