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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
41

Utilização da levedura alcoólica (Sacharomy cerevisae) como fonte protéica na alimentação de juvenis de pacu (Piractus mesopotamicus, Pisces, Teleostei) : aspectos metabólicos e de desempenho produtivo /

Pádua, Delma Machado Cantisani. January 1996 (has links)
Orientador: Elisabeth Criscuolo Urbinati / Coorientador: Dalton José Carneiro / Banca: Elisabete Maria Macedo Viegas / Banca: Nancy Carneiro / Resumo: O presente experimento avaliou o efeito de diferentes níveis de levedura seca de destilaria alcoólica (Saccharomyces cerevisiae) em dietas para juvenis de pacu (Piaractus mesopotamicus) sobre aspectos do metabolismo, desempenho produtivo e composição corporal. Em delineamento em blocos casualizados, em esquema de parcela subdividida no tempo ("Split Plot in Time") foram testados quatro níveis de substituição da farinha de peixe por levedura, 25, 50, 75 e 100 %, com duas avaliações, aos 45 e 87 dias do início do experimento. As dietas foram fornecidas duas vezes ao dia, ad libtum. Duzentos peixes foram distribuídos em 20 tanques com capacidade para 1330 l, instalados no interior de uma estufa e com fluxo individual de água. Os parâmetros de qualidade de água mantiveram-se adequados ao longo do experimento. Foi possível a substituição da farinha de peixe por levedura até o nível de 75 % sem se constatar prejuízo nos diversos parâmetros analisados. O nível mais elevado de levedura na dieta (100 %) levou aos piores resultados de desempenho produtivo, com menor taxa de crescimento instantâneo. Não houve influência significativa dos tratamentos sobre a composição corporal dos peixes, exceto pela maior concentração de material mineral no corpo dos peixes que receberam 100 % de substituição. Este nível de substituição provocou alta mortalidade. Foi observado, nos peixes alimentados com dietas contendo 100 % de substituição de farinha de peixe por levedura, hiperglicemia e decréscimo no glicogênio hepático, conteúdo total de lipídios e proteína plasmática. Seguindo o mesmo padrão de resposta, os hepatócitos apresentaram a mais baixa área e volume do citoplasma no mesmo tratamento. Aumento nos níveis de hematócrito foram detectados nos peixes que receberam dieta com 100 % de proteína fornecida pela levedura, aos 87 dias. As demais dietas com levedura... / Abstract: The present experiment assessed the effect of inclusion of different levels of the single cell protein molasses yeast (Saccharomyces cerevisiae) in the diet of juvenile pacu (Piaractus mesopotamicus) replacing fish meal. Five isoproteic (26 % CP) and isocacloric (4000 kcal GE/kg) diets were formulated in which the levels of substitution by yeast were 25, 50, 75 and 100 % and tested in two periods, following a Split Plot in Time design. Diets were fed twice a day ad libitum. Two hundred fish were allotted in 20 cement tanks of 1330 l, with continuous water flow, and sampled at 45 and 87 days after start feeding. It was possible to include until 75 % of molasses yeast in substitution of fish meal without negative effects in the parameters analyzed. The highest level of yeast in the diet (100 %) showed delayed growth, with low specific growth rate and did not affected significantly the body composition, excepting for higher mineral content. The same level of yeast provoked high mortality of fish. Its was observed hyperglycemia and decrease in liver glycogen, total liver lipid content and plasma protein in fish fed on diet containing 100 % molasses yeast. Following the same pattern of response hepatocytes showed the lowest area and volume of cytoplasm, at the same treatment. Increase in hematocrit levels appeared at 100 % molasses yeast diet only at 87 days. The other molasses yeast diets (25, 50 and 75 %) presented similar performance compared to control diet. Concluding, the results of the present study suggest that the diet with total replacement of fish meal by molasses yeast showed an antinutritional effect / Mestre
42

Qualidade da água e desempenho produtivo da tilápia do Nilo alimentada em diferentes freqüências e períodos por meio de dispensador automático

Sousa, Rodrigo Morgado Ramalho de [UNESP] 02 March 2007 (has links) (PDF)
Made available in DSpace on 2014-06-11T19:30:22Z (GMT). No. of bitstreams: 0 Previous issue date: 2007-03-02Bitstream added on 2014-06-13T19:46:54Z : No. of bitstreams: 1 sousa_rmr_me_botfmvz.pdf: 208473 bytes, checksum: dd00b3321ca18be8e70cfe03bfd4c437 (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Universidade Estadual Paulista (UNESP) / O objetivo deste experimento foi avaliar o desempenho da tilápia criada em tanque-rede, provido com dispensador automático de ração, com fornecimento em diferentes freqüências (de hora em hora e de duas em duas horas) e períodos (diurno, noturno e ambos). Foram utilizados dezoito tanques-rede de 1,0 m3, distribuídos em um viveiro de 2000 m2, com profundidade média de dois metros e renovação de água de 5,0 %. As tilápias, com peso inicial de 16,0,0l4,9 g, foram distribuídas nos tanques-rede na densidade de 170 peixes por md e, a quantidade de ração foi ajustada a cada 21 dias, coincidindo com as biometrias. Os dados foram coletados de março a julho de 2006 (outono/inverno) e a análise estatística mostrou diferença significativa (P<0,05), entre tratamentos, para o peso final. O aumento da freqüência alimentar melhora o desempenho produtivo da tilápia nilótica em tanques-rede e, o maior número de alimentações permite melhor aproveitamento do alimento. / The aim of this experiment was to evaluate the performance of oreochromis niloticus reared in cages, fed in different frequencies (hourly and once each two hours) and periods (diurnal, nocturnal and both) using an experimental automatic feeder. in a 2000 mø pond, with mean depth of 2 m and water renewal 5%, the several experimental levels were placed in 18 cages of 1 md. the initial weight of tilapias were 16,0.0 l 4.9g, in a density of 170 fishes/md. from march to july, 2006 (autumn/winter) the ration supply was adjusted each 21 days, concomitantly with fish biometry. statistical differences of final weight were fond (anova, p<0.05) and higher feeding frequencies improved growth performance, probably in response to enhancement of food assimilation.
43

Relação entre helmintos gastrointestinais ambiente e alimentação de pacus (Piaractus mesopotamicus Holberg, 1887) em tanques de piscicultura / Relation among gastroeintestinal helminthes environment and feeding Pacus (Piaractus mesopotamicus Holberg, 1887) in fishponds

Barreto, Ermelindo 15 August 2018 (has links)
Orientador: Silmara Marques Allegretti / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Biologia / Made available in DSpace on 2018-08-15T15:01:23Z (GMT). No. of bitstreams: 1 Barreto_Ermelindo_M.pdf: 2333180 bytes, checksum: 51b623e799efcc142a93cd0b22a890d3 (MD5) Previous issue date: 2009 / Resumo: O Brasil possui diversas espécies nativas de peixes com grande potencial para exploração na aquicultura. Entretanto, a maioria delas carece de estudos científicos e tecnológicos que permitem a máxima viabilidade zootécnica e econômica. Dentre as espécies de peixes nativas da América do Sul, o pacu, Piaractus mesopotamicus (Holmberg, 1887) é uma das mais cultivadas em pisciculturas de todo o Brasil. O pacu é uma espécie onívora, nativa da Bacia do Rio da Prata, ocorrendo principalmente nos rios Paraná e Paraguai e seus afluentes, adapta-se a diversos sistemas de criação, tem excelente crescimento e conversão alimentar. Sua alta capacidade reprodutiva, crescimento rápido e fácil aceitação comercial, fazem desta espécie uma das preferências no cultivo de peixes no território brasileiro. No período de julho de 2008 a setembro de 2009 foram examinados 142 pacus de tamanhos variados, coletados nos tanques do Centro de Pesquisa e Conservação de Peixes Continentais - Instituto Chico Mendes de Conservação da Biodiversidade - CEPTA/ICMBio, Pirassununga, SP. Os peixes foram medidos, pesados e determinados o sexo e maturidade sexual. Foram encontrados Rondonia rondoni (prevalência de 63,38%, intensidade média de 2589,59 vermes/peixe e abundância média de 1641,29) e Goezia sp. (prevalência de 51,41%, intensidade média de 2,52 vermes/peixe e abundância média de 1,29). Os conteúdos gastrointestinais foram divididos em 3 grupos alimentares: G1 (essencialmente matéria vegetal), G2 (mistura de vegetais com ração) e G3 (essencialmente ração). As análises estatísticas demonstraram haver relação entre o número de R. rondoni presentes no peixe e o grupo alimentar (P<0,0001), sendo o grupo G1 com a menor média no número de vermes (207 vermes/peixe), o G2 com a maior média (4198,42 vermes/peixe) e o G3 com 403,54 vermes/peixe. Outro resultado significativo mostrou que o tanque também influenciou na característica da infecção por ambos os nematódeos: no tanque com grande quantidade de vegetação as prevalências eram baixas e as intensidades altas e tanques sem vegetação houve uma elevação na prevalência e diminuição na intensidade de infecção. / Abstract: Brazil has several native fish species with great potential for exploitation in aquaculture. However, most of them lack scientific and technological advances that allow for maximum performance and economic feasibility. Among the fish species native from South America, the pacu, Piaractus mesopotamicus (Holmberg, 1887) is one of the most cultivated in farms throughout Brazil. Pacu is an omnivorous species, native to the basin of the River Plate, occurring mainly in the Paraná and Paraguay rivers and their affluents. It is a species adapted to different farming systems, it has an excellent growth and feed conversion. Their high reproductive capacity, rapid growth and easy commercial acceptance, make this species very attractive for fish cultivation in the Brazilian territory. A total of 142 specimens of Pacu of different sizes were collected in tanks of the Center for Research and Conservation of Fish Continental - Chico Mendes Institute for Biodiversity Conservation - CEPTA / ICMBio, Pirassununga, SP and examined from July 2008 to September 2009. The fishes were weighed, measured and classified according to sex and sexual maturity. The gastrointestinal helminths found were: Rondonia rondoni (prevalence of 63.38%, mean intensity of infection of 2589.59 worms/fish and mean abundance of 1641.29) and Goezia sp. (prevalence of 51.41%, mean intensity of infection of 2.52 worms/fish and mean abundance of 1.29). The gastrointestinal contents were divided into three food groups: G1 (mainly vegetable matter), G2 (mixed vegetables with fish food) and G3 (fish food). Statistical analysis showed relationship between the number of R. rondoni and food group (p <0.0001). G1 with the lowest average in the number of worms (207 worms/fish), G2 with the highest average (4198.42 worms/fish) and G3 with 403.54 worms/fish. Another significant result showed that the maintenance tank also influence the characteristic of infection by both nematodes. In tank without vegetation there was an increase in the prevalence and decrease in the intensity of infection. / Mestrado / Mestre em Parasitologia
44

Investigations into the nutritional requirements of juvenile dusky kob, Argyrosomus japonicus (Pisces sciaendae), under ambient culture conditions

Daniel, Simon James January 2004 (has links)
The effect of dietary protein, protein and energy ratios, fish meal replacement by Soya bean meal and feeding frequency was investigated on the growth, feed efficiency and body composition, of juvenile dusky kob, Argyrosomus japonicus. The effect of dietary protein levels was investigated by comparing isocaloric diets containing 35, 40, 45 and 55% protein. Dietary protein inclusion level significantly affected specific growth rates, feed efficiency and body composition (in terms of fat deposition) and results show that a minimum of 45% and maximum of 52.3% dietary protein is optimal. The protein and energy requirements were investigated by comparing three protein levels (35,40 and 45%) with three lipid levels (6, 9 and 12%) in a 3x3 factorial design. A diet 45% protein and 9% lipid, with a P: E ratio of29 mglkJ and DE of 15.5 kJ/g resulted in an optimal specific growth rate (1.6± 0.2), feed efficiency (FCR= 1.7±0.44; PER= 1.36) and body composition for A. japonicus. To investigate the effect of partial fish meal replacement by Soya bean meal (SBM) in the diet, 20-50% of the protein from fish meal was substituted by protein from SBM, and were compared with a control diet containing only fish meal. No significant differences in the specific growth rates, feed efficiencies and the body composition were recorded for the fish fed the control diet and for fish fed the 20 and 30% SBM treatments. Results show that up to 30% of the protein from fish meal can be replaced with protein from SBM in the diet of this species. The effect of feeding frequency and gut evacuation time was investigated by comparing four feeding frequencies. Fish were fed to satiation either once, twice, three or four times a day. Feed intake was significantly affected by feeding frequency and fish fed 2, 3 and 4 meals a day ate significantly more food (p< 0.05) than the fish fed one meal a day. No significant differences (p> 0.05) in the specific growth rates, feed efficiencies and body composition were recorded for fish fed 2, 3 and 4 times a day. Feed intake was used to calculate an optimal daily ration and feeding two meals a day resulted in an optimal daily ration of 4% BW/day. A gut evacuation time of 7.25 hours indicates that fish fed twice a day probably had sufficient time to digest their food and evacuate their guts, resulting in the same daily feed intake as fish given 3 and 4 meals a day. Results conclude that under the present experimental conditions, a minimum daily ration of 4% BW/day, fed twice a day (in the morning and evening) is required for optimal growth (SGR= 1.33± 0.1), feed efficiency (FCR= 1.96± 0.4; PER= 1.44± 0.2) and body composition in juvenile dusky kob.
45

The development of a practical diet for juvenile dusky kob, Argyrosomus japonicus, for the South African mariculture industry

Woolley, Lindsey January 2009 (has links)
The lack of locally manufactured marine finfish diets motivated the current project, which aimed to develop a practical diet specifically formulated for dusky kob. The first growth trial investigated the effect of pellet texture (i.e. hard versus soft pellets) and the inclusion of an additional binder, test treatments were compared to two reference diets. There was no significant difference in weight gain between fish fed the hard or soft pellets (p=0.17), over nine weeks. The fish fed the local trout feed weighed significantly less than those fed the test diets (p=0.003). There was no significant difference in leaching rate amongst treatments (p=0.45). A hard pelleted diet without gelatin is recommended in the commercial culture of dusky kob. Pellets with different physical shapes were tested to determine the effect of shape on settling speeds. A square shaped pellet had a slower sinking rate compared to a round shaped pellet (p<0.0001). Juvenile dusky kob, held in cages, fed the square pellets grew significantly faster than the fish fed the round pellet, with a mean weight gain of 16.81 ± 0.45 g (p=0.018). A growth trial was used to optimize the protein to energy (PE) ratio by adjusting dietary protein and lipid levels. Fish fed the diets with high levels of protein (46 % protein) achieved the better growth rates (125 % weight gain) compared to the lower protein diets (92 % weight gain) (p<0.0001). There was no significant difference in total ammonia production (TAN) level for the 46 and 42 % protein diets (p=0.68). The overall performance of the prototype diet was investigated in a closed recirculating system. Growth and FCR of the fish fed the prototype diet was on a par to those fed the commercially available diet currently used in the local farming industry. There was no significant difference in the blood chemistry for fish held at increased stocking densities. The prototype diet is suitable for use in recirculating systems, as there were no negative effects on water quality parameters. This study has laid a foundation for the manufacture of a practical commercial dusky kob diet in South Africa.
46

Estresse de dominância e respostas metabólicas da tilápia-do-Nilo

Genovez, Lara Wichr [UNESP] 16 June 2014 (has links) (PDF)
Made available in DSpace on 2014-08-13T14:50:59Z (GMT). No. of bitstreams: 0 Previous issue date: 2014-06-16Bitstream added on 2014-08-13T17:59:44Z : No. of bitstreams: 1 000775314.pdf: 522390 bytes, checksum: f7e49e04c3fd7e84ff8472a1bb097a67 (MD5) / A hierarquia de dominância e o confronto agonístico causam estresse aos animais. Essa pesquisa objetivou quantificar o efeito do estresse após o estabelecimento da hierarquia social avaliando as respostas metabólicas entre juvenis de tilápia-do-Nilo. Foram distribuídos 20 peixes machos em 10 aquários com capacidade de 110 litros, adotado um delineamento inteiramente cazualizado totalizando cinco tratamentos com quatro repetições. Os animais foram alimentados com ração prática contendo 28,0% de proteína bruta e 3000 kcal de energia digestível. Foi realizada a divisão hierárquica dos indivíduos em dominantes e submissos segundo Falter (1983). Para o tratamento de comunicação visual, os aquários foram divididos com placas de vidro translúcidas, onde os animais não tiveram contato “físico” não havendo nenhum tipo de contato coma água do coespecífico; para o tratamento de comunicação química havia um sistema de bombeamento que homegeneizava a água dos animais, não havendo nenhum tipo de contato visual com o coespecífico. O animal isolado não recebeu água de nenhum outro peixe e nem teve contato visual. As avaliações do efeito do estresse hierárquico foram medidas por meio de três estudos: a) digestibilidade aparente, b) tempo de trânsito gastrintestinal e c) morfometria do epitélio intestinal dos peixes. O dados de tempo de trânsito gastrointestinal foram representados em forma de gráficos e os dados morfométricos foram avaliados pela análise de variância multivariada, considerando o par altura de vilo (AV) e profundidade de cripta (PC). Com base nos resultados obtidos pode-se concluir que o estresse hierárquico tem efeito significativo no trânsito gastrointestinal, aumentando a velocidade de trânsito da ingesta em até duas horas em animais submissos e que a porção proximal do intestino é a mais adequada para avaliar o efeito do estresse hierárquico por meio ... / The dominance hierarchy and agonistic confrontation cause stress to the animals. This study aimed to quantify the effect of stress after the establishment of social hierarchy evaluating metabolic responses between the juvenile Nile tilapia. 20 male fish were distributed in 10 tanks with a capacity of 110 liters, adopted an outline fully cazualizado total of five treatments with four replications. The animals were fed a practical diet containing 28.0% crude protein and 3000 kcal of digestible energy. The hierarchical division of the individuals were in dominant and submissive second Falter (1983). For the treatment of visual communication, aquaria were divided plates with translucent glass, where the animals had no physical contact not having any type of contact water conspecific eat; for the treatment of chemical communication had a pumping system that homegeneizava water animals, without any eye contact with the conspecific. The isolated animal received no water no other fish and even had eye contact. The effect of the hierarchical stress ratings were measured by means of three studies: a) digestibility, b) and c gastrointestinal transit time) morphology of the intestinal epithelium of the fish. The data gastrointestinal transit time were represented as graphs and morphometric data were evaluated by multivariate analysis of variance, considering the pair villi height (AV) and crypt depth (PC). Based on the results obtained it can be concluded that the hierarchical stress has significant effect on the gastrointestinal transit, increasing the speed of transit of food intake within two hours in submissive animals and the proximal portion of the intestine is the most appropriate to evaluate the effect of hierarchical stress by pair (AV: PC).
47

Estresse de dominância e respostas metabólicas da tilápia-do-Nilo /

Genovez, Lara Wichr, 1984. January 2014 (has links)
Orientador: Luiz Edivaldo Pezzato / Coorientador: Márcia M. Pereira Sartori / Banca: Elyara Maria Pereira-da-Silva / Banca: Ademir Fernandes Calvo Junior / Banca: Ana Lúcia Salaro / Banca: Hamilton Hisano / Resumo: A hierarquia de dominância e o confronto agonístico causam estresse aos animais. Essa pesquisa objetivou quantificar o efeito do estresse após o estabelecimento da hierarquia social avaliando as respostas metabólicas entre juvenis de tilápia-do-Nilo. Foram distribuídos 20 peixes machos em 10 aquários com capacidade de 110 litros, adotado um delineamento inteiramente cazualizado totalizando cinco tratamentos com quatro repetições. Os animais foram alimentados com ração prática contendo 28,0% de proteína bruta e 3000 kcal de energia digestível. Foi realizada a divisão hierárquica dos indivíduos em dominantes e submissos segundo Falter (1983). Para o tratamento de comunicação visual, os aquários foram divididos com placas de vidro translúcidas, onde os animais não tiveram contato "físico" não havendo nenhum tipo de contato coma água do coespecífico; para o tratamento de comunicação química havia um sistema de bombeamento que homegeneizava a água dos animais, não havendo nenhum tipo de contato visual com o coespecífico. O animal isolado não recebeu água de nenhum outro peixe e nem teve contato visual. As avaliações do efeito do estresse hierárquico foram medidas por meio de três estudos: a) digestibilidade aparente, b) tempo de trânsito gastrintestinal e c) morfometria do epitélio intestinal dos peixes. O dados de tempo de trânsito gastrointestinal foram representados em forma de gráficos e os dados morfométricos foram avaliados pela análise de variância multivariada, considerando o par altura de vilo (AV) e profundidade de cripta (PC). Com base nos resultados obtidos pode-se concluir que o estresse hierárquico tem efeito significativo no trânsito gastrointestinal, aumentando a velocidade de trânsito da ingesta em até duas horas em animais submissos e que a porção proximal do intestino é a mais adequada para avaliar o efeito do estresse hierárquico por meio ... / Abstract: The dominance hierarchy and agonistic confrontation cause stress to the animals. This study aimed to quantify the effect of stress after the establishment of social hierarchy evaluating metabolic responses between the juvenile Nile tilapia. 20 male fish were distributed in 10 tanks with a capacity of 110 liters, adopted an outline fully cazualizado total of five treatments with four replications. The animals were fed a practical diet containing 28.0% crude protein and 3000 kcal of digestible energy. The hierarchical division of the individuals were in dominant and submissive second Falter (1983). For the treatment of visual communication, aquaria were divided plates with translucent glass, where the animals had no "physical" contact not having any type of contact water conspecific eat; for the treatment of chemical communication had a pumping system that homegeneizava water animals, without any eye contact with the conspecific. The isolated animal received no water no other fish and even had eye contact. The effect of the hierarchical stress ratings were measured by means of three studies: a) digestibility, b) and c gastrointestinal transit time) morphology of the intestinal epithelium of the fish. The data gastrointestinal transit time were represented as graphs and morphometric data were evaluated by multivariate analysis of variance, considering the pair villi height (AV) and crypt depth (PC). Based on the results obtained it can be concluded that the hierarchical stress has significant effect on the gastrointestinal transit, increasing the speed of transit of food intake within two hours in submissive animals and the proximal portion of the intestine is the most appropriate to evaluate the effect of hierarchical stress by pair (AV: PC). / Doutor
48

Food Habits, Dietary Overlap and Electivity of Non-Game Insectivorous Fishes in an Ozark Foothills Stream

Todd, C. Stan (Charles Stan) 05 1900 (has links)
Etheostoma spectabile, E. punctulatum, and Cottus carolinae were sampled Mar., 1983, - Feb., 1984, in Flint Creek, Oklahoma. Immature E. spectabile ate primarily microcrustaceans, while mature fishes relied more on mayflies and amphipods. Juvenile E. punctulatum fed upon mayflies, amphipods, and Asellus. Mature E. punctulatum ate primarily mayflies, and other relatively larger prey. Cottus carolinae consumed chironomids almost exclusively in Jan. - Feb., 1984, while mayflies were predominant the remainder of the year. No significant habitat partitioning between the two darters, and seasonal habitat segregation between C. carolinae and the two darters was found. Dietary overlap between the darters was significantly correlated (p<0.0005) to differences in x prey sizes.
49

Health risk assessment of dioxin-like compounds in complex samples /

Öberg, Mattias U. L., January 2003 (has links)
Diss. (sammanfattning) Stockholm : Karol. inst., 2003. / Härtill 5 uppsatser.
50

Fishes in the Mngazi and Mngazana estuaries, with particular emphasis on the community structure and primary carbon sources

Mbande, Sekiwe January 2004 (has links)
The fish community structure of two contrasting estuaries, one with a well developed mangrove forest (Mngazana) and the other without mangroves (Mngazi) was compared. Both the Mngazi and Mngazana estuary fish communities were dominated by marine species, reflecting the importance of these systems as nursery areas for marine fishes. The Mngazi Estuary contained 18% more estuarine fishes in terms of catch per unit effort (CPUE) than the Mngazana Estuary. The reduced tidal influence due to the narrow mouth opening is a possible reason for the heightened CPUE of estuarine species in the Mngazi estuary. The recorded higher diversity of fish species in the Mngazana Estuary when compared with the Mngazi Estuary was attributed to the greater influence of the marine environment due to the wide permanently open mouth, as well as the presence of a variety of habitats in this system. In both estuaries tropical and temperate species were captured, confirming the transitional nature of their biogeographic location which is situated close to the boundary between the subtropical and warm temperate regions of the Southern African coastline. Contrary to previous studies, which recorded seasonal changes in the proportions of tropical and temperate species, the proportions of tropical species remained unchanged at approximately 70% during the January and June sampling occasions. Global warming as a possible reason for the increased dominance of tropical species is discussed. Although several studies in southern Africa have investigated estuarine food web structure, none have compared mangrove and non-mangrove estuaries. In this study, the primary sources of carbon utilised by the fish fauna in the Mngazi and Mngazana estuaries was investigated. The carbon isotopic values of fishes in both estuaries displayed a continuum rather than a tight clustering around particular energy sources. Most detritus feeders of the family Mugilidae (mullets) from both estuaries were relatively more enriched than other fish taxa. The isotopic values of the mullet species suggest a diet derived from relatively enriched carbon sources such as benthic microalgae, the eelgrass Zostera capensis and associated epiphytes. Based on the isotopic values, piscivorous fishes from both estuaries could not be linked to specific prey fish taxa, but clearly the mullet species were not their main food source. The invertebrate feeders that were found in both estuaries showed greater isotopic variations in the Mngazana Estuary than in the Mngazi Estuary, probably reflecting the higher diversity of habitats (carbon sources) and invertebrate prey species in the Mngazana system. Generally the isotopic signatures of fishes from the Mngazi Estuary were more enriched than those from the Mngazana Estuary, thus indicating the possible effect of δ¹³C depleted mangrove derived carbon in the latter system.

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