26 research outputs found
Do herbivorous minnows have âplug-flow reactorâ guts? Evidence from digestive enzyme activities, gastrointestinal fermentation, and luminal nutrient concentrations
Few investigations have empirically analyzed fish gut function in the context of chemical reactor models. In this study, digestive enzyme activities, levels of gastrointestinal fermentation products [short chain fatty acids (SCFA)], luminal nutrient concentrations, and the mass of gut contents were measured along the digestive tract in herbivorous and carnivorous minnows to ascertain whether their guts function as âplug-flow reactorsâ (PFRs). Four of the species, Campostoma anomalum, C. ornatum, C. oligolepis, and C. pauciradii, are members of a monophyletic herbivorous clade, whereas the fifth species, Nocomis micropogon, is a carnivore from an adjacent carnivorous clade. In the context of a PFR model, the activities of amylase, trypsin and lipase, and the concentrations of glucose, protein, and lipid were predicted to decrease moving from the proximal to the distal intestine. I found support for this as these enzyme activities and nutrient concentrations generally decreased moving distally along the intestine of the four Campostoma species. Furthermore, gut content mass and the low SCFA concentrations did not change (increase or decrease) along the gut of any species. Combined with a previous investigation suggesting that species of Campostoma have rapid gut throughput rates, the data presented here generally support Campostoma as having guts that function as PFRs. The carnivorous N. micropogon showed some differences in the measured parameters, which were interpreted in the contexts of intake and retention time to suggest that PFR function breaks down in this carnivorous species
Oportunismo alimentar de Knodus moenkhausii (Teleostei, Characidae): uma espécie abundante em riachos do noroeste do Estado de São Paulo, Brasil
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A Simple System of Replicated Recirculating Experimental Streams
Impacts of differential consumption by the grazing fish, Plecoglossus altivelis, on the benthic algal composition in the Chikuma River, Japan
Habitat use by a Midwestern U.S.A. riverine fish assemblage: effects of season, water temperature and river discharge
Working Backwards: Instrumental analysis as a policy discovery procedure
Following up on suggestions of Adolph Lowe, the paper draws on the work of Peirce, Polya and Michael Polanyi to elaborate the notion of Lowe's instrumental analysis as a policy discovery procedure. It is argued that such an interpretation of Lowe's instrumentalism may contribute to the formulation of effective practical policies. It is also argued in the paper that this interpretation throws light on some issues concerning markets and planning that relate to the debate on socialist calculation that has been revived in the name of the 'knowledge problem' by contemporary Austrian economists. In particular, it is argued that Lowe's Instrumentalism brings to the fore the role of discovery and creativity-which are central to Austrian conceptions of entrepreneurial activity in the market-in policy formulation. In this sense Lowe's work may be seen as an antecedent to more recent work in planning that critiques-and promotes nonessentialist alternatives to-optimal or rational planning.
Diet of Astyanax species (Teleostei, Characidae) in an Atlantic Forest River in Southern Brazil
Feeding habits of six species of Astyanax from river MaquinĂ© are described. Fishes were sampled bi-monthly from November/95 to September/96 in two zones of the river. Items were identified, counted and had their abundance estimated according to a semi-quantitative scale. Frequency of occurrence, alimentary importance index (IFI) values and a similarity analysis of diets for each species-river zone sample were examined. All the species were considered typically omnivorous, with insects and vegetal matter being the most important items in their diet. These species could act as seed dispersers, particularly for macrophytes. Intra-specific spatial differences were not observed in comparisons of samples from two diferent regions of the river, except for A. fasciatus. The presence of Podostemaceae macrophytes in the mid-course of the river seemed to be important both as an autochthonous food resource and as habitat for several organisms preyed by the Astyanax species.<br>Seis espĂ©cies do gĂȘnero Astyanax, presentes no rio MaquinĂ©, RS, foram estudadas quanto aos seus hĂĄbitos alimentares. Os exemplares foram amostrados bimensalmente de novembro de 1995 a setembro de 1996 nas zonas ritral e potamal do rio. Os itens alimentares foram identificados e quantificados de acordo com uma escala semi-quantitativa de abundĂąncia, utilizando-se para anĂĄlise a frequĂȘncia de ocorrĂȘncia e um Ăndice de importĂąncia alimentar para cada espĂ©cie e zona do rio. AnĂĄlises multivariadas de agrupamento e ordenação foram utilizadas para comparar as dietas intra e interespecĂficas. Todas as espĂ©cies foram consideradas onivoras, sendo que os itens mais importantes foram os insetos e restos de vegetais superiores. Sugere-se que as espĂ©cies estudadas possam atuar como dispersoras de sementes, particularmente para macrĂłfitas. Diferenças espaciais intraespecĂficas nĂŁo foram encontradas, exceto para A. fasciatus. A presença de Podostemaceae no curso mĂ©dio do rio parece ser uma fonte importante de alimento para as espĂ©cies, alĂ©m de servir de refĂșgio para diversos organismos que sĂŁo predados por Astyanax sp