In some fish, hypertrophic growth of white muscle leads to very large fibers. The associated low-fiber surface area-to-volume ratio (SA/V) and potentially long intracellular diffusion distances may influence the rate of aerobic processes. We examined the effect of intracellular metabolite diffusion on mass-specific scaling of aerobic capacity and an aerobic process, phosphocreatine (PCr) recovery, in isolated white muscle from black sea bass (Centropristis striata). Muscle fiber diameter increased during growth and was >250 mum in adult fish. Mitochondrial volume density and cytochrome-c oxidase activity had similar small scaling exponents with increasing body mass (-0.06 and -0.10, respectively). However, the mitochondria were more clustered at the sarcolemmal membrane in large fibers, which may offset the low SA/V, but leads to greater intracellular diffusion distances between mitochondrial clusters and ATPases. Despite large differences in intracellular diffusion distances, the postcontractile rate of PCr recovery was largely size independent, with a small scaling exponent for the maximal rate (-0.07) similar to that found for the indicators of aerobic capacity. Consistent with this finding, a mathematical reaction-diffusion analysis indicated that the resynthesis of PCr (and other metabolites) was too slow to be substantially limited by diffusion. These results suggest that the recovery rate in these fibers is primarily limited by low mitochondrial density. Additionally, the change in mitochondrial distribution with increasing fiber size suggests that low SA/V and limited O(2) flux are more influential design constraints in fish white muscle, and perhaps other fast-twitch vertebrate muscles, than is intracellular metabolite diffusive flux.

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The incidental mortality of albatrosses Diomedeidae and petrels Procellariidae by longline fishing vessels, has been assessed and analysed in several areas of the globe. We provide the first direct estimates of incidental mortality rates of albatrosses and petrels along the Argentine Shelf and shelf break. The estimated by-catch rate for the whole period analysed (1999-2001) was 0.04 birds/1,000 hooks, with a maximum of 0.20 birds/1,000 hooks observed in 1999. Annual captures averaged 1,160 birds; however, the large variation observed indicates that annual by-catch may be in the order of thousands, with around 10,000 seabirds being killed by longliners through the study period. Most of the captures were observed along the Patagonian shelf break. At least 12 bird species were incidentally taken, with Black-browed Albatrosses Thalassarche melanophris and White-chinned Petrels Procellaria aequinoctialis accounting for about 80% of total captures. The information provided in this study allowed the design and future implementation of mitigation measures and new survey methods onboard longliners operating in Atlantic waters on the Argentine shelf.

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Desde mediados del siglo XX se ha venido argumentando que el emprendimiento es un componente vital para el crecimiento económico, la innovación y el empleo Adicionalmente, se espera que los egresados universitarios impulsen la creación de empresas innovadoras sin embargo, es poco lo que se sabe sobre las razones que llevan a un universitario a tomar la decisión de emprender. Este artículo tiene como objetivo presentar los resultados preliminares de la investigación sobre las intenciones emprendedoras de los estudiantes de la Facultad de Minas de la Universidad Nacional de Colombia ”“ Sede Medellín. La investigación fue de tipo exploratorio con diseño no experimental, transversal y de campo. Se realizaron 477 encuestas a estudiantes de la Facultad durante los meses de octubre y noviembre del año 2010, las cuales fueron procesadas con el paquete estadístico R. Se identificaron y caracterizaron cuatro tipologías básicas de estudiantes según sus intenciones emprendedoras, con las cuales se verificó la capacidad explicativa del Modelo de Intención Emprendedora propuesto en el 2005 por Segal, Borgia, y Schoenfeld. Se concluye proponiendo mejoras al Modelo de Intención Emprendedora que permitan incrementar su poder explicativo.