CONICET | Buscador de Institutos y Recursos Humanos

Seasonal growth of G. maculatus in Tierra del Fuego, at the southern limit of its distribution, would be explained by the variation of extrinsic factors, and experiments of fasting under summer conditions would allow researchers to potentially focus on feeding/fasting conditions independent of other seasonal cues, and thus discriminate the effect of fasting from other winter factors that influence fish growth. The current study presents information about muscle growth of Galaxias maculatus and the results of an experiment evaluating the effect of fasting on growth rate, total muscle growth and energy density in this species, under summer-like conditions. Uniform pattern of muscle fibers suggest the absence of mosaic hyperplastic growth in G. maculatus. Hyperplasic growth was over before puyen reached 65 mm total length, and hyperplasia cessation was correlated to the transition from juvenile to adult stage. In the experimental animals, where hypertrophic growth was the unique process responsible for adult muscle growth, fasting decreased mass, condition and energy density of experimental individuals, and stopped the hypertrophic growth. These results proof that reduced food consumption in southerly puyen populations during winter might contribute to the seasonality of growth previously reported for this species. A provisional summer growth rate of 2?3 mm/month is suggested for populations inhabiting the southern limits of this species? distribution. We propose G. maculatus as a useful model species to study hypertrophic muscle growth.

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