Diel and seasonal changes in nutritional condition of the anadromous twaite shad Alosa fallax fallax (Lacépède, 1803) larvae |
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Authors: | E. Esteves T. Pina J. P. Andrade |
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Affiliation: | Centro de Ciências do Mar, CCMar –CIMAR Laboratório Associado, Faculdade de Ciências do Mar e Ambiente da Universidade do Algarve, Faro, Portugal |
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Abstract: | Abstract – In this work we aim to study: (i) the diel and seasonal changes in nutritional condition, herein RNA/DNA ratios, of twaite shad ( Alosa fallax fallax ) larvae and (ii) the influence of environmental and biological covariates on those changes. Samples were collected in the River Mira (Portugal) from February 1998 to July 2000. The RNA/DNA ratios were significantly lower than average during dawn and dusk hours. This pattern can be attributed to: the absence of better-fit specimens escaping the net; a nightly increase in the RNA content in response to circadian rhythm; and/or nucleic acids of prey items remaining in the gut of larvae during daylight. Thus, the time of day is important when examining RNA/DNA ratios of twaite shad. Generalised additive model of seasonal data showed that water temperature, freshwater pulses and/or turbidity largely contribute to create adequate environments. These might enhance the nutritional condition of twaite shad larvae during the period that they remain in the upper reaches of River Mira. |
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Keywords: | RNA/DNA twaite shad environmental effects statistical modelling |
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