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The importance of dietary phosphorus and highly unsaturated fatty acids for sockeye (Oncorhynchus nerka) growth in Lake Washington — a bioenergetics approach

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Abstract:



Juvenile sockeye salmon (Oncorhynchus nerka) in Lake Washington experience very high growth rates, but the mechanisms regulating their growth rates are poorly understood. The potential for food quality limitation of growth was tested using a coupled bioenergetics and mass balance model. Sockeye and zooplankton prey species were analyzed for their fatty acid composition. Ratios of phosphorus to carbon (P:C) for both sockeye and zooplankton were obtained from the literature. Based on sockeye stomach contents and zooplankton weights, diets of zooplankton biomass were calculated and monthly values of specific fatty acids and P:C ratios in the diet were derived. An increase in highly unsaturated fatty acids, especially in the liver, was observed with increased fork length up to smoltification size, with a subsequent decrease in smolts and kokanee. Measurements of docosahexaenoic (DHA) in daphnids were significantly lower than in cyclopoids. Model predictions suggest that sockeye are not limited by the availability of phosphorus or eicosapentaeinoic acid (EPA) in their diet but may experience limited growth because of DHA deficiencies. Thus, the ability and efficiency of sockeye at elongating 18:3 3, 18:4 3, and EPA to DHA may be of critical importance to lacustrine growth and production.

Les jeunes saumons rouges (Oncorhynchus nerka) du lac Washington ont des taux de croissance très élevés, mais les mécanismes qui contrôlent ces taux restent mal connus. Nous avons évalué la possibilité d'une limitation de la croissance par la qualité de la nourriture en couplant une étude énergétique et un modèle de bilan de masse. La composition en acides gras a été déterminée chez les saumons et leurs proies dans le zooplancton. Les rapports phosphore:carbone (P:C) du saumon et du zooplancton ont été tirés de la littérature. L'étude des contenus stomacaux des saumons et de la masse du zooplancton nous a permis de calculer la biomasse du zooplancton dans le régime alimentaire et d'obtenir les mesures mensuelles des acides gras spécifiques et du rapport P:C dans le régime. On observe une augmentation des acides gras hautement insaturés, particulièrement dans le foie, à mesure de l'accroissement de la longueur à la fourche jusqu'à la taille de la transformation en saumoneaux; ces acides gras diminuent ensuite chez les saumoneaux et les kokanis. Les concentrations d'acide docosahexanoïque (DHA) sont significativement plus basses chez les daphnies que chez les cyclopoïdes. Les prédictions du modèle font croire que les saumons rouges ne sont pas limités par la disponibilité du phosphore ou de l'acide eicosapentanoïque (EPA) dans leur régime, mais que leur croissance peut être restreinte par manque de DHA. Ainsi, la capacité et l'efficacité du saumon rouge à allonger les acides gras 18:3 3, 18:4 3 et l'EPA en DHA peuvent être des facteurs déterminants de la croissance et de la production dans le lac.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: January 1, 2003

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  • Published continuously since 1901 (under various titles), this monthly journal is the primary publishing vehicle for the multidisciplinary field of aquatic sciences. It publishes perspectives (syntheses, critiques, and re-evaluations), discussions (comments and replies), articles, and rapid communications, relating to current research on cells, organisms, populations, ecosystems, or processes that affect aquatic systems. The journal seeks to amplify, modify, question, or redirect accumulated knowledge in the field of fisheries and aquatic science. Occasional supplements are dedicated to single topics or to proceedings of international symposia.
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