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Physiological effects of simultaneous, abrupt seawater entry and sea lice (Lepeophtheirus salmonis) infestation of wild, sea-run brown trout (Salmo trutta) smolts

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For wild, sea-run brown trout (Salmo trutta) smolts, the physiological consequences of abrupt transfer to seawater and simultaneous challenge with copepodid larvae of the sea louse, Lepeophtheirus salmonis (Krøyer, 1837), were investigated in the laboratory. Analysis of osmoregulatory, metabolic, and stress markers allowed the derivation of a sublethal threshold burden of L. salmonis, above which the host suffers major physiological stress. Noticeable lice effects, consistent across all measured markers, were not observed until L. salmonis developed to the mobile preadult and adult stages. Preadult L. salmonis caused significant increases in plasma chloride, osmolality, glucose, lactate, and cortisol and a significant reduction in haematocrit. Piecewise linear statistical approaches allowed the determination of abrupt changes in these physiological markers, attributable to the intensity of L. salmonis infestation on individual fish, and identification of overall threshold lice burdens. Thirteen mobile lice·fish–1 (weight range 19–70 g) was a consistent breakpoint across several physiological measures. This information will provide a valuable, objectively derived tool to aid in the formulation of effective wild fisheries management policy concerning S. trutta conservation.

Nous avons étudié en laboratoire chez des saumoneaux sauvages de la truite brune (Salmo trutta) anadrome les conséquences physiologiques d'un transfert abrupt en eau de mer accompagné d'une confrontation simultanée avec des larves copépodites du pou de mer, Lepeophtheirus salmonis (Krøyer, 1837). L'analyse des indicateurs d'osmo régulation, de métabolisme et de stress permet de déterminer une charge seuil sublétale deL. salmonis au-dessus de laquelle l'hôte souffre d'un stress physiologique important. Les effets manifestes des poux, signalés de façon cohérente par tous les indicateurs, n'apparaissent que lorsque L. salmonis atteint les stades mobiles préadultes et adultes. Les L. salmonis préadultes causent des augmentations significatives du chlorure, de l'osmolalité, du glucose, du lactate et du cortisol du plasma, ainsi qu'une réduction significative de l'hématocrite. Des méthodes statistiques linéaires pas à pas permettent de déterminer les changements abrupts de ces indicateurs physiologiques causés par l'intensité de l'infestation des L. salmonis chez des poissons individuels et d'identifier les charges seuils globales de poux. Une charge de 13 mobiles poux·poisson–1 (étendue des masses 19–70 g) représente un point seuil commun à plusieurs mesures physiologiques. Ces données pourront servir d'outil utile et objectif pour la formulation d'une politique de gestion efficace des pêches de populations sauvages de S. trutta dans un objectif de conservation.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: December 1, 2006

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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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