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Effects of stress on plasma homeostasis, endolymph chemistry, and check formation during otolith growth in rainbow trout (Oncorhynchus mykiss)

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Abstract:

This is the first study in which the effects of an external stress were analysed at different levels: plasma ho meostasis, endolymph chemistry, and otolith growth. Stress was applied to rainbow trout (Oncorhynchus mykiss) by exposure to Cl2 gas. In the plasma of Cl2-stressed trout, Na+ and Cl decreased (70 mmol·L–1) and K+ increased (2.0 mmol·L–1), whereas total Ca was unchanged. A slight hypercapny (+2.4 mmHg (1 mmHg = 133.322 Pa)) was observed related to a significant rise (40%) in total CO2 without pH variation. In the endolymph, Na+ and Cl also decreased, whereas other parameters (K+, PO43–, Mg, and, peculiarly, total Ca) remained stable. The important effect provoked by Cl2 stress in endolymph was an increase of proteins (factor of 2.6) and total CO2 (factor of 3.1) concentrations at the proximal side of the endolymph. The stress induced a decrease in otolith growth rate and produced a discontinuity (check) in the microstructure pattern of the otolith characterized by a large D zone. The variations in the endolymph composition are discussed and we propose that they result not only from changes in plasma concentrations, but also from changes (organic and crystallization) in otolith deposition.

C'est la première fois que les effets d'un stress externe sont analysés simultanément à plusieurs niveaux, soit l'homéostasie du plasma, la chimie de l'endolymphe et la croissance des otolithes. Le stress provient d'une exposition de truites arc-en-ciel (Oncorhynchus mykiss) au Cl2 gazeux. Dans le plasma des truites stressées au Cl2, il y a réduction de Na+ et de Cl(70 mmol·L–1) et accroissement de K+ (2,0 mmol·L–1), alors que le Ca total reste inchangé. On observe une légère hypercapnie (+ 2,4 mmHg (1 mmHg = 133.322 Pa)) qui est reliée à une augmentation significative (40 %) du CO2 total, sans variation de pH. Dans l'endolymphe, il y a aussi une diminution de Na+ et de Cl, alors que les autres paramètres (K+, PO43–, Mg et en particulier aussi le Ca total) restent stables. L'effet remarquable du stress au Cl2 dans l'endolymphe est une augmentation des concentrations de protéines (par un facteur de 2,6) et du CO2 total (par un facteur de 3,1) dans la portion proximale de l'endolymphe. Le stress provoque une réduction du taux de croissance des otolithes et produit une discontinuité (marque) dans la microstructure de l'otolithe caractérisée par une importante zone D. Les variations de composition de l'endolymphe font l'objet d'une discussion et nous proposons qu'elles résultent de modifications de la composition du plasma et de l'endolymphe ainsi que du processus de cristallisation de l'otolithe.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: 2004-07-01

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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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