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First published online August 23, 2004
Journal of Experimental Biology 207, 3419-3430 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.01166

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Arachidonic acid reduces the stress response of gilthead seabream Sparus aurata L.

R. D. Van Anholt^1,*, F. A. T. Spanings¹, W. M. Koven², O. Nixon² and S. E. Wendelaar Bonga¹

¹ Department of Animal Ecology and Ecophysiology, Faculty of Science, University of Nijmegen, Toernooiveld 1, 6525 ED Nijmegen, The Netherlands
² Department of Larval Rearing, The National Center for Mariculture, PO Box 1212, Eilat 88112, Israel

^* Author for correspondence (e-mail: rvanholt{at}sci.kun.nl)

Accepted 28 June 2004

In this study the influence of the dietary level of the fatty acid arachidonic acid (ArA, 20:4n-6) was determined on the acute stress response and osmoregulation of adult gilthead seabream Sparus aurata L. Seabream were fed a diet containing either 0.9% or 2.4% of total fatty acids as ArA for 18 days before being subjected to a 5 min period of net confinement. Prior to this stressor, a subgroup of fish from both dietary treatment groups was treated with acetylsalicylic acid (ASA), an irreversible blocker of cyclooxygenase (COX). This would indicate whether any effects were caused by an enhanced synthesis of prostaglandins derived from ArA. The highest ArA levels were found in the kidneys, and these were further enhanced by dietary ArA-supplementation. In gill tissues, there were significant changes in all selected fatty acid classes 24 h after confinement, except for the docosahexaenoic acid (DHA, 22:6n-3): eicosapentaenoic acid (EPA, 20:5n-3) ratio. ArA feeding strongly reduced the cortisol response to confinement, which was partially counteracted by ASA treatment. ArA also attenuated the stress-associated increase in plasma osmolality and, in combination with ASA, enhanced the osmolality and plasma chloride levels, but reduced plasma sodium levels after confinement. Furthermore, ArA enhanced the branchial Na⁺, K⁺-ATPase activity both before and after confinement, whereas feeding ASA diminished this effect. It appeared that the effects of ArA-supplementation could not always be ascribed to an increase in prostaglandin synthesis. It is advisable to determine the long-term effects of replacing fish oils in commercial diets with vegetable oils that contain no long-chain fatty acids, particularly in carnivorous/marine species with low fatty acid elongation and desaturation activities. The effects of a low dietary intake of ArA (and other polyunsaturated fatty acids) should be studied over a longer term, taking into account any consequences for the health of the fish.

Key words: acetylsalicylic acid, arachidonic acid, cyclooxygenase, cortisol, eicosanoid, osmoregulation, prostaglandins, gilthead seabream, Sparus aurata

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