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lab3 - Marine Biology(2005 147 855862 DOI...

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RESEARCH ARTICLE A. Chatelier Æ D. J. McKenzie Æ G. Claireaux Effects of changes in water salinity upon exercise and cardiac performance in the European seabass ( Dicentrarchus labrax ) Received: 22 September 2004 / Accepted: 16 March 2005 / Published online: 18 May 2005 Ó Springer-Verlag 2005 Abstract The European seabass is an active euryhaline teleost that migrates and forages in waters of widely differing salinities. Oxygen uptake ( M O2 ) was measured in seabass (average mass and forklength 510 g and 34 cm, respectively) during exercise at incremental swimming speeds in a tunnel respirometer in seawater (SW) at a salinity of 30 & and temperature of 14 ° C, and their maximal sustainable (critical) swimming speed ( U crit ) determined. Cardiac output ( Q ) was measured via an ultrasound flow probe on their ventral aorta. The fish were then exposed to acute reductions in water salinity, to either SW (control), 10 & , 5 & , or freshwater (FW, 0 & ), and their exercise and cardiac performance mea- sured again, 18 h later. Seabass were also acclimated to FW for 3 weeks, and then their exercise performance measured before and at 18 h after acute exposure to SW at 30 & . In SW, seabass exhibited an exponential in- crease in M O2 and Q with increasing swimming speed, to a maximum M O2 of 339±17 mg kg À 1 h À 1 and maxi- mum Q of 52.0±1.9 ml min À 1 kg À 1 (mean±1 SEM; n =19). Both M O2 and Q exhibited signs of a plateau as the fish approached a U crit of 2.25±0.08 bodylengths s À 1 . Increases in Q during exercise were almost exclu- sively due to increased heart rate rather than ventricular stroke volume. There were no significant effects of the changes in salinity upon M O2 during exercise, U crit or cardiac performance. This was linked to an exceptional capacity to maintain plasma osmolality and tissue water content unchanged following all salinity challenges. This extraordinary adaptation would allow the seabass to maintain skeletal and cardiac muscle function while migrating through waters of widely differing salinities. Introduction European seabass (Family Moronidae) pursue an active pelagic life-history that comprises widescale migrations. Although predominantly marine as adults, seabass are euryhaline and juveniles often enter estuaries where they migrate and forage through waters of different salinities (Pickett and Pawson 1994 ). Relatively little is known about the cardio-respiratory, exercise and osmoregula- tory physiology of seabass (Jensen et al. 1998 ; Claireaux and Lagarde ` re 1999 ; Varsamos et al. 2001 , 2002 ; Ax- elsson et al. 2002 ) and, therefore, also about the physi- ological adaptations that they may have evolved for their migratory euryhaline lifestyle. Previous studies on fish species that migrate through waters of different salinities have shown a direct link between their ability to perform aerobic exercise and their homeostatic regulation of body-fluid osmolality (Brauner et al. 1992 , 1994 ; McKenzie et al. 2001a , 2001b ). In coho salmon ( Oncorhynchus kisutch ) smolts and Adriatic sturgeon ( Acipenser naccarii ) juveniles, acute increases in water salinity (‘‘seawater challenges’’)
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