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The critical swimming velocity (Ucrit) and haematology of wild and hatchery-reared coho salmon (Oncorhynchus kisutch) juveniles were examined in either fresh water or seawater following a 24-h seawater challenge, at the time of smoltification. In fresh water, wild smolts swam faster than hatchery-reared fish but this could largely be accounted for by scaling for body size. Transfer to seawater significantly elevated resting plasma [Na+] and reduced subsequent Ucrit in hatchery fish (by 12%) relative to that determined in fresh water but had no significant effect on resting plasma [Na+] and Ucrit in wild fish. Swimming the fish a second time in seawater after the initial 2-h exercise period resulted in a significant reduction in Ucrit relative to that in fresh water in both wild fish (16%) and hatchery fish (a further 14%); this relatively greater impairment in Ucrit in hatchery fish was due to a reduced hypo-osmoregulatory ability following seawater transfer that impairs conditions for muscle contractility and aerobic metabolism. Aerobic metabolism in seawater-exposed fish was affected in part through a reduction in haematocrit and an increase in plasma volume, reducing oxygen carrying capacity of the blood relative to conditions in fresh water.

Effect of short-duration seawater exposure on plasma ion concentrations and swimming performance in coho salmon (Oncorhynchers kisutck) parr. Can. 1. Fish. Aquat. Sci. 49: 2399-24635.The effect of seawater (sw) on plasma ion concentrations and critical swimming velocity (U,,,,) was investigated in hatchery-reared coho salmon (Oncsrkynchus kisutch) parr exposed to one of four treatments: 24 h of seawater exposure (SWI), 5-7 d sf seawater (SW5), 24 h in seawater followed by 24 h in fresh water (SW-FW), and a freshwater control (FWC). Only the SW1 fish demonstrated a reduced UCrit and, at rest, elevated plasma [Na*], [CI '-1, and [ SO: -1. With exercise, SW1 fish were characterized by an increase in plasma ion concentrations and a decrease in both hematocrit (Hct) and muscle moisture content. There is a strong relationship between plasma [Na'] at rest and U, , , , , where an optimal swimming velocity is obtained in animals with resting levels of approximately 147 mEq-h-'. Traditionally, the 24-h seawater challenge is used to test the hypoosmoregulatory ability in smolting salmsnids, however, our data suggest that it may also predict the aerobic swimming potential sf salmonids following seawater transfer. We suggest that the reduction in Hct and increase in plasma [!la+] result in reduced oxygen delivery to the muscle and that decrease in muscle moisture content impairs the contractile process. h'effet de I'eau de mer sur Ies concentrations plasmatiques d'ions et la vitesse natatoire critique (U,,,,) a kt6 etudie chez des tacons de saumon coho (Oncoahynchus kisutch) eleves en ecloserie et exposes A I'un des quatre traitements suivants : exposition de 24 h i 3 I'eau de mer (SWI), exposition de 5 2 7 jours a I'eau de mer (SWS), 24 h dans ['eau de mer puis 24 h dans I'eau douce (SW-FW), et un traitement tkmoin dans I'eau douce (FWC). Chen les poisssns SW1, on a observe une reduction de U,,,, et, au repos, des concentrations plasmatiques elevees de !la+, de CI-et de korsqu'ils etaient en mouvement, les poissons SW1 etaient caracterisks par une augmentation des concentrations plasmatiques d'ions et une diminution de I'h6matocrite (Hct) et de la teneur musculaire en eau. II existe une forte relation entre la concentration plasmatique de Na+ au repos et e/ , , , , , oC !a vitesse natatoire optimale est atteinte chez les animaux ayant des niveaux au repos d'environ 147 mEq-L-'.Traditionnellement, I'epreuve de 24 h dans Ireau de rner est utilisee pour mettre 21 lpessai la facult6 hypo-osmoregulatrice des salmonid6s en cours de smoltification; toutefois, nos donnees semblent indiquer qu'elle peut egalement predire le potentiel natatoire aerobie des salmonides apr6s transfer! dans I'eau saI&. Nous pensons que la reduction de I'hkrnatocrite et Ifaugmentation de la concentration plasmatique de Na* se traduisent par une diminution de I'apport droxygene dans les muscles et que la diminution de la teneur en eau des muscles altitre le processus contractile.almon smolts moving from fresh water into an estuary are prone to extremely h...

The armoured catfish (Hoplosternum littorale) from the Amazon River system is a facultative air breather that is tolerant to both acidic and hydrogen sulphide rich waters. Facultative air breathing in fishes is known to be an important strategy for surviving hypoxia, but its importance for surviving in acidic and hydrogen sulphide rich waters has not previously been investigated. Air-breathing frequency in H. littorale increased from 2 to 28 breaths/h as the partial pressure of oxygen [Formula: see text] in the water was reduced from 137 to 105 mmHg (1 mmHg = 133.322 Pa). Further reduction in [Formula: see text] to 55 mmHg resulted in a reduction in air-breathing frequency and depression of the metabolic rate. During exposure to acidic water (pH 2.8, [Formula: see text] = 155 mmHg), air-breathing frequency was 28 breaths/h, and during exposure to hydrogen sulphide in water buffered to pH 5.6 (700 μM, [Formula: see text] = 155 mmHg), air-breathing frequency was 40 breaths/h. In fish denied access to air, 200 μM hydrogen sulphide is lethal. Thus, in the armoured catfish, air breathing may be more important for surviving in hydrogen sulphide rich and acidic waters than for surviving in mild hypoxia.

Atlantic salmon (Salmo salar) presmolts, smolts, and postsmolts compensate for a respiratory acidosis associated with 96 h of exposure to hyperoxia (100% O 2 ; hO 2 ), hypercapnia (2% CO 2 and 98% air; hCO 2 ), and combined hO 2 /hCO 2 in freshwater (FW) by increasing strong ion difference, predominantly through a reduction in plasma [Cl -] (presumably via branchial Cl -/HCO 3 -exchange). In smolts, compensation during hO 2 or hCO 2 occurred within 24 h, whereas that in combined hO 2 /hCO 2 was much slower, resulting in 33% mortality by 96 h. FW hO 2 and combined hO 2 /hCO 2 appeared to impair gill function, likely through oxidative cell damage. This resulted in reduced hypoosmoregulatory ability following subsequent transfer to seawater (SW), as indicated by changes in plasma ion levels, osmolality, and muscle water content, resulting in considerable mortalities. Interestingly, FW hCO 2 appeared to enhance hypoosmoregulatory ability during subsequent SW transfer. Smolts are often transported from FW to a subsequent SW release site, and these data indicate that care should be taken to minimize the degree of hyperoxia experienced by the smolts. Hypercapnia, which results from metabolic CO 2 production and inadequate water aeration, does not impair SW transfer, provided it does not occur in conjunction with hyperoxia.Résumé : Les pré-smolts, smolts et post-smolts de saumon atlantique (Salmo salar) compensent l'acidose respiratoire associée à une exposition de 96 h à une hyperoxie (100% O 2 ; hO 2 ), une hypercapnie (2% de CO 2 et 98% d'air; hCO 2 ) et une combinaison de hO 2 /hCO 2 en eau douce en augmentant la différence des ions forts, principalement par une ré-duction du [Cl -] plasmique (vraisemblablement par échange branchial de Cl -/HCO 3 -). Chez les smolts, la compensation pendant hO 2 ou hCO 2 se produisait dans les 24 h, tandis qu'elle était beaucoup plus lente pour la combinaison hO 2 /hCO 2 , qui causait une mortalité de 33% en 96 h. Des conditions de hO 2 en eau douce et la combinaison hO 2 /hCO 2 semblaient entraver la fonction branchiale, vraisemblablement par dégradation oxydative des cellules. Cela provoquait une réduction de la capacité d'hypoosmorégulation suite au transfert dans l'eau de mer, comme le montraient des changements dans les concentrations plasmiques d'ions, l'osmolalité et la teneur en eau des muscles, qui causaient des mortalités considérables. Il est intéressant de constater que la condition de hCO 2 en eau douce semblait améliorer la capacité d'hypoosmorégulation pendant le transfert subséquent en eau salée. Les smolts sont souvent transportés de l'eau douce à un point de lâcher en eau salée, et nos données indiquent qu'il faut prendre soin de minimiser le degré d'hyperoxie qu'ils peuvent connaître. L'hypercapnie, qui provient de la production métabolique de CO 2 et d'une aéra-tion insuffisante de l'eau, ne nuit pas au transfert en eau salée à condition qu'elle ne survienne pas en même temps que l'hyperoxie.[Traduit par la Rédaction] Brauner et al. 2064

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This study assessed the effect of tissue storage duration and accuracy of the metabolic inhibitor tissue homogenate (MITH) method on intracellular pH (pHi) values of tissues of white sturgeon Acipenser transmontanus during hypercarbia. No effect of storage in liquid nitrogen of up to 30 days was observed and MITH appears appropriate for measurement of pH in fish exposed to up to 10% CO2 (10000 Pa pCO2).

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