Changes in circulatory, ventilatory and acid-base variables were studied in Siberian sturgeon (Acipenser baeri) exposed to acute and severe hypoxia (Pw(O2) = 10 torr), followed by a rapid return to normoxia. This treatment caused a significant stress, revealed by the high levels of plasma catecholamines and cortisol. The moderate circulatory changes firstly observed would represent the effects of increased plasma catecholamine levels together with an increased adrenergic nervous tone on the cardiovascular system. Then, these effects were masked by a possible vagal reflex resulting in bradycardia. Deep hypoxia induced a ventilatory alkalosis combined with a moderate metabolic acidosis. The latter amplified concomitantly with a massive flush of lactate into the blood stream. The initial hyperventilation was followed by a deep ventilatory depression. During return to normoxia, hyperventilation resumed consistent with the repayment of an oxygen debt. Thus, the sturgeon, although considered as an archaic fish, developped the same adaptative responses as teleosts submitted to comparable hypoxic conditions.

The effects of trout recombinant growth hormone (rtGH) treatment (0.25 μg g−1 by intraperitoneal implant) on plasma ionic regulation, extracellular acid-base status and respiration were investigated in freshwater rainbow trout and during a 4-day period after direct transfer into seawater (35 g 1−1).

Changes in respiratory and acid-base variables were studied in siberian sturgeon, Acipenser baeri, during progressive deep hypoxia followed by recovery under normoxic conditions. During hypoxia, both ventilatory frequency and amplitude increased and this sturgeon was able to maintain standard oxygen consumption down to a low critical level of ambient PO2 (PWO2 < 40 mmHg). During the posthypoxic period, an O2 debt was repaid by an elevated oxygen consumption (nearly double control value at 1 h), indicating that a shift to anaerobic metabolism had occurred during exposure to severe hypoxia. Gradually increasing ambient hypoxia initially induced a respiratory alkalosis. Below the critical PWO2 level and during normoxic recovery, a sudden flush of lactate into the blood was associated with a typical metabolic acidosis which was almost totally compensated 3.5 h after return to normoxia. Thus, as for most other fish, respiratory responses of the sturgeon to progressive hypoxia reveal a typical O2 regulatory behavior.

Standard oxygen consumption was greater in parr than in smolts throughout the freshwater growth period February–July 1987. However, the weight-specific rate, corrected for differences in body size, was markedly higher in smolts than in parr. Routine O2 consumption showed an endogenous circadian rhythm initially, in both parr and smolts. Metabolic activity was markedly higher in daylight than in darkness. The diurnal increase in O2 consumption was correlated with sunrise, and its duration with daylength. However, in smolts this circadian rhythm was replaced by a multi-peak pattern after normal smolting time, suggesting that preventing seaward migration induced physiological disturbance. The influence of temperature on both standard and routine O2 consumption decreased gradually during seasonal warming. However, this thermal acclimation was much less apparent at smolting, when the increase in metabolic activity could be related to endocrine changes.

1. The intrinsic effects of adrenaline on the myocardium of the eel in winter were investigated in the isolated perfused eel heart. 2. Adrenaline was ineffective both on the pacemaker activity and auricular action potentials but markedly increased ventricular action potential duration, thus leading to an auriculo-ventricular desynchronisation. 3. This effect was not reversed by propranolol but was by phentolamine and was attributed to the stimulation of alpha receptors. 4. Clonidine reproduced the effect of adrenaline but also decreased the cardiac rhythm, possibly via alpha 2 adrenoceptors. 5. No direct inotropic effect was observed.

1.1. Uptake and metabolism of serotonin in eels was investigated in vivo and in vitro.2.2. After infusion for 10 min of [3H] serotonin, liver, plasma and brain contained radioactivity associated with serotonin and transformation products.3.3. The same transformations occurred after incubation for 2 min of slices of brain and liver tissues.4.4. Radioactivity being 4–6 times greater in liver than in brain after infusion, the blood-brain barrier is not fully effective for serotonin.5.5. Metabolites being mostly found in the medium after incubation of brain slices, a larger uptake of serotonin with a lesser effectiveness of the blood-brain barrier are suggested.

aux périodes d'activité respiratoire correspondent des phases de tachycardie,