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Metabolic rate, branchial morphology, and modes of gill ventilation were studied in young (2-10 g) North American paddlefish, Polyodon spathula, with anatomical, behavioral, and physiological methods. Polyodon lacks the oral and opercular valves that are typical for fishes that rely on a buccal pump system to ventilate the gills, and the jaw opening system of Polyodon is poorly suited for regular pumping movements. Unrestrained, undisturbed juvenile paddlefishes swim constantly at a mean speed of 1.1-1.5 body lengths · $s^{-1}$ (bls). The maximum speed sustainable for > 10 min is 1.6-1.8 bls. When forced to swim at slow speeds in flow tanks or water tunnels, ventilation of the gills by buccal pumping occurs at a frequency of 50-80 · $min^{-1}$. As swimming speed increases, buccal ventilation becomes intermittent and continuous ram ventilation occurs above 0.6-0.8 bls, which means that Polyodon is essentially an obligate ram ventilator under normal conditions. Oxygen consumption ($\dot{M}O_{2}$), carbon di...

The duration of natural intertidal air exposure was determined for a population of Chiton stokesii from the rocky intertidal zone of Naos Island, Panama. On-site measurement indicated that chitons seek protected locations during air exposure and are little affected by increased air temperatures. Construction of an artificial tidal system allowed hemolymph sampling and assessment of physiological compensation of chitons during air exposure in the laboratory. During air exposure chitons showed significant hemoconcentration associated with reduction in heart rate and intracardiac hemolymph pressure. Air exposure was also associated with the buildup of hemolymph Pco₂ and the development of significant but largely compensated hemolymph acidosis. No consequent decrease in postbranchial hemolymph oxygenation occurred; indeed, the partial pressure of O₂ in postbranchial hemolymph (Pao₂) had increased slightly but significantly at 17 h air exposure. This increased oxygenation was not associated with significant ch...

Hemolymph volume in restrained land crabs (Cardisoma guanhumi) was altered in 5% increments by rapid infusion of filtered seawater into, or rapid withdrawal of hemolymph from, an infrabranchial sinus. Associated changes in intracardiac hemolymph pressure and in heart rate were measured. Elevation of hemolymph volume resulted in a brief (

Tadpoles of the frogs Rana berlandieri and Rana catesbeiana increased total oxygen uptake through lungs, gills, and skin as temperature increased. However, the partitioning of oxygen uptake among lungs, gills, and skin was similar at all experimental temperatures (15, 25, and 33 C), with the skin being the major site of O₂ uptake. This constancy of partitioning in tadpoles differs from the increased predominance of pulmonary respiration with rising temperatures reported for many other amphibious vertebrates. We suggest that neither the costs nor the physical constraints of aquatic O₂ exchange limit its predominance at high temperatures in tadpoles and perhaps in other forms.

Buccal movements at the air-water interface causing surface water and air bubble inhalation ("surface breathing") and the resultant effects on blood O₂ transport have been quantified as a function of inspired water Po₂ in the goldfish, Carassius auratus. At 26 C, surface breathing occurred below a Po₂ of about 70 mmHg and increased to a peak of 180 surface breathing periods/h at Po₂ 20 mmHg. At this severe level of hypoxia, surface breathing resulted in a significant elevation of arterial Po₂ by 1.2 mmHg above that in control goldfish, which were not surface breathing. This very small rise in arterial Po₂ caused a sharp rise in arterial blood O₂ saturation from 16% to 33%, because of the high oxygen affinity ($P_{50} = 2.6 mmHg$) and steep slope of the blood O₂ equilibrium curve. The net effect of surface breathing at the air-water interface during severe aquatic hypoxia is a 2.5 times increase in the arterial-venous O₂ saturation difference compared with strictly aquatic ventilation. Surface breathing wi...

Periodically breathing animals that store O₂ primarily in the lungs must efficiently transfer O₂ to arterial blood during apnea. Previous experiments on diving freshwater turtles indicate that such transferral is continuous during most dives, but there have been occasional observations of much more periodic O₂ transfer between lung gas and blood. This study investigates the dynamics of lung O₂ utilization and blood transfer during voluntary diving in the Australian long-necked turtle, Chelodina longicollis. Pulmonary arterial blood flow was measured by a relatively noninvasive impedance technique. The PO₂ of pulmonary gas and systemic arterial blood was measured continuously with extracorporeal catheter loops, which minimize sampling disturbances. Lung gas PO₂ declined relatively constantly during apnea at a rate of about 3 mmHg/min. Changes in arterial blood PO₂ showed one of two very distinctive patterns during apnea. In the first pattern, evident in about two-thirds of 87 dives monitored in seven turtl...

Changes in oxygen uptake in response to stepwise changes in environmental temperature have been measured in anomuran decapod Crustacea inhabiting a subtidal habitat (Paguristes turgidus, Elassochirus tenuimanus), an intertidal habitat (Pagurus granusimanus, Pagurus hirsutisculus) and a supratidal habitat (Coenobita clypeatus, Coenobita rugosus). Individuals of each species were housed in respirometers and subjected to three rapid, progressive 5 C increases above their initial acclimation temperature, with $\dot{M}_{O_{2}}$ (μM O₂/g/h) measured during a 2-3-h pause at each temperature increment. The $Q_{10}$ for $\dot{M}_{O_{2}}$ is correlated with habitat, with intertidal species having a $Q_{10}$ of 1.4-1.6, which is significantly lower (P < .05) when compared with $Q_{10}$ values of 2.1-2.4 for subtidal species and 2.6-2.7 for the supratidal forms. Intertidal hermit crabs also showed a smaller $\dot{M}_{O_{2}}$ overshoot and a more rapid $\dot{M}_{O_{2}}$ acclimation to abrupt temperature change compare...

Earlier studies of gelatinous egg masses laid by many amphibians suggested that the egg mass center was extremely hypoxic and that embryos located there suffered delayed growth and high mortality. The present study has reassessed conditions for respiration within the spherical egg masses of the pickerel frog, Rana palustris. Partial pressures of O₂ and CO₂, and the pH of egg jelly, as well as lactate concentration of embryonic tissue, were measured at 1-cm depth increments from surface to center of the egg mass. Oxygen uptake of intact egg masses and eggs separated from the mass was determined as a function of temperature and ambient O₂ levels. Although significant gradients for O₂, CO₂, and pH existed from surface to center, the magnitude of these gradients was too small to directly affect O₂ uptake of the egg mass or individual eggs under a variety of experimental conditions likely to occur in nature. Exchange of gases between the egg mass surface and center occurs primarily by diffusion through the egg...

Ventilation volume ($\dot{V}w$), beat frequency of right scaphognathite ($fR_{r}$), total stroke volume of the scaphognathite pair ($Vs_{u}$), and the amplitude of the pulse (PP) and mean standing pressure (Pbr) developed within the postbranchial chamber by scapihognathite action have been measured in the crayfish Orconectes virilis. Data were recorded from crayfish acclimated to normoxia (PO₂ = 130 mm Hg), and during acute ( 4 days) exposure to hypoxia (PO₂ = 40-60 mm Hg). At values of $fR_{r}$ below 100 beats/min $\dot{V}w$ varied as a function of both $Vs_{u}$ and $fR_{r}$, both in normoxic and acutely hypoxic animals. Above 100 beats/min, $Vs_{u}$ remained constant in both groups. In acutely hypoxic crayfish, stroke volume was elevated above normoxic values at any given $fR_{r}$. Long-term acclimation to hypoxia was accompanied by a significant decrease in $\dot{V}w$ through reduction in both $fR_{r}$ and $Vs_{u}$. In addition, the stroke volume at higher scaphognathite frequenci...