P. Gallaugher

Hematocrit in oxygen transport and swimming in rainbow trout (Oncorhynchus mykiss)

The optimal hematocrit (Hctopt) hypothesis was tested by altering Hct (and arterial blood oxygen content, CaO2) between extreme states of anemia and polycythemia (Hct = 8-55%) in the rainbow trout. Since blood viscosity (eta) effects on cardiac output (Q) and O2 transport (TO2) are likely to be greatest when O2 demand and Q are maximal, we challenged fish to swim to their critical swimming velocity (Ucrit) in a swim-tunnel respirometer at 13 degrees C and measured maximal oxygen uptake (VO2max), maximum Q(Qmax), and other cardiovascular variables. In addition, experimental temperature was lowered to 5 degrees C to increase eta. Consistent with the Hctopt hypothesis, the decreased CaO2 in anemic (Hct < 22%) fish caused significant reductions in Ucrit and VO2max. In contradiction to the Hctopt hypothesis, and despite an exponential relationship between eta and Hct, maximal TO2 (TO2max) and Ucrit increased with polycythemia up to Hct 55%. Although there was a peak for VO2max, it occurred at an Hct (42%) well above the normocythemic range (23-33%). These results clearly demonstrate that eta is not significant in setting normocythemia in rainbow trout. The novel finding of an Hct-dependent relationship for exercise-induced arterial hypoxemia may be indicative of a diffusion limitation to normocythemia. We suggest that factors involved in setting normocythemia in vertebrates should include diffusion limitations to oxygen transfer in addition to blood viscosity and oxygen transport constraints.

Cardiac Output in Swimming Rainbow Trout, Oncorhynchus mykiss, Acclimated to Seawater

This is the first study to report absolute measurements of cardiac output (Q̇) with Transonic flow probes during prolonged swimming in a salmonid. Simultaneous measurements of hematocrit and arterial blood O₂ content in seawater-acclimated rainbow trout (Oncorhynchus mykiss) (body mass 401-1,025 g) at 10° ± 1° C indicated that the fish were in good physiological condition, while measurements of resting heart rate, arterial blood pressure, and systemic resistance suggested relatively low levels of stress. Maximum Q̇ Q̇max (48. 7 mL · min⁻¹ · kg⁻¹) was reached at 97.3% of the maximum prolonged swimming speed and is similar to the Q̇max estimated by the Fick principle during swimming in freshwater rainbow trout. Maximum Q̇ was 84% greater than the resting Q̇ (Q̇rest) (26.6 mL · min⁻¹ · kg⁻¹) and was brought about by a 38% increase in heart rate (fH) and a 25% increase in stroke volume (SVH). Correlation analysis showed that individual variability in Q̇max was mainly due to variability in maximum SVH ; maximum fH was relatively invariant among individuals. At rest, SVH and fH , were negatively correlated. Individual fish with a high Q̇max were characterized by a low resting fH and a high resting SVH.

Reducing Gill-Net Mortality of Incidentally Caught Coho Salmon

Abstract The abundance of coho salmon Oncorhynchus kisutch has declined dramatically over much of the southern part of its range along the Pacific Coast of North America. This decline has created the need to reduce fishing mortalities, including bycatch mortalities in fisheries that are targeting other species. Traditional gill-net fishing causes an estimated 35–70% mortality rate on incidentally caught coho salmon. A reduction in this high mortality rate is necessary if gill nets continue to be used in fisheries that inadvertently intercept depressed coho salmon stocks while fishing other species. By using modified gear, short net soak times, careful handling of fish on removal from the gill net, and a newly designed recovery box, the short-term mortality rate on incidentally caught coho salmon can be reduced to as little as 6%, possibly even lower in some circumstances. This substantial reduction in mortality on nontargeted species expands the possible role of gill nets in the development of selective f...

CO2 transport and excretion in rainbow trout (Oncorhynchus mykiss) during graded sustained exercise

A quantitative analysis of CO2 transport and excretion was conducted in seawater acclimated rainbow trout (Oncorhynchus mykiss) swimming at different sustained swimming velocities. CO2 excretion increased linearly with cardiac output during exercise but arterial P(CO2) (Pa(CO2)) and total CO2 levels also increased indicating a diffusion limitation to CO2 excretion. The elevated Pa(CO2) was not accompanied by a decrease in pH, indicating that the acid-base compensation was rapid. Mixed-venous P(CO2) increased to a greater extent than Pa(CO2) resulting in a large increase in the venous arterial difference in P(CO2) (Pv(CO2) - Pa(CO2)). The Pv(CO2) - Pa(CO2) difference was used to calculate the proportion of total CO2 excreted comprised of dissolved CO2 which accounted for less than 1% of total CO2 excreted in fish swimming at 11 cm sec(-1) but increased to about 9% at the greatest swimming velocity indicating that the pattern of CO2 excretion changes during exercise. There was no effect of exercise on the proportion of CO2 excreted which was dependent upon HCO3-/Cl- exchange (54%) or that which was dependent upon the dehydration of HCO3- that resided within the red cell prior to gill blood entry (42%). The large proportion of total CO2 excreted that was dependent upon HCO3-/Cl- exchange is significant because this is thought to be the rate limiting step in CO2 excretion.

The interaction between O2 and CO2 exchange in rainbow trout during graded sustained exercise.

A quantitative analysis of O2 and CO2 transport was conducted in resting and exercising rainbow trout, and these data were used to quantify the magnitude of coupling between O2 and CO2 exchange, in vivo. The release of Bohr protons during haemoglobin-oxygenation was non-linear over the Hb-O2 equilibrium curve used in trout subjected to different levels of sustained exercise. At low swimming speeds, when venous blood O2 content (CvO2) was high, there was a small acidosis as blood passed through the gills, indicating more protons were released during oxygenation of Hb than were consumed during HCO3- dehydration. At higher swimming speeds, when CvO2 was low, there was a significant alkalosis in arterial relative to venous blood, indicating that fewer protons were released upon oxygenation than HCO3- ions were dehydrated to CO2. Haldane coefficients (moles of protons released per mole of O2 which binds to Hb), calculated from steady state arterial and mixed-venous parameters, revealed that under resting conditions all blood CO2 removed from the blood during gill transit was stoichiometrically related to O2 uptake through the release of Bohr protons during Hb oxygenation. The magnitude of coupling between CO2 excretion and O2 uptake decreased from 100% to less than 40% at the maximal swimming velocity when the largest region of the Hb-O2 equilibrium curve was used for gas exchange. The non-linear release of Bohr protons over the range of Hb-O2 saturation in the blood reduces HCO3- dehydration at the gills during greater work loads elevating arterial P(CO2) levels, leading to an increase in HCO3- buffer capacity of the blood and tissues.

INFERENCE ON SEGMENTED POLYNOMIAL MODELS

Segmented polynomial regression models with unknown change-points are used in a wide variety of biological settings. The application that stimulated this work uses a segmented polynomial model to examine the optimal hematocrit hypothesis. We discuss problems in the fitting of these models and compare, by simulation, two methods of inference in these models: that based on the chi-squared approximation to the distribution of the likelihood ratio statistic and that based on the asymptotic normality of the least-squares estimates. The results show that, of the two, only the likelihood ratio statistic produces reliable inference concerning the change-point.

Opportunities and Barriers for Adaptation and Local Adaptation Planning in Canadian Rural and Resource-Based Communities

This chapter describes various forces that influence the ability of decision-making and institutional structures in Canadian rural and resource-dependent communities to manage, plan for, and respond to future risks and uncertainties resulting from climate change. The context within which such communities make decisions related to capacity building is the outcome of historical development trajectories, interactions with higher levels of government, and macro-level economic structures and processes. The success of future capacity building and planning will be strongly influenced by such factors as improved coordination across different levels of government, the provision of locally geared information about environmental and climate change, economic diversification and the ability to adjust to and take advantage of rapidly changing demographic patterns in such communities.