Anthony P. Farrell

Physiology and Climate Change

Studies of physiological mechanisms are needed to predict climate effects on ecosystems at species and community levels.

Feeding aquaculture in an era of finite resources

Aquacultures pressure on forage fisheries remains hotly contested. This article reviews trends in fishmeal and fish oil use in industrial aquafeeds, showing reduced inclusion rates but greater total use associated with increased aquaculture production and demand for fish high in long-chain omega-3 oils. The ratio of wild fisheries inputs to farmed fish output has fallen to 0.63 for the aquaculture sector as a whole but remains as high as 5.0 for Atlantic salmon. Various plant- and animal-based alternatives are now used or available for industrial aquafeeds, depending on relative prices and consumer acceptance, and the outlook for single-cell organisms to replace fish oil is promising. With appropriate economic and regulatory incentives, the transition toward alternative feedstuffs could accelerate, paving the way for a consensus that aquaculture is aiding the ocean, not depleting it.

Differences in Thermal Tolerance Among Sockeye Salmon Populations

Environmental conditions encountered during migration shape cardiorespiratory physiology in sockeye salmon. Climate change–induced increases in summer water temperature have been associated with elevated mortality of adult sockeye salmon (Oncorhynchus nerka) during river migration. We show that cardiorespiratory physiology varies at the population level among Fraser River sockeye salmon and relates to historical environmental conditions encountered while migrating. Fish from populations with more challenging migratory environments have greater aerobic scope, larger hearts, and better coronary supply. Furthermore, thermal optima for aerobic, cardiac, and heart rate scopes are consistent with the historic river temperature ranges for each population. This study suggests that physiological adaptation occurs at a very local scale, with population-specific thermal limits being set by physiological limitations in aerobic performance, possibly due to cardiac collapse at high temperatures.

The effect of temperature on swimming performance and oxygen consumption in adult sockeye (Oncorhynchus nerka) and coho (O. kisutch) salmon stocks

SUMMARY Our knowledge of the swimming capabilities and metabolic rates of adult salmon, and particularly the influence of temperature on them, is extremely limited, and yet this information is critical to understanding the remarkable upstream migrations that these fish can make. To remedy this situation, we examined the effects of temperature on swimming performance and metabolic rates of 107 adult fish taken from three stocks of sockeye salmon Oncorhynchus nerka and one stock of coho salmon O. kisutch at various field and laboratory locations, using large, portable, swim tunnels. The salmon stocks were selected because of differences in their ambient water temperature (ranging from 5°C to 20°C) and the total distance of their in-river migrations (ranging from ∼100 km for coastal stocks to ∼1100 km for interior stocks). As anticipated, differences in routine metabolic rate observed among salmon stocks were largely explained by an exponential dependence on ambient water temperature. However, the relationship between water temperature and maximum oxygen consumption (ṀO2max), i.e. the ṀO2 measured at the critical swimming speed (Ucrit), revealed temperature optima for ṀO2max that were stock-specific. These temperature optima were very similar to the average ambient water temperatures for the natal stream of a given stock. Furthermore, at a comparable water temperature, the salmon stocks that experienced a long and energetically costly in-river migration were characterized by a higher ṀO2max, a higher scope for activity, a higher Ucrit and, in some cases, a higher cost of transport, relative to the coastal salmon stocks that experience a short in-river migration. We conclude that high-caliber respirometry can be performed in a field setting and that stock-specific differences in swimming performance of adult salmon may be important for understanding upstream migration energetics and abilities.

Pacific salmon in hot water: applying aerobic scope models and biotelemetry to predict the success of spawning migrations.

Concern over global climate change is widespread, but quantifying relationships between temperature change and animal fitness has been a challenge for scientists. Our approach to this challenge was to study migratory Pacific salmon (Oncorhynchus spp.), fish whose lifetime fitness hinges on a once‐in‐a‐lifetime river migration to natal spawning grounds. Here, we suggest that their thermal optimum for aerobic scope is adaptive for river migration at the population level. We base this suggestion on several lines of evidence. The theoretical line of evidence comes from a direct association between the temperature optimum for aerobic metabolic scope and the temperatures historically experienced by three Fraser River salmon populations during their river migration. This close association was then used to predict that the occurrence of a period of anomalously high river temperatures in 2004 led to a complete collapse of aerobic scope during river migration for a portion of one of the sockeye salmon (Oncorhynchus nerka) populations. This prediction was corroborated with empirical data from our biotelemetry studies, which tracked the migration of individual sockeye salmon in the Fraser River and revealed that the success of river migration for the same sockeye population was temperature dependent. Therefore, we suggest that collapse of aerobic scope was an important mechanism to explain the high salmon mortality observed during their migration. Consequently, models based on thermal optima for aerobic scope for ectothermic animals should improve predictions of population fitness under future climate scenarios.

From Hagfish to Tuna: A Perspective on Cardiac Function in Fish

This perspective takes a comparative view of cardiac physiology in fish to provide insights into cardiac control mechanisms and the degree of cardiac plasticity between species. Between the extremes represented by tuna and hagfish, there is a 15-fold difference in cardiac output that is largely accounted for by species differences in heart rate rather than in stroke volume. The relative importance of heart rate and stroke volume is reversed in many fish in terms of explaining the up to threefold increase in cardiac output observed during swimming A conspicuous and unexplained observation is that all fish studied so far, with the exception of tuna, have heart rates lower than 120 bpm. In many fish, luminal O₂, in venous blood is the sole myocardial O₂, supply, and a venous PO₂ threshold may ultimately limit cardiac performance. More active fish have bigger ventricles that generally beat faster and generate higher blood pressures and flows. The bigger ventricle in active fish, while improving convection to working skeletal muscle, requires the development of a coronary circulation to supplement to varying degrees the luminal myocardial O₂ supply. It is hoped that these generalities will act as a framework for future research.

What is conservation physiology? Perspectives on an increasingly integrated and essential science †

The definition of ‘conservation physiology’ is refined to be more inclusive, with an emphasis on characterizing diversity, understanding and predicting responses to environmental change and stressors, and generating solutions. The integrative discipline is focused on mechanisms and uses physiological tools, concepts, and knowledge to advance conservation and resource management.

Abnormal migration timing and high en route mortality of sockeye salmon in the Fraser River, British Columbia

Abstract Since 1995, several stocks of Fraser River sockeye salmon (Oncorhynchus nerka) have begun upriver spawning migrations significantly earlier than previously observed. In some years, the timing of peak migration has shifted more than 6 weeks. Coincident with this early migration are high levels of en route and pre-spawning mortality, occasionally exceeding 90%. These phenomena pose risks to the perpetuation of these fisheries resources. At present, although there are many competing hypotheses (e.g., energetics, osmoregulatory dysfunction, oceanic conditions, parasites) that may account for early migration and high mortality, there are no definitive answers, nor any causal evidence that link these issues. With poor predictive ability in the face of uncertainty, fisheries managers have been unable to effectively allocate harvest quotas, while ensuring that sufficient fish are able to not only reach the spawning sites, but also successfully reproduce. If trends in mortality rates continue, several imp...

The Effect of Temperature Acclimation and Adrenaline on the Performance of a Perfused Trout Heart

Cardiac performance was examined with in situ perfused trout hearts at two acclimation temperatures, 5 C and 15 C. In series I, adrenaline-free perfusion and a cumulative dose response up to 1 μgmol adrenaline · L⁻¹ was examined. In series II, tonic adrenergic stimulation (5 nmol · L⁻¹) and a cumulative dose response up to 50 nmol · L⁻¹ was examined Tonic adrenergic stimulation was important for chronotropic and inotropic stability, especially at5 C. Heart rate and maximum cardiac output were significantly higher at 15 C than at5 C. Maximum stroke volume at 5 C was the same as or greater than the maximum stroke volume at 15 C Adrenergic stimulation produced quantitatively different positive chronotropic and inotropic effects at both temperatures and partially compensated for the direct efect of temperature; the chronic Q10 values for heart rate and maximum cardiac output were 1.30-1.40. Trout acclimated to 5 C had a relatively larger ventricle mass, which permitted a higher absolute stroke work at 5 C than at 15 C

Excess post-exercise oxygen consumption in adult sockeye ( Oncorhynchus nerka) and coho (O. kisutch) salmon following critical speed swimming

SUMMARY The present study measured the excess post-exercise oxygen cost (EPOC) following tests at critical swimming speed (Ucrit) in three stocks of adult, wild, Pacific salmon (Oncorhynchus sp.) and used EPOC to estimate the time required to return to their routine level of oxygen consumption (recovery time) and the total oxygen cost of swimming to Ucrit. Following exhaustion at Ucrit, recovery time was 42–78 min, depending upon the fish stock. The recovery times are several-fold shorter than previously reported for juvenile, hatchery-raised salmonids. EPOC varied fivefold among the fish stocks, being greatest for Gates Creek sockeye salmon (O. nerka), which was the salmon stock that had the longest in-river migration, experienced the warmest temperature and achieved the highest maximum oxygen consumption compared with the other salmon stocks that were studied. EPOC was related to Ucrit, which in turn was directly influenced by ambient test temperature. The non-aerobic cost of swimming to Ucrit was estimated to add an additional 21.4–50.5% to the oxygen consumption measured at Ucrit. While these non-aerobic contributions to swimming did not affect the minimum cost of transport, they were up to three times higher than the value used previously for an energetic model of salmon migration in the Fraser River, BC, Canada. As such, the underestimate of non-aerobic swimming costs may require a reevaluation of the importance of how in-river barriers like rapids and bypass facilities at dams, and year-to-year changes in river flows and temperatures, affect energy use and hence migration success.