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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.

Aquaculture's 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.

This review and data analysis outline how fish biologists should most reliably estimate the minimal amount of oxygen needed by a fish to support its aerobic metabolic rate (termed standard metabolic rate; SMR). By reviewing key literature, it explains the theory, terminology and challenges underlying SMR measurements in fishes, which are almost always made using respirometry (which measures oxygen uptake,ṀO 2 ). Then, the practical difficulties of measuring SMR when activity of the fish is not quantitatively evaluated are comprehensively explored using 85 examples ofṀO 2 data from different fishes and one crustacean, an analysis that goes well beyond any previous attempt. The main objective was to compare eight methods to estimate SMR. The methods were: average of the lowest 10 values (low10) and average of the 10% lowestṀO 2 values, after removing the five lowest ones as outliers (low10%), mean of the lowest normal distribution (MLND) and quantiles that assign from 10 to 30% of the data below SMR (q 0⋅1 , q 0⋅15 , q 0⋅2 , q 0⋅25 and q 0⋅3 ). The eight methods yielded significantly different SMR estimates, as expected. While the differences were small when the variability was low amongst theṀO 2 values, they were important (>20%) for several cases. The degree of agreement between the methods was related to the c.v. of the observations that were classified into the lowest normal distribution, the c.v. MLND (C.V. MLND ). When this indicator was low (≤5⋅4), it was advantageous to use the MLND, otherwise, one of the q 0⋅2 or q 0⋅25 should be used. The second objective was to assess if the data recorded during the initial recovery period in the respirometer should be included or excluded, and the recommendation is to exclude them. The final objective was to determine the minimal duration of experiments aiming to estimate SMR. The results show that 12 h is insufficient but 24 h is adequate. A list of basic recommendations for practitioners who use respirometry to measure SMR in fishes is provided.

. (2003). The effect of temperature on swimming performance and oxygen consumption in adult sockeye (Oncorhynchus nerka) and coho (O. kisutch) salmon stocks. J. Exp. Biol. 206,[3239][3240][3241][3242][3243][3244][3245][3246][3247][3248][3249][3250][3251] In both the on-line and printed versions of this paper, some of the equations in the legends to Figs 2-4 were printed incorrectly.On page 3245, in the legend to Fig.·2, the two equations should read:M O 2 routine =2.12+0.09e 0.18t (ambient; broken line) and M O 2 routine =1.39+0.54e 0.08t (adjusted; solid line).On page 3246, in the legend to Fig.·3 The authors apologise for any inconvenience these errors may have caused.Temperature has been coined the 'ecological master factor' for fish (Brett, 1971), and important physiological functions such as growth, swimming performance and active metabolic rate can have species-specific temperature optima that are near a species-preferred or acclimated temperature (Fry, 1947;Brett, 1971;Dickson and Kramer, 1971;Beamish, 1978;Houston, 1982;Bernatchez and Dodson, 1985;Johnston and Temple, 2002). Thus, when fish are exposed to temperature changes, they can obtain optimal performance by altering either their behaviour (preference/avoidance) or their physiology (adaptation and acclimation), when the temperature change is sufficiently long. Certain short-term variations in temperature may be unavoidable, however, and this is particularly the case for adult migratory salmon that are returning to their natal streams to spawn. For example, water temperatures in one of the world's greatest salmon-bearing rivers, the Fraser River, BC, Canada, may vary annually on a given date by as much as 6°C. Furthermore, the river temperatures encountered by the Early Stuart stock of Fraser River sockeye salmon Oncorhynchus nerka during its 25-day migration can vary by as much as 10.5°C (Idler and Clemens, 1959) and reach up to 22°C .Given the adult salmon's short migration window and its exposure to a wide variation in temperature, it is possible that acclimation mechanisms that would normally compensate for temperature change may be incomplete. Conversely, Guderley and Blier (1988) suggest that swimming performance and most of its components demonstrate thermal compensation on an evolutionary time scale (i.e. adaptation) such that optimal performance and lowest thermal sensitivity are typically within the temperature range most frequently encountered by the organism. In the case of adult salmon stock, the prediction is that they would retain sufficient physiological flexibility to accommodate the range of temperatures most frequently 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 sto...

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.

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.

Depending on population, wild Fraser River sockeye salmon Oncorhynchus nerka travel distances of <100 km to >1100 km and ascend elevations ranging from near sea-level to 1200 m to reach spawning areas. Populations embarking on distant, high elevation migrations (i.e. Early Stuart, Chilko and Horsefly populations) began their upriver spawning migrations with higher densities of somatic energy (c. 9Á2 to 9Á8 MJ kg À1) and fewer eggs (c. 3200 to 3800) than populations making shorter, low elevation migrations (i.e. Weaver and Adams; c. 7Á1 to 8Á3 MJ kg À1 gross somatic energy and c. 4300 to 4700 eggs). Populations making difficult upriver migrations also had morphologies that were smaller and more fusiform than populations making less difficult migrations, traits that may facilitate somatic energy conservation by reducing transport costs. Indeed, fish travelling long distances expended less somatic energy per unit of migratory difficulty than those travelling shorter distances (2Á8 to 3Á8 kJ v. 10-1400 kJ). Consistent with evolutionary theory, difficult migrations appear to select for energy efficiency but ultimately fish making more difficult migrations produce fewer eggs, even when differences in body length have been accounted for. Despite large among-population differences in somatic energy at the start of upriver migration, all populations completed migration and spawning, and subsequently died, with c. 4MJkg À1 of energy remaining, a level which may reflect a threshold to sustain life.