A rapidly aging global population has motivated the development and use of models for human aging. Studies on aging have shown parallels between zebrafish and humans at the internal organization level; however, few parallels have been studied at the whole-organism level. Furthermore, the effectiveness of exercise as a method to mitigate the effects of aging has not been studied in zebrafish. We investigated the effects of aging and intermittent exercise on swimming performance, kinematics and behavior. Young, middle-aged and old zebrafish (20-29, 36-48 and 60-71% of average lifespan, respectively) were exercised to exhaustion in endurance and sprint swimming tests once a week for four weeks. Both endurance and sprint performance decreased with increased age. Swimming performance improved with exercise training in young and middle-aged zebrafish, but not in old zebrafish. Tail-beat amplitude, which is akin to stride length in humans, increased for all age groups with training. Zebrafish turning frequency, which is an indicator of routine activity, decreased with age but showed no change with exercise. In sum, our results show that zebrafish exhibit a decline in whole-organism performance and trainability with age. These findings closely resemble the senescence-related declines in physical ability experienced by humans and mammalian aging models and therefore support the use of zebrafish as a model for human exercise and aging.

As fish approach fatigue at high water velocities in a critical swimming speed (U crit) test, their swimming mode and oxygen cascade typically move to an unsteady state because they adopt an unsteady, burst-andglide swimming mode despite a constant, imposed workload. However, conventional rate of oxygen uptake (_ M O2) sampling intervals (5-20 min) tend to smooth any dynamic fluctuations in active _ M O2 (_ M O2active) and thus likely underestimate the peak _ M O2active. Here, we used rainbow trout (Oncorhynchus mykiss) to explore the dynamic nature of _ M O2active near U crit using various sampling windows and an iterative algorithm. Compared with a conventional interval regression analysis of _ M O2active over a 10-min period, our new analytical approach generated a 23% higher peak _ M O2active. Therefore, we suggest that accounting for such dynamics in _ M O2active with this new analytical approach may lead to more accurate estimates of maximum _ M O2 in fishes.

The life histories of anadromous Arctic Char Salvelinus alpinus are complex and vary greatly between populations and environments. Here, we detail key aspects of the physical environment and life history of a population of Arctic Char from Nulahugyuk Creek, Nunavut, Canada, to characterize migration traits in a highly variable environment. Over the course of this migration, creek discharge declined precipitously, forcing Arctic Char to migrate through shallow water with large diel temperature fluctuations (>10°C) and high temperature extremes (>21°C). The downstream migration of adults (>55 cm) began in mid‐June and continued into early July, while the downstream migration of smolts (<30 cm) began in late June and continued until late July. The upstream adult migration began in late June and ended in late July, far earlier than most upstream migrations in the region. There was no appreciable upstream migration of juveniles, and Arctic Char 30 to 55 cm in length were absent from the up‐ and downstream migrations. The average age at first migration was 4 years, and the youngest adult Arctic Char migrating upstream were 8 and 9 years old. The missing size‐ and age‐classes, and the fact that most upstream migrants were near reproductive maturity, indicate that Arctic Char in this system typically leave at a length of 19 cm and an age of 4 years and do not return for 4 to 5 years, when they are ready to reproduce. Anadromous Nulahugyuk Creek Arctic Char appear to employ strategies that limit their exposure to restrictive migratory conditions and facilitate their existence in an otherwise uninhabitable system. Understanding such population‐specific migratory strategies is critical to the management of Arctic Char fisheries, which are comprised of populations with highly diverse life histories, and to our understanding of how these life histories may contribute to the adaptability and persistence of the species as climate change progresses. Received November 24, 2015; accepted March 23, 2016 Published online July 28, 2016

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This study hypothesized that oxygen uptake (ṀO 2) measured with a novel protocol of chasing rainbow trout Oncorhynchus mykiss to exhaustion inside a static respirometer while simultaneously monitoring ṀO 2 (ṀO 2chase) would generate the same and repeatable peak value as when peak active ṀO 2 (ṀO 2active) is measured in a critical swimming speed protocol. To reliably determine peak ṀO 2chase , and compare to the peak during recovery of ṀO 2 after a conventional chase protocol outside the respirometer (ṀO 2rec), this study applied an iterative algorithm and a minimum sampling window duration (i.e., 1 min based on an analysis of the variance in background and exercise ṀO 2) to account for ṀO 2 dynamics. In support of this hypothesis, peak ṀO 2active (707 ± 33 mg O 2 h −1 kg −1) and peak ṀO 2chase (663 ± 43 mg O 2 h −1 kg −1) were similar (P = 0.49) and repeatable (Pearson's and Spearman's correlation test; r ≥ 0.77; P < 0.05) when measured in the same fish. Therefore, estimates of ṀO 2max can be independent of whether a fish is exhaustively chased inside a respirometer or swum to fatigue in a swim tunnel, provided ṀO 2 is analysed with an iterative algorithm and a minimum but reliable sampling window. The importance of using this analytical approach was illustrated by peak ṀO 2chase being 23% higher (P < 0.05) when compared with a conventional sequential interval regression analysis, whereas using the conventional chase protocol (1-min window) outside the respirometer increased this difference to 31% (P < 0.01). Moreover, because peak ṀO 2chase was 18% higher (P < 0.05) than peak ṀO 2rec , chasing a fish inside a static respirometer may be a better protocol for obtaining maximum ṀO 2 .