Non-invasive sampling of water-borne hormones demonstrates individual consistency of the cortisol response to stress in laboratory zebrafish (Danio rerio).

Glucocorticoid (GC) stress hormones are well-known for their impact on phenotypic traits ranging from immune function to behaviour and cognition. For that reason, consistent aspects of an individual's physiological stress response (i.e. GC responsiveness) can predict major elements of life-history trajectory. Zebrafish (Danio rerio) emerge as a promising model to study such consistent trait correlations, including the development of individual stress coping styles, i.e. consistent associations between physiological and behavioral traits. However, consistency in GC responsiveness of this popular animal model remains to be confirmed. Such a study has so far been hampered by the small-bodied nature and insufficient blood volume of this species to provide repeated measurements of circulating GCs. Here, we adopted a technique that allows for repeated, non-invasive sampling of individual zebrafish by quantifying GCs from holding water. Our findings indicate consistency of the magnitude of post-stress GC production over several consecutive stress events in zebrafish. Moreover, water-borne GCs reflect individual variation in GC responsiveness with the strongest consistency seen in males.

Recent advances in telemetry for estimating the energy metabolism of wild fishes.

Metabolic rate is a critical factor in animal biology and ecology, providing an objective measure that can be used in attributing a cost to different activities and to assessing what animals do against some optimal behaviour. Ideally, metabolic rate would be estimated directly by measuring heat output but, until recently, this has not been easily tractable with fishes so instead metabolic rate is usually estimated using indirect methods. In the laboratory, oxygen consumption rate is the indirect method most frequently used for estimating metabolic rate, but technical requirements preclude the measurement of either heat output or oxygen consumption rate in free-ranging fishes. There are other field methods for estimating metabolic rate that can be used with mammals and birds but, again, these cannot be used with fishes. Here, the use of electronic devices that record body acceleration in three dimensions (accelerometry) is considered. Accelerometry is a comparatively new telemetric method for assessing energy metabolism in animals. Correlations between dynamic body acceleration (DBA) and oxygen consumption rate demonstrate that this will be a useful proxy for estimating activity-specific energy expenditure from fishes in mesocosm or field studies over extended periods where other methods (e.g. oxygen consumption rate) are not feasible. DBA therefore has potential as a valuable tool for attributing cost to different activities. This could help in gaining a full picture of how fishes make energy-based trade-offs between different levels of activity when faced with conflicting or competing demands arising from increased and combined environmental stressors.

Flume length and post-exercise impingement affect anaerobic metabolism in brook charr Salvelinus fontinalis.

The effect of flume length and impingement time on post-exercise lactate concentrations in brook charr Salvelinus fontinalis were examined. Swimming in longer flumes increased lactate concentrations, as does impingement after swimming in short flumes.

The effect of temperature and ammonia exposure on swimming performance of brook charr (Salvelinus fontinalis).

The effects of water temperature and ammonia concentration on swimming capacity of brook charr (Salvelinus fontinalis, Mitchill, 1814) were determined by measuring gait transition speed (U(gt), cms(-1)), maximum burst speed (U(max), cms(-1)), tail-beat amplitude (a, cm), tail-beat frequency (f, Hz), maximum acceleration of bursts (A(max), cms(-2)), number of bursts, distance of bursts (cm) and total swimming distance (cm) in a 4.5m long experimental raceway with increasing upstream water velocity. Temperatures other than the acclimation temperature of 15 degrees C significantly reduced swimming characteristics of gait transition, i.e. U(gt) and A(max), while increased ammonia concentration reduced the measures of swimming after U(gt): U(max), the relationship between f and swimming speed above U(gt), a, A(max) and the distance travelled with each swimming burst above U(gt). This study, using a novel raceway set-up shows various effects of temperature and ammonia exposure on the swimming performance of brook charr and can be used to establish threshold values for environmental management.