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Abstract: Hypoxia is an ever increasing threat to aquatic systems. While fluctuating levels of dissolved oxygen (DO) can be a natural phenomenon, hypoxia caused by eutrophication and organic pollution is [...]

Abstract: There is often considerable variation in the intensity of behavioural responses of prey to predation cues. The purpose of the current study was to determine the role of standard [...]

Circadian rhythms in the Syrian hamster can be markedly phase shifted by 3 h of wheel running or arousal stimulation during their usual daily rest period ('subjective day'). Continuous wheel running is predictive but not necessary for phase shifts of this 'nonphotic' type; hamsters aroused by gentle handling without running can also show maximal shifts. By contrast, physical restraint, a standard stress procedure and thus presumably arousing, is ineffective. To resolve this apparent paradox, phase-shifting effects of 3-h sessions of restraint or other stress procedures were assessed. In a preliminary study, phase shifts to arousal by gentle handling were significantly potentiated by the cortisol synthesis inhibitor metyrapone, suggesting that stress-related cortisol release may inhibit phase shifts to arousal. Next, it was confirmed that restraint in the subjective day does not induce phase shifts, but behavioral observations revealed that it also does not sustain arousal. Restraint combined with noxious compressed air blasts did sustain arousal and induced a significant cortisol response compared with arousal by gentle handling but did not induce shifts. Restraint combined with continuous horizontal rotation was also ineffective, as was EEG-validated arousal via confinement to a pedestal over water. However, 3 h of resident-intruder interactions (an intense psychosocial stress) or exposure to an open field (a mild stress) did induce large shifts that were positively correlated with indexes of forward locomotion. The results indicate that large phase shifts associated with arousal in the usual sleep period are neither induced nor prevented by stress per se, but are dependent on the expression of at least low levels of locomotor activity. Sustained arousal alone is not sufficient. circadian rhythms; nonphotic zeitgeber; wheel running; sleep deprivation; immobilization stress; psychosocial stress; cortisol; electroencephalogram

Numerous aquatic animals release chemical cues when attacked by a predator. These cues "warn" other individuals of danger and have been termed alarm cues. Cross-species responses to alarm cues are common and in some cases result from learned recognition. However, little is known about the ecological factors that could influence this learned recognition. The current study focuses on the role of habitat complexity in the learning of heterospecific alarm cues. We introduced brook stickleback (Culaea inconstans) into outdoor pools containing fathead minnows (Pimephales promelas) naïve to stickleback. The pools all contained a predatory fish (northern pike, Esox lucius) but varied in habitat characteristics. Pools representing high-complexity habitats had a large amount of structure to obscure the visual environment, while pools representing low-complexity habitats had minimal structure. After 8 days, fish were removed from the pools and behavioural assays were conducted in the laboratory. We tested the minnows for a response to either stickleback skin extract (experimental) or swordtail (Xiphophorus helleri) skin extract (control) and found that minnows conditioned in pools with little structure had learned to recognize stickleback alarm cues, while those from pools with complex structure did not recognize stickleback alarm cues. [ABSTRACT FROM AUTHOR]