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Hypoxia is known to provoke a wide range of effects on aquatic animals. Here we use laboratory and field data on Atlantic cod, Gadus morhua, to illustrate that many of these responses can be explained within the metabolic scope (MS) framework, i.e. taking into account the directive and limiting effects of dissolved oxygen (DO) on the ability of animals to acquire energy for growth and activity. A MS model for cod shows that scope for activity (swimming, feeding, etc.) is proportional to DO and becomes nil, jeopardising survival, when DO isapproximately 20% air saturation. Laboratory studies have confirmed this lethal threshold and demonstrated that growth and food ingestion were significantly reduced below 70% sat. This loss of appetite has been linked to a reduction of the peak value and an increase in duration of postprandial metabolism, in agreement with the MS model. Dwindling MS during hypoxia imposes an upper limit to swimming performance. Cod may also opt to reduce spontaneous swimming activity to spare oxygen for other activities such as digestion. In the Kattegat, the Baltic Sea, and the Gulf of St. Lawrence, eastern Canada, cod completely avoid waters where their MS is near zero. Furthermore, cod density increases exponentially with DO up to approximately 70% sat in the Gulf of St. Lawrence. Although hypoxia results in other direct and indirect effects as well, the MS framework allows modelling of many of the responses to hypoxia for individual cod that ought to be reflected at the population and community levels. The MS framework is also useful to compare species responses. We show that the impact of hypoxia on MS is similar, when expressed as a proportion of MS in normoxia, in cod, European sea bass (Dicentrarchus labrax), the common sole (Solea solea) and turbot (Psetta maxima). Data are required for other species to evaluate how general these findings are.

We measured the heart rate (HR) and oxygen consumption ( $$\dot V_{O_2 } $$ ) of wapiti (Cervus elaphus canadensis) before, during, and after presentation of biologically irrelevant odors (pentane, thiophene, and a perfume), artificial predator odors (an ether extract of cougar feces, and PDT, a compound found in mustelid anal gland secretion), stale predator odors (dog feces and urine and fox urine, kept at ambient temperature for a few weeks), and fresh predator odors (wolf, coyote, and cougar feces and the odor of a dead coyote, kept frozen between collection and test). Overall, responses to odors were small compared to other stressful stimuli. Individual variability was high among scents and among wapiti, but two of the fresh predator odors (cougar and wolf feces) produced larger HR and $$\dot V_{O_2 } $$ responses than the other scents and were more often successful at producing responses. As a group, fresh predator odors produced larger tachycardias and elicited a larger number of significant HR responses than biologically irrelevant novel odors. although the two classes of odors did not differ in their effect on $$\dot V_{O_2 } $$ . Although several other studies have shown that ungulates have reduced feeding levels when their food is scented with predator odors, it is not clear if this is due to reduced palatability or antipredator behavior. This study is the first demonstration that a wild ungulate species reacted more strongly to predator odors than to other odors in a nonfeeding situation.

Data on heart rate can be analyzed in terms of beats per unit of time (heart rate) or its reciprocal, time per beat (interbeat interval). We show that counting beats (including fractions), averaging interbeat intervals, and measuring the time for a fixed number of beats are correct techniques to measure heart activity within observation periods. QRS counts are less precise, but not systematically biased. Conversely, averaging instantaneous heart rates always overestimates true heart rate. Arithmetic means across trials of equal duration are correct only when heart activity for each trial is expressed as mean heart rate. For observation periods with equal numbers of beats, heart activity for each trial must be expressed as mean interbeat interval. A literature survey showed that biased techniques were frequently used to calculate heart rate, and that about half of the studies did not provide sufficient information on the methods used.

Heart rate (HR) telemetry was used in studies of bighorn sheep (Ovis canadensis canadensis) to determine HR associated with normal daily activities and detect changes in HR signalling arousal. HR was measured in wapiti (Cervus elaphus) to clarify the effects of normal activities, arousal and imposed work on FIR and metabolic rate (MR). The instrumentation used was analogue. The electrocardiogram (ECG), obtained from two electrodes on the sternum of the subject, was used to frequency modulate the 148.8 MHz carrier. The signal was transmitted with a power of about one milliwatt and was received by a very sensitive single side band receiver up to distances of about 6 km. The output signal could be checked aurally for adequate quality and was stored on cassette tape for later processing. The original ECG was recovered and either displayed on a strip chart recorder or analyzed with a computer acquisition system. HR was found to be a better indicator of arousal due to external stimuli than was the behavior of the animal. In free-ranging bighorn sheep many factors external to the animal (natural or experimentally-induced) elicited HR responses. In captive wapiti HR was found to be a good predictor of energy utilization in both calm and aroused animals.

An Atlantic Halibut (Hippoglossus hippoglossus) (41.4 cm fork length) with the same pigmentation on the blind side as on the ocular side (ambicoloration) was captured in the lower St. Lawrence estuary, Canada, on 24 June 2004. This specimen represents the most extreme case of ambicoloration published for this species to date. As in other cases of extreme ambicoloration, this specimen shows other signs of abridged metamorphosis and reduced asymmetry, such as incomplete migration of the left eye and a hooked dorsal fin. Studies of hatchery-reared larvae have shown that the most common cause of malpigmentation, including ambicoloration, in halibut is a diet containing inadequate amounts and proportions of essential unsaturated fatty acids shortly before metamorphosis. Even though not expected to be common in the wild, inadequate diet for a short duration before metamorphosis is the most likely cause of ambicolouration in wild halibut.