Aspects of the physiological ecology of pike from an upland Scottish loch have been studied. A small laboratory stock was maintained in a healthy, feeding condition to allow measurements of a range of physiological and behavioural parameters. Resting and maximum metabolic rates increase with body size and the relationship between weight and oxygen consumption can be described by regression equations of the form: Y = ax⁶. The ratio of resting : maximum oxygen consumption (the metabolic expansibility coefficient) increases with body-weight. Heart rate increases during activity and feeding, accurately reflecting fluctuations in metabolic rate; so it can be used as a measure of metabolic rate in the field using heart rate telemetry techniques. For pike in the laboratory, the relationship between heart rate and oxygen consumption (VO₂, mg/h standardised to a 500g fish weight) can be described by a significant regression valid for heart rates below 55 beats/min. Post-prandial oxygen consumption was measured directly in small pike (< 300g) or calculated in large pike from heart rate. Peak post-prandial oxygen consumption was found to utilise the total metabolic scope in small pike but not larger individuals. Weight specific peak post-pradial oxygen consumption decreases with increasing pike size; consequently smaller pike have the physiological capability to grow more quickly. In adult pike metabolic scope cannot be fully utilised by a combination of the maximum power demands of food processing and aerobic swimming; there seems to be a generous allowance for the metabolic demands of recovery from burst activity. Analysis of the electrocardiogram (ECG) indicates that pike show a reflex bradycardia in response to most sensory stimuli. Amplitude of the ECG increases after feeding events and following burst activity. The interval between Q and T waves of the ECG decreases as heart rate increases reflecting changes in the time for ventricular systole. A telemetry system for monitoring heart rate and movements of free-swimming wild pike has been developed and field tested. A preliminary track of movements by a pike over several days indicated that activity levels in the wild are low, however the fish was by no means sedentary. Using data from this and other studies of pike, a hypothesis is put forward that whilst young pike tend to maximise growth rates, adults feed well within their physiological limits for feeding and growth over much of the year, even in the presence of excess prey. It is suggested that sub-maximal feeding may have a selective advantage through decreasing mortality probability and increasing lifetime reproductive output.

Thesis (M.S.)--University of Wisconsin--Madison. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 92-98).

Thesis (Ph. D.)--Ohio State University, 1985. / Includes vita. Includes bibliographical references (leaves 82-89). Available online via OhioLINK's ETD Center.

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The mechanisms behind speciation have been subject of debate for centuries. The presence of resource polymorphism has been discovered to play a significant part in this process, and has been proven to induce phenotypic and genetic divergence. Although resource polymorphism has been intensely studied during the last few decades, there is a gap of information as to why this can be observed in some systems but not in others. Recent studies of European whitefish (Coregonus lavaretus) in Scandinavian lakes have shown that predation, in this case by Northern pike (Esox lucius), could be the factor that induces resource polymorphism. European whitefish is known to diverge into several ecomorphs in Scandinavian lakes, but only in the presence of pike. Divergence is assumed to be caused by the size selectivity of pike, and the following niche separation and eventually reproductive isolation. In this study, pike prey selectivity was studied in the field through sample fishing using hooks baited with whitefish of different sizes. The hypothesis was that pike prefers smaller prey over larger and mainly hunts in the littoral zone. This should causes smaller whitefish ecomorphs to be prone to predation in the littoral and thus utilize refuge spawning grounds with low predation pressure. However, no pike were caught on whitefish spawning grounds, and fishing at two additional pike rich sites displayed a preference towards medium-sized whitefish (p &lt; 0.05). This indicates a size selectivity, although further and improved studies would be required to answer the question of the pike’s role in resource polymorphism.

In resource polymorphism, ecological opportunity and selective predatory pressure can be considered key factors in phenotypic divergence. In post-glacial lakes of Scandinavia, the European whitefish (Coregonus lavaretus L.) is a common species and has repeatedly diverged along the benthic - pelagic resource axis. Recent studies suggest that predation by northern pike (Esox lucius L.) induces rapid divergence in whitefish, leading to two reproductively isolated ecotypes: a dwarf planktivore and a giant benthivore. In lakes where pike is absent, whitefish are only found as monomorphic populations. In this study I estimated growth rates in two monomorphic and two polymorphic populations having giant and dwarf ecotypes. The aim was to use growth rates as a tool to distinguish between juvenile giants and dwarfs, but also to find out if a population's resource use was reflected in the growth rate. Scales were used to calculate growth rate, where like trees, variations in seasonal growth could be observed in a ring-like structure. Growth rates differed between the morphs, and mirrored their use of resources. The two monomorphic populations had the highest average growth rate the first six years (40.1 and 35.5 mm/year), and quickly reached maximum size. Dwarfs and giants in the dimorphic systems had equal growth the first two years, after which giants grew at a substantially higher rate. Categorization between juvenile giants and dwarfs could be done if an individual had passed its third growth season.

Metabolic power budgeting, the regulation of metabolism with respect ot metabolic scope, was studied in the laboratory in zebra fish using respirometry, and in the field on pike using heart-rate telemetry. Increased food consumption by zebra fish resulted in higher growth, mortality and metabolism. The magnitudes of the components of metabolism: maximum metabolism, standard metabolism, routine metabolism and feeding metabolism were measured. Power budgets for zebra fish fed high and low rations were constructed. Fish fed high rations worked harder than fish fed lower rations, but were apparently not working near the upper limit of the metabolic scope. Possible mechanisms for growth-related mortality are considered. Biological information on the populations of pike in Lochs Kinord and Davan (Grampian Highlands) were gathered. The population of L. Kinord was dominated by young, small fish; apparently due to exploitation. L. Davan is unexploited and had a pike population consisting of a much wider range of ages and sizes. Methods for assessing regurgitation by pike were developed. Effects of long and short-term temperature fluctuations, and feeding on heart rate of captive pike were studied. Resting heart rate increased exponentially with increasing temperature; heart rate appeared to accommodate all changes in resting metabolism. Post-prandial heart-rate records could be used to accurately estimate meal size. Gastric evacuation rates corresponded to digestion times estimated from heart-rate records. Heart-rate telemetry was used to study metabolic power budgeting, feeding and activity of wild pike from Lochs Kinord and Davan in June 1988. Pike worked mainly at low power levels relative to metabolic scope. Tachycardias associated with localized movement were frequent, and such movement was accurately recorded by heart-rate telemetry but frequently undetected by conventional means. Feeding events were identified and the metabolic costs of survival estimated. Some unusually energetically-expensive localized movements were recorded; the possible reasons for this are discussed. Intraperitoneal implantation techniques were developed for transmitter attachment on pike. Experments using dummy transmitters on pike and rainbow trout showed no effect on growth, survival or reproduction, but tissue reactions differed. Male and female pike, location-tracked with implanted transmitters before, during and after spawning time exhibited increased overall activity during the apparent spawning period, as well as changes in diet activity. Males were significantly more active than females in three out of seven weeks. Spawning appears to be a period of high energy expenditure for pike.