Sympatric populations of S. malma and S. alpinus from Alaska were compared using a discriminant function analysis. The comparison indicated little or no hybridization. S. malma is, therefore, regarded as a distinct species. S. malma has fewer gill rakers, pyloric caeca and pores along the lateral line than S. alpinus. Five hundred specimens of S. malma from 42 North American localities were examined. Considerable geographic variability was observed. The variation showed no correlation with latitude. Evidence is presented that subspecific distinctions are invalid in S. malma. It is suggested that S. malma evolved in the North Pacific area sometime during the Pliestocene. / Science, Faculty of / Zoology, Department of / Graduate

Coho underyearlings settle toward the bottom when illumination decreases. The critical intensity for this response was found to be approximately 1 foot candle. A study of the nipping phenomenon in coho and kamloops trout revealed that coho nip more Intensively than trout in a homotypic group. However; in a heterotypic group of equal numbers, trout nip more readily. In a heterotypic group coho nip less frequently and show a preference to nip other coho. By comparison, the nipping Intensity of trout is not reduced and they nip either species equally. Factors affecting nipping are size, color and light intensity. In a group of coho or trout, there is a marked tendency for the larger members to nip the smaller. Red and orange colors are least effective in eliciting a nipping response. Light intensity changes between 4- and 12 foot candles have no significant effect; however, below k foot candles nipping declines rapidly as illumination is decreased. The social releaser for nipping is movement but size and color are important components of the releaser. Additional patterns of behavior have been described for trout, namely, "threatening" and fighting. / Science, Faculty of / Zoology, Department of / Graduate

The object of this study was to test the hypothesis that prey abundance in large part regulates dispersion, territory size and aggressive behavior of young rainbow trout during the stream rearing phase of their life history. In laboratory test channels, where age 0+ fry were introduced into channels receiving three different amounts of prey and permitted to emigrate voluntarily, density of fry remained highest at the highest prey level. Also, the distribution of fry was positively associated with a gradient in prey abundance. Both territory size and frequency of aggressive encounter varied inversely with prey level; the higher the prey level, the smaller the territory and the lower the frequency of aggressive encounter. Emigration from the test channels was neither as rapid nor as marked when prey level was abruptly reduced, compared to when fry were initially introduced to the different prey levels. However, frequency of aggressive encounter significantly increased when the prey level was decreased and significantly decreased when the prey was increased. In Loon Outlet Creek, the abundance of prey was positively associated with summer fish biomass in one study section, while a positive association was not apparent for a second study section. The second, located closer to Loon Lake, on the average tended to have throughout the summer a higher fish biomass and higher prey density. In addition, the spring lakeward migration of juvenile rainbow trout was negatively correlated with prey density and positively correlated with temperature. It is suggested that in the natural stream habitat, the density of fry and juvenile rainbow trout is strongly influenced by prey density especially when associated with the metabolic effects of temperature and fish size. / Science, Faculty of / Zoology, Department of / Graduate

The temporal and spatial variations in the activity of cutthroat trout in a small coastal British Columbia lake (49°19'N, 122°34’W) were examined in order to determine the Impact of activity on the production of fish, and the factors controlling activity. Sonar tracking, diving, netting and tagging, rise observation, stomach content-prey distribution comparision, and echo sounding were used in the Investigation. Average activity levels were at least an order of magnitude below any published values. Energy values were correspondingly low; the maximum estimate of annual energy expenditure in activity (including routine metabolism) was 2330 kCal/kg/yr, which is well below the accepted 'rule' of field metabolism being twice the routine metabolism (3860 kCal/kg/yr). Fish behavioral problems and methodological shortcomings are considered responsible for this result. Activity over 5 min intervals was quite variable. Daily activity peaked during dawn and dusk. The level of activity decreased in late fall and early spring, and there was a shift from the littoral zones during summer. The cutthroat in the lake appear to maintain home ranges-for up to 5 months. Factors affecting activity can be broken into 3 categories: Temperature, light, and oxygen primarily determine the depth zones that are accessible to fish. Substrates such as Potamogeton beds and logs may act to concentrate fish within accessible depth zones; attraction is likely due to the higher food levels and/or increased cover found in these areas. Bottom slope, by affecting foraging efficiency in the productive littoral areas, might also affect the summer offshore distribution of fish within an accessible depth zone. It is suggested that the indirect effects of activity (specifically, the offshore movement of fish in summer) can be equally or even more important to the production of fish than is the direct use of energy for activity. higher food levels and/or increased cover found in these areas. Bottom slope, by affecting foraging efficiency in the productive littoral areas, might also affect the summer offshore distribution of fish within an accessible depth zone. It is suggested that the indirect effects of activity (specifically, the offshore movement of fish in summer) can be equally or even more important to the production of fish than is the direct use of energy for activity. / Science, Faculty of / Zoology, Department of / Graduate

The purpose of this study was to describe the cardiovascular changes that occur when fish swim, and to determine some of the mechanisms by which these changes are regulated. Two levels of exercise were used: moderate and severe. Moderate exercise was induced by conditioning the fish to swim against a moderate water velocity (1.7 ft/sec) in a respirometer tube. The effects of severe exercise were studied by forcing the fish to swim by chasing it. Changes in blood pressures in the ventral aorta, dorsal aorta, and sub-intestinal vein as well as changes in heart rate and breathing rate during swimming activity in rainbow trout were measured. Blood pressures both afferent and efferent to the gills increased during moderate swimming and then returned to pre-exercise levels within 30 min. Dorsal aortic blood pressure tended to increase during severe exercise, and tended to decrease lower than pre-exercise levels after severe exercise. The increases in blood pressure during swimming may be due in part to the interaction of circulating catecholamines with ∝-adrenergic receptors and to an increase in cardiac output. Venous blood pressure was characterized by periodic increases during moderate swimming. The pressure changes were not in phase with body movements. Heart rate increased about 15% during both moderate and severe exercise and then gradually returned to normal. The increase in heart rate was aneural in origin. Breathing rate increased about 30% during moderate exercise and about 60% during severe exercise. It took about 10 minutes to return to pre-exercise levels after moderate exercise, and about 60 min after severe exercise. Changes in partial pressure of oxygen and carbon dioxide in blood and water, afferent and efferent to the gills of rainbow trout, were determined before, during and after moderate swimming activity. Neither blood nor water PO₂ afferent or efferent to the gills changed markedly during or after exercise. Arterial blood was always greater than 95% saturated with oxygen. Venous blood was 38% saturated with oxygen, falling to a minimum of 29% during exercise. Arterial blood PCO₂ was 2.3 mm Hg. Venous blood PCO₂ increased from 5.7 mm Hg to 8.0 mm Hg during exercise and remained elevated throughout the recovery period. Cardiac output, stroke volume, ventilation volume, and the volume of water pumped par breath all increased by a factor of between 4 and 5 during moderate exercise. All tended to remain elevated from 10 to 30 minutes after exercise and then, gradually decreased to pre-exercise levels. From the above data it was possible to analyse the effects of exercise on the gas exchange, process. The analysis included calculating effectiveness (the ratio of actual gas transfer to the maximum rate of gas transfer possible expressed as a percentage) and the transfer factor (the actual rate of gas transfer ÷mean partial pressure gradient between the blood and the water). The transfer factor for oxygen increased almost 5 fold during exercise indicating that there was an increase in effective exchange area, a decrease in diffusion distance, an increase in diffusion coefficient, or a combination of these factors. The relative volume of blood in various tissues before and after severe swimming activity was estimated by injecting a small amount of radioiodinated serum albumin into the vascular compartment. There were no major changes in the distribution of blood in trout, after 5 or 15 minutes severe exercise. In both resting and exercised fish the ratio of blood, volume in the red muscle to that in white muscle was about 3. In summary, the compensatory changes which occur when rainbow trout swim, are primarily those which increase the flow of blood and water across the respiratory interface in order to maintain the arterial blood saturated with oxygen. The increase in blood flow also enables the fish to deliver more oxygen to its tissues. / Science, Faculty of / Zoology, Department of / Graduate

A study of factors affecting gas exchange at the gills of rainbow trout during hypoxia was made. Techniques for implanting cannulae in the buccal and opercular chambers, the dorsal aorta, and the ventral aorta are described. The responses of afferent and efferent blood and water pressures, Po₂, PCo₂, pH, and the hematocrit of efferent blood were made while the unanaes thetized free swimming trout was in a sealed respirometer. The fish were allowed to consume the oxygen in the respirometer to produce conditions of hypoxia. Determination of oxygen uptake and a knowledge of the solubility of oxygen in blood and water allowed indirect estimation of ventilation volume, cardiac output and stroke volume of the heart. With this knowledge, inferences on the function of circulatory and respiratory mechanisms during hypoxia were drawn. The rainbow trout possesses a number of homeostatic mechanisms which augment oxygen uptake during hypoxia. It was found that the trout could maintain a fairly uniform oxygen uptake in environmental oxygen tensions as low as 30 to 50 mm Hg„ The major homeostatic responses to hypoxia affecting oxygen uptake were: an increase in ventilation volume, an increase in the functional capacity of the blood, and an apparent vascular shunting of blood closer to the surface of the respiratory epithelium. No significant increase in cardiac output was observed. Since there was a pronounced bradycardia with hypoxia the stroke volume was apparently increasing. The role of the bradycardia, which has usually been associated with a reduction in cardiac output, is not clear. Possible reasons and functions of the bradycardia are discussed. / Science, Faculty of / Zoology, Department of / Graduate

The purpose of this study was to examine the effects of exercise of short duration, and the effects of re-exercise on carbohydrate metabolism. I feel that the levels of severe exercise studied approximate the levels of severe exercise which a rainbow trout probably experiences in its natural environment. The level of blood lactate, blood hemoglobin, muscle lactate, muscle glycogen, and liver glycogen were determined in unanesthetized, intact, one and one-half year old rainbow trout acclimated to 10.5°C. Samples were taken immediately after exercise of 3 seconds to 5 minutes, after recovery of 3 minutes to 60 minutes, and after re-exercise of 3 seconds to 5 minutes. The results indicate that exercise of even the shortest duration studied causes an immediate increase in the level of blood lactate, muscle lactate, and blood hemoglobin. Exercise also causes an immediate decrease in muscle glycogen, but does not cause a change in the level of liver glycogen. Changes during the 60 minute recovery period are slight. In general, the effects of re-exercise after a 60 minute recovery period are additive. A correlation analysis between muscle glycogen and muscle lactate indicates that there is a source of muscle lactate other than muscle glycogen at exercise levels of long duration. The source of this muscle lactate does not appear to come from liver glycogen. The energy may be supplied by catabolism of protein or lipid, or by absorption of foodstuffs from the gut. This study provides evidence that rainbow trout are not well adapted for recovery from severe exercise of short duration. / Medicine, Faculty of / Cellular and Physiological Sciences, Department of / Graduate

The predatory behaviour of rainbow trout was studied to identify some of the major factors that influence their response to prey. Two benthic-living amphipods Cranqonyx sp. and Hyalella sp. were selected as representative prey. In some experiments, artificial food was utilized. Rainbow trout adopt a searching position some 10 to 15 cm from a substrate and locate food visually. As a result, they can detect only organisms that are exposed. In the presence of a complex substrate, trout were able to recognize moving prey with greater success (74%) than stationary targets (39%) with the same visual characteristics. The distance from which trout will react to food was shown to be dependent upon the size, inherent contrast and activity of the object as well as the ambient illumination, turbidity of the water and complexity of the substrate. After 6 to 7 days of experience with a new but palatable food, trout can increase their reactive distance through learning. A general system of equations was developed to describe the effect of each of these parameters on reactive distance. On the average, trout successfully capture 82% of the prey they attack. In the laboratory, the rate of capture reached a maximum level when the density of prey was increased to 240 animals per sq. m. Irrespective of the abundance of food, however, decreasing hunger motivation was found to depress the predator's rate of capture as was the presence of a substrate in which the prey could conceal themselves. The effect of water temperature on the vertical and horizontal movements of Cranqonyx and Hyalella was also examined. The vertical activity of both prey increased exponentially with a rise in temperature. In contrast, 10° C. was suggested to be the optimum temperature for the movement of exposed animals. A general simulation model was developed to test the hypothesis that the selective exploitation of 4 major invertebrate groups in Marion Lake, by trout, occurs at the perceptual level. The model considered the predatory behaviour of the fish as well as the density and physical characteristics of their prey, and was able to predict with some accuracy the occurrence of different foods in trout stomachs. The model was also able to account for the size -selective exploitation of Cranqonyx and Hyalella, the seasonal changes in the vulnerability of these species, and the fact that the less numerous Cranqonyx was captured just as frequently as Hyalella. Trout require a threshold rate of capture (about 2 captures / min.) to maintain a specific pattern of search. If they do not attain this threshold they will switch their attention to other hunting patterns. As a result, the population should converge, temporarily, into areas in which food is relatively more abundant. Since trout can also learn to increase their responsiveness to prey, both of these characteristics would improve their hunting efficiency. The results of this study indicate that visual predators will discover and, subsequently may exploit, large prey that tend to be exposed and active, with greater success than smaller, less active or less conspicuous species. Moreover, if a visual predator maintains a searching position, it may not detect benthic-living food organisms less than a critical size. The significance of these conclusions is discussed. / Science, Faculty of / Zoology, Department of / Graduate

The effect of temperature on the oxidative-decarboxylation of isocitrate by the soluble NADP+-linked isocitrate dehydrogenase (NADP-IDH, EC 1.1.1.42) from rainbow trout (Salmo gairdnerii) liver has been investigated. A particular interest was given those properties of the enzyme which might help to explain the temperature-independent function of the Krebs cycle and the large increase in fatty acid synthesis known to occur during low temperature acclimation. Within the thermal range experienced by rainbow trout, control of catalysis by this enzyme is temperature-independent. Acclimation to an altered thermal regime is accompanied by an increase in the relative proportion of the slowest migrating isozyme of liver NADP-IDH on starch-gel electrophoresis. These cold- and warm-isozyme variants display different and adaptive Km-temperature relationships, and allow for temperature-independent modulation of enzyme activity through the entire thermal range this species is likely to encounter in nature. Other trout species, including the brook (Salvelinus frontinalis), lake (Salmo namaycush) and their hybrid, the splake trout, were investigated for similar responses. The elaboration of enzyme variants in brook and splake trout are complexly regulated by temperature changes, but the lake trout genome contains a single gene coding for liver NADP-IDH which is not affected by temperature. Catalysis by the trout liver enzyme is modulated not only by temperature, but also ADP and ɣ-KGA. Both of these metabolites alter the Km of DL-isocitrate; at physiological ADP concentrations, the Km is reduced as it is with ɣ-KGA below 0.05 mM, but at higher ɣ-KGA concentrations it is markedly increased. These two controls suggest this enzyme may be important for the Krebs cycle oxidation of isocitrate. The availability of a purified NADP-IDH from pig heart allowed a study of the kinetic properties of homologous enzymes from both a poikilotherm and a homeotherm. Even though the molecular weights, Ea values, substrate, cofactor and inhibitor specificities are similar, subtle changes in enzyme structure and/or conformation as identified by electrophoresis, may result in the observed differences in temperature characteristics. These apparent adaptive enzyme responses are of importance to the rainbow trout which lives in a fluctuating thermal regime, but not the pig which does not experience these changes. In vivo, the response of enzymes to temperature fluctuations may be quite different to those seen in vitro. The locus(i) coding for rainbow trout liver NADP-IDH was found to contain a large amount of heterogeneity; in fact, seven distinct phenotypes were found to coexist in one hatchery population. The kinetics of three of these phenotypes were investigated and it was found that by increasing the number of slow moving isozymes, an increase in Km(DL-isocit) at high assay temperatures occurs. This suggests that irrespective of changes in the cellular milieu, isozymal content can determine the Km-temperature response. The data from this study suggest that changes in enzyme-substrate affinity with temperature as a result of either the temperature directed production of enzyme variants and/or their genetic expression, are important in controlling the catalytic activity of NADP-IDH from the eurythermal rainbow trout. Also, unlike the mammalian enzyme, the trout liver enzyme may be important in both fatty acid synthesis and the Krebs cycle oxidation of isocitrate. / Science, Faculty of / Zoology, Department of / Graduate

The permeability of the teleost branchial exchanger to oxygen and carbon dioxide is apparently enhanced during exercise by increased blood perfusion of thin walled high surface area pathways in the gills, the secondary lamellae. However this augmented permeability to respiratory gases may well be accompanied by unfavourable elevations of water and electrolyte fluxes between internal and external environments. The object of the present study was to investigate the effect of imposed swimming activity on sodium and water regulation in the fresh water adapted rainbow trout, Salmo gairdneri. Radiotracer methods were used to measure unidirectional components of branchial sodium exchange in fish at rest, during one hour of swimming, and during one hour of recovery from this exercise condition. Sodium fluxes during extended exercise (up to 8 hours) were quantified by similar techniques in a second series of experiments. These long term swimming trials provided flux rate data.at a wide range of external sodium concentrations; analysis of these results helped to elucidate the relative importance of different mechanisms of branchial sodium transfer in the rainbow trout. Finally, determinations of urine flows and body weight changes under controlled exercise conditions in a swimming respirometer permitted an analysis of water regulation and direct measurement of renal electrolyte losses during activity. The sodium uptake system of Salmo gairdneri in the present study had an extremely high affinity for the ion (half saturation concentration = .014 mEq Na+/L). Both unidirectional flux rates at the gills of rainbow trout were greater than those reported for any other fresh water teleost of comparable size, despite external sodium levels much lower than those used by other workers. The presence of an exchange diffusion mechanism for sodium in the trout gill was strongly indicated but not confirmed.. Branchial transport of the electrolyte was tentatively divided into a large exchange diffusion component, and smaller active influx and simple diffusional efflux elements. In resting animals, branchial sodium influx and efflux rates were equal. However short term activity (1 hour) was associated with a 70% increase in efflux of sodium across the gills, creating a net sodium deficit. This effect was quickly reversed (within 5 minutes) upon the termination of swimming. As influx did not vary, these phenomena probably represented changes in the simple diffusional efflux component without disturbance of carrier mediated sodium transport mechanisms. Branchial water entry was also greatly elevated at the start of exercise. These results were interpreted in terms of augmented passive movements of sodium and water caused by increased blood perfusion of the high permeability respiratory pathways of the gills during swimming. The extended exercise experiments revealed that the high sodium efflux rate of the first hour of activity diminished, during the second hour, and had returned to resting levels by the third and subsequent hours of swimming; influx again remained unchanged. The initial high branchial water entry was also apparently curtailed, but over a shorter time interval (15 - 60 minutes after the onset of activity). These reductions in branchial permeability to water and sodium were interpreted as compensations to decrease the osmotic penalty of exercise. As water entry through the gills declined, urinary output was augmented; an elevated renal sodium loss accompanied the diuresis. However sodium efflux through the kidney remained small relative to the efflux of this electrolyte through the gills. A final equilibrium between branchial entry and renal excretion of water was attained, but at a higher turnover rate than during rest. Before this balance, however, urinary elimination had over-compensated for the initial water gain. The resulting net water deficit reduced the blood space below resting volume, causing a slight increase in plasma sodium levels despite enhanced branchial and renal losses of the ion. An ischemia of "white" muscle may also have accompanied the haemoconcentration. In summary, the results indicated that an initial osmoregulatory disturbance was associated with a redistribution of blood flow through the gills during swimming, but that both branchial hydromineral permeability and the functioning of other systems could be modified by compensations necessary to maintain sodium and water balance during extended exercise. / Science, Faculty of / Zoology, Department of / Graduate