In May, adult Yellowstone cutthroat trout (Salmo clarkii lewisii) moved from Kiakho Lake into its outlet to spawn. Upon emergence from the gravel, most young fry descended at night from the fast flowing, gravel bottom areas into slow flowing, mud and sand bottom regions where they spent the summer. The majority of fry over-wintered in the creek before ascending to the lake. The research was conducted in the summers of 1959 and 1960. It had two objectives: (1) to describe fry distribution and (2) to examine some characteristic fry "behavior" including movement. Traps and an experimental trough were operated. Behavior was observed, movements of marked fish were studied, and fry distribution was determined. Temperature, barometric pressure, water level, and light were recorded. Darkness apparently influenced the downstream movement of recently emerged fry for 90% of it occurred at night. A slow current apparently greatly slowed the rate of descent. The gradual descent of these fry in the "sluggish" Beaver Meadow during July evidently produced the late July uniform Beaver Meadow fry density. Long distance upstream and downstream movement of "healthy" fry in August was quite limited though short temporary movements of fry from their "home", may have been common. At least 60% of the fry held the same "home" for two weeks. Fry defended territories. The August 1960 Beaver Meadow fry population decrease was due to natural mortality. Month-old Beaver Meadow descending fry were characterized by small size and "physical weakness". In a week, the number of day versus night descenders was about equal, but within a 24 hour period, there was no correlation between the two. Bright moonlight appeared to depress night downstream movement, a fluctuating water level may have increased it, and a week long drop in creek temperature apparently depressed all downstream movement. Fry moving upstream were generally larger than average size fry. There was a moderate association between rising daily maximum water temperature over a period of several days and increased upstream movement. Fry in a trough ascended more at 20°C. than at 9°C. A week long drop in water temperature likely depressed movement. Because more than 80% of the movement occurred in the day, a certain minimum light intensity may be required before fry ascend much. The Kiakho outlet observations were compared to the findings of other researchers. Generally, stream dwelling Salmoninae appear to exhibit territorialism, homing, and limited movement,, Several other generalizations about stream dwelling trout, were suggested,, / Science, Faculty of / Zoology, Department of / Graduate

Tests showed that, in Kamloops trout, Salmo gairdneri kamloops Jordan, egg number produced at spawning is dependent on egg size for fish of a given length. Mean egg size in trout from Paul lake was considerably smaller than that of Penask lake trout. The difference is associated with natural selection pressures of low and high population densities, respectively. Egg number was inversely correlated with egg size in all samples. Pew differences were found between age classes within the natural populations. Starvation during early ovarian maturation produced a reduction in numbers of eggs shed at spawning. Experimental starvation treatments of hatchery trout indicated that increasing degrees of starvation resulted in commensurately fewer eggs reaching maturity. Pull diet conditions for the remainder of maturation resulted in no compensatory change in egg size. Maturing ovaries and stomach content volumes from trout reared naturally indicated a positive correlation between reduced food intake and increased follicular degeneration. Variations in egg number are therefore attributable to differences in egg size, fish size and adequacy of food supply. Egg size is apparently genetically controlled. Direct reduction of fecundity by starvation has an adaptive value in partially limiting population density. / Science, Faculty of / Zoology, Department of / Graduate

The oxygen consumptions of gill and kidney tissues of the cutthroat trout (Salmo clarki clarki) were determined by the direct method of Warburg. The respiration rates of tissues from fish ranging from 10 to 100 gm. were examined in relation to body weight. A decline in weight specific oxygen consumption for both tissues was observed. On a log-log plot, the regression coefficient for kidney was -.148 while that for gill was -.139. The decline did not support the .73 rule (Brody, 1945) at the level of tissue respiration. The oxygen consumptions of kidney and gill tissues were examined during a 168 hour period after transfer of the fish from fresh water to 65% standard sea water. A sharp initial rise in QO₂ of kidney tissue was noted during the first 48 hours after transfer, reaching a maximum at 20 hours. The kidney tissue respiration during the remainder of the experimental period remained significantly higher than the parallel control level. The gill tissue respiration declined rapidly during the first 10 hours after transfer and remained significantly below the control level during the whole experimental period. The results are discussed in relation to recent observations of Holmes, Chester Jones, Phillips, and Sexton, concerning possible hormonal regulation of salt-electrolyte and water metabolism by vasopressin and adrenocortical steroids in euryhaline species of salmonids. / Science, Faculty of / Zoology, Department of / Graduate

Although empirical evidence suggests that interactions occur between serotonin (5- HT) and the hypothalamic-pituitary-interrenal (HPI) axis teleost fish, the mechanisms of serotonergic regulation of the HPI axis require elucidation. The hypothesis that 5-HT regulates the stress response in rainbow trout (Oncorhynchus mykiss) by acting at multiple levels in the HPI axis through tissue-specific 5-HT receptor subtypes was examined. Messenger RNA for 5-HT1A, 5-HT2 and 5-HT4 receptor subtypes was expressed in all HPI axis tissues. Administration of 5-HT in vivo in cannulated trout caused significant increases in plasma cortisol and glucose concentrations. In vitro head kidney preparations revealed a stimulatory effect of 5- HT, acting through the 5-HT4 receptor, on cortisol production. Collectively, these data suggest that 5-HT plays a role in HPI axis activation in rainbow trout, and that at the head kidney level, these effects likely are mediated by the 5-HT4 receptor.

Rainbow trout {Oncorhynchus mykiss) and coho salmon (0. kisutch) produce males which mature at an abnormally early age. The objectives of this study were to critically describe the role of growth rate in early sexual maturation of male salmonids by monitoring growth rate and precocious sexual development in individually identified fish. Underyearling rainbow trout were individually identified using coded tags. These fish were reared at 9°C and 15°C and growth was monitored twice a month in both groups over a 9 month period starting January 24, 1989. The number of precocious males in the 9°C and 15°C groups were 11% and 18% respectively. Yearling coho salmon were similarly tagged, reared at ambient temperature, and monitored for growth over an 8 month period starting March 22nd, 1989. Ten percent of the coho salmon matured precociously. In both experiments there was a similar relationship between fast growth in early spring and precocious maturation. The growth rate of fish that matured declined in autumn relative to non-maturing individuals. Condition factor (length to weight relationship) was greater among those fish that matured precociously. Plasma growth hormone was monitored in the coho salmon. Most samples fell below the detection limits of the assay (1.5. to 3.0 ng/ml). A strategy to reduce the number of precocious males in cultured salmonids is suggested. / Land and Food Systems, Faculty of / Graduate

The fry of the very similar salmonids, coho salmon (Oncorhynchus kisutch) and steelhead trout (Salmo gairdnerii), live in very close association with each other during their first year of life in fresh water. The present study was designed to measure the effects of competition between these species. Populations of different densities of coho and steelhead fry in four identical artificial stream-channels were studied. Observations were made on survival, growth rates, and some aspects of behavior. Among the various groups of fry, survival was apparently dependent upon interspecific factors; the presence of another similar species had no observable effect. Low-density populations survived well, even when another species was present at a high-density. Survival of the fish at high-densities was always depressed, even when the companion species was present at low density. Steelhead fry demonstrated a faster initial growth rate than the coho, enabling them to exceed the coho in growth despite the latter’s earlier hatching and consequent initial size advantage. Growth rates were inversely related to density, both inter- and intraspecific effects being noticeable. The two species tend to be spatially segregated, coho occupying positions in the middle and upper layers of the streams, and steelhead remaining close to the bottom. This stratification was reflected in their feeding behavior and diet. Emigration activity occurred to a greater degree among the coho than the steelhead. Emigrants of both species were observed, to undergo substantial weight loss subsequent to their disappearance from the stream-channels. It was concluded that coho and steelhead fry live in close association with one another without experiencing extensive interspecific competition. This is because of segregation of the species by having differing habitats, feeding habits, growth and survival rates, and consequent population dynamics. / Science, Faculty of / Zoology, Department of / Graduate

Various aspects of rainbow trout (Salmo gairdneri) predation on migrating sockeye salmon (Oncorhynchus nerka) fry and rainbow trout eggs were studied during 1970-71 in specially-constructed artificial streams, and in the laboratory. Tests involving sockeye fry as prey were conducted near Babine Lake, British Columbia, while those using rainbow trout eggs were done near Abbotsford, British Columbia. Examination of the effects of physical factors such as water velocity, water turbidity, and light intensity on predation on migrating sockeye fry showed mortality to be inversely related to water velocity and water turbidity; inversely related to light intensity at low light levels but directly related at very low levels. Other stream tests showed mortality to be inversely related to the amount of exposure of predators to fry, before the beginning of a nightly fry migration. Exposing predators to abnormal light for varying periods of time, immediately prior to fry migration, reduced over-all mortality during fry migration. Mortality was not proportional to the length of exposure of predators to abnormal light. Fry experience with predators was shown to increase the ability of fry to escape or avoid predation on subsequent predator encounters. Additional experience served to further increase their ability to escape or avoid predators. Conclusions drawn from stream tests and a behavioral study are that experienced fry migrate in a manner rendering them less susceptible to predation and the migration pattern (compact and in mass) is influenced in part, or completely, by encounter and escape from predator-prey interactions experienced earlier. "Handling" or other fright-evoking stimuli appeared to have similar effects. Rainbow trout feeding on colored fish eggs indicated color preference patterns which are influenced by background coloration (color contrast between food and background), and light intensity. Preference was for colors showing the most contrast with the background at a particular light intensity. At low light levels, on a pale-blue background, preference was for lighter colors, while it was for darker colors at high light levels. Mortality differences increased proportionately with contrast between colors. Finally, trout displayed what appears to be a behavioral preference for red, and possibly blue, regardless of surrounding environmental conditions. In a food deprivation study rainbow trout displayed an S-shaped hunger response curve when fed on eggs. Indications were that rainbow trout will feed to gut capacity when given the opportunity. Finally, beyond an upper limit of food deprivation, the amount of food eaten by an individual remains fairly constant. / Science, Faculty of / Zoology, Department of / Graduate

Mitochondria were isolated from heart and mosaic muscle of rainbow trout (Salmo qairdneri R.). State 3 respiratory rates were determined at 5 and 15°C using pyruvate, malate, lactate, glutamate or acetyl—carnitine as substrate. The final three substrates were used to generate pH profiles. Pyruvate was oxidized at high rates in all cases, indicating good potential for aerobic carbohydrate metabolism. At 15°C, malate was an equally good substrate for heart mitochondria, while all substrates were oxidized at similar rates to pyruvate in muscle mitochondria. Maximal oxidation rates of heart mitochondria were greater than or equal to those of muscle. State 3 Q₁₀ for oxidation of most substrates in heart was approximately 2, except for malate which had a Q₁₀ of 3. Mitochondrial oxidation tended to be more sensitive to decreased temperature in muscle than in heart, particularly with respect to acetyl—carnitine and glutamate oxidation which in muscle had Q₁₀ values of 4 and 7, respectively. Based on RCR values at 5 and 15°C, there was no indication that membrane permeability to H⁺ ions was altered by a 10°C change in temperature in mitochondria from either tissue. At pH above 7.6 respiratory rates decreased with increasing pH. State 3 respiratory rate increased in heart mitochondria as pH decreased, below 7.6 while in muscle mitochondria, no such pH dependence was observed. RCR values were above 4 in all experiments except at high pH. Muscle mitochondria were the more sensitive to extreme pH with respect to RCR. Heart mitochondria had higher oxidative rates than those of muscle and were less sensitive to decreased temperature, in keeping with the greater oxidative demands of that tissue relative to mosaic muscle. Muscle mitochondria which typically face larger fluctuations in extramitochondrial pH in vivo than do those of heart, were less sensitive to pH in vitro. It was concluded that substrate utilization patterns and response to changes in temperature and extramitochondrial pH in the two mitochondrial populations was different and reflected both the intracellular environment of the mitochondria and the different needs of each tissue for aerobic energy supply. / Science, Faculty of / Zoology, Department of / Graduate

The response of rainbow trout (Salmo gairdneri) to lures was investigated in trolling experiments at Loon Lake, British Columbia. The "action" of a lure was found to be an important parameter in determining its efficiency: of four actions tested, the flatfish caught the greatest number of fish. Although the color of lure was not significant, red lures were more efficient than yellow, green, and blue, and more efficient than various color patterns of red and white. The presence of a dodger with lures did not affect their efficiency, but larger fish were caught. No size selection occurred with either colors or actions of lures. In laboratory feeding experiments using dyed trout eggs as food, red was selected first or second more often than yellow, green, or blue. The color of background against which the fish were fed, and individual differences among fish caused significant changes in the preference shown for various colors of food. Combining two colors also affected the selection intensity, depending upon the contrast between the two colors. Preferences for different colors of food were not influenced by the hunger level of the fish, measured in terms of the quantity of food in the fish's gut. In the course of the experiments it was incidentally observed: (1) that rainbow trout possess a striking ability to match the hue of their skin (mainly in the dorsal region) to that of the background in which they are kept; (Z) the color of background affects the activity level of rainbow trout: yellow produces the highest level of activity and green the lowest. / Science, Faculty of / Zoology, Department of / Graduate

Trout were introduced into a flow-through enclosure constructed in the headwaters of a small fishless stream to examine the effects of trout predation on the density, standing crop and production of lotic insect populations. Following the trout introduction, the density and standing crop of 3 of the 9 insect species examined decreased in the experimental stream study section (enclosure) while the density and standing crop of 2 insect species increased in the experimental stream section compared with the control stream section. Data on the food habits of the trout indicated that trout predation had reduced the density and standing crop of these insect populations in the experimental stream section. Competitive release was suggested as the reason for the increase in density and standing crop of the insect populations in the experimental stream section. The role of trout predation in structuring stream insect communities is briefly discussed. Production estimates of lotic species in the experimental stream section were not significantly different from those in the control section. Trout consumed only 0.4 times the mean standing crop or 9-10% of the production of prey species. However, trout were thought to be intensively grazing the available food supply. / Science, Faculty of / Zoology, Department of / Graduate