Stunting is widespread among brook trout Salvelinus fontinalis populations in high alpine lakes in the eastern Sierra Nevada, California. Due to their small size and poor condition, stunted brook trout are undesirable as sport fish. In the same area, a few lakes contain large brook trout. Population density was the primary difference between lakes with different sized fish. I hypothesized that in lakes with large fish the food ration per individual was sufficient and that in lakes with stunted fish the food ration was the limiting factor. I carried out removal experiments on eight brook trout populations to test the hypothesis (1) that fish size is inversely related to population density, and by that evaluate density reduction as a means of improving growth in stunted brook trout. I considered seven additional hypotheses regarding the relationships between brook trout population density and growth, fecundity, and recruitment: (2) growth response is proportional to density reduction; (3) growth response is inversely proportional to pre-reduction density; (4) growth responses of juvenile and senescent fish are less affected by density reductions than mature, reproductively active fish; (5) growth response to density reduction is inversely proportional to lake elevation; (6) fish size is proportional to angling pressure; (7) fecundity response is proportional to the reduction in population density; and (8) recruitment response is inversely related to density. I used gillnets to simultaneously remove part of the population and estimate population size through catch depletion methods that allow variable catchability. Catchability varied with lake size and with abundance, increasing as population abundance declined. Increased catchability can be explained by behavioral responses. I measured and aged 16000+ brook trout from 71 lakes, 9800+ from the eight experimental lakes. I validated annual structures on otoliths using a fluorochrome mark. For the experimental lakes, I back-calculated previous population sizes using estimates of number at age in 1989, catch at age in 1987-1988, and survival rates at age estimated from catch data collected in 1987-1989. I converted population estimates into density estimates of fish and biomass per lake surface area and volume. I tested hypothesis 1 by using survey data from 61 populations and by experimentally manipulating density in eight populations. The survey data suggested that size differences between populations of brook trout are a function of population density. Results from the eight removal experiments showed that fish size was inversely related to population density, though the increases in fish size were minor. The relationship between change in length and weight was roughly proportional to the change in density (hypothesis 2). Hypothesis 3 suggested differences in the severity of stunting in alpine lakes, and that the growth response of severely stunted populations would be more pronounced than the response of less stunted fish in lower density populations. The result was opposite; the growth response in lower density populations was greater than the response in higher density populations, suggesting that the growth response may have been proportional to the pre-reduction density. Hypothesis 4 suggested that the growth response for juvenile brook trout would be less than that for the pre-senescent adult population. The results refuted the juvenile portion of hypothesis 4: response for juveniles was greater than the response of the adults, perhaps because of greater recuperative abilities in young fish. The data supported the hypothesis that the growth response would be diminished in older fish. There was no relationship between elevation and growth response (hypothesis 5). Sport fishing had little effect on the growth of brook trout populations (hypothesis 6). Heavily fished populations were also stunted. Stunted brook trout had fecundities similar to non-stunted brook trout of the same size (hypothesis 7). Individual fecundity did increase in response to density reduction, but no more than would be expected from the increase in size. In several populations mean absolute fecundity decreased with age. Ovary weight was maintained by an apparent increase in mean egg size in older fish. The recruitment response varied between lakes (hypothesis 8). Recruitment did increase, likely in response to reduced cannibalism or competition, but I also found recruitment failure at the highest levels of density reduction. Strong cohorts were produced by increased juvenile survival rather than increased population fecundity, since population fecundity had decreased due to removal of most of the adult population. In one lake with almost no recruitment, densities remained low and fish weight doubled. For density reduction to be an effective means of increasing fish size, recruitment must be inhibited. / Science, Faculty of / Zoology, Department of / Graduate

Rainbow trout (Salmo gairdneri) from two wild stocks native to British Columbia, and a non-native domestic strain were reared under varying conditions to examine effects of growth rate and body size, genetic stock, and photoperiod on the incidence and timing of testis development. The ratio of gonad weight to body weight (Gonadosomatic index) was found to be useful for separating mature and immature male fish and for determining the onset of gonadal development. In Premier lake fish testis development began one year before the expected date of spawning. At this time, signs of maturation were evident primarily among males that reached a body weight of between ten and twenty grams, whereas most of the fish smaller than this "critical" size remained immature (i.e. no testis developmment). Apparently, this critical size must be reached by a certain time of the year. Thus, a time 'window' exists wherein fish achieving a certain size begin preparation for spawning the following year. Altering photoperiod regime during the time window had no effect on the incidence of sexual precociousness, but did delay spermatogenesis by an undetermined length of time. / Science, Faculty of / Zoology, Department of / Graduate

A deterministic simulation model is used to explore the relationship between juvenile pink, chum and coho salmon growth and size-related survival in the Fraser River estuary. Parameters most sensitive to change are identified and the results related to proposals for enhancement. These results suggest that increasing the initial size of enhancement pink and chum fry, relative to the size of wild fry, prior to seaward migration and releasing them early in the spring may increase their chances of survival. If increasing total (enhancement plus wild) fry density decreases fry growth rate, the presence of enhancement fry in the estuary could reduce the survival chances of wild fry. The decrease in wild stock survival may not be apparent from estimates of adult return for many years due to errors in measurement and to the effect on survival of environmental variability. The model can be used to suggest and evaluate enhancement proposals. Areas needing further research are also indicated. / Science, Faculty of / Zoology, Department of / Graduate

Highly unsaturated marine lipids are common ingredients in salmon diets, and they are prone to oxidative change. The present study was undertaken to examine the growth and health of coho salmon (Oncorhynchus kisutch) fed diets containing herring oil autoxidized to different degrees. The efficacy of dietary vitamin E in ameliorating any adverse effect on performance was investigated. Herring oil was oxidized to one of two levels (relative to a control) by aeration and mild heating (40 °C). Peroxide values and iodine numbers were recorded to monitor the extent of autoxidation. Depletion of dietary linolenic acid series fatty acids (n3FA), and the labile vitamins A, C, and E, provided further evidence of the progress of lipid oxidation. The mean initial body weight was 5.1 g/fish, and growth (weight and length) was measured at 3 or 6 week intervals for 28 weeks. Experimental diets contained 16.8% lipid, primarily as herring oil. One diet was made with corn oil replacing herring oil, and another contained a combination of low and highly oxidized oil. Vitamin E (as dl-ɑ-tocopheryl acetate) was added at either 30 IU/kg dry diet or 1000 IU/kg dry diet. At 23 weeks, 1/3 of the fish were vaccinated against vibriosis. At 28 weeks the fish were twice challenged with live Vibrio sp. Immunocompetence was estimated by mortality and by plasma agglutination. The inclusion of autoxidized herring oil reduced the nutritive value of the diets. The poorer growth and feed efficiency of fish fed diets containing oxidized oils appears to have resulted from a combination of appetite suppression and nutrient deficiency. The relative importance of these factors in influencing growth and feed efficiency depended upon the extent of the oxidation, with appetite suppression being most apparent in fish fed diets containing moderately oxidized oil. Dietary supplementation with a high level of vitamin E had no ameliorating effect on growth or feed efficiency. Health and immunocompetence were not impaired by the presence of oxidized dietary lipid, or improved by the addition of vitamin E. / Land and Food Systems, Faculty of / Graduate

This study provides comparative data on the effects of temperature on zygote and alevin survival, rate of development to 50 percent hatching and emergence, and alevin and fry size for five species of Pacific salmon (Oncorhynchus) and for rainbow trout (Salmo gairdneri). Fertilized eggs from each species were incubated in controlled temperature baths at five constant temperatures (2°, 5°, 8°, 11° and 14°C). At 2°C, survival for coho salmon zygotes was high (85 percent), moderate for sockeye salmon zygotes (40 percent) and low for chinook salmon zygotes (4 percent). No pink and chum salmon or rainbow trout zygotes survived at 2°C. However, at 14°C survival for chum salmon and rainbow trout zygotes was high (67 and 85 percent), moderate for chinook and pink salmon zygotes (50 and 55 percent) and low for sockeye salmon zygotes (10 percent). No coho salmon zygotes survived at 14°C. The same general pattern for temperature and survival holds for alevins. These data suggest that coho and sockeye salmon are adapted to lower incubation temperatures than the other species. All six species showed an inverse relationship between temperature and incubation time to 50 percent hatching and emergence. The data were analysed using linear regression but, even after a series of transformations, the relationship between temperature and development time remained curvilinear. The only exceptions were for chum salmon at hatching and pink salmon at emergence. Incubation temperature also influences both alevin and fry size. In general, low incubation temperatures produce larger alevins and fry than high incubation temperatures. In addition to data on constant incubation temperatures, the effects of varying temperature regimes on the survival, rate of development and size of coho salmon and rainbow trout alevins and fry were also documented. Fertilized eggs from coho salmon and rainbow trout were incubated at two varying temperature regimes. The varying temperature regimes either gradually increased from 5° to 14°C (the spring regime) or gradually decreased from 14° to 5°C (the fall regime). The increasing temperature regime produces higher survival in rainbow trout zygotes and alevins than the decreasing temperature regime. However, in coho salmon there was no clear difference in zygote and alevin survival with either regime. The rate of development to hatching for zygotes incubated at either varying temperature regime was similar within a species because of similar mean incubation temperatures between regimes. But, the rate of development to emergence for alevins incubated at either varying temperature regime was different because of different mean temperatures between regimes. The linear regressions to hatching and emergence for coho salmon and rainbow trout were used to predict rates of development for zygotes and alevins incubated with each varying temperature regime. The actual and predicted rates of development to hatching and emergence are similar within a species. Varying temperature regimes also affect both alevin and fry size. The decreasing temperature regime produces larger alevins and fry in coho salmon and rainbow trout than the increasing temperature regime. / Science, Faculty of / Zoology, Department of / Graduate

A feeding experiment was designed to examine how fish growth rates are affected by the size abundance of pelagic zooplankton. Juvenile chinook salmon, Oncorhynchus tshawytscha , were raised in 90 m³ mesh enclosures in Saanich Inlet, B.C. The enclosures permitted ample water and zooplankton circulation while retaining 5-6 gram juvenile salmon. The enclosed fish grew at an average rate of 1.8% wet body weight/day for a six week experimental period. Weekly growth rates ranged from 3.9%/day while food was abundant, to -0.5%/day when food was scarce. Several analytical methods were used to establish a relationship between fish gr.owth and the size and abundance of zooplankton in the enclosures. There is a strong relationship between the fish growth rates and the abundance of 1.4-4.5mm prey. Rates of successful search vary directly with the size and inherent contrast of a prey item. A minimum rate of successful search of 2.0m³/hour was estimated from a functional response curve for salmon feeding on 1.4-4.5mm zooplankton. This value is discussed in relation to a salmonids physical capabilities and results from previous field studies and tank experiments. Daily growth increments on the otoliths of the enclosed fish were examined with respect to daily variations in water temperature and zooplankton abundance. Extremes in food abundance appear to have a significant and consistent effect on the spacing of the growth rings. However, water temperatures would have to be kept constant in order to establish any closer relationship between food abundance and otolith growth rings. / Science, Faculty of / Zoology, Department of / Graduate