<p> The aim of this research was to determine how freshwater fish respond to dietary lead (Pb) in their environment with a respect to both physiological and toxicological endpoints. Previous acute exposure studies have shown that waterborne Pb accumulates in the internal tissues, resulting in hematological alterations and disruptions in Na+, cr and Ca2+ ion-regulation, with waterborne Ca2+ being protective against Pb tissue burden. In comparison with other metals such as silver, zinc, cadmium and copper, very little is known about Pb toxicity via the trophic food chain. </p> <p> Using rainbow trout as the model freshwater fish species, it was discovered that dietary Pb accumulated mainly in the gastrointestinal tract, with the intestine and the stomach being suggested as the primary tissues involved in Pb toxicity. Mild physiological disruptions in terms of plasma Ca2+, Mg2+ and Na+ levels were evident. On a per fish weight basis, the bone accumulated the greatest Pb burden (38%) followed by the anterior intestine (19%) and white muscle (12%). The order of Pb accumulation reflected the exposure pathway of dietary Pb in the internal tissues after 42 days; anterior intestine> stomach> mid intestine> posterior intestine> bone> posterior kidney> anterior kidney> liver> spleen> gill> carcass> brain> white muscle (JJ.g Pb/g tissue wet weight). Despite this accumulation of Pb into the internal tissues, there were no effects on growth and survival rates, indicating that growth is not a sensitive indicator of dietary Pb toxicity in fish. Elevated dietary Ca2+ levels had an overall effect in reducing dietary Pb burdens in the whole body and most of the internal tissues analysed. The red blood cells (RBC) accumulated 99% of the Pb in the blood, with less than 1% in the plasma. The enzyme 8-aminolevulinic acid dehydratase (ALAD), important in hemoglobin synthesis was significantly inhibited by the end of the experiment in fish exposed to high concentrations of dietary Pb. In contrast to waterborne Pb studies, ALAD was not a sensitive biomarker of dietary Pb toxicity. </p> <p> Overall, this study has shown the mild physiological and toxicological disturbances of dietary Ph exposure to juvenile rainbow trout. It encourages studies on transport mechanisms at the intestine and in the blood of fish exposed to dietary Pb. It is the hope that the work from this thesis will be used in risk assessments and environmental policies that mitigate the toxic effects of dietary Pb in the aquatic environment. </p> / Thesis / Master of Science (MSc)

Freshwater rainbow trout were exposed to 9.2 µg/L total Ag (as AgNO3, a level approximately equal to the 168 h LC50) for 144 h to clarify the toxic mechanism of silver in freshwater teleosts. It was found that silver inhibits active Na+ and Cl- uptake at the gills, resulting in a net loss of both ions from the fish and creating a metabolic acidosis. This leads to a classic stress response (mobilization of cortisol and glucose into the blood plasma), and hyperventilation as a respiratory response to decreased blood pH. Plasma ammonia levels rise without any decrease in ammonia excretion; ammonia excretion later increases. This suggests that the increased plasma levels are due to increased metabolic production. Increased [H+] (decreased pH) results in excess H+ ions in the internal fluids, which are either complexed with ammonia to form NH4+ or are buffered in muscle tissue. The latter results in increased movement of K+ ions into the plasma, which are then excreted at the gills, preventing hyperkalemia. In the end, freshwater teleosts probably die from iono-and osmo-regulatory failure and associated cardiovascular collapse. Seawater teleosts (rainbow trout, tidepool sculpins, English sole, and plainfin midshipmen) and elasmobranchs (Pacific spiny dogfish and long nose skate) were exposed to constant concentrations on total Ag (as AgNO3) ranging from 1.5 to 50.0 µg/L for periods of up to 21 d at salinities of 18 ppt or 30 ppt. These exposure levels are well below those causing acute toxicity in seawater. Silver appears to enter marine teleosts and marine elasmobranchs differently. Seawater teleosts drink the seawater, so the intestines are a major site of silver uptake, along with the gills. Since marine elasmobranchs do not drink, the gills appear to be the sole site of silver uptake from the water. As in freshwater, the liver is the main site for silver accumulation in all marine fish studied. Despite similar terminal liver silver concentrations, marine elasmobranchs have a higher rate of silver accumulation since the livers in elasmobranchs are 10-20 fold larger than in teleosts. Both environmental salinity and exposure concentration play direct roles in determining silver bioaccumulation in marine teleosts. Increasing salinity alters the speciation of silver in the water, which decreases the amount of silver able to enter the fish. Increased silver concentrations mean more silver is available to enter the fish and subsequently cause sublethal toxic effects. Oxygen consumption decreased during the first 7 d of chronic exposure to sublethal silver levels in marine teleosts, with the decrease being more pronounced at higher (still sublethal) silver levels. Ammonia excretion, unaltered during acute exposure (48 h) to high silver levels (250 µg/L), was decreased during the first 7 d of exposure to sublethal silver levels (14.5-50.0 µg/L). This suggests that silver interferes with energy demanding processes such as protein synthesis or iono-regulation. Activity levels of the main enzyme involved in iono-regulation, namely Na+/K+ -ATPase, was affected differently in different fish. In a marine teleost that lives solely in seawater (plainfin midshipmen), silver inhibited the gill ATPase activity after 7 d of exposure, with the inhibition being more effective at higher silver levels. In the tidepool sculpin, a truly euryhaline species, gill ATPase activity increased as the silver levels increased, the latter probably representing a compensatory strategy. Similarly, intestinal ATPase activity was unchanged in the midshipmen, but was increased in the sculpins. Drinking rate in tidepool sculpins, which is involved with both iono-and osmo-regulation, was unaffected by salinity, but was decreased in fish exposed to silver for 8 d. Overall, Ag is far less toxic in seawater than in freshwater, but the mechanisms of toxicity are similar. In both waters, Ag interferes with iono- and osmo-regulation. In seawater, Ag exhibits a significant potential for bioaccumulation and interference with physiological processes during long term low level exposures of marine fish, especially at lower salinity levels. / Thesis / Master of Science (MSc)

In aquatic environments Cu is both a vital nutrient and an important toxicant. Consequently fish require Cu as a micronutrient and can obtain this metal from either water or their diet. Inadequate intake of Cu is associated with reduced growth and development, while decreased growth rates, mortality and reduced swimming capacity have been reported in fish when Cu accumulates in excess of cellular needs. Characterization of Cu uptake is therefore critical in understanding the dynamics that govern toxicity and the risks associated with exposure to an aquatic contaminant. While mechanisms of waterborne uptake and toxicity are well understood, far less is known about gastrointestinal Cu uptake in fish. In vivo and in vitro techniques were therefore used in this study to investigate dietary Cu uptake in freshwater rainbow trout. The mid and posterior regions of the intestine emerged as important sites for Cu absorption in trout, while the role of the stomach and anterior intestine in Cu absorption requires further investigation. The intestinal uptake route was kinetically characterized as a low affinity absorption pathway as compared to the branchial route. Cu uptake appeared to occur via a hypoxia-resistant, carrier-mediated, saturable process which could be fueled by Cu(II)^2+ at concentrations typically found in the fluid phase of chyme in the trout intestine. Experimental manipulation of mucosal NaCl levels stimulated Cu uptake, Na2SO4 had an identical effect, implicating Na rather than the anion. These responses were unrelated to solvent drag, osmotic pressure or changes in TEP. The presence of excess luminal Ag and L-histidine stimulated Cu and Na uptake indicating that a portion of Cu transport was mediated by a Na-Cu co-transport system. Partial inhibition of Cu and Na uptake by phenamil and hypercapnia stimulated Na and Cu transport suggest Cu entry could also occur via the apical Na channel. The Na-dependent mechanism thus either involves more than one component or a unique Na-Cu co-transport mechanism with these combined characteristics mediates part of Cu uptake. Cu uptake was sensitive to pH and competed by Fe and Zn implicating DMT1 in the transport of Cu in the trout intestine. These factors had no effect on Na uptake, leading to the identification of a Na-independent mechanism for Cu uptake in the trout intestine. While the Na dependent nature of Cu uptake and Ag stimulated Cu transport argue against a role for Ctrl in this process, Cu transport characteristics identified in this study compare well with a recently identified Cu transporter in Ctr1 deficient mouse embryonic cells, indicating the existence of a similar transport mechanism in the trout intestine. / Thesis / Master of Science (MSc)

Relative to other metals, little is known about lead toxicity in fish. The use of predictive models such as the biotic ligand model (BLM) has been limited, a situation that is at least partially due to the lack of understanding of lead's acute toxic mechanism and characterization of key binding sites involved in this toxicity. Using the rainbow trout as a model species, the acute toxic mechanism for lead was found to be ionoregulatory disruption. While having no apparent respiratory or acid/base effects, Pb exposure resulted in significant ionoregulatory impacts that affected Ca2+ homeostasis, as well as Na+ and Cl- balance. Active Ca2+ uptake by the gills obeyed typical Michaelis-Menten kinetics, and Pb interacted in a competitive fashion with the uptake process. Exposure to increasing waterborne Pb concentrations resulted in significant increases in Km value while Jmax showed little or no change. A slower, non-competitive interaction occurred after prolonged Pb-exposure, evidenced by a significant reduction of high-affinity Ca2+ -ATPase activity that correlated well with branchial Pb accumulation. Conversely, calcium had a protective effect against branchial Pb accumulation, this relationship being predominately competitive in nature. Voltage-independent calcium channel blockers La3+, Cd, and Zn significantly reduced gill Pb burden while the voltage-dependent, L-type calcium channel blockers, nifedipine and verapamil, did not, suggesting Pb enters fish by a similar mechanism to that of Ca2+. Stimulated stanniocalcin release by CaCl2 injection also significantly reduced branchial Pb accumulation. Based on the evidence presented in this thesis, it is apparent that acute Pb toxicity occurs by ionoregulatory disruption. It is likely that Pb shares a similar uptake pathway as that for Ca2+ and that resulting accumulation results in disruption of Ca2+ influx as well as Na+ and Cl- balance. This study has provided data essential to the characterization of key binding sites involved in Pb toxicity, and ultimately, validates the development and application of predictive models such as the BLM. / Thesis / Master of Science (MSc)

This thesis is missing pages 87, 172 and 255. No other copies of the thesis have these pages. -Digitization Centre / This thesis examined the effects of exhaustive exercise on acid-base and metabolite status in the intracellular and extracellular compartments of two very different fish species: the active, pelagic rainbow trout, and the sluggish, benthic starry flounder. In both species, exhaustive exercise resulted in an acidosis in the extracellular compartment of mixed respiratory and metabolic origin. Despite the reduction in pHe, red blood cell pHi was well regulated, though more precisely in trout than in flounder. Catecholamines were mobilized into the blood after exercise in trout but not in flounder. Circulating catecholamines may play an important role in regulating red blood cell (RBC) pHi in trout after exercise. In trout, lactate appeared in the blood in excess of H+ ; the reverse pattern was observed in flounder. H+ appearance was similar in both species. Differential release of lactate from the muscle mass was apparently responsible for this discrepancy. After exhaustive exercise, both trout and flounder experienced a severe intracellular acidosis in the white muscle, as measured by 14c-DMO (5,5-dimethyl -2,4-oxazolidinenione) distribution. H+ and lactate were not produced in equimolar quantities, with H+ produced in excess of lactate. Muscle lactate and H+ production was about 3-fold lower in flounder than in trout. The muscle intracellular acid-base disturbance was corrected more rapidly in flounder (4-8h) than in trout (8-12h). In flounder, this occurred prior to , but in trout after , correction of the extracellular acidosis. In flounder, a more rapid correction of muscle metabolite status was associated with the more rapid correction of the intracellular acidosis. After exercise there was a reduction in the whole body extracellular fluid volume and expansion of the intracellular fluid volume, largely reflecting changes within the muscle. This fluid shift resulted in a general hemoconcentration. Exercise led to a transient increase in net H+ excretion in both trout and flounder. Negligible amounts of lactate were transferred to the water. In flounder, about 20% of the total H+ load produced passed through the extracellular space and was transiently stored in the water, which appeared to hasten correction of the intracellular acid-base disturbance. In contrast, in trout, a much smaller portion of the acid load (about 6%), though about the same absolute amount as in flounder, was transferred to the water. This appeared to expedite correction of the extracellular acidosis.The results of this thesis argue against a prominent role for the Cori cycle in the final disposition of the lactate burden produced during exercise. Instead, it is suggested that the bulk of the lactate was metabolized in situ, either by oxidation or glyconeogenesis. In flounder, this was almost the sole fate of lactate, as very little appeared in the blood space. In trout, a significant portion of the lactate was exported to the blood, which was taken up and metabolized by aerobic tissues. / Thesis / Doctor of Philosophy (PhD)

In commercial settings, broiler chickens and rainbow trout are housed in barren environments under high stocking densities, due to an emphasis on production efficiency. These monotonous housing conditions do not provide broilers or trout with the ability to perform functional, highly-motivated behaviors and increase their susceptibility to excessive anxiety and fear, resulting in negative affective states and poor animal welfare. Affective state (or emotional state) is a cumulative product of short-term life experiences, ranging from positive to negative. Because affective states are largely influenced by environmental condition, determining animal affective state can provide useful information on how to improve housing conditions in order to ensure positive experiences and good animal welfare. Cognitive processes are closely associated with affective state; a "cognitive bias" occurs when affective state influences aspects of cognition, such as judgement and attention. Animals in positive affective states make optimistically-biased decisions during ambiguous situations, judging the situation as if it will produce a positive outcome, and show less bias towards a perceived threat, responding in a less anxious and calm manner. Animals in negative affective states make pessimistically-biased decisions during ambiguous situations, judging the situation as if it will result in a negative outcome. Additionally, animals in negative affective states will bias their attention towards a perceived threat rather than alternative stimuli, responding in an anxious manner. Therefore, judgement and attention bias tests can be used to determine animal affective states. In Chapter 3, a judgement bias test was used to determine affective state of broiler chickens housed in either complex (perches, dust bath, pecking stones, and rotating enrichment objects) or barren (no enrichment) environments under either high or low stocking densities. Broilers housed in complex environments responded more optimistically during the judgement bias test than broilers from barren environments, indicating the former were in a positive affective state. Stocking density did not impact their responses in the judgement bias test, indicating that affective states were not impacted by that treatment. In Chapter 4, an attention bias test was used to determine level of anxiety and a tonic immobility test was used to determine fear in order to investigate affective state of broilers housed in the same conditions as described for Chapter 3. Broilers housed in complex environments were less anxious during the attention bias test than broilers from barren environments, indicating environmental complexity reduced anxiety in broilers. Stocking density did not impact anxiety. Broilers from high stocking density environments had shorter tonic immobility durations than broilers from low stocking density environments, suggesting the former were less fearful. Environmental complexity did not impact fearfulness. In Chapter 5, a judgement bias test was used to determine affective state of rainbow trout housed in either complex (shelter structure and artificial plants) or barren (no enrichment) tanks under either low or high stocking densities. Trout housed in high stocking density tanks responded optimistically during the judgement bias test, indicating they were in a more positive affective state compared to trout housed in low stocking density tanks. Environmental complexity did not impact their responses in the judgement bias test, indicating no effect of enrichments on affective states was found. These results indicate a beneficial relationship of a complex environment on broiler chicken affective state, observed through an optimistic judgement bias and reduced attention bias (anxiety) towards a perceived threat. Thus, providing a complex housing environment for broilers can improve their welfare and result in a positive affective state. Rainbow trout reared at the tested high density resulted in a positive affective state, although complexity did not benefit their welfare. Our results contribute much needed information on stocking densities to ensure fish welfare. Overall, environmental complexity, not stocking density, had a positive impact on broiler chicken affective states. Rainbow trout affective states were positively impacted by stocking density, but not environmental complexity. / Master of Science / Conventional housing of broiler chickens and rainbow trout (both raised for meat) causes concern for their welfare and affective states. Environmental conditions can greatly impact animals' affective states–their long-term emotional state, ranging from positive to negative. In barren environments at high stocking densities, broiler chickens and rainbow trout are prevented from showing normal behaviors and these conditions can compromise their affective state and welfare. By 'asking' chickens and trout whether the glass is half full or half empty, we can determine level of optimism or pessimism, and level of anxiety or calmness, therefore gaining a better understanding of their affective states. This can be done using a judgement bias test and attention bias test, where animal responses (optimism and anxiety) are recorded during ambiguous situations (judgement) and threatening situations (attention). Animals in positive affective states judge ambiguous situations optimistically (glass half full) and pay little attention towards perceived threats, while animals in negative affective states judge the same ambiguous situations pessimistically (glass half empty) and pay more attention towards perceived threats. In Chapter 3, responses to ambiguous situations were used to determine the affective state of broiler chickens housed in either enriched (perches, dust bath, pecking stones, rotating toys) or barren environments at either high or low stocking densities. Broiler chickens housed in enriched environments had an optimistic judgement bias of ambiguous situations (glass half full), suggesting they were in a more positive affective state compared to broilers housed in barren environments. Stocking density did not impact their level of optimism. In Chapter 4, responses to a perceived threat were used to determine level of anxiety and a tonic immobility test was used to determine fear of broilers housed under the same conditions as in Chapter 3. Broilers housed in enriched environments paid less attention to a perceived threat than broilers housed in barren environments, indicating the former were less anxious (glass half full) and in a positive affective state. Fear was not impacted by the tested enrichments, but birds kept under higher stocking densities did show reduced fear compared to birds in low-density environments. In Chapter 5, rainbow trout were housed in either enriched (shelter structure and artificial plants) or barren tanks at either high or low stocking densities. Affective state was evaluated through their responses to ambiguous situations. Trout housed in high stocking density environments had an optimistic judgement bias of ambiguous situations (glass half full), suggesting they were in a more positive affective state than trout housed in low stocking density environments. The enrichments did not impact their responses during the test, suggesting they did not impact fish optimism. These results indicate that an enriched environment improves broiler affective state and welfare compared to conventional housing conditions, the tested densities did not impact their welfare. Although an enriched environment did not positively impact responses of trout during ambiguous situations, our results show that housing rainbow trout in large groups results in a positive affective state and improved welfare status compared to housing trout in small groups. Overall, environmental enrichment, not stocking density, had a positive impact on broiler chicken affective states. Rainbow trout affective states were positively impacted by stocking density, but not environmental enrichment.

The activity of erythrocyte amino levulenic acid dehydratase (ALA-D) and liver and bone lead concentrations were measured in 141 wild rainbow trout from two highway-influenced and two pristine streams. A significant relationship between ALA-D activity and liver lead concentrations among streams (r = 0.157) was observed. However, this relationship was opposite of expected. Trout tissue lead and stream-water lead concentrations were lower than most concentrations observed for control laboratory trout. At these low tissue and water lead concentrations observed in the present study, ALA-D activity cannot be used to document exposure of fish to environmental lead. Other significant correlations with the activity of the enzyme included: trout length (r = -0.411); trout age (r = -0.385); and sediment lead (r = 0.093). Erythrocyte ALA-D activity significantly varied due to sampling period. However, reasons for this deviation cannot be explained from the present study. Multiple regression techniques revealed little concerning trout liver lead concentrations and ALA-D activity relationships. Like ALA-D activity, liver lead concentrations were deemed a poor indicator of organisms' exposure to environmental lead. Bone lead concentrations were the best indicator of environmental contamination. However, the best regression model, which regressed water lead on bone lead, explained only 20.6% of the variation in bone lead burden. In both roadside streams, water lead was positively correlated to turbidity and area precipitation. Water lead concentrations were also positively correlated to discharge in one roadside stream. / M.S.

Performance data for three rainbow trout (Oncorhynchus mykiss) strains (Erwin, Shasta, and Duncan River Kamloops) were collected to guide fish culture operations at White Sulphur Springs National Fish Hatchery (NFH). The performance of the strains was evaluated in terms of survival, growth, disease resistance, reproductive performance (number of ripe and culled females, spawning time, number of egg takes, number of eggs per female, egg size, and percent eye up), feed conversion, and feed costs, and was compared with data from Ennis NFH, MT, and two Arizona Game and Fish Department hatcheries. Prespawning survival rates were higher for Erwin (90%) and Shasta (95%) strains than for the Kamloops strain (<75%). The Shasta strain exhibited the lowest feed conversion ratio (mean=1.89) and feed costs ($0.15 per stockable individual and $0.92 per spawning individual) than Erwin (1.96, $0.16, $1.56) and Kamloops (1.66, $0.18, N/A) strains. The Shasta strain exhibited larger egg size (mean=15,967/1) than the Erwin strain (mean=21,900/1). Reproductive performance for the Kamloops strain was not evaluated, as the strain was not sexually mature at the close of the study. Vulnerability of Erwin strain rainbow trout to cold water disease, Cytophaga psychrophila, bacterial kidney disease, Renibacterium salmoninarum, and four other bacteria was observed, while Shasta and Kamloops strains were less vulnerable to disease. Based on findings of this study and on programmatic considerations, the Shasta strain will be the only one to remain in full production at White Sulphur Springs NFH. / Master of Science

The antioxidant properties of various blends of rosemary extract and tocopherols, either alone or with citric and ascorbic acid, were compared in filleted, headed and gutted, and minced rainbow trout (Oncorhynchus mykiss). The filleted and headed and gutted products were stored at -29 degrees C for twelve months, while the minced was stored at the same temperature for 24 weeks. Oxidation was measured by following changes in thiobarbituric reactive substances, conjugated diene hydroperoxides, texture, drip loss, pH, sensory evaluation, and gas chromatographic detection of aldehydes. Natural antioxidants, in particular those that contained citric and ascorbic acids, were effective at retarding the development of conjugated diene hydroperoxides and malonaldehyde (p<0.05). Furthermore, sensory evaluation indicated that treated samples were less oxidized. In subsequent studies, however, it was determined that the herbal flavor notes associated with natural antioxidants complicated the ability of the experienced panel to judge extent of oxidation. Also, using filleted samples, further consumer sensory panels indicated that after 12 months frozen storage, the treated and control samples were equally acceptable. For both the filleted and headed and gutted samples, no texture differences were noted over storage time or between control or variable treatments. When using natural antioxidant products, drip loss and pH were found unreliable predicators of oxidation or muscle degradation. / Master of Science

Aquaculture, the cultivation of aquatic organisms in a controlled environment, offers both economic and nutritional benefits to human society. As there is an increased demand to feed a growing human population, many wild-caught fisheries have struggled due to the overexploitation of resources. Currently, production relies heavily on wild-caught fish to produce fishmeal to feed farm-raised fish. The demand for alternative materials in fish feeds has grown rapidly as fishmeal resources have become limited. Antibiotic resistance emergence in aquaculture systems is another area of concern. Reducing antibiotic use via alternate prophylactic measures to increase host health is an essential area of research; modulation of the host intestinal bacterial community via prebiotics is one possibility. Prebiotics refer to non-digestible food ingredients that are thought to stimulate the growth of beneficial bacteria, consequently benefiting host health by indirectly reducing the possibility of bacterial pathogen proliferation. This occurs through various measures such as competition for space and resources. The intestinal bacterial community has a significant impact on a variety of host factors that include host development, physiology, immunity, and nutrient acquisition. In turn, there are multiple factors impacting the bacterial community, including the presence of pathogens and/or antibiotics, environmental conditions, host genetics, and the diet consumed. To promote environmental sustainability and improve production and animal health in aquaculture, a collaboration was created with Anheuser-Busch of the brewing industry and Maltento, a functional ingredient company. With breweries around the globe, Anheuser-Busch produces consistent, food grade byproducts that are safe for human consumption. Two of the most prevalent brewery byproducts are brewer's spent yeast (BSY) and brewer's spent grain (BSG). BSY contains a variety of beneficial nutrients such as proteins, essential amino acids, and carbohydrates. BSG is high in fiber but low in protein; however, black soldier fly larvae can be cultured on BSG to convert the low-value product into insect biomass to be used in fish feed, as insects themselves are full of beneficial lipids and proteins. The objective of the work presented in this thesis was to evaluate the efficacy of using low-value brewery waste products, converted into high-value feed additives, for aquaculture practices. Specifically, the effects of dietary feed additives on the production, health, and intestinal bacterial community of aquaculture-raised rainbow trout were examined. Inadvertently, benefits of the feed additives on fish subjected to chronic and acute thermal stress were also assessed. Overall, the results of the study found that the feed additives did not significantly change the production efficiency of the rainbow trout, though some increase in growth was observed. When subjected to chronic thermal stress conditions, fish fed the experimental diets outperformed those fed the control diet regarding growth parameters. The intestinal bacterial community of the fish was significantly altered from the beginning of the trial compared to the end of the trial, though differences were not attributed to the feed additives. Instead, the resulting intestinal dysbiosis is believed to have stemmed from the physiological response of the fish to thermal stress conditions. When the fish underwent an acute thermal stress event, causing mortality, fish fed three of the five experimental diets were found to have higher survival rates compared to the control. Ultimately, results of this project suggest that the BSY and BSG-fed insect feed additives may have increased the health and robustness of the fish during a period of thermal stress. However, further research under controlled conditions is needed to evaluate if the observed host health benefits can directly be attributed to the feed additives. / Master of Science / Aquaculture refers to the method of rearing aquatic organism such as fish and shellfish under controlled conditions. Within the food industry, aquaculture is one of the fastest growing sectors, and provides important economic and nutritional benefits to humans. Additionally, aquaculture is an important alternative to fisheries that rely on catching fish from the natural environment. Wild-caught fisheries have struggled due to the overfishing, and unfortunately, many aquaculture practices still rely on wild-caught fisheries to produce fishmeal used in feed for carnivorous fish. Research into alternate protein sources to use in fish feed has been on the rise. Additionally, as the emergence of multi-drug resistant bacteria continues to increase, reducing antibiotic use has become a priority across all fields whether it be healthcare or the food industry. Within aquaculture, using alternative prophylactic measures such as prebiotics to increase animal health and disease resistance could lead to the overall reduction of antibiotic use. Prebiotics are non-digestible food ingredients believed to help the beneficial bacteria within the intestinal track to grow. In turn, the increased numbers of beneficial bacteria reduce the possibility of pathogenic bacteria invading and establishing a presence in the intestinal track. The intestinal microbiome refers to the various organisms, such as bacteria, viruses, and fungi, that live commensally within the host digestive tract. The bacterial community within the intestinal microbiome has many important roles, including effects on host development, physiology, immunity, and nutrient acquisition. Many factors also impact the bacterial community, including the presence of pathogens and/or antibiotics, environmental conditions, host genetics, and the diet consumed. To promote environmental sustainability and improve production and animal health in aquaculture, a collaboration was created with Anheuser-Busch of the brewing industry and Maltento, a functional ingredient company. With breweries around the globe, Anheuser-Busch produces consistent, food grade byproducts that are safe for human consumption. Two of the most prevalent brewery byproducts are brewer's spent yeast (BSY) and brewer's spent grain (BSG). These low-value waste products can consequently be converted into high-value feed additives for use in aquaculture. The objective of the work presented in this thesis was to evaluate the effects of BSY and BSG-fed insect dietary feed additives on the production, health, and intestinal bacterial community of aquaculture-raised rainbow trout. Unintentionally, benefits of the feed additives on fish subjected to chronic and acute high-temperature thermal stress were also explored. Overall, the results of the study found that while the feed additives did not significantly increase the growth of the rainbow trout, benefits were still observed. When subjected to chronically high-water temperatures, fish fed the experimental diets outperformed those fed the control diet regarding growth parameters. The intestinal bacterial community of the fish was significantly altered from the beginning of the trial compared to the end of the trial, though differences are not believed to be caused by the feed additives. Instead, the resulting shift in the bacterial community is believed to have stemmed from the stress-response of the fish triggered by high water temperature. When the fish underwent an acute thermal stress event, which caused mortality, fish fed three of the five experimental diets were found to have higher survival rates compared to the control. Ultimately, results of this project suggest that the feed additives may have increased the health and robustness of the fish while undergoing thermal stress. However, further research under controlled conditions is needed to evaluate if the observed host health benefits can be attributed directly to the feed additives.