In boreal forest streams, woody debris is an important habitat component. Stream invertebrates and salmonids such as brown trout benefit from in-stream wood. The studies presented in this thesis explore how drifting stream invertebrates respond to addition of fine woody debris, and how young-of-the-year (0+) brown trout behave in habitats with and without fine woody debris. The first paper reports results from a field experiment where fine woody debris was added to streams, and invertebrate drift was measured in order to detect impacts of the fine woody debris on drift density, biomass and taxon diversity. In the end of the season, the fine woody debris-affected drift samples showed higher density, biomass and taxon diversity than the control samples. In the second paper, I describe effects of fine woody debris on 0+ brown trout, studied in laboratory stream channels. Trout were tested in habitats without fine woody debris, with an intermediate fine woody debris density, and with a high fine woody debris density. Swimming activity and foraging time were significantly lower when fine woody debris was present than when it was absent. More time was spent sheltering at the high fine woody debris density than at the intermediate one. The increasing exploitation of fine woody debris for biofuel purposes should be considered in relation to the effects on brown trout and stream invertebrate habitat. / <p>Artikel 1 ingick i avhandlingen som manuskript med titeln "Effects of fine wood addition on invertebrate drift in boreal forest streams". Nu publicerad.</p>

One common consequence of ontogenetic niche shifts is that juveniles and adults of the same species often use different resources and habitats. Theory suggests that variation in productivity and/or habitat size for the respective life stage regulates size distribution of individuals and population biomass. Low resources/habitat availability for juveniles relative to adults results in populations with many small juveniles with high mortality and few but large adults, while the opposite situation results in a population with small and slow growing adults with high densities. I tested this theory using lake-living brown trout (Salmo trutta), where adults inhabit lakes and use connected streams for spawning and nurseries for juveniles. My hypothesis was that the relative habitat availability for juveniles respectively adults determines the size structure of adult brown trout in lakes. This was done by quantifying available stream habitats in relation to lake area via GIS analysis of 101 allopatric brown trout lakes in Sweden and Norway. My results showed that the proportion of large trout, mean length and maximum length decreased with increasing juvenile habitat in relation to adult habitat availability. This suggests that relative variation in availability of juvenile and adult habitats can affect the size structure of lake-living brown trout, most likely due to size dependent niche shifts and competitive and cannibalistic interactions. As the lake brown trout is highly valued both for commercial and recreational purposes, these findings can be highly valuable for sustainable management of the ecosystems services that the brown trout provides.

Opening migratory pathways is crucial for the brown trout´s ability to recolonize spawning- and rearing areas, in order to complete its lifecycle. Damming rivers for hydropower production has created obstacles for migration, and nature-like fishways are one measure used to recreate connectivity. The purpose of this bachelor´s thesis was to find out how the nature-like fishway, constructed in 2016, at Billsta power plant, central Sweden, was used by migratory brown trout for upstream and downstream passage, and to observe if the migration pattern changed over time, between 2018-2020. The collected data comes from an automatic fish-counter that has been located upstream of the nature-like fishway. To analyze the data, recorded trout were categorized into two length classes, spawning-size and smolt-size, according to criteria from the Swedish Agency for Marine and Water Management (HaV). Since individual fish could not be identified, a method for daily “net migration” was been developed to estimate the direction of migration. The results showed that net migration of spawning-size trout was greater upstream than downstream. Net upstream migration of spawning size trout tended to increase over time, but not the net downstream migration. There was no difference between net upstream and net downstream migration smolt-size trout, but the net downstream migration smolt-size trout increased over time. The study showed that there was substantial use of Billsta nature-like fishway for brown trout of both spawning- and smolt-sizes, for both upstream and downstream migration. The migration pattern was partly as expected but, upstream migration of smolt-size trout suggests that there is a considerable population of stationary trout passing the fish-counter. The study highlights the importance of monitoring the results of the restoration and implementing improvement measures where necessary. Billstaån has regained open migration pathways, but more time is needed to evaluate its effect and find out if the ecosystem works so that Storsjöns unique, large sized, migratory brown trout stocks once again have the conditions to complete their lifecycle in Billstaån. / Fria vandringsvägar är avgörande för öringens förmåga att återkolonisera lek- och uppväxthabitat, vid fungerande lek- och smoltvandring kan öringen fullborda sin livscykel. Vattenkraftsproduktion har skapat vandringshinder och naturlika fiskvägar är en åtgärd för att återskapa konnektivitet. Syftet med den här kandidatuppsatsen var att ta reda på hur den nedersta naturlika fiskvägen, skapad 2016 vid Billsta kraftverk i mellersta Sverige, nyttjades av vandrande öringar för uppströms och nedströms passage och observera om vandringsmönstret förändrades över tid, mellan 2018–2020. Rådatan kommer från en automatisk fiskräknare som funnits placerad uppströms den naturlika fiskvägen. För att analysera datan delades öringen in efter två längdstorlekar, lek- och smoltstorlek, enligt kriterier från Havs- och vattenmyndigheten. Eftersom individuell fisk inte gick att identifiera har en metod för daglig ”nettovandring” utarbetats för att uppskatta vandringens riktning. Resultatet visade att fler öringar i lekfiskstorlek nettouppvandrade än nettonedvandrade. Nettouppvandring av lekfiskstorlek tenderade att öka över tid men inte nettonedvandringen. Det var ingen skillnad mellan nettoupp- och nettonedvandrande öring i smoltstorlek, men nettonedvandringen av öring i smoltstorlek ökade över tid. Studien visade att Billsta naturlika fiskväg nyttjades väl av öring i både lekfisk- och smoltstorlek för både uppströms- och nedströmsvandring. Vandringsmönstret var delvis som förväntat, men när det gäller smoltstorlekens vandring var det snarare bäcköringens vandring än smoltens vandringsmönster som analyserades. Studien belyser vikten av att övervaka resultatet av restaureringen och implementera förbättringsåtgärder där så behövs. Billstaåån har återfått fria vandringsvägar men mer tid behövs för att utvädera dess effekt och ta reda på om ekosystemet fungerar så att Storsjöns unika, storvuxna, lekvandrande öringstam återigen fått förutsättningar att fullborda sin livscykel i Billstaån.

During the past quarter of a century there has been considerable investigation into the effects of fluorides on living organisms. It has been well established, as a result of these studies, that both small and elevated amounts of fluorides present in the environment may have a marked toxic effect upon gaining entry into the organism. Much of the research involving fluorides and the living organism has been confined to experimentation with animals, although considerable evidence indicates that plants are also subject to injury if fluorides are present in the atmosphere or the soil. The great majority of the research dealing with effects of fluorides on animals has been confined to higher vertebrates, principally domestic farm species. The concentration of fluoride research in this area has been prompted by economic pressures arising from natural, industrial, or accidental fluoridation of livestock. For the most part, these investigations have been confined to determination of toxicity levels to various domestic species, while the mode of fluoride action upon living organisms has often been neglected. Some investigators, however, have postulated "defense mechanisms" within the organism whereby active fluoride ion is removed from systemic circulation and is either deposited in less active tissues of the body, or, is excreted in some manner. Such mechanisms would offer a degree of temporary protection of the organism from harmful effects of the fluoride ion.

Juvenile rainbow trout Oncorhynchus mykiss stocked into mid-elevation reservoirs in Utah are vulnerable to predation from piscivorous fish and birds. I determined how effectively juvenile trout used cover to avoid these predators by (1) direct observations (snorkel transects) of habitat selection in two reservoirs and (2) measurements of survival and growth rates in a pond experiment where adult brown trout Salmo trutta were predators. Observations of juvenile trout were conducted within five weeks of stocking in 1988 and 1989. During the day, juvenile trout were abundant in complex inshore habitats and avoided simple habitats such as sand and gravel. Measurements of gut fullness indicated that juvenile trout fed during the day but not during the night. Large Daphnia comprised more than 95% of the diet of juvenile trout. Because large Daphnia were often higher offshore than inshore in both reservoirs, selection of inshore cover is believed to be primarily a response to reduce predation risk. At night, trout in both reservoirs selected more exposed areas and rested on the bottom. In the pond experiment, the presence of brown trout significantly increased mortality of juvenile trout, decreased their growth rates, and caused them to avoid offshore areas. The presence of cover significantly decreased predation rates but did not affect growth of the juvenile trout.

Effects of exercise and the relative condition of exercised fish were viii evaluated for two strains of rainbow trout. Circular tanks fitted with a paddle were used to continuously exercise the fish and a stamina tunnel was used to evaluate the condition of exercised trout. Trout were exercised continuously at one fish-length per second and one-half fish length per second. Serum LDH activity in Shephard-of-the-Hills (Missouri) rainbow trout acclimated to 10 C increased two fold during the first four days of exercise. Serum LDH activity returned to control levels by the tenth day of exercise. Serum LDH activity in Shephard-of-the-Hills rainbow trout exercised at one-half length per second did not increase significantly. Serum LDH activity in Fish Lake stock acclimated to 17 C did not increase significantly. Shephard-of-the-Hills and Fish Lake rainbow trout exercised at one length per second were better conditioned to water velocities of two lengths per second than were controls.

The Logan River flowing southwesterly through the mountains of Cache County, Utah is comparatively cold to the mouth of Logan Canyon. The stream is characterized by steep gradient, a high velocity and relatively few pools. A total of 1053 brown trout were examined during the course of this study; 286 were retained for age and growth determinations. The body scale relationship is L : 40.46 mm. + 0.4l85R + 0.01908R^2 where L equals standard length in millimeters and R equals scale radius times 80.

Snack food development studies were conducted to iii utilize trout (Oncorhynchus mykiss) frames, a by-product of the filleting operation, using extrusion and conventional technology. Twin screw extrusion studies were conducted to study the effect of fish mince, non-fat dry milk, process temperature, and moisture content on the physicochemical properties of the extruded snack food. Response surfaces were plotted to understand the effects of the independent variables on dependent variables such as bulk density, expansion ratio, shear strength, and water absorption index. Quadratic models expressed the relationship between the dependent and independent variables. Based on the extrusion studies, conditions suitable for further development of a ready-to-eat snack food were obtained. Conventional technology was also studied in the development of a fish cracker called keropok. A well expanded, tasty snack food was obtained using the minced fish and tapioca starch. Physicochemical characteristics of the developed snack were determined. Taste panel ratings for texture and taste of the cracker indicated a good potential for acceptance of this product for production and sale by local fish processors. Further studies may be undertaken to develop a continuous process to prepare the crackers on a larger scale.

I described the spawning ecology of the Bear Lake Bonneville cutthroat trout (BLBCT) in St. Charles Creek. I tracked cutthroat trout with used radio telemetry. I conducted redd counts to describe spawning conditions. Most cutthroat trout in the Big Arm strayed into the Bear River. Cutthroat trout migrations in the Little Arm and main fork were very limited (<4 km). Redd distributions showed very similar patterns between 1989, 2000 and 2001 with most redds being built in the lowest kilometer of stream. Artificial fish transportation changed the redd distribution in 2002. More redds were built in the main fork and redds were distributed throughout the stream. Redds built in the main fork were characterized by lower levels of fine sediment and higher water velocities as compared to the redds built on the Little Arm. The results of this research will be used to aid resource managers in developing a management plan for wild BLBCT.

Different strains of rainbow trout (Salmo gairdneri), Ten Sleep, Sand Creek, Beitey, Shepherd-of-the-Hills, New Zealand, Fish Lake- Desmet, Desmet, were compared for survival to the creel, growth and catchability after being stocked in a fluctuating 80 ha Utah reservoir . Fish were stocked in the spring and fall as fingerlings and monitored by creel censusing, gill netting and electrofishing. Fish were tagged with coded wire snout tags prior to stocking . An angler opinion survey was conducted to determine angler satisfaction with numbers and size of fish caught. Regardless of strain, spring stocking was superior to fall stocking in survival to the creel. In the spring 78 stocking the Ten Sleep strain had the highest survival to the creel (33.7 percent), followed in order by Shepherd-of-the-Hills (11.0 percent), Beitey (5.5 percent), Sand Creek (5.4 percent), New Zealand (4.1 percent), and Fish Lake-Desmet (2 .9 percent). In the spring 79 stocking the Shepherd-of-the- Hills strain had the highest survival to the creel (7 .6 percent), followed in order by the Sand Creek (7.3 percent) and the Ten Sleep (6.5 percent). Similar trends in survival were found in gill netting and electrofishing samples. Migration out of the reservoir was negligible for each strain. There were no strain differences in catchability by different methods (shore, boat) or gear (bait, artificial lure). Differences in growth between the fastest growing strains (Ten Sleep, Sand Creek) and the slowest growing strains (New Zealand, Fish Lake-Desmet) averaged as great as 16 mm in length and 43 g in weight. Differences in growth and survival among strains were great enough to span the range of angler satisfaction with numbers caught and size of fish caught from satisfactory to unsatisfactory. Therefore, strain selection can be a useful tool to improve fingerling stocking programs and manipulate the number of anglers who are satisfied with the angling experience.