Selenium (Se) is known to cause chronic toxicity in aquatic species. In particular, dietary exposure of fish to selenomethionine (SeMet), the primary form of Se in the diet, is of concern. Previous studies reported that chronic exposure to elevated dietary SeMet altered swimming performance, aerobic metabolism, and energy and endocrine homeostasis in adult fish. However, little is known about the direct effects of dietary SeMet exposure in juvenile fish. Therefore, the overall objective of this thesis was to investigate sublethal pathophysiological effects of subchronic dietary SeMet exposure in two juvenile fish species, fathead minnow (Pimephales promelas) and rainbow trout (Oncorhynchus mykiss). In the first experiment, 20 days post hatch (dph) juvenile fathead minnow were exposed to different measured concentrations (2.8, 5.4, 9.9, 26.5 µg Se/g dry mass [dm]) of Se in food in the form of SeMet for 60 days. In the second experiment, 14 dph juvenile rainbow trout were exposed for 37 days to different measured concentrations (1.0, 4.1, 11.2, 26.1 µg Se/g dm) of Se in food in the form of SeMet. Following exposure, samples were collected for Se analysis and fish were subjected to a swimming performance challenge to assess critical swim speed (Ucrit), tail beat frequency and tail beat amplitude, oxygen consumption (MO2), cost of transport (COT), standard metabolic rate (SMR), active metabolic rate (AMR), and factorial aerobic scope (F-AS). Dietary SeMet exposure impaired swimming ability in both fathead minnow and rainbow trout. Juvenile fathead minnow showed alterations in aerobic metabolism with increased MO2, COT and AMR at the 9.9 and 26.5 µg Se/g diets, while dietary SeMet exposure did not appear to affect aerobic metabolism in juvenile rainbow trout. After swim performance experiments, swam fish were considered fatigued and metabolic and energy storage endpoints were compared to non-swam (non-fatigued) fish. Energy storage capacity was measured via whole body (fathead minnow) and liver and muscle (rainbow trout) triglyceride and glycogen concentrations. For fathead minnow, triglyceride concentrations in non-swam fish were significantly elevated in the 5.4 µg Se/g group relative to controls, and swam fish had significantly lower whole body triglycerides than non-swam fish. All non-swam SeMet exposure groups had significantly decreased whole body glycogen concentrations compared to controls while the 5.4 and 26.5 µg Se/g exposure groups had significantly greater whole body glycogen concentrations in swam versus non-swam fish. In juvenile rainbow trout, liver triglyceride concentrations were significantly lower in all SeMet exposed groups compared to controls in non-swam fish. Swimming decreased liver and muscle triglycerides in the control and 11.2 µg Se/g treatment groups. Liver glycogen concentrations were greater in swam trout in the 4.1 µg Se/g dm exposure group. Muscle glycogen concentrations in non-swam fish, were significantly decreased in the 4.1 and 11.2 µg Se/g exposed groups compared to controls, while muscle glycogen in swam fish was unaffected by dietary SeMet exposure. For the swim status factor, muscle glycogen concentrations were significantly greater in swam versus non-swam trout in all treatment groups. Therefore, dietary SeMet exposure caused impaired swimming performance and metabolic alterations in both juvenile fathead minnow and juvenile rainbow trout. Species differences were apparent, especially in the patterns of altered energy status between swam and non-swam fish exposed to Se. Overall, the pathophysiological implications of these sublethal effects are unclear, but suggest that dietary SeMet exposure may negatively influence juvenile fish survivability in natural habitats.

Alarm substances, released by injured prey, and odours from predators, such as northern pike, are chemical cues associated with increased predation risk in aquatic ecosystems. In laboratory studies, individual prey can respond to the presence of such cues by reducing conspicuous behaviours, such as foraging and by seeking shelter. These responses may reduce growth and reproduction, which could have effects at the population-level. The objective of my study was to determine if alarm substances or pike odour have population-level effects on fathead minnow. In the cattle trough experiment, alarm substances and pike odour had no effect on breeding behaviour and recruitment of young; however, spawning occurred earlier with exposure to alarm substances relative to water controls. In a larger-scale pond experiment, alarm substances had no effect on reproduction or recruitment. Despite individual-level effects in the laboratory, exposure to alarm substances and pike odour had no impact at the population scale. / Ecology

Thesis (M.S.)--Baylor University, 2008. / Includes bibliographical references (p. 68-74)

The main subject of this experiment was to explain the behaving of the minnow during its reproduction, the preferation of the spawning substratum, the length of the incubation of eggs, the evolution and the growth of the juvenile and the fry. Brood fish were taken by elektrical unit in the Blanice river, in the area between the railway bridge and the weir in the village of Blanice. These were put into the experimental pond of 75 square metres. There were two spawning processes. The first took place on 10 June , the fry hatched after ten days and in the next ten days it could be found all over the pond looking for food. In the selection of the substratum the gravel (of the size of 2-5cm) was prefered at all. The standard length of the fry at the end of the process of breeding (after a hundred days) was 39{--}48 mm (the amount of 800 individuals). The second spawn took place on 11 August. The fry hatched after eight days and the next week it was hidding in the substratum and consuming yolk sack. The standard length at the end of the breeding was 18{--}26mm. The ammount of the breeded fry was 350 individuals.

The 96-hr LC50 of cyfluthrin in Pimephales promelas ata temperature of 23*C and a pH of 8 was 1.08 g/L. The toxicity of cyfluthrin was inversely related to temperature and pH. A temperature of 10*C and a pH of 6 significantly decreased the 96-hr LC50 to 0.009 gg/L. Likewise, sublethal exposures to cyfluthrin significantly affected the fathead minnow's ability to tolerate high and low temperatures. Cyfluthrin compromised the fathead minnow's lower temperature tolerance (CTMin) by 60C and the upper temperature tolerance (CTMax) by 20C. Although cyfluthrin may not be present in the environment in large amounts due to its physical and chemical properties, small concentrations ( g/L) may adversely affect fish populations.

Mercury (Hg) is a ubiquitous environmental contaminant, which is capable of global atmospheric transport. As a result, even the most pristine aquatic ecosystems are affected by atmospheric Hg deposition, following which microbial transformation yield organic Hg forms, the most concerning of which is methylmercury (MeHg). Methylmercury is capable of bioaccumulation and biomagnification in food webs, resulting in potentially toxic body burdens due to regular dietary exposure in long-lived organisms at higher trophic levels. It is also a molecular mimic of some endogenous amino acids, providing a route of transfer from mother to offspring via large amino acid transporters. Exposure during neurodevelopment can lead to serious, irreversible neurological dysfunction, associated with a variety of cognitive and motor abnormalities across species. The present studies evaluate the effects of maternally-transferred dietary MeHg, at environmentally relevant concentrations on early life stage fathead minnows (Pimephales promelas). Embryos were collected from adult fatheads exposed to one of three diets with varying concentrations of MeHg for 30 days. Adult reproductive metrics were also monitored over the course of the study, with results indicating no effects on spawning frequency, clutch size, or total egg output. In embryos, Hg concentration was a function of female diet and the duration (number of days) of female exposure. Offspring spawned in tanks administered the low Hg diet displayed altered embryonic movement patterns (hyperactivity), decreased time to hatch, decreased mean larval size, and alterations to several metabolite abundances when compared with controls. Significantly altered metabolites include those associated with cellular energetics, fatty acid metabolism, and polyamine synthesis, indicating current environmental exposure scenarios are sufficient to disrupt important cellular pathways. Dysregulation of the dopaminergic system of embryos is also characterized, and may be a possible mechanism by which hyperactive behaviors are observed in these embryos. Offspring from tanks administered the high Hg diet exhibited delayed hatching, increased mortality, and physiological abnormalities. Brain tissue of exposed adults from the low diet were dissected into regions, and also evaluated for alterations in dopamine cycling. Collectively, these results indicate current exposure scenarios in North American lakes and rivers are sufficient to cause reductions in fitness and survival of early life stage fish. The potential for community structure impacts exists, as sensitive individuals and species become disproportionately affected by chronic, low-level MeHg exposure.

No description available.

<p>²²⁶Ra is a radionuclide of much concern since it poses a high risk of radio-toxicity when ingested and is well known for its invariably long half life of 1600 years. As such ²²⁶Ra concentrations were measured in whole body tissue of fathead minnows (Pimephales promelas) in an experimental set up. Fathead minnows obtained were about two months old and fed on a Radium-226 spiked diet until 115 days. A simple and direct method to determine ²²⁶Ra ingested by fish using a homogeneous liquid scintillation counting was developed. The study consisted of three groups; a sham, Radium treatment and acid treatment. Fathead minnows were sampled 75 and 115 days after feeding, and the following end points; mass (w/w), length, specific growth rate, condition factor and radionuclide measurements obtained. Mean end point results were (0.24 ± 0.03 g), (2.78 ± 0.1 cm), (1.75 ± 0.13 % day^-1), (1.10 ± 0.06 g cm^-3) and (577.06 ± 572.13 mBq g^-1) respectively. Also mean total ²²⁶Ra level was calculated as (1911.43 ± 868.64 mBq g^-1) while the activity in sham and acid treatment resulted in levels below the Minimum Detectable Activity of 7.46 mBq g^-1. The mean rate of ²²⁶Ra accumulation, known as the concentration factor, by the fathead minnows was determined as 0.35 ± 0.19. Assuming that the ²²⁶Ra Isotope is evenly distributed in the fish whole body, the derived dose rate was found to be 5.26 μGy h^-1.</p> / Master of Science (MSc)

In this research a test system was developed that is designed as a tool to evaluate the potential hazard of chemicals to aquatic ecosystems. The system developed is a linear three-trophic level food chain consisting of an alga (Ch/ore/la vulgaris), rotifer (Brachionus calyciflorus), and fish (Pimephales promelas). The chemostat design used for the lower two trophic levels was crucial in being able to supply the top trophic level with sufficient food on a continuous basis. The system was initially evaluated using copper (Cu) and selenium (Se) as toxicants. In the copper experiments, results of a 7 day three-trophic level toxicity test were compared with a series of single species tests. The LOEC was 31.5 µg/L based on a temporary impairment of the algal population growth, with a corresponding NOEC of 16.2 µg/L. The algal population at all initially impaired treatment levels demonstrated recovery to control levels by the end of the test. Single species tests with the same species showed impairment at treatment concentrations lower than the corresponding value from the three-trophic level test. The difference in sensitivity is attributable to the fact that most of the Cu in the single species tests was in the dissolved form (approximately 80 %), whereas in the trophic level test most of the Cu was not ( < 15 % dissolved Cu). The three-trophic level Se experiment lasted for 25 days, with both short-term and long-term impacts evident. At the algal trophic level, growth was not impaired on a daily basis at any of the exposure levels (110.3, 207.7, and 396.1 µg/L Se). However, algal densities were slightly reduced at the 207. 7 and 396.1 µg Sell treatments, although not significantly different when the data was pooled across days. Rotifer populations were impaired at these same levels by day 4, and succumbed to the Se by day 7. Fathead minnow growth was also impaired at these two concentrations by day 7. In addition, sub lethal impairment of rotifer and fish growth was evident at the 110.3 pg/L level after day 20 indicating a more subtle trophic impact. Bioconcentration factors ranged between 100 and 1000 µg/L and were found to be dependent on the species, treatment, and day. / Ph. D.

Chronic toxicity of zinc to Pimephales promelas was estimated by conducting replicate static and static-renewal short-term embryo-larval tests and static-renewal seven-day larval tests. The two test methods were highly reproducible. Daily renewal of test solutions had little effect on the toxicity of zinc, however, the stage of development at which exposure was initiated affected the sensitivity of the toxic endpoints measured. The most sensitive and reproducible endpoint in the embryo-larval tests was survival of viable (non-deformed) larvae and in the seven-day larval test was growth of the larvae, which was slightly more sensitive than the embryo-larval test endpoint. The estimated MATC of 0.18 and 0.15 mg/L mean total and mean soluble zinc, respectively, compared well with published results. Because of its advantages and similar sensitivity, the short-term embryo-larval test was recommended for estimating chronic toxicity.