Wilderless Experience

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Sublethal toxicant effects on fish foraging behavior: A mechanistic approach

Previous studies of toxicant effects on fish foraging behavior have taken a strictly empirical approach which had little basis in ecological theory and did not allow development of a testable hypothesis a priori to field verification of laboratory results. A mechanistic approach was taken in this study to examine the sublethal effects of four copper concentrations (0, 25, 150, 1800 ug/l) on the foraging behavior of bluegill Lepomis macrochirus. Twelve separate laboratory experiments were conducted. Two experiments assessed copper effects on the reaction distance of bluegill to untreated zooplankton. Ten experiments were done to assess copper effects on the functional response of bluegill to untreated (5 tests) and treated (5 tests) invertebrate prey of different types. Copper had no effect on the reaction distance of fish to zooplankton. Copper reduced bluegill consumption rates of all untreated prey but not treated prey groups. Prey handling time for bluegill capturing treated and untreated prey increased significantly with copper concentration and was the most consistently sensitive parameter measured. Capture efficiency by bluegill was not as consistent a measure of toxicant stress. These experiments suggest that mechanistic measures are consistent indicators of toxicant effects on fish feeding behavior and that copper concentrations as low as the USEPA water quality criteria may alter food consumption and reduce growth of fish in the wild;Laboratory results were incorporated into an optimal foraging model to predict the diet breadth of treated and untreated fish in a lake. Bluegill in replicated, littoral-zone mesocosms were exposed to 1 of 3 copper concentrations (0, 36, 130 ug/l) for four days. The stomach contents of the fish were compared with ambient prey availability and the diet predicted by the optimal foraging model. The model did not provide a good estimate of diet breadth for fish in the mesocosms. Small differences in the energetic return rate between optimal and suboptimal diets, and errors in determining estimates of model parameters may account for discrepancies between the observed and predicted diet

Fish Associated with Dikes, Revetments, and Abandoned Channels in the Middle Missouri River

Fish associated with dikes, revetments, and abandoned channels along the Iowa-Nebraska portion of the Missouri River were collected by seining, electrofishing, and hoop netting in June, August, and October 1983. Samples collected by seining dike fields and abandoned channels were\u27 dominated by Cyprinidae and Centrarchidae. Electrofishing samples were dominated by flathead catfish (Pylodictus olivaris), gold eye (Hiodon alosoides), common carp (Cyprinus carpio), river carpsucker, (Carpiodes carpio), gizzard shad (Dorosoma cepedianum), and blue sucker (Cycleptus elongatus) in dike fields and revetted banks and by gizzard shad, river carpsucker, and bigmouth buffalo (lctiobus cyprinellus) in the abandoned channels. Among fish collected in unbaited hoop nets, blue suckers and channel catfish (lctalurus punctatus) were prevalent in dike fields; blue suckers, flathead catfish, and shortnose gar (Lepisosteus platostomus) along revetted banks; and white crappie (Pomoxis annualaris), black crappie (P. nigromaculatus), river carpsucker, black bullhead (lctalurus melas), bigmouth buffalo, and gizzard shad in abandoned channels. Gear selectivity and differences in sampling efficiency in the diverse riverine habitats precluded statistical comparisons of most samples and stressed the need for development of improved sampling techniques and designs for large river fishery research

Use of Artificial Enclosures to Determine the Survival of Rana pipiens Larvae in Upper Midwestern Agricultural Ponds

Amphibians in the upper Midwest use agricultural ponds for breeding. Unfortunately, the risks (both direct and indirect) associated with using these ponds are poorly understood in both amphibian adults and larvae. In order to quantify these risks, we performed a comparison of larval survival rates between agricultural and natural ponds in southeastern Minnesota during the spring and summer of 2001. During this time, larval survival was observed in Rana pipiens tadpoles raised through metamorphosis in enclosures placed in agricultural and natural ponds. In addition, we measured the levels of nutrients commonly linked with agricultural ponds (i.e., ammonia, total phosphorous, and total nitrogen), and whether or not nutrient concentration was associated with larval survival. No differences were detected in nutrient levels or survival of larvae reared in agricultural and natural ponds. Furthermore, neither nutrient levels nor pond type significantly predicted larval survival. Our data were highly variable, making the interpretation of our results difficult. The enclosures used to rear tadpoles were highly effective and can be easily incorporated into future studies

Flow Cytometry Used to Assess Genetic Damage in Frogs from Farm Ponds

Flow cytometry (FC) is a laboratory method used to detect genetic damage induced by environmental contaminants and other stressors in animals, including amphibians. We tested FC methods on three species of ranid frogs collected from farm ponds and natural wetlands in southeastern Minnesota. We compared FC metrics for Rana clamitans between ponds with direct exposure to agricultural contaminants and reference (unexposed) ponds. Concentrations of atrazine in water from our farm ponds ranged from 0.04 to 0.55 ppb. We found that R. clamitans from exposed ponds had DNA content similar to frogs from unexposed ponds. Pond-averaged C-values (a measure of DNA content) ranged from 6.53 to 7.08 for R. pipiens (n = 13), 6.55 to 6.60 for R. clamitans (n = 40) and 6.74 for R. palustris (n = 5). Among all species, the mean sample CVs ranged from 1.91 (R. palustris) to 6.31 (R. pipiens). Deformities were observed in only 2 of 796 individuals among all species and occurred in both reference and exposed ponds. Although we did not detect evidence of DNA damage associated with agriculture in our study, we demonstrated the potential of FC for screening amphibian populations for genetic damage. Metrics from a variety of amphibian species and locations as well as laboratory studies are needed to further assess the value of FC for monitoring amphibian genetic integrity in contaminated sites

Toxicity of dietary methylmercury to fish: Derivation of ecologically meaningful threshold concentrations

Threshold concentrations associated with adverse effects of dietary exposure to methylmercury (MeHg) were derived from published results of laboratory studies on a variety of fish species. Adverse effects related to mortality were uncommon, whereas adverse effects related to growth occurred only at dietary MeHg concentrations exceeding 2.5 µg g −1 wet weight. Adverse effects on behavior of fish had a wide range of effective dietary concentrations, but generally occurred above 0.5 µg g −1 wet weight. In contrast, effects on reproduction and other subclinical endpoints occurred at dietary concentrations that were much lower (<0.2 µg g −1 wet wt). Field studies generally lack information on dietary MeHg exposure, yet available data indicate that comparable adverse effects have been observed in wild fish in environments corresponding to high and low MeHg contamination of food webs and are in agreement with the threshold concentrations derived here from laboratory studies. These thresholds indicate that while differences in species sensitivity to MeHg exposure appear considerable, chronic dietary exposure to low concentrations of MeHg may have significant adverse effects on wild fish populations but remain little studied compared to concentrations in mammals or birds. Environ. Toxicol. Chem. 2012; 31: 1536–1547. © 2012 SETACPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/92130/1/etc_1859_sm_SupplReferences.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/92130/2/1859_ftp.pd

Gene Expression Changes Related to Endocrine Function and Decline in Reproduction in Fathead Minnow (Pimephales promelas) after Dietary Methylmercury Exposure

BACKGROUND: Methylmercury (MeHg) is a known neurotoxic agent, but the mechanisms by which MeHg may act on reproductive pathways are relatively unknown. Several studies have indicated potential changes in hormone levels as well as declines in vertebrates with increasing dietary MeHg exposure. OBJECTIVES: The purpose of this study was to identify alterations in gene expression associated with MeHg exposure, specifically those associated with previously observed changes in reproduction and reproductive biomarkers. Fathead minnows, Pimephales promelas, were fed one of three diets that were similar to documented concentrations of MeHg in the diets of wild invertivorous and piscivorous fish. We used a commercial macroarray in conjunction with quantitative polymerase chain reaction to examine gene expression in fish in relation to exposure to these environmentally relevant doses of MeHg. RESULTS: Expression of genes commonly associated with endocrine disruption was altered with Hg exposure. Specifically, we observed a marked up-regulation in vitellogenin mRNA in individual Hg-exposed males and a significant decline in vitellogenin gene expression in female fish with increasing Hg concentrations. Other genes identified by the macroarray experiment included those associated with egg fertilization and development, sugar metabolism, apoptosis, and electron transport. We also observed differences in expression patterns between male and female fish not related to genes specifically associated with reproduction, indicating a potential physiological difference in the reaction of males and females to MeHg. CONCLUSION: Gene expression data may provide insight into the mechanisms by which MeHg affects reproduction in fish and indicate how MeHg differs in its effect from other heavy metals and endocrine-disrupting compounds

Sublethal toxicant effects on fish foraging behavior: A mechanistic approach

Previous studies of toxicant effects on fish foraging behavior have taken a strictly empirical approach which had little basis in ecological theory and did not allow development of a testable hypothesis a priori to field verification of laboratory results. A mechanistic approach was taken in this study to examine the sublethal effects of four copper concentrations (0, 25, 150, 1800 ug/l) on the foraging behavior of bluegill Lepomis macrochirus. Twelve separate laboratory experiments were conducted. Two experiments assessed copper effects on the reaction distance of bluegill to untreated zooplankton. Ten experiments were done to assess copper effects on the functional response of bluegill to untreated (5 tests) and treated (5 tests) invertebrate prey of different types. Copper had no effect on the reaction distance of fish to zooplankton. Copper reduced bluegill consumption rates of all untreated prey but not treated prey groups. Prey handling time for bluegill capturing treated and untreated prey increased significantly with copper concentration and was the most consistently sensitive parameter measured. Capture efficiency by bluegill was not as consistent a measure of toxicant stress. These experiments suggest that mechanistic measures are consistent indicators of toxicant effects on fish feeding behavior and that copper concentrations as low as the USEPA water quality criteria may alter food consumption and reduce growth of fish in the wild;Laboratory results were incorporated into an optimal foraging model to predict the diet breadth of treated and untreated fish in a lake. Bluegill in replicated, littoral-zone mesocosms were exposed to 1 of 3 copper concentrations (0, 36, 130 ug/l) for four days. The stomach contents of the fish were compared with ambient prey availability and the diet predicted by the optimal foraging model. The model did not provide a good estimate of diet breadth for fish in the mesocosms. Small differences in the energetic return rate between optimal and suboptimal diets, and errors in determining estimates of model parameters may account for discrepancies between the observed and predicted diet.</p

Wilderless Experience

god in mans image gazed upon aesthetic artifacts from tiki torch lawn chair comfort shouting false greeting to strangers a hot breath away...</p