Browsing by Subject "fish"
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Item Aquatic macrophyte and animal communities in a recently restored brackish marsh: possible influences of restoration design and the invasive plant species Myriophyllum spicatum(2012-07-16) Bell, Michael ThomasThe numerous benefits that wetlands provide make them essential to ecosystem services and ecological functions. Historically, wetland losses have been caused by natural and anthropogenic changes. In Texas, nearly 50% of coastal wetland habitat has been lost since the 1930s and losses in the Lower Neches watershed have been some of the most extensive. Restoration is a way to mitigate these losses and can be accomplished in many ways. Each restoration design creates different aquatic habitats that can influence both submerged aquatic vegetation (SAV) and faunal communities. The restoration of the Lower Neches Wildlife Management Area (LNWMA) has created the conditions for the growth of the invasive submerged macrophyte, Myriophyllum spicatum (Eurasian watermilfoil) which may be competing with the native aquatic grass, Ruppia maritima (widgeongrass) for essential nutrients. In this study, an attempt was made to link restoration design with both SAV and aquatic fauna community structures by using a throw trap to characterize assemblages observed in three different types of restored marshes. We also performed two controlled mesocosm experiments in 0.5 gal aquariums to determine growth inhibition by M. spicatum on R. maritima. Analyses using Kruskal-Wallis non-parametric test determined that temporal variations in fauna and SAV community composition was greater than any restoration effect. Discriminant Function Analyses (DFAs) determined two to three key faunal species that best predicted association among restoration designs, but linear regressions could not determine any consistent relationship between individual species density and biomass of the dominant SAV species, M. spicatum. For the mesocosm experiments, M. spicatum inhibited the biomass production and branch count of R. maritima when the two species are grown together (ANOVA, p = 0.004 and 0.003, respectively). Changes in SAV assemblages due to competition and habitat characteristics could play a major role in determining faunal community. In order to minimize the temporal effect observed and better determine any habitat pattern that may be present, a much longer study is necessary.Item Associations of watershed and instream environmental factors with aquatic macrofauna in tributaries of the Pedernales River, Texas(Texas A&M University, 2005-08-29) Birnbaum, Jenny SueIntermittent headwater streams serve important functions in semi-arid rangelands, both for humans and wildlife. However, few studies have assessed species-environment relationships for fish and benthic macroinvertebrate assemblages in these systems. Additionally, no published studies could be found that addressed the influence of juniper coverage in watersheds on assemblage structure of these taxa. Increased juniper coverage in recent decades is believed to be associated with decreased water yields in central Texas streams. During summer 2003 and spring 2004, I examined potential effects of juniper cover on aquatic ecology. Fishes, benthic macroinvertebrates, and the physicochemical habitat were investigated in spring-fed headwater tributaries of the Pedernales River. My objectives were to: 1) describe the typical fish and benthic macroinvertebrate assemblages in headwater creeks of the Pedernales River basin; 2) compare seasonal variability of fish and benthic macroinvertebrate assemblages; 3) identify species-environment relationships in this river basin; and 4) evaluate the influence of juniper coverage in the watershed, relative tolocal and landscape-level environmental factors, on the structure of fish and benthic macroinvertebrate assemblages. A total of 4,181 individual fish were collected in summer 2003 samples, 551 fish were collected in spring 2004, 59,555 macroinvertebrates were captured in summer 2003 samples, and 51,500 macroinvertebrates were collected in spring 2004. Assemblages were typical for the area and habitat conditions. Faunal richness was lower in spring than in summer, possibly due to a combination of sampling after a relatively dry period in the spring, and lack of winter refugia in the form of deep pools. Fish assemblages may structure based principally on abiotic factors in spring, the harsher season (less available water), whereas predation pressure may influence structure in summer. Another important environmental gradient for both fish and invertebrate assemblages contrasts pool and run mesohabitats. In general, juniper cover was weakly associated with fish and invertebrate assemblages, although it tended to be associated with relatively high quality habitat for sensitive taxa (flowing runs with coarse substrate; deep, connected pools). In these intermittent streams, local-scale environmental factors probably are the dominant influences on fish and benthic macroinvertebrate assemblages. Implications for future studies are discussed.Item Calcium Montmorillonite for the Mitigation of Aflatoxicosis and Gastrointestinal Inflammation(2014-08-06) Zychowski, Katherine EClays have been used for centuries as ?ancient medicine? for their therapeutic benefits. One particular clay, calcium montmorillonite, has historically been used as an anti-caking agent in animal feeds, but has also demonstrated the ability to bind toxins and alleviate infectious diarrhea. The full breadth of therapeutic applications and molecular mechanisms of montmorillonite is still unknown. Therefore, the purpose of this research was to explore novel therapeutic applications for NovaSil (NS), a calcium montmorillonite clay to reduce the risk of aflatoxicosis in farm-raised fish and alleviate gastrointestinal inflammation and dysbiosis in a mouse model of Crohn?s disease (CD). Aflatoxin B_(1) (AFB_(1)) is a fungal mycotoxin that commonly contaminates corn and peanut crops. It is produced by the fungi Aspergillus flavus and A. parasiticus during times of drought or due to improper post-harvest storage. Aflatoxin B_(1) is known to cause hepatocellular carcinoma, immunosuppression and growth stunting in several species. Recently, incorporation of plant-based alternatives into feed for farm-raised fish has become a trend, thereby increasing the risk for mycotoxin contamination. Inexpensive strategies to reduce AFB_(1) exposure are needed. Calcium montmorillonite clay, which is both inexpensive and abundant, has a dioctahedral structure that is known to sequester AFB_(1) in its negatively-charged interlayer, thereby reducing systemic bioavailability. There is also some evidence to suggest that calcium montmorillonite clays may possess gastrointestinal anti-inflammatory properties. NovaSil was used as a strategy to reduce the effects of AFB_(1) in Nile tilapia (Oreochromis niloticus) and red drum (Scieanops ocellatus). Juvenile tilapia and red drum were dosed with AFB_(1) and NS over the course of 10 and 7 weeks, respectively. Additionally, proinflammatory cytokine-clay binding was characterized using isothermal analysis, X-ray diffraction (XRD) and transmission electron microscopy (TEM). Furthermore, a TNBS (2,4,6-Trinitrobenzenesulfonic acid)-colitis gastrointestinal mouse model was employed to study the anti-inflammatory properties of NS and its ability to protect the gut microbiome. Results suggest that NS can prevent aflatoxicosis in red drum at a 2% inclusion level over the course of 7 weeks. NovaSil also prevented some toxicity in Nile tilapia; however, these results were not significant. In vitro results also indicate that NS sorbs proinflammatory cytokines such as TNF? and IL-1? in its interlayers. Additionally, NS was found to reduce serum pro-inflammatory cytokine levels in TNBS-induced mice and reduce gut dysbiosis. These results could positively impact both human and animal populations with AFB_(1) exposure and/or chronic gastrointestinal inflammation.Item The Architecture of Phenotypes in a Naturally Hybridizing Complex of Xiphophorus Fishes(2013-04-08) Johnson, James BradleyThe origin and maintenance of phenotypic variation has generated considerable interest among students of functional morphology, sexual selection and behavioral ecology. In particular, hybridization has been suggested as a phenomenon which may generate novel phenotypic variation. In this dissertation I focus on the Xiphophorus birchmanni - X. malinche hybrid system to assess the role of hybridization in altering behavioral, morphological, sexual and non-sexual traits. I determine the relationship between the sword sexual ornament and body condition to support previous work which suggests that the sword is an inexpensive means to increase apparent size. My findings support the prediction that, while body size is condition-dependent, the sword is not. I show a trend toward hybrid populations displaying increased phenotypic variance and reduced phenotypic integration in sexual ornaments and body size. These findings provide evidence for a potential answer to a central question in the study of sexual selection, that of reduced genetic and phenotypic variance in sexual ornaments as the result of persistent direction selection generated by female choice. I take advantage of reduced phenotypic integration in hybrids allowing the evaluation of locomotor performance across a broad range of multivariate trait values. Sexual ornaments did not impair swimming performance per se. Rather, the sword negatively affected performance only when paired with a sub-optimal body shape. I evaluated how natural hybridization changes the relationship between boldness and anti-predator response. In poeciliid fishes, bold individuals have increased survival in the presence of predators. This non-intuitive observation may result from bold individuals being more likely to engage in anti-predator behaviors. Counter to my prediction, bold individuals were less likely to perform a fast-start response to a predator threat. This correlation was consistent among populations and species but was only significant in hybrids. My findings suggest that hybridization could influence correlations between behavioral traits in a manner similar to that documented for morphological traits.Item The role of piscivores in a species-rich tropical river(Texas A&M University, 2004-11-15) Layman, Craig AnthonyMuch of the world's species diversity is located in tropical and sub-tropical ecosystems, and a better understanding of the ecology of these systems is necessary to stem biodiversity loss and assess community- and ecosystem-level responses to anthropogenic impacts. In this dissertation, I endeavored to broaden our understanding of complex ecosystems through research conducted on the Cinaruco River, a floodplain river in Venezuela, with specific emphasis on how a human-induced perturbation, commercial netting activity, may affect food web structure and function. I employed two approaches in this work: (1) comparative analyses based on descriptive food web characteristics, and (2) experimental manipulations within important food web modules. Methodologies included monthly sampling of fish assemblages using a variety of techniques, large-scale field experiments, extensive stomach content and stable isotope analyses. Two themes unite the information presented: (1) substantial spatial and temporal variability in food web structure, and (2) how body-size can be used to generalize species-interactions across this complexity. Spatial variability occurred at various scales, from among small fish assemblages on seemingly homogeneous sand banks, to differences among landscape scale units (e.g. between lagoons and main river channel). Seasonal variability was apparent in predation patterns, with relative prey availability and body size primarily resulting in decreasing prey sizes with falling water levels. Body size was also related to functional outcomes of species interactions, for example, a size-based response of prey fishes to large-bodied piscivore exclusion. This pattern was further substantiated at the landscape-scale, as differences in assemblage structure among netted and un-netted lagoons were largely size-based. Trophic position of fish and body size was not found to be related, likely due to the diversity of prey available to consumers, and may signify that commercial netting activity will not decrease food chain lengths. In sum, by describing human impacts within a food web context, I endeavor to provide predictive power regarding a specific human-induced environmental problem, yet still allowing for generality that will broaden the theoretical foundations and applications of food web ecology.