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Elasmobranch fishes use electroreception to detect electric fields in the environment, particularly minute bioelectric fields produced by potential prey. A single elasmobranch family (Potamotrygonidae) is composed of obligate freshwater stingrays endemic to the Amazon River. A freshwater existence has imposed morphological adaptions on their electrosensory system due to life in a high impedance medium. Because their electrosensory morphology differs from their marine relatives, freshwater stingrays may demonstrate corresponding differences in behavioral sensitivity. The objective of this study was to quantify behavioral sensitivity of the obligate freshwater stingray Potamotrygon motoro to prey-simulating voltage. The voltage produced by common teleost prey of P. motoro were measured and replicated for behavioral trials. The best response was 10.62 cm, and the smallest voltage gradient detected was 0.005 mVcm-1. This sensitivity is reduced compared to marine species. The conductivity of the medium, more so than ampullary morphology, may dictate sensitivity of the elasmobranch electrosensory system. / by Lindsay L. Harris. / Thesis (M.S.)--Florida Atlantic University, 2013. / Includes bibliography. / Mode of access: World Wide Web. / System requirements: Adobe Reader.

The lateral line canal system is a sensory organ found in all teleost fish that has a wide range of morphological variation. Variation in morphology may often be the result of evolutionary necessity where the need for function dictates form. Xiphister mucosus is an amphibious Stichaeid fish that inhabits the rocky intertidal zone of the northeastern Pacific Ocean. The rocky intertidal is considered an extreme environment where crashing waves and ebbing tides may require the specialization of adaptations for surviving the many abiotic stressors encountered there. The lateral line trunk canal of Xiphister is regarded as unique among teleosts with multiple, branching, zigzag shaped canals that are morphologically complex. The X. mucosus canal was found to not serve as a mechanosensory organ, rather the findings presented here suggest a new role as a water transport organ. This may be an exaptation to help X. mucosus avoid desiccation during low tides when the fish remain upon the rocky shore and exposed to dehydration. While emersed, Xiphister relies on cutaneous respiration as its primary means of aerial respiration.

Electroreception is a sensory modality found in some fish, which enables them to sense the environment through the detection of electric fields. Biological experimentation on this ability has built an intricate framework that has identified many of the components involved in electroreception's production, but lack the framework for bringing the details back together into a system-level model of how they operate together. This thesis builds and tests a computational model of the Electrosensory Lateral Line Lobe (ELL) in mormyrid electric fish in an attempt to bring some of electroreception's structural details together to help explain its function. The ELL is a brain region that functions as a primary processing area of electroreception. It acts as an adaptive filter that learns to predict reoccurring stimuli and removes them from its sensory stream, passing only novel inputs to other brain regions for further processing. By creating a model of the ELL, the relevant components which underlie the ELL's functional, electrophysiological patterns can be identified and scientific hypotheses regarding their behavior can be tested. Systems science's approach is adopted to identify the ELL's relevant components and bring them together into a unified conceptual framework. The methodological framework of computational neuroscience is used to create a computational model of this structure of relevant components and to simulate their interactions. Individual activation tendencies of the different included cell types are modeled with dynamical systems equations and are interconnected according to the connectivity of the real ELL. Several of the ELL's input patterns are modeled and incorporated in the model. The computational approach claims that if all of the relevant components of a system are captured and interconnected accurately in a computer program, then when provided with accurate representations of the inputs a simulation should produce functional patterns similar to those of the real system. These simulated patterns generated by the ELL model are compared to recordings from real mormyrid ELLs and their correspondences validate or nullify the model's integrity. By building a computation model that can capture the relevant components of the ELL's structure and through simulation reproduces its function, a systems-level understanding begins to emerge and leads to a description of how the ELL's structure, along with relevant inputs, generate its function. The model can be manipulated more easily than a biological ELL, and allows us to test hypotheses regarding how changes in the structures affect the function, and how different inputs propagate through the structure in a way that produces complex functional patterns.

The Deepwater Horizon oil spill released millions of barrels of oil into the Gulf of Mexico, impacting economically and ecologically important fishes. Polycyclic aromatic hydrocarbons (PAHs) present in the oil have been shown to cause developmental impairments in early life stage fishes, such as morphological and behavioral changes related to eye formation and visual processing following PAH exposure. Prior research reported reduced eye growth in open water, pelagic species, as well as reduced photoreceptor-specific transcription factors associated with eye development following exposure to crude oil. Though changes in transcriptomic-level pathways associated with vision and visual processing have been reported, it has yet to be determined how these changes relate to physiological or behavioral-level effects in fish. Therefore, the present studies evaluated the effect of weathered crude oil on eye development and visual function in mahi-mahi, red drum, sheepshead minnow, and zebrafish larvae. Fish were assessed through several visually-mediated behavioral assays, analyzed histologically and immunohistologically, along with subsequent transcriptomic analyses and associated gene expression changes. Larvae exposed to crude oil experienced significantly reduced abilities to exhibit optomotor or optokinetic responses relative to controls, with associated reductions in retinal development. Furthermore, genes associated with eye development and phototransduction were downregulated, with subsequent decreases in the immunofluorescence of neurological connections within the retina and a choroid-specific increase in apoptotic activity. We related oil-induced transcriptomic-level effects to morphological, physiological, and behavioral-level impairments in larval teleost fishes.