Spectral sensitivity and retinal anatomy of the weakly electric fish, Gnathonemus petersii.
Item
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Title
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Spectral sensitivity and retinal anatomy of the weakly electric fish, Gnathonemus petersii.
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Identifier
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AAI8915585
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identifier
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8915585
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Creator
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Ciali, Samuel Paul.
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Contributor
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Adviser: Peter Moller
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Date
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1988
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Language
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English
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Publisher
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City University of New York.
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Subject
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Psychology, Psychobiology | Agriculture, Fisheries and Aquaculture
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Abstract
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The current project explored spectral sensitivity in Gnathonemus petersii under two conditions of light adaptation. Two groups of four fish were exposed to brief (500 msec) flashes of monochromatic light stimuli. The startle response, an immediate and temporary acceleration in electric organ discharge (EOD) rate, was the dependent measure and served as the indice of detection and/or response by the fish.;In both conditions of light adaptation, the fish demonstrated greatest sensitivity to a 525 nm light ({dollar}\lambda{dollar} max). This finding was consistent with Bridges' (1972) nomogram for a freshwater fish species under conditions of dark-adaptation. The fish also exhibited relatively acute sensitivity to long wavelength light. Relative sensitivity among wavelengths varied between the two conditions of light adaptation with light-adapted fish demonstrating less pronounced relative sensitivity differences among wavelengths compared to dark-adapted fish.;These results suggest that the rod photoreceptors contain visual pigment which is most sensitive to a 525 nm light (i.e., a porphyropsin, vitamin A{dollar}\sb2{dollar}). As such, peak sensitivity (spectral absorbance) is red-shifted to wavelengths longer than 500 nm, the typical {dollar}\lambda{dollar} max for rhodopsinoid, vitamin A{dollar}\sb1{dollar} pigments found in most marine species. The presence of a second visual pigment type most sensitive to light of about 625 nm is suggested by a second peak located at the long wavelengths and the broad shoulder of relatively acute sensitivity to long-wavelength light. The startle response, as the dependent measure, was found to be graded such that the amount of acceleration in rate of EOD varied as a function of light intensity.;Investigation of retinal anatomy was performed at the level of light microscopy. The results of the histological investigation confirmed McEwan's (1938) original findings for related mormyrid species. The retina contained photoreceptors which were grouped into bundles with some 15-30 receptors per group.;The effects of the light-dark cycle, testing in clear-water conditions, and the intensity of the adapting light were discussed. Environmental conditions and behavioral ecology were viewed as correlated with the visual system of G. petersii. Mormyrid fish are able to integrate across visual and electric senses environmental information critical to their survival.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
