Mahurin Honors College Capstone Experience/Thesis Projects

Department

Biology

Document Type

Thesis

Abstract

The morphology of the peripheral and inner ear structures was studied in the loricariid catfish Pterygoplichthys gibbiceps. Specimens (n=6) were preserved in fixative (4% paraformaldehyde, 2% glutaraldehyde in 0.1M phosphate buffer) and dissected for examination of the gross morphology (using light microscopy) and ultrastructure of the auditory sensory epithelia (using scanning electron microscopy). One additional specimen was cleaned in a dermestid beetle colony in order to examine the osteology of the skull. The swim bladder of P. gibbiceps is divided along the midline of the fish into two reduced but equal lobes residing in two laterally oriented bony encapsulations. Immediately lateral to the swim bladders, fenestrations were observed in the pterotic + supracleithrum. A single Weberian ossicle was attached to the medial apex of the bladder, which translates external sound pressure energy into interaural hydrodynamic motion of the fluid within the pars inferior. The single ossicle bends 90o through a bone which acts as a pivot point allowing linear motion at the extreme ends of the ossicle. Otoliths (solid calcareous bones in the inner ear) were similar in shape to those of other loricariids. The asteriscus was disk-like and had a large crescent shaped sulcus that covered the macular striola. Sagittae were slender at their caudal apex and exhibited two wing-like projections about the rostral region of the otolith. Utricular otoliths were thick, having a bulbous rostral region and a laterally flattened triangular caudal region. On its ventral surface there was a deep sigma-shaped sulcus which was not in contact with the utricular maculae. Auditory endorgan-specific patterns of the orientation of sensory hair cell kinocilia were observed on each macular surface. Maculae exhibited areas of reversed hair cell orientation called the striola. Sacculi possessed a vertical striolar pattern. The lagenar patterns were crescent shaped in similar fashion as the sulcus of the otolith, and the pattern of the utricle was unlike the shape its otolith and curved sigmoidally to terminate at the lateral extremities of the otolith. In general, while there are unique peripheral auditory structures in P. gibbiceps (bi-lobed and encapsulated swim bladders and a single Weberian ossicle), the inner ear maculae and striolar patterns found in P. gibbiceps are similar to those found in other catfishes.

Advisor(s) or Committee Chair

Micheal E. Smith

Disciplines

Biology | Life Sciences

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