Degree Name

Master of Science (MS)

Semester of Degree Completion

1981

Thesis Director

Leonard Durham

Abstract

This investigation was undertaken to determine if annual marks were present in the otoliths of the Bluegill sunfish, Lepomis macrochirus, and to explore their possible use as ageing structures in a thermally perturbed environment.

Two populations were studied; one from a farm pond with marked seasonal changes and the other from Lake Sanchris which serves as a cooling reservoir in central Illinois. Age determinations were made on 53 and 45 fish from the farm pond and Lake Sanchris respectively.

Annual marks were found to occur in the sagittae otoliths of the bluegill. These marks showed bright amber in sectioned otoliths under transmitted light. Confirmation of the marks as annual was accomplished by comparison with scale ages and growth curves. Total percent agreement between readers was 68% and 87% for scales and otoliths respectively, (x2 = 0.9878, .1

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