An Inexpensive Image Analysis System for Fish Otoliths

Abstract

This paper evaluates the feasibility of using flatbed scanners and free computer software for image analysis of fish otoliths. Scanned images of whole and cross-sectioned otoliths from bluegill Lepomis macrochirus, freshwater drum Aplodinotus grunniens, largemouth bass Micropterus salmoides, warmouth L. gulosus, and white crappie Pomoxis annularis provided adequate resolution for visualizing and counting annuli as well as for measuring interannual growth increments. I found concordant relationships between interannual growth measurements taken with a microscope-based image analysis system and those taken with the scanning technique. The use of flatbed scanners for age and growth analyses could substantially reduce costs, and such scanners may already be available for many persons interested in otolith image analysis. This could widen the access to otolith research for those who previously could not afford imaging equipment. Depending on user experience and computer and scanner speeds, 25–40 already cross-sectioned or whole otoliths can be digitized per hour into high-quality photographs, a process rate that is comparable with that of contemporary image analysis systems.