Comparison of manual measurements and computer-assisted image analysis in fish morphometry

Abstract

Fish usually have a simple body shape and many morphological characters can be easily obtained by 2-dimensional image analysis. Measuring errors are often analyzed using data from several researchers or repeated measurements, but the testing of accuracy and repeatability based on different methods has rarely been examined. Here we report the comparison of manual measurements using Proma 150D digital calipers and computer-assisted image analysis in LUCIA software to evaluate the accuracy of both methods and the suitability of digital images for exploration of fish morphology. Eighteen morphometric characters of 20 specimens of Prussian carp were examined by 2 researchers. The mean of the relative bias within and between researchers separately for the manual and computer-assisted methods (expressed as a percentage of a character's value) varied from -4.27% to 9.48%. Comparison of interresearcher results using digital caliper, interresearcher results using LUCIA, intraresearcher results using digital caliper, and the 2 methods using manual caliper and LUCIA revealed significant differences in several characters. Only testing of intraresearcher relative bias using LUCIA showed no significant difference.