Validation of auto-counting method by NIH Image using otoliths of white-spotted char Salvelinus leucomaenis

Abstract

The ages of individual specimens of white-spotted char Salvelinus leucomaenis, collected from the Furuu River in Hokkaido, Japan, were determined from otoliths using NIH Image. We employed two methods to determine age. First, for a surface method (traditional method), the ages were made from examinations of otoliths under a microscope by experienced readers A, B and an unexperienced reader C. Second, for an auto-counting method, a computer program was used to detect the peaks from otolith images. We made a mathematical model to estimate the probability of a correct reading for each reader, using the results of the age determination and the per cent age agreement among readers. The ability to determine the age of white-spotted char depended on whether or not the reader had ever previously made age determinations. The ability of auto-counting method was below that of reader A (one of the experts), and the method was slightly superior to reader B (the other expert).