Bull. Jpn. Soc. Fish. Oceanogr. 69(1), Page 18-26, 2005   Body Length Measurements Using a Photo Image Analyzing Technique: An Application for Estimating the Total Length Composition of Landed Spotted Sole Chifumi Imai†1, Yoshinobu Miyazaki1, Muneharu Tokimura2 and Keisuke Yamamoto3 1 National Fisheries University, 2-7-1, Nagatahonmachi, Shimonoseki, Yamaguchi 759-6595, Japan 2 National Research Institute of Fisheries and Environment of Inland Sea, Fisheries Research Agency, 2-17-5, Maruishi, Ohno, Saeki, Hiroshima 739-0452, Japan 3 Seikai National Fisheries Research Institute, Fisheries Research Agency, 1551-8, Tairamachi, Nagasaki, Nagasaki 851-2213, Japan †e-mail: cimai@fish-u.ac.jp A method of measuring fish body lengths at a fish market was developed using a photo image analyzing technique. The method was used to obtain total length composition (commercial categories) of the spotted sole, Eopsetta grigorjewi, landed at the fish wholesale market in Shimonoseki, Yamaguchi Prefecture, Japan. The greatest advantage of the method was the freedom given from handling specimens, allowing quick and easy application under various circumstances. Fish total lengths could be measured with very high precision from photographs of individual fish placed on a flat surface. Because spotted sole was packed according to commercial size categories in separate styrofoam containers before landing, accurate total lengths could be obtained relative to the inner length of the container at the same level as that of the fish snout (TLib). Major errors in TLib arose from fish inclination (caudal fin tip generally located 0-5 cm higher than snout level) and the convex body shape. Fish inclination resulted in an overestimation of length and the convex body in an underestimation. Because these two factors showed a positive relationship, body convexity increasing with fish inclination, the two error factors essentially cancelled each other out, resulting in a minimal overall measurement error. Between 25% and 50% of fish in photographs of packed fish were entirely visible and able to be measured. No significant difference was found in mean lengths between measurements of visible fish only and all individuals in the container. Mean total length (cm) for each commercial size category N (N: number of sole per container) was formulated by the allometric equation, =55.9N-0.23. Key words: Eopsetta grigorjewi, body length measurement, photo image analyzing technique, spotted sole