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The J-QUEST instrument package is being developed to measure precise TS and body length simultaneously. In situ fish target strength (TS) measurements are important in acoustic assessment surveys since TS is the key information to estimate fish abundance. J-QUEST consists of a quantitative echo sounder and a stereo HARP TV camera system installed in a pressure housing rated to depth of 300 m. The stereo TV camera system is used to identify fish species and to estimate length and tilt angle of observed fish. These biological measurements complement measurements by the quantitative echo sounder. The first trial of J-QUEST was conducted off the coast of Kashima to Sanriku, Japan during December 2003. We observed a Pacific saury (Cololabis saira) aggregation acoustically and optically. Optical measurements of 24 fish were used to estimate the distribution of body lengths.