Measuring fish target strength (TS) is the foundation of fisheries acoustic research and its applications. TS measurements focused on fish in the Yangtze River are lacking or do not meet the needs for a fisheries resource assessment. Variations in TS of four freshwater cultured fish species with different swim bladder structures were measured with a BioSonics DT-X (199 kHz) split beam echosounder in the horizontal direction. The four fish were Vachell's bagrid fish (), crucian carp (ex situ experiment was carried out in a small T-shaped tank during June and October 2015. The tank was constructed of eight fiberglass-reinforced plastic boards. Polyurethane foaming plastic cotton was pasted on the internal face of the tank to absorb any sounds reverberating from multiple echoes. Twenty-nine individuals were anaesthetized and tethered on a horizontal rotation support, in turn, and TS was measured at different horizontal angles. The angles were changed from -90° to 90° at an interval of 5°. Individual TS was measured for 300 pings at each angle. The results showed that mean TS of fish was affected by the aspect angle. Maximum TS occurred in the lateral direction, and minimum TS occurred in the head-tail direction. The difference between the maximum and minimum TS was about 10 dB. A cos functional relationship was observed between the measured TS and the sound wave incident angle, as well as from the fish dorsal-ventral direction. Fish TS values were smaller in the dorsal aspect than those in the side aspect. These differences may have been affected by the shape of the swim bladder and its position in the body. Two X-ray images were taken from the side and dorsal aspects of each fish to understand the inner structure of the fish and the swim bladder. TS of fish with a one-chambered swim bladder was smaller than that fish with a multi-chambered swim bladder, even though standard length (SL) of the one-chambered fish was longer. Relationships between TS-length (TS-total length, TS-standard length), and TS-weight (TS-fish weight) were derived in three orientations:lateral (from -90° to -80° and from 80° to 90°), oblique (from -75° to -20° and from 20° to 75°), and in all of directions. Linear regression equations were prepared for the side and dorsal aspects of the four fish species. The side aspect linear regression equations for mean TS with fish SL in the lateral position were:TS__vbf=19.5lg(SL)-63.4(=0.66), TS__cc=19.7lg(SL)-56.6(2=0.89), respectively, where SL is fish standard length, vbf is a fish with a one-chambered swim bladder (Vachell's bagrid fish), mf is mandarin fish, cc is crucian carp, and gc is grass carp.). The dorsal aspect linear regression equations for mean TS with fish SL in the lateral position were:TS__vbf=28.7lg(SL)-75.7(=0.88), TS__cc=19.1lg(SL)-59.9(2=0.99), respectively. In this experiment, the fish's body was tethered tightly on a rotational support, so fish behavior was limited. The beam was narrow in the short distance. Although the beam covered the entire body, mean TS was affected by the swim bladder position in the body. Hence, some differences between the measurements were observed. In the future, the mean TS of these fish species should be measured or in a net cage, so researchers can compare the results with this study to improve the accuracy of converting length and assessing resources from the TS measure-ments. This study will help guide fish behavior research and fisheries resource assessments in the Yangtze River.