目标强度（target strength，TS）是将回波积分值转换成绝对资源量的关键参数，同时也是渔业声学技术的热点研究内容。2012年12月及2013年6-7月，在三峡水库中华鲟基地网箱内使用BioSonics DT-X（199 kHz）分裂波式科学回声仪测定了4种共计31尾不同鳔室构造和体型的长江淡水鱼类背腹方向的目标强度，并将此结果与基尔霍夫近似模型法测定结果进行比较。实验鱼包括鳊（Silurus asotus）10尾及长江鲟（）7尾。结果表明，模型法测定结果与网箱控制法所测结果无显著性差异。构建4种鱼TS值（dB）与体长（BL，cm）的标准方程分别为鳊：TS=20lg（BL）-70.1（=0.80）；鲇：TS=20lg（BL）-74.5（=0.94）。模型法获得实验鱼目标强度的分布表明，鱼类不同的形态学特征及鳔室数量会影响目标强度的大小与分布特征。低频（38 kHz）下鳊、鲇及长江鲟目标强度最大值对应的姿态倾角出现在-10°~0°，而鲢目标强度最大值出现在-20°~-10°，且不同种类鱼的目标强度最大值所对应姿态倾角的位置各不相同。本研究通过网箱控制法和模型法测定了4种不同鳔室构造和体型的长江淡水鱼类目标强度，可为长江淡水鱼类目标强度研究提供有益借鉴，为采用渔业声学方法进行长江淡水鱼类垂直原位监测评估资源量提供相关参数。

Target strength (TS) is a pivotal parameter for converting echo integral values into absolute fish abundance. It is also a hot research topic in the research and application of fishery acoustic technology. However, the TS-length relationships have been studied in very few freshwater species. Most studies focused on commercially important species, while TS in fish of different physiological structures is investigated less frequently. In this study, cage method and KRM (the Kirchhoff ray-mode approximation model) method were used to measure TS of 4 fish species (Acipenser dabryanus) which represent different morphological and ecotypic characteristics. Thirty-one individuals were measured by a calibrated 199-kHz BioSonics DT-X split beam echosounder in the vertical direction in a net cage, using the Visual Acquisition software. The cage method experiment was conducted in the Chinese sturgeon farm base which is located in the Three Gorges Reservoir, in December 2012 and from June to July in 2013. During the cage experiment, one fish was measured each time. Then, the body length and weight of each species were measured after the fish were euthanized in Tricaine-S (MS-222). The acoustic data were processed by Sonar-5 Pro software. Two X-ray images were taken from the dorsal and side of fish to understand the internal physiology and the shape of the swim bladder of the fish. The TS of six individuals was calculated using KRM model, and the results were verified by cage method. The results showed that it was feasible to determine TS of freshwater fishes using the cage method, and the results of this method were not significantly different from the model method. The linear regression equations for mean TS with fish BL were derived in dorsal aspect were:TS_pp=20lg(BL)-70.1 (=0.80), TS_sa=20lg(BL)-74.5 (=0.94), respectively, where BL is fish body length, pp is , and ad is . The linear regression equations for mean TS with fish TL in dorsal aspect were:TS_pp=20lg(TL)-71.4 (=0.80), TS_sa=20lg(TL)-75.1 (=0.94), respectively, where TL is total fish length. Under the same body length conditions, the TS of the four fish species was compared:S. asotus. The results of KRM model support that swim bladder is the primary contributor to backscattered energy. The values of TS and their distribution calculated by the cage method and model method were affected by the morphological characteristics and the swim bladder structure of fish species. Maximum TS of occured between -10° and 0° at 38 kHz, while the maximum TS of appeared between -20° and -10°. The position of maximum TS occurred differently for each fish species. At the low frequency of 38 kHz, the model method results showed that there was significant difference in the distribution of TS with the angle of incidence of sound waves between fish with a one-chambered swim bladder and those with a multi-chambered swim bladder. Compared to immobilized and unconscious fish, the fish in the net cage can swim freely. However, the narrow beam lowers the probability of the fish being detected, which increases the time of the experiment. In the future, it is necessary to appropriately reduce the size of the cage to optimize the implementation conditions. Our study enriches the TS of freshwater fishes and accumulates basic data for acoustic identification.

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国家自然科学基金项目（31711540294，51641909，31602160和31772854）；中国水产科学研究院基本科研业务费资助项目（2018JBF16）；农业部财政专项子课题“长江中游渔业资源与环境调查”（CJDC-2017-14）.