Abstract: The paper analyzes existing in situ methods of fish target-strengthestimation with speciał emphasis on an indirect method that utilizes statistical manipulation on a backscattered acoustic echoes set. The inverse problem in question requires finding the unknown probability density distribution (PDF) of target strength inthe logarithmic "domain" or PDF of a backscattering cross-section in the "domain" of absolute variables. These PDFs can be estimated by solving the so called "single-target single-beam integral equation", relating distributions of echo variable, target strength and beam pattem of the echo sounder transducer. In the presented analysis special attention is given to four newly developed TS-estimation methods, viz.: Expectation, Maximization and Smoothing (EMS), Discrete "Mellin Deconvolution", Windowed Singular Value Decomposition (WSVD) and Regularization. These methods use more sophisticated estimation techniques than conventional deconvolution and related methods. A comparison of the resulting estimates obtained from the analyzed methods (using simulations as well as real data from acoustic surveys) concludes the paper.