The relationship between fish target strength and the orientation of fish in horizontal (yawing) and vertical (pitching) planes was modelled by the equation TS = m. cos 2 alpha + b (also with cos3, cos5 and cos7). The cos3 model gave the best fit of data for three fish species: brown trout, roach and rudd. The model can be used for 1) estimation of the most probable aspect in the horizontal plane; 2) estimation of the mean all-aspect target strength of fish and 3) calculation of probability of recording of a fish of given size when a known noise threshold is applied.