Abstract: Behaviour of fish is one of most potential sources of bias in fisheries acoustics. The paper describes methods and results of analyses of unique acoustic, hydrologic, and biologic data base collected by RV "Profesor Siedlecki" and RV "Baltica" in the southern. Baltic in the autumns 1994-2000. In comparison to the first part of the paper, presented in 2000, the influence of fish behaviour was examined separately in two different and specific sub-areas. On the basis of numeric models of measurements, interactions between environmental and behavioural factors and fish acoustic response for two different circumstances have been estimated and classified. Significant influence of environmentally modulated fish behaviour on effective value of the acoustic back-scattering cross-section was described and discussed.