1. The property of resistance to flow in a fluid or semi fluid. By analogy, in fisheries: the property of resistance of elements of a stock to move and mix together. As a consequence of stock "viscosity," mixing of individuals is neither complete nor instantaneous and the transfer of the local impact of fishing to the entire stock (through directional or turbulent mixing) is a function of the stock´s "viscosity. " If there is zero mixing, the viscosity is infinite. Because of lack of data on mixing rates, the term "viscosity" is often used only in a qualitative fashion.