A density‐dependent function for the instantaneous fishing mortality rate is presented. It is shown that this function may be readily incorporated into the age‐specific probability of survival in a Leslie‐matrix population model. A method is presented for indirectly determining the probability of survival for age‐class 0 of a fish population using a density‐dependent Leslie matrix. The method involves the two constraints that the population be at equilibrium and that the index of absolute population size in the density‐dependent function be assigned a value. In addition, given the probability of survival for age‐class 0, it is shown that the probability of survival through a selected life stage within age‐class 0 can be indirectly determined. Three problems in modeling a fish population using a Leslie model are discussed in light of the difficulties involved in modeling density dependence due to insufficient information and lack of understanding concerning density‐dependent phenomena.