Аннотация:We consider an age-structured model of fish population with time-constant fertility and mortality coefficients subject to periodic harvesting. Fishing technology does not allow to catch the fish younger than a certain age, e.g. because it passes through the net cells. Thus, fishing intensity is age specific with one-dimensional fishing efforts (control). We show that the maximization of average profit results in a periodic optimal control problem. One of the main task of ours is to find the conditions for existence of a time-periodic control showing better performance than any constant (steady state) control.