In theoretical, stabilized fish populations it is shown that maximum yield in weight depends not only on the rates of natural and fishing mortality but also on the nature of growth in weight. Families of yield curves at various combinations of natural and fishing mortality rates are presented for three growth types with point of inflection (A) early in life, (B) about mid-life, and (C) late in life. Maxima appear in all three types but at progressively lower natural mortality rates. The curves are of limited practical value because of the many assumptions which are involved.