Size, Age and Demography of Metamorphosis and Sexual Maturation in Fishes

Understanding what determines the timing of transitions between life-history stages in fishes is crucial to an understanding of their demography. Most theoretical treatments assume that these transitions are age dependent, but evidence accumulating from a variety of organisms indicates that size is an important variable also. In the starry flounder, Platichthys slellatus (Pallas), the onset of metamorphosis is more closely related to size than age. In the platyfish, Xiphophorus maculatus (Gunther), the onset of sexual maturation depends on both size and age. I compare these results with those reported for other organisms, and outline the expected ecological correlates of age- and sizedependent transitions between life history stages in general.