Fitness differences among remnant populations of the endangered sonoran topminnow.

Four correlates of fitness were measured in three stocks of the endangered Sonoran topminnow, Poeciliopsis occidentalis, from Arizona. Survival, growth, early fecundity, and developmental stability were greatest in laboratory-reared fish from the most heterozygous natural population studied. Conversely, all four traits were poorest in fish from a population with no electrophoretically detectable genetic variation. These results emphasize the need for genetic as well as demographic information for the development of comprehensive species recovery programs.