We examine variation in ovarian traits over a 24-month period in Cyprinodon rubrofluviatilis, an inhabitant of highly variable stream environments in the southern Great Plains of western Texas and Oklahoma. The smallest females bearing clutches are ca. 20 mm in standard length. Ovarian traits indicate that maximum reproduction occurred from March into July, but some degree of reproduction was potentially possible throughout the year. Most ovaries had atretic oocytes as early as September when the gonadosomatic index and the percentage of females with clutches were declining, but a small proportion had mature eggs in all fall and winter months (0–2%, average 0.8%, October–January, across all years) except, possibly due to sampling error, in October. Detailed analysis of females from April and July indicate greater reproduction in 2002 than in 2003 and greater in spring than in mid-summer. There was marginal evidence from estimates of dry weight of oocytes that females invest more energy in individual offspring in spring than in mid-summer.