As land use conversion increases through urban development, there are noticeable increases in the impervious cover that heavily contribute to urban stream syndrome. These modifications are associated with shifts in water quality, altered hydrology, and reduction of biotic richness. Some tolerant fish species modulate their life-history traits, such that they increase or retain their reproductive rate and persist in urbanized environments. The Western mosquitofish, Gambusa affinis, is a native species of live-bearing fish that is tolerant to change. We hypothesized that increasing urbanization, defined by percent developed land in the water-shed around each site, will affect life-history traits of female mosquitofish. We sampled fish from 6 streams with varying levels of urbanization. We found that total embryo size was largest in the most urbanized (51%) followed by the least urbanized populations (2, 5%). The intermediately urbanized populations (32, 25, 21%) had the smallest total brood size. The most urbanized (51%) population showed a trade-off in brood number and brood size with the lightest individual embryo mass. But the second least developed (5%) and the intermediate populations did not show trade-offs as their individual embryo masses were not as small. Our findings suggest that mosquitofish tolerate urbanization by altering their life-history tradeoffs.