The Texas fatmucket, Lampsilis bracteata, is a unionid mussel endemic to the Colorado and upper Guadalupe River basins of Central Texas and a candidate for federal listing under the Endangered Species Act. There is increased interest in propagation and population restoration of threatened mussels in Texas as a potential conservation method, but still little is known about their life histories and how local populations may differ in aspects of their reproductive ecology, e.g. timing of brooding and potential local adaptations to host fish. The purpose of this study was to compare host fish compatibilities and seasonality of reproduction between two populations: (a) by cross‐infesting fish from the San Saba and Llano Rivers in the Colorado River basin with sympatric and allopatric mussel larvae in the laboratory (hatchery‐produced Guadalupe bass and largemouth bass were also infested); and (b) by assessing gamete concentration, brooding period, viability of larvae and sex ratios using monthly sampling events between February 2017 and February 2018. Reproduction varied with season and between populations. The proportion of females brooding tended to be lower in the summer and the autumn, and higher during winter and spring months before peak water temperatures were reached. The sex ratio in both populations did not significantly differ from 1:1. Fecundity and larvae viability were higher in the Llano River population compared with the San Saba population. Trematode flatworms were found in several female gonad samples from the San Saba population and in a few samples from the Llano population. The highest metamorphosis success occurred on wild green sunfish and largemouth bass, and hatchery‐produced largemouth and Guadalupe bass. The average metamorphosis success tended to be higher for some mussel–fish pairings originating from the same tributary, suggesting that mussels may be locally adapted to host fish, which should be considered in conservation efforts.