Mixed mating strategies offer the benefits of both self-fertilizing one’s own eggs (selfing) and outcrossing, while limiting the costs of both methods. The economics of mixed mating is further determined by the individual’s level of self-compatibility. Individuals that are more self-compatible can exploit the benefits of selfing when the costs of outcrossing are high, perhaps better than individuals with less self-compatibility. In gynodioecious (hermaphrodites and females) and androdioecious (hermaphrodites and males) species, the level of self-compatibility of the hermaphrodites also acts as a selection pressure on the fitness of the other sex. The mangrove rivulus fish is an androdioecious species and populations are comprised of selfing hermaphrodites and males that result from hermaphrodites changing sex. Although hermaphrodites overwhelmingly reproduce through internal selfing, they occasionally oviposit unfertilized eggs. Males can externally fertilize these eggs, resulting in outcrossed progeny. Here, we reveal that fecundity and self-compatibility varies within individuals across ontogeny and among individuals derived from lineages that vary in their propensity to change sex. Hermaphrodites from high sex changing lineages were significantly less fecund and self-compatible than hermaphrodites from low sex changing lineages. We also demonstrate that fecundity and self-compatibility change across ontogeny from sexual maturity to about 365 days post hatch. These differences in self-compatibility and fecundity have the potential to drive evolutionary changes on mating strategy and the fitness of males in populations of the mangrove rivulus. This study also illustrates the importance of including lineage variation when estimating the costs and benefits of mixed mating strategies.