Surfperches (Embiotocidae) are a unique family of viviparous fishes that have internal fertilization, gestation to the sub-adult stage, and live-birth; therefore, maternal investment is extremely high. This invokes the expectation that brood size is limited and females should be choosy and select few mates. Yet multiple paternity occurs in all eight species examined to date, with high prevalence ranging from 92–100%. Most surfperches are found along the Eastern Pacific coast, but Ditrema temminckii is distributed in the Western Pacific and we found differences in their mating strategy compared to other surfperches. In D. temminckii, prevalence of multiple paternity was only 60%. Further, the average number of sires was only 1.86 per brood even though brood sizes ranged from 12–45, and paternity was skewed, with the majority of paternity allocated to a single male. We propose that these differences may be associated with strong female selection on males in this species. Finally, we evaluated whether the number of fathers is an accurate estimate for the number of mates by comparing the number of alleles detected from fathers within the brood to the number of alleles from mates via genotyping alleles from spermatozoa within the uterine sac and found no significant difference, suggesting that the number of sires is a reasonable estimate for the number of mates in D. temminckii.

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