Ovarian fluid enhances sperm velocity based on relatedness in lake trout, Salvelinus namaycush.

Studying mate choice at the gamete level can provide valuable insights into proximate mechanisms that underlie the evolution of mating systems. The objective was to assess whether ovarian fluid enhances sperm performance based on relatedness of mates in lake trout, Salvelinus namaycush, an iteroparous salmonid. Twelve trios were used, each composed of a female and two male fish; one male was related (full sibling) to the female, whereas the other was unrelated. Sperm from each male was activated in hatchery water or ovarian fluid from each corresponding female. No significant difference in sperm velocity was detected between the related and unrelated male fish when activated in hatchery water. However, when sperm was activated in ovarian fluid, sperm velocity from the related male was significantly higher than that of the unrelated male fish. Overall, ovarian fluid enhanced sperm performance of related male fish and might act as part of a recognition system to select sperm of a specific genotype.