Abstract
This work assesses the present knowledge on Pacific oyster sperm biology in comparison to two marine fish species (turbot and seabass) whose sperm characteristics are well described. Sperm morphology mainly differs by the presence of an acrosome in Pacific oyster which is absent in both fish species. In turbot as in Pacific oyster, a sperm 'maturation process' along the genital tract is observed. Sperm motility is triggered by changes in osmolality for seabass and turbot and in pH for Pacific oyster. However, complementary factors are involved to maintain sperm immotile in the genital tract. Sperm movement duration is very long in Pacific oyster (20-24 h), compared to turbot (3-5 min) and seabass (40-50 s). A high capacity of ATP regeneration is observed in Pacific oyster sperm, sustained by the limited changes in its morphology observed at the end of the swimming phase. Then, the total distance covered by spermatozoa is very different among the studied species (seabass: 2 mm, turbot: 12 mm, Pacific oyster: 1 m). Considering the main characteristics of sperm movement, the three studied species can be separated in two groups: the sprint racer group (seabass: high velocity and short distance covered) and the marathonian racer one (Pacific oyster: low velocity but covering long distances). To an intermediate extent, turbot sperm belongs to the sprint racer group. Then, the two different sperm movement strategies observed in the three species, are compensated by the behaviour of the breeders.