K252a inhibition of sperm viability for efficient crossbreeding of hermaphroditic bivalves

Bivalve mollusks are economically important shellfish, representing 56.3% of aquaculture production. Cross-breeding is a popular approach for the genetic improvement of aquaculture species, including bivalves. However, it is difficult for simultaneous hermaphrodites due to the difficulty in collecting unfertilized oocytes. Male infertility or subfertility could be a solution. Considering that protein phosphorylation is critical in spermato-genesis, we investigated the effects of the protein kinase inhibitor K252a on germ cell development, gamete quality and embryonic/larval development of the simultaneously hermaphroditic scallop Argopecten irradians and evaluated its feasibility in crossbreeding. The results showed that 20% K252a injection at the gonad growth stage led to significant decreases in sperm number and progressive motility rate. Abnormal axoneme arrange-ment in flagella may have caused reduced sperm motility. Normal oocytes fertilized with K252a-treated sperm showed significant decreases in fertilization rate (38.24%), cleavage rate (83.42%) and D-stage survival rate (15.93%), and K252a-treated oocytes did not show obvious defects in early development. Interspecific hybrid-ization using K252a-treated A. irradians fertilized with Argopecten purpuratus sperm resulted in a 3.19-fold in-crease in the hybrid ratio (67%) over that of the control group (16%). Our study indicated that K252a influenced sperm development without affecting oocytes in A. irradians, indicating that K252a treatment may facilitate the mass production of crossbreeds and hybrids for simultaneous hermaphrodites. The approach reported here will greatly assist in genetic improvement programs for mollusk hermaphrodites.