Induction of spawning and oocyte maturation by 5-hydroxytryptamine in the surf clam

Gamete shedding can be induced in male and female surf clams (Spisula solidissima and sachalinensis) by injecting 5‐hydroxytryptamine (5‐HT) into the gonads. The administration of 0.4 ml of 2.0 mM 5‐HT induced spawning in all the clams tested. Shedding of gametes occurred within 2 to 3 min after the treatment and continued for about 40 min. The majority of the shed oocytes retained their germinal vesicles and underwent maturation upon insemination. The fertilized oocytes developed normally to the trocophora stage. The motility of the shed sperm was normal. 5‐HT added to the suspending medium to the final concentrations of 10 to 100, μM induced maturation of isolated Spisula oocytes in vitro. The oocytes underwent germinal vesicle breakdown, chromosomal condensation, extrusion of the first and second polar bodies, and pronuclei formation. The neurotrans‐mitter‐induced production of maturation‐promoting factor. In conclusion, 5‐HT induces gamete spawning and initiates oocyte maturation in the surf clam.