Light-controlled production of spawning-inducing substance in jellyfish ovary

Abstract

THE jellyfish Spirocodon saltatrix, a bell-shaped member of the hydromedusae between 5 and 8 cm in diameter, spawns soon after nightfall; placing the animal in the dark causes a copious release of mature gametes within approximately 2 h, regardless of the day–night relationship^1–3. Oocytes taken from the ovaries during the morning and early afternoon are immature and contain germinal vesicles whereas spawned eggs are always fully mature⁴. When isolated from the animals, the ovaries discharge eggs in the light 1–2 h later and the remaining oocytes inside the ovaries are small⁵. When these ovaries are placed in the light (about 8,000 Ix at the surface of the water) they gradually increase in size, becoming fully grown after 15 h. We report here that the isolated ovaries discharge eggs 50–70 min after a 30-min exposure to the dark, during which period a spawning-inducing substance of low molecular weight is produced in the ovaries. The ovaries fail to produce this substance in continuous illumination.